NOAA Diving Manual : For Science And Technology Dive 1991

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Diving

manual

DIVING FOR SCIENCE

AND

TECHNOLOGY

U.S.

DEPARTMENT OF COMMERCE

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Digitized by the Internet Archive
in

2012 with funding from

LYRASIS Members and Sloan Foundation

http://archive.org/details/noaadivingmanualOOunit

NOAA DIVING
MANUAL
DIVING

FOR SCIENCE AND TECHNOLOGY

October 1991

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U.S.

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DEPARTMENT OF COMMERCE
Robert A. Mosbacher, Secretary

National Oceanic and Atmospheric Administration
John

A. Knauss,

Under Secretary

Oceanic and Atmospheric Research
Ned

A. Ostenso, Assistant Administrator

Office of

Undersea Research

David B. Duane, Director

Mention of a commercial company or
product does not constitute an endorsement
by NOAA. Use for publicity or advertising
purposes of information from this publication concerning proprietary products or
the use of such products is not authorized.

No photograph appearing in this publication
may be reproduced in any fashion without
prior written permission from NOAA.

Information contained in this
May 1990.

Manual was

current as of

Library of Congress Cataloging in Publication Data

United States. National Oceanic and Atmospheric
Administration. Office of Undersea Research.

NOAA

diving manual.

Bibliography: p.
Includes index.
1.
I.

A

Diving, Scientific.

publication

Changes
cally;

2.

Hyperbaric Physiology.

Title.

is

of value only

if it is

check your original source for

Updates

kept up to date.

to this publication will be issued periodi-

will also

all

updates.

be available through the Superin-

tendent of Documents.

TABLE OF CONTENTS
V
vii

ix

xiii

xxi

SECTION 1
SECTION 2
SECTION 3
SECTION 4

SECTION

5

SECTION 6

FOREWORD
PREFACE

CONTRIBUTORS
LIST OF FIGURES
LIST OF TABLES
HISTORY OF DIVING
PHYSICS OF DIVING
DIVING PHYSIOLOGY

COMPRESSED AIR AND
SUPPORT EQUIPMENT
DIVER AND DIVING
EQUIPMENT
HYPERBARIC CHAMBERS
AND SUPPORT EQUIPMENT

SECTION

7

SECTION

8

SECTION

9

AND SUPPORT
PERSONNEL TRAINING
WORKING DIVE
PROCEDURES
PROCEDURES FOR

SECTION

10

SCIENTIFIC DIVES
DIVING UNDER SPECIAL

SECTION
SECTION

11

SECTION
SECTION

13
14

SECTION

15

DIVER

CONDITIONS
12

POLLUTED-WATER DIVING
HAZARDOUS AQUATIC
ANIMALS

WOMEN AND

DIVING

AND
DECOMPRESSION
MIXED GAS AND OXYGEN

AIR DIVING

DIVING

SECTION
SECTION

16
17

SECTION
SECTION

18
19

SATURATION DIVING

SECTION 20

UNDERWATER SUPPORT
PLATFORMS
EMERGENCY MEDICAL CARE
ACCIDENT MANAGEMENT
AND EMERGENCY
PROCEDURES
DIAGNOSIS AND TREATMENT

APPENDIX A

OF DIVING CASUALTIES
DIVING WITH
DISABILITIES
111

APPENDIX B
APPENDIX C

NAVY AIR
DECOMPRESSION TABLES
TREATMENT FLOWCHART
AND RECOMPRESSION
TREATMENT TABLES
U.S.

APPENDIX D

NOAA NITROX DIVING
AND DECOMPRESSION

APPENDIX E

GLOSSARY

I

TABLES

REFERENCES
INDEX

IV

FOREWORD
NOAA,

the largest

component of the Department of Commerce,

an agency with a broad mission

is

mental monitoring, prediction, and understanding of the oceans and the atmosphere.
systems agency" because

studies the relationship between the natural

it

important duties we perform

is

I

components of our

call

NOAA

planet.

in

environ-

the "earth

Among

the most

the monitoring of the oceans and Laurentide Great Lakes.

NOAA

operates a variety of sensors and platforms that permit observation and measurement of change in the
and
Great
Lakes. We operate satellites, ships, and submersibles, as well as the world's only underwater
seas
habitat. To add a uniquely human dimension to ocean research and marine services, NOAA conducts wet diving
operations throughout the Great Lakes, the territorial sea, the U.S. Exclusive Economic Zone, and wherever the
agency is involved in marine operations and research.

NOAA

—

more than 250 men
and technicians who dive under the
auspices of NOAA-sponsored research grants, a factor that significantly increases that number.) As befits the
variety of their missions, NOAA's divers are scientists, engineers, technicians, and officers in the NOAA Corps,
and all have volunteered to be divers.
numbers among

its

staff the largest diving

and women. (This number does not include those

Because the tasks

NOAA
NOAA

complement

of any civil Federal agency

civilian scientists, engineers,

divers carry out are as varied as those of any group of underwater workers in the world,

—

—

Diving Manual greatly expanded and revised contains instructions, recommendaand general guidance on the broadest possible range of underwater living conditions and dive situations.
Thus, while the Manual is directed toward NOAA, it will be useful, as were previous editions, to working divers
who have other affiliations and to those who dive for pleasure only.
this

version of the

tions,

Under authority delegated by the Secretary of Commerce, NOAA takes seriously the mandate under Section
21(e) of the Outer Continental Shelf Lands Act Amendments of 1978 to "conduct studies of underwater diving
."
techniques and equipment suitable for protection of human safety and improvement in diver performance
.

NOAA

is

proud of

its

record of safe diving and the assistance

it

.

.

has provided to the diving community.

To continue that record, the Manual has been revised to incorporate recommendations and information obtained
from the entire diving community. The various issues addressed and the procedures recommended reflect the
wisdom, experience, and specialized skills of working and recreational divers, equipment manufacturers, medical
and scientific authorities, and many others.
Under ordinary circumstances, the guidance

in this

mission and a failure. In an extreme situation, however,

those

who contributed

assistance in

making

to this revision,

this revision of the

I

Manual could mean the difference between a
it could make the difference between life and

express, on behalf of

Manual

a truly useful

all

document

of

NOAA, my

deep appreciation

for all divers.

John A. Knauss

Under Secretary of Commerce
for Oceans and Atmosphere

successful
death.

To

for their

1

PREFACE
This

Manual

NOAA

has been developed for use by

divers.

are shallower than 250 feet (76 m), the depth range in which

focuses principally on diving to depths that

It

NOAA

divers generally operate. Other sources should

be referred to for information on deep-water mixed-gas diving procedures.
this

Manual

Manual

contains

been used liberally to keep
This version of the

to a

manageable

As

in previous versions, references

many changes from

the first and second editions. Immediately noticeable

the loose-leaf format, which will greatly facilitate revision and additions. This format will permit the

updated no matter how large or small the section needing revision,

Manual

This edition of the

7 are largely

Manual

to

is

be

e.g., a section,

a paragraph, or a single table.

Of

these units, 6 are new, 12 have

has 25 distinct parts: 20 sections and 5 appendixes.

undergone major revision, and

have

size.

unchanged, as noted below:

New:
Section

1

Section

1

History of Diving

Polluted-Water Diving

Section 13

Women

Appendix A
Appendix C
Appendix E

Diving With Disabilities

and Diving

Treatment Flowchart and Recompression Treatment Tables
Glossary

Substantially revised:

Section 7

Compressed Air and Support Equipment
Diver and Diving Equipment
Hyperbaric Chambers and Support Equipment
Diver and Support Personnel Training

Section 9

Procedures for Scientific Dives

Section 4

Section

5

Section 6

Section 10

Diving Under Special Conditions

Section 14

Air Diving and Decompression

Section 15

Section 19

Mixed Gas and Oxygen Diving
Emergency Medical Care
Accident Management and Emergency Procedures

Section 20

Diagnosis and Treatment of Diving Casualties

Section 18

Appendix

NOAA

D

Nitrox

I

Diving and Decompression Tables

Largely unchanged:
Physics of Diving

Section 2
Section

Diving Physiology

3

Section 12

Working Dive Procedures
Hazardous Aquatic Animals

Section 16

Saturation Diving

Section 17

Underwater Support Platforms
U.S. Navy Air Decompression Tables

Section 8

Appendix B

Although the recommendations and guidelines contained in this Manual are based on the best information
judgment and expert opinion or to restrict the application of science and
technology that may become available in the future. NOAA also recognizes that some procedures may have to be
modified under controlled experimental conditions to permit the advance of science. Because the information in
this Manual reflects the thinking and experience of many specialists in the field of diving, procedural variations
available, they are not intended to replace

should be

As

made

only on the basis of expert advice.

stated above, this

responsibilities are the

Manual

has been developed for

NOAA's

divers,

whose missions are varied but whose chief

conduct of oceanic and Great Lakes research and the support of such research

activities.

vn

NOAA

also recognizes that this

Manual

will

be useful for others who dive because

The information

it

contains a wealth of

Manual, however, should not be
taken to reflect any endorsement or approbation on the part of NOAA or its Undersea Research Program for any
products illustrated, nor can either accept any liability for damage resulting from the use of incorrect or incomplete
information on applied diving techniques and technology.

in this

information.

The multidisciplinary nature

of underwater exploration and research

is

such that the assistance of numerous

experts in diving-related specialties was essential to the preparation of this Manual.

number

of individuals involved in the task, the reader

is

referred to the

list

To gain an appreciation

of the

of contributors and reviewers for this

and previous editions. Special thanks go to all of these contributors and reviewers, but particular gratitude is
extended to: the NOAA Diving Safety Board for its review and comments; Dr. Morgan Wells for his very thorough
editing, including checking of tables and example problem calculations throughout; Dr. James W. Miller for
numerous helpful suggestions, but especially for accepting the task of producing the Glossary; Marthe Kent, whose
persistence, knowledge, and attention to detail drove the entire process; and Marcia Collie, who had to translate
everyone's handwritten notes to intelligible and intelligent prose, cross-check every draft through to galley and the
final page proofs, and in general to see to production.

Comments on

this

Manual

are welcome.

They should be directed

to:

Director

NOAA's Undersea

Research Program,

1335 East-West Highway,
Silver Spring,

R/OR2

Room 5262

Maryland 20910
David

B.

Director

Vlll

Duane,

CONTRIBUTORS
AND REVIEWERS
Bachrach, Arthur

J.,

Breese, Dennison

Ph.D.

New Mexico

Taos,

Sea-Air-Land-Services
Southport, North Carolina

Bangasser, Susan, Ph.D.

Redlands, California

Busby, Frank

Busby Associates

Barsky, Steven

Arlington, Virginia

Diving Systems International

Santa Barbara, California

Butler,

Glenn

Underwater Contractors,
New York

International

Bassett, Bruce, Ph.D.

Human Underwater Biology,
San Antonio, Texas

City Island,

Inc.

Clark,

James

Inc.

M.D., Ph.D.

D.,

Environmental Medicine
University of Pennsylvania Medical Center
Philadelphia, Pennsylvania

Bauer, Judy

Institute for

Hyperbaric Medicine Program
University of Florida
Gainesville, Florida

Clarke, Richard E.,

George C, Lt. Col., M.C., USAF
Lackland Air Force Base, Texas

Bell,

Bell,

M.D.

Department of Hyperbaric Medicine
Richland Memorial Hospital
Columbia, South Carolina

Richard, Ph.D.

Department of Chemical Engineering

Clifton, H.

Edward, Ph.D.

University of California

Geological Survey

Davis, California

United States Department of the Interior

Bennett, Peter, Ph.D.

Menlo Park, California

Duke Medical Center
Durham, North Carolina
Berey, Richard

Cobb, William F.
Northwest and Alaska Fisheries Center
National Oceanic and Atmospheric Administration
Pasco, Washington

W.

Fairleigh Dickinson University

National Undersea Research Center
National Oceanic and Atmospheric Administration
St. Croix,

Corry, James A.

U. S. Virgin Islands

Technical Security Division

Department of Treasury

Black, Stan

Naval
Port

Civil Engineering

Washington, D.C.

Laboratory

Hueneme, California

Crosson, Dudley

Bornmann, Robert, M.D.
Limetree Medical Consultants

J.,

Ph.D.

Harbor Branch Oceanographic

Institution, Inc.

Fort Pierce, Florida

Reston, Virginia

Daugherty, C. Gordon, M.D.
Bove, Alfred, M.D.

Austin, Texas

Temple University
Davis, Jefferson

Philadelphia, Pennsylvania

C, M.D.

Hyperbaric Medicine
Affiliations, titles,

and academic degrees are as they were
was made.

the time contribution

at

Southwest Texas Methodist Hospital

San Antonio, Texas
IX

Contributors and Reviewers

Desautels, David

Halstead, Bruce

Hyperbaric Medicine Program

World

University of Florida

Colton, California

W.

Life Research Institute

Gainesville, Florida

Dingier, John R.

Hamner, William M., Ph.D.
Department of Biology

Geological Survey

University of California

U.S. Department of the Interior

Los Angeles, California

Menlo Park, California
Hamilton, R.W., Ph.D.

Dinsmore, David A.

Hamilton Research Ltd.

University of North Carolina at Wilmington

Tarrytown,

New York

National Undersea Research Center
National Oceanic and Atmospheric Administration

Heine, John N.

Wilmington, North Carolina

Moss Landing Marine Laboratory
California State University

Eckenhoff, Roderic G., M.D.

Moss Landing, California

Wallingford, Pennsylvania

Hendrick, Walter,
Edel, Peter

Sea Space Research Co.,
Harvey, Louisiana

Inc.

Department of Kinesiology
Los Angeles, California

Emmerman, Michael
Lifeguard Systems, Inc.

York,

New York
C,

Farmer, Joseph

New

York,

New York

Hennessy, T. R., Ph.D.

Egstrom, Glen, Ph.D.

New

Jr.

Lifeguard Systems, Inc.

London, U.K.
High, William L.
Western Administrative Support Center
National Marine Fisheries Services
National Oceanic and Atmospheric Administration
Seattle, Washington

M.D.

Jr.,

Edmund

Division of Otolaryngology

Hobson,

Duke University Medical Center
Durham, North Carolina

Tiburon Laboratory

Southwest Fisheries Center
National Oceanic and Atmospheric Administration

Feldman, Bruce A., M. D.

Tiburon, California

Washington, D.C.
Hollien, Harry, Ph.D.
Fife,

William, Ph.D.

A&

Texas

M University

College Station, Texas
Flynn,

Edward

T.,

Advanced Study
Communication Processes

Institute for

Hyperbaric Laboratory

of

University of Florida
Gainesville, Florida

M.D.,

Hubbard, Dennis, Ph.D.

Capt., Medical Corps

West

USN

Fairleigh Dickinson University

Diving Medicine Department

Naval Medical Research Institute

Indies Laboratory

St. Croix,

Virgin Islands

National Naval Medical Center

Hussey, Nancy R.

Bethesda, Maryland

Washington, D.C.
Francis, Art, Lt.

(j-g-),

NOAA

NOAA Diving Office
Rockville,

Maryland

Jenkins, Wallace T.

Naval Coastal Systems Laboratory

Panama

City, Florida

Graver, Dennis

National Association of Underwater Instructors

Kent, Marthe B.

Montclair, California

Kensington, Maryland

Contributors and Reviewers

Ann

Kinney, Jo
Surry,

S.,

Newell, Cliff

Ph.D.

Maine

Chief, Diving Operations

National Oceanic and Atmospheric Administration

Lambertsen, Christian
Institute for

M.D.

J.,

Seattle,

Washington

Environmental Medicine
Norquist, David S.

University of Pennsylvania

University of Hawaii

Philadelphia, Pennsylvania

National Undersea Research Center
Lanphier,

Edward

H., Ph.D.

National Oceanic and Atmospheric Administration

BIOTRON

Waimanalo, Hawaii

University of Wisconsin

Orr,

Madison, Wisconsin

Dan

Academic Diving Program

Lewbel, George, Ph.D.

Florida State University

LGL

Tallahassee, Florida

Ecological Research Associates

Bryan, Texas

Pegnato, Paul, Lt. Cdr.,

NOAA

Loewenherz, James W., M.D.

National Oceanic and Atmospheric Administration

Miami, Florida
Long, Richard

NOAA

Diving Program

Maryland

Rockville,

W.

Pelissier,

Michael

Diving Unlimited International, Inc.

Ocean Technology Systems

San Diego, California

Santa Ana, California

NOAA

Macintyre, Ian G., Ph.D.

Peterson, David H., Lt. Cdr.,

Department of Paleobiology

National Oceanic and Atmospheric Administration

Museum

National

of Natural History

Maryland

Rockville,

Smithsonian Institution

Peterson, Russell, Ph.D.

Washington, D.C.

Westchester, Pennsylvania

Mathewson, R. Duncan,

Summerland Key,

III,

Ph.D.

Phoel, William

C,

Ph.D.

Sandy Hook Laboratory

Florida

Northeast Fisheries Center

Mayers, Douglas, M.D., MC,
Naval Medical Command

Naval Medical Research
Bethesda, Maryland

USN

Institute

National Marine Fisheries Service
National Oceanic and Atmospheric Administration

Highlands,

New

Jersey

Reimers, Steve, P.E.

McCarthy, James

Reimers Engineering

Navy Experimental Diving Unit
Panama City, Florida

Alexandria, Virginia

Miller,

James W., Ph.D.

Big Pine Key, Florida

Robinson,
Jill

Jill

Robinson

&

Associates

Arlington, Virginia

Rogers, Wayne, M.D.
Miller,

John N., M.D.

University of South

Mobile,

Big Pine Key, Florida

Alabama

Alabama

Roman, Charles M.
Office of

NOAA Corps Operations

Murray, Rusty

National Oceanic and Atmospheric Administration

Moray Wheels

Rockville,

Maryland

Nahant, Massachusetts
Rounds, Richard

Murru, Frank
Curator of Fishes
Sea World

West

Orlando, Florida

St. Croix,

Indies Laboratory

Fairleigh Dickinson University

National Undersea Research Center

U. S. Virgin Islands
XI

Contributors and Reviewers

Rutkowski, Richard L.

Hyperbarics International

Thompson, Terry
Ocean Images, Inc.

Miami, Florida

Berkeley, California

Schroeder, William W., Ph.D.

Thornton,

Marine Science Program

Texas Research

University of

Alabama
Dauphin Island, Alabama

Austin, Texas

Schane, William, M. D.

Geological Survey

J.

Scott, Ph.D.
Institute, Inc.

Valentine, Page, Ph.D.

West

Indies Laboratory

Fairleigh Dickinson University

United States Department of the Interior

Woods

Hole, Massachusetts

National Undersea Research Center
St. Croix,

U. S. Virgin Islands

Vorosmarti, James,
Rockville,

Jr.,

M.D.

Maryland

Somers, Lee, Ph.D.

Department of Atmospheric and Oceanic Sciences
University of Michigan
Ann Arbor, Michigan

Walsh, Michael, Ph.D.
National Institute on Drug Abuse
U.S. Public Health Service
Rockville,

Maryland

Spaur, William, M.D.
Norfolk, Virginia

Waterman, Stanton A.
East/West Film Productions,

Staehle, Michael

Lawrenceville,

New

Inc.

Jersey

Staehle Marine Services, Inc.

North Palm Beach, Florida

Webb

Stanley, Chet

NOAA Diving Safety Officer
Rockville,

Webb,

Maryland

Paul,

M.D.

Associates

Yellow Springs, Ohio
Wells, Morgan, Ph.D.

Stewart, James R., Ph.D.

NOAA Diving Program
Maryland

Scripps Institution of Oceanography

Rockville,

La

Wicklund, Robert

Jolla, California

Stewart, Joan, Ph.D.

Scripps Institution of Oceanography

La

I.

National Undersea Research Center

Jolla, California

Caribbean Marine Research Center
Lee Stocking Island, Bahamas

Stone, Richard B.

Wilkie, Donald W., Ph.D.

National Marine Fisheries Service

Scripps Institution of Oceanography

National Oceanic and Atmospheric Administration

University of California

Silver Spring,

Maryland

Strauss, Michael B.,

M.D.

Memorial Medical Center of Long Beach
Long Beach, California
Swan, George
Northwest and Alaska Fisheries Center
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
Pasco, Washington

xn

La

Jolla, California

Williscroft, Robert, Ph.D.

Williscroft Manuscripts

Dayton, Washington

Workman,

Ian

Southeast Fisheries Center

Pascagoula Facility
National Oceanic and Atmospheric Administration
Pascagoula, Mississippi

1

1

LIST

OF FIGURES

SECTION 1
HISTORY OF DIVING

Page

l-l

Breath-Hold Pearl Divers

1-2

Alexander the Great's Descent Into The Sea

1-3

Halley's Diving Bell, 1690

1-3

1-4

Triton Diving Apparatus

1-4

1-5

Rouquayrol-Denayrouse Semi-Self-

1-2
...

Contained Diving Suit
1-6

1-5

Fernez-Le Prieur Self-Contained Diving

Apparatus
1-7

1-3

World War

II

1-5

Military

Swimmer Dressed

in

Lambertsen Amphibious Respiratory Unit

1-6

SECTION 2
PHYSICS OF DIVING
2-1

Equivalent Pressures, Altitudes, and Depths

2-2

Effects of Hydrostatic Pressure

2-3

Boyle's

2-4

Gas Laws
Objects Under Water Appear Closer

2-5

....

2-4
2-5

Law

2-9

2-12
2-13

SECTION 3
DIVING PHYSIOLOGY
3-1

3-2
3-3

3-4

The Process of Respiration
The Circulatory System
Oxygen Consumption and Respiratory Minute
Volume as a Function of Work Rate
Relation of Physiological Effects to Carbon

3-1

3-3

3-4

Dioxide Concentration and Exposure
Period
3-5

3-6

Effects of Hydrostatic Pressure on Location
of Breathing Bags Within a Closed-Circuit

Scuba

3-9

3-6

Principal Parts of the Ear

3-1

3-7

Location of Sinus Cavities

3-12

3-8

Lung Volume
Complications From Expansion of Air

3-13

3-9

Pressure Effects on

in

the

Lungs During Ascent

3-15

3-10

Isobaric Counterdiffusion

3-19

3-1

Effect of Exposure Duration on Psychomotor

Task Performance

in

Cold Water

3-26
xiii

—

A

List of Figures

Page

SECTION 4

COMPRESSED AIR AND SUPPORT EQUIPMENT
4-1

Production of Diver's Breathing Air

4-6

4-2

Steel Cylinder Markings

4-7

4-3

Aluminum Cylinder Markings

4-8

4-4

Valve Assemblies

4-11

4-5

Gauges

4-12

SECTION

5

DIVER AND DIVING EQUIPMENT
5-1

Open-Circuit Scuba Equipment

5-1

5-2

First-Stage Regulators

5-3

5-3

Breathing Hoses

5-4

5-4

5-5

5-5

Mouthpieces
Check and Exhaust Valves

5-6

Lightweight Helmet

5-8

5-7

Face Masks

5-12

5-8

Flotation Devices

5-13

5-9

Swim

5-14

5-10

5-15

5-13

Neoprene Wet Suit
Effects of Water Temperature
Cold- Water Mitt, Liner Included
Open-Circuit Hot-Water Suit

5-14

Snorkels

5-19

5-15

Dive Timer

5-20

5-16

5-20

5-17

Depth Gauges
Pressure Gauges

5-18

Diving Lights

5-23

5-19

Signal Devices

5-23

5-20

Shark Darts
Shark Screen in Use
Diver Communication System
Schematics of Diver Communication Systems
Modulated Acoustic Communication System...

5-25

5-11

5-12

5-21

5-22
5-23

5-24

5-6

Fins

5-16
5-17
5-18

5-22

.

5-25

5-26
5-26
5-27

SECTION 6
HYPERBARIC CHAMBERS AND
SUPPORT EQUIPMENT

6-2

Double-Lock Hyperbaric Chamber
Exterior View
Double-Lock Hyperbaric Chamber
Interior View
Mask Breathing System for Use in Hyperbaric

6-3

Transportable Chambers

6-4

Certification Plate for Hyperbaric

6-5

Burning Rates of Filter Paper Strips
Angle of 45° in N -0 Mixtures

6-1

6- IB

6-1

6-2

Chamber

6-3

2

xiv

2

6-4

Chamber
at

....

6-4

an
6-15

List of

Figures

Page

Combustion in N->-Ot Mixtures Showing the
Zone of No Combustion

6-6

SECTION

6-16

7

DIVER AND SUPPORT PERSONNEL TRAINING
No

Figures

SECTION

8

WORKING DIVE PROCEDURES
Deep-Sea Dress

8-1

Surface-Supplied Diver

8-2

Predive Environmental Checklist

8-3

Lightweight Surface-Supplied

8-4

Surface-Supplied Diver In Lightweight

8-5

8-6

in

8-2
8-3

Mask

8-4

Mask

and Wet Suit
Major Components of a Low-Pressure
Compressor-Equipped Air Supply System
Typical High-Pressure Cylinder Bank Air
Supply System

8-5

....

8-10

8-10
8-12

8-7

Circular Search Pattern

8-8

Circular Search Pattern for

8-9

Circular Search Pattern Through Ice

8-14

8-10

Arc

8-15

8-11

Jackstay Search Pattern

8-12

Searching Using a

8-13

8-17

8-15

Diver-Held Sonar
Using a Compass for Navigation
Underwater Hydraulic Tools

8-16

Explosive Hole Punch

8-22

8-17

8-22

8-21

Oxy-Arc Torch
Salvaging an Anchor With Lift Bags
Aquaplane for Towing Divers
Underwater Cameras
Basic Equipment for Closeup and Macro

8-22

Diurnal Variation of Light Under Water

8-23

Selective Color Absorption of Light as a

8-24

Lighting

8-25

8-26

Video Recording Systems
Commercial Underwater Video System

SECTION

9

Two

Diver/Searchers

8-14

8-18

8-19

8-20

(Fishtail)

8-12

Search Pattern

Tow Bar

Photography

8-16

8-18
8-21

8-26
8-30
8-33

8-34

Function of Depth

Arms and

8-16

in

Clear Ocean Water

8-35

8-36

Brackets for Strobe

Systems

8-40
8-45

8-46

PROCEDURES FOR SCIENTIFIC DIVES
Tape

9-3

9-1

Fiberglass Measuring

9-2

Bottom Survey in High-Relief Terrain
High-Frequency Sonic Profiler

9-3

9-3

9-4

Multipurpose Slate

9-6

9-5

xv

List of Figures

Page

9-5

Counting Square for Determining Sand Dollar
9-8

Density
9-6

Diver-Operated Fishrake

9-8

9-7

Underwater Magnification System
Hensen Egg Nets Mounted on a Single Diver

9-9

9-8

9-9

Propulsion Vehicle
9-9

A Circle Template

for

Determining Benthic
9-10

Population Density

9-1

Coring Device With Widemouth Container
Infauna Sampling Box

9-12

Use of a Hand-Held Container

9-13

Use of

9-10

9-10
9-1

to Collect

Zooplankton

9-12

a Plexiglas Reference

Frame

for

Estimating Population Densities
in

Midwater

9-13

9-14

Benthic Environment of the American

9-15

Diver With Electroshock Grid

9-15

9-16

Tagging a Spiny Lobster on the Surface
Tagging a Spiny Lobster in Situ
Elkhorn Coral Implanted on Rocky Outcrop
Algal Cover of Rock Substrate
Diver in Giant Brown Kelp (Macrocystis) Bed
Fish Using Tires as Habitat
An Artificial Reef Complex
Underwater Geological Compass
Box Cores (Senckenberg) for Determining

9-15

9-14

Lobster

9-17
9-18
9-19

9-20
9-21

9-22
9-23

9-24

Internal Structure in

Sand

9-17

....

9-19

9-18

9-21
9-21

9-23

9-25

9-34

Greased Comb for Ripple Profiling
Diver Using Scaled Rod and Underwater
Noteboard
Aerial Photograph and Composite Map
Dip and Strike of Rock Bed
Geologist Measuring Dip (Inclination) of
Rock Outcrop
Coring in a Deep Reef Environment With a
Hydraulic Drill
Pneumatic Hand Drill
Diver Taking Vane Shear Measurement
Undersea Instrument Chamber
Dye-Tagged Water Being Moved by Bottom

9-35

Diver Using Water Sample Bottle

9-36

Water Sample

9-37

Diver Recovering Indian Artifacts

9-37

9-38

Archeologist Exploring the Golden Horn

9-38

9-39

Heavy Overburden Air Lift
Prop Wash System Used for Archeological

9-39

9-40
9-41

Fish Trap

9-42

9-42

Diver Checking Fish Trawl

9-43

9-43

Slurp

9-25

9-26

9-27
9-28
9-29

9-30

9-31

9-32
9-33

9-26

9-26
9-27

9-28

9-28

9-28
9-29
9-31

9-32

9-35

Current
Bottle

Backpack

Gun Used

9-36
9-36

9-41

Excavation

xvi

9-16
....

to Collect

Small Fish

9-45

1

List of

Figures

Page

SECTION
DIVING

10

UNDER SPECIAL CONDITIONS

lO-l

Schematic Diagram of Waves

in

the Breaker

Zone

10-8

10-2

Near-shore Current System

10-3

Shore Types and Currents

10-4

Entering the Water Using the Roll-In

10-5

10-7

Transom-Mounted Diver Platform
Side-Mounted Diver Platform
Down-line Array for Open-Ocean Diving

10-8

Three Multiple Tether Systems (Trapezes)

10-9

Safety Reel Used

10-6

Used

10-10
lO-l

Method

10-1

Open-Ocean Diving
in Cave Diving
Water Temperature Protection Chart
Diver Tender and Standby Diver in Surface

10-12

Cross Section of a Typical Hydroelectric

10-10

for

Shelter

Dam

in the

Northwestern United States

Diver Protected by Cage and Ready to be

10-14

A

10-16

10-12
10-13
10-15

10-16
10-18
10-20

10-21

10-13

10-15

l

10-12

Lowered into Dam Gatewell
Fish Ladder at a Hydroelectric Dam in
the Northwest
Creeper A Device Used to Move Across
Rocky Substrates in Strong Currents

10-29

10-30

10-30

—

10-32

Support Ship, Trawl, Diver Sled, and
Support Boat

10-35

SECTION 11
POLLUTED-WATER DIVING
ll-l

Diver Working

in

Contaminated Water

Dry Suit

1

1-2

Diver

1

1-3

NOAA-Developed Suit-Under-Suit (SUS)

1

1-4

Dressing a Diver for Contaminated-Water

in

System
Diving
11-5

Decontamination

SECTION

12

Team

at

Work

11-2
1

1-4

1

1-5

1

1-5

11-6

HAZARDOUS AQUATIC ANIMALS

12-2

Sea Urchin Echinothrix diadema on
Hawaiian Reef
Stinging Hydroid

12-3

Stinging or Fire Coral

12-2

12-4

Portuguese Man-of-War

12-3

12-5

Large Jellyfish of Genus Cyanea
Bristleworm

12-3

12-4

12-8

Cone Shell
Anatomy of

12-9

Rare Australian Blue-Ring Octopus

l

2-1

12-6
12-7

a

Cone

Shell

a
12-1

12-2

12-4

12-5
12-5

xvn

1

1

List of Figures

Page

12-10

Dasyatid Stingray

12-6

12-1

Myliobatid Stingray

12-6

12-12

Lionfish

12-7

12-13

Surgeonfish

12-7

12-14

12-8

12-16

Sea Snake
Great White Shark
Gray Reef Shark

12-17

Moray Eel

12-10

12-18

Barracuda

12-11

12-19

12-12

12-20

Torpedo Ray
Examples of Pufferfish

SECTION

13

12-15

12-8
12-9

12-12

WOMEN AND DIVING
13-1

SECTION

Scientist on Research Mission

13-5

14

AIR DIVING

AND DECOMPRESSION

14-1

Sea States

14-2A

Hand

14-2B

Additional

14-3

Deliverable Volumes at Various

14-4

Typical High Pressure Cylinder Bank Air

14-5

Repetitive Dive Flowchart

14-25

14-6

Repetitive Dive Worksheet

14-26

14-5

14-10

Signals

Hand

Signals

14-1

Gauge
14-16

Pressures

Supply

14-18

SECTION 15
MIXED GAS AND OXYGEN DIVING
15-1

Minimum

Safe Inspired Gas Temperature
15-5

Limits
15-2

Percentage of Oxygen
as a Function of

in

Breathing Mixtures

Depth and Oxygen

Partial

Pressure Relative to Ranges for Hypoxia

and

CNS Toxicity

15-3

Closed-Circuit Mixed-Gas Scuba

15-4

Closed-Circuit

(Rebreather)

15-1

15-5

Oxygen Scuba (Rebreather)
Air Analysis Kit for On-Site Use

15-14

15-6

Direct-Reading Colorimetric Air Sampler

15-15

SECTION 16
SATURATION DIVING
No
xviii

15-6

Figures

15-1

List of

Figures

Page

SECTION

17

UNDERWATER SUPPORT PLATFORMS
Complex

17-1

Saturation Diving

17-2

Open Diving

17-3

17-4

17-9

System
Open Bell Showing Control Lines
Open Bell Emergency Flow-Chart
Cutaway Showing Mating Position With
Deck Decompression Chamber
Undersea Habitat Specifications and
Operational Data
Edalhab
Hydrolab

17-10

Tektite

17-14

17-11

La Chalupa

17-15

17-12

Aegir

17-16

17-13

17-17

17-15A

Underwater Classroom
Aquarius
Sublimnos

17-15B

Subigloo

17-19

17-15C

17-19

17-15D

Lake Lab
Undersea Instrument Chamber

17-16

Diver Propulsion Vehicle

17-20

17-17

JIM System

17-21

17-18

17-19

WASP System
ROV System Components

17-22

17-20

Mitsui Engineering and Shipbuilding

17-21

Examples of

SECTION

18

17-4
17-5
17-6

17-7

17-8

17-14

Bell

17-2

on Deck of Seahawk

Bell

17-3

17-5

17-6

17-7

17-8

17-12
17-13

17-17
17-18

17-19

17-21

RTV-100

17-23

ROV

David Work Tasks

17-23

EMERGENCY MEDICAL CARE
18-1

Life-Support Decision Tree

18-2

Jaw-Lift

18-3

Bag-Valve-Mask Resuscitator

18-2

Method

18-4
18-6

SECTION 19
ACCIDENT MANAGEMENT AND

EMERGENCY PROCEDURES
19-1

Buddy Breathing
Mask

19-2

Clearing a Face

19-3

Do-Si-Do Position

for

19-6
19-8

Administering

In-Water Mouth-to-Mouth

Artificial

Resuscitation

19-1

19-4

Mouth-to-Mouth In-Water

19-5

Mouth-to-Snorkel Artificial Resuscitation

19-6

Towing

Artificial

Resuscitation

Position for Mouth-to-Snorkel

Artificial Resuscitation

19-7

19-12
19-13

Tank-Tow Method

19-14
19-18
xix

List of Figures

Page

(DAN)

19-8

Divers Alert Network

19-9

19-24

19-10

Modified Trendelenberg Position
Diving Accident Management Flow Chart

19-11

Evacuation by Helicopter

19-27

19-22

19-25

SECTION 20
DIAGNOSIS AND TREATMENT OF DIVING
CASUALTIES
20-1

Structure of External, Middle, and Inner Ear

20-2

Summary

20-3

20-4
20-5

xx

20-8

of Decompression Sickness and

Gas Embolism Symptoms and Signs
Decompression Sickness Treatment From
Diving or Altitude Exposures
Treatment of Arterial Gas Embolism
Treatment of Symptom Recurrence

20-10
20-12

20-14
20-16

1

LIST

OF TABLES

SECTION 1
HISTORY OF DIVING
No

p age

Tables

SECTION 2
PHYSICS OF DIVING
2-1

Conversion Factors, Metric

2-2

Conversion Table for Barometric Pressure

2-3

Colors That Give Best Visibility Against a

to English Units....

2-2

2-3

Units

Water Background

2-16

SECTION 3
DIVING PHYSIOLOGY
Carboxyhemoglobin

3-1

as a Function of

Smoking

3-8

Narcotic Effects of Compressed Air Diving

3-2

SECTION

4

COMPRESSED

AIR

AND SUPPORT EQUIPMENT

Composition of Air

4-1

SECTION

3-22

in its

Natural State

4-1

5

DIVER AND DIVING EQUIPMENT
No

Tables

SECTION 6
HYPERBARIC CHAMBERS AND
SUPPORT EQUIPMENT
6-1

Hyperbaric Chamber Predive Checkout
6-5

Procedures
6-2

Ventilation Rates and Total Air

Requirements

for

Two

Patients and

One Tender Undergoing Recompression
Treatment

6-8

6-3

Chamber

6-4

Pressure Test Procedures for

Post-Dive Maintenance Checklist

NOAA

Chambers
6-5

Standard

NOAA

6-9

6-1

Recompression Chamber

Air Pressure and Leak Test

6-12
xxi

List of

Tables

Page

SECTION

7

DIVER AND SUPPORT PERSONNEL TRAINING
No

Tables

SECTION

8

WORKING DIVE PROCEDURES
8-1

Wind Speed and Current

8-2

Diver Power Tools

8-3

Selection Guide for Discharge Pipe and

8-4

Characteristics of Principal U.S. Explosives

8-5

Color Correction Filters

8-6

Manual and Through-the-Lens (TTL)

8-7

Through-the-Lens (TTL) Mini Strobes for

Automatic and Manual Exposure
Exposure Compensation for Underwater

8-38

8-8

Photography
Underwater Photographic Light Sources
Still Films Suited for Underwater Use
Processing Adjustments for Different
Speeds
Motion Picture Films Suited for Underwater
Use

8-38

Estimations

Air Line

Used

for Demolition Purposes

Strobes for Closeup Photography

8-9

8-10
8-1

8-12

SECTION

8-11

8-19

8-28

8-32
8-36

8-37

8-39
8-41

8-42

8-43

9

PROCEDURES FOR SCIENTIFIC DIVES
9-1

Micro-Oceanographic Techniques

9-33

9-2

Levels of Anesthesia for Fish

9-44

9-3

Fish Anesthetics

9-47

SECTION
DIVING
10-1

10-2

10-3

10

UNDER SPECIAL CONDITIONS
Comparison of Differences in Time Limits
(in Minutes of Bottom Time) for
No-Decompression Dives
Theoretical Ocean Depth (TOD) (in fsw) at
Altitude for a Given Measured Diving Depth

10-25

Pressure Variations with Altitude

10-27

SECTION 11
POLLUTED-WATER DIVING
No
xxii

Tables

10-26

List of

Tables

Page

SECTION

12

HAZARDOUS AQUATIC ANIMALS
No Tables

SECTION

13

WOMEN AND DIVING
No

Tables

SECTION

14

AIR DIVING

AND DECOMPRESSION

14-1

Sea State Chart

14-6

14-2

Signal Flags, Shapes, and Lights

14-9

14-3

Hand

14-12

14-4

Line Pull Signals for Surface-to-Diver

14-5

Respiratory Minute

14-6

Air Utilization Table at Depth

14-15

14-7

Cylinder Constants

14-16

14-8

Scuba Cylinder Pressure Data

Signals

Communication
Different

1

4-9

14-13

Volume (RMV)

at

Work Rates

14-14

Estimated Duration of 7 1 .2

ft

3

14-17
Steel

14-17

Cylinder
14-10

Flow-Rate Requirements for SurfaceSupplied Equipment

14-19

14-1

No-Decompression Limits and Repetitive
Group Designation Table for NoDecompression Air Dives

14-21

1

14-12

Residual Nitrogen Timetable for Repetitive

14-13

Optional Oxygen-Breathing Times Before

Air Dives

14-22

Flying After Diving

14-31

SECTION 15
MIXED GAS AND OXYGEN DIVING
15-1

Oxygen

Partial Pressure

and Exposure Time

Limits for Nitrogen-Oxygen Mixed Gas
15-2

1

5-3

15-4

Working Dives
Depth-Time Limits for Breathing Pure
Oxygen During Working Dives
NOAA NITROX-I (68% N 2 32% 2 ) No-

15-3

15-7

,

Decompression Limits and Repetitive
Group Designation Table for NoDecompression Dives
Equivalent Air Depths (EAD) and Maximum
Oxygen Exposure for Open-Circuit Scuba

15-8

68%
32% Oxygen (NOAA

Using a Breathing Mixture of
Nitrogen and
Nitrox-I)
15-5

Air Purity Standards

15-9
15-11
xxiii

List of

Tables

Page

SECTION 16
SATURATION DIVING
Summary

16-1

of Air and Nitrogen-Oxygen

Saturation Exposures
16-2

Characteristics of Three

16-2

Carbon Dioxide

Absorbents
1

6-3

Hazardous Materials

SECTION

16-10
for Habitat Operations

16-14

17

UNDERWATER SUPPORT PLATFORMS
17-1

Desirable Features of Underwater Habitats

SECTION

17-1

18

EMERGENCY MEDICAL CARE
No

Tables

SECTION 19
ACCIDENT MANAGEMENT AND

EMERGENCY PROCEDURES
19-1

Summary

of Probable Causes of

Non-

Occupational Diving Fatalities

from 1976-1984

19-5

19-2

Sources of Emergency Assistance

19-21

19-3

Ground-to-Air Visual Signal Code

19-23

19-4

Diving Casualty Examination Checklist

19-26

SECTION 20
DIAGNOSIS AND TREATMENT OF
DIVING CASUALTIES
20-1

Characteristics of Inner Ear Barotrauma and

20-2

List of U.S.

20-3

Tables
General Patient Handling Procedures

Inner Ear Decompression Sickness

xxiv

20-5

Navy Recompression Treatment
20-1

20-15

Page

SECTION 1
HISTORY OF

1.0

General

1.1

Free (Breath-Hold) Diving

1-1

DIVING

1.2

Diving Bells

1-1

1.3

1-2

1.4

Helmet (Hard-Hat) Diving
Scuba Diving

1.5

Saturation Diving

1-6

1.6

1-1

1-3

1.5.1

Saturation Diving Systems

1-6

1.5.2

Habitats

1-7

1.5.3

Lockout Submersibles

1-7

Summary

1-7

(

(

HISTORY

OF DIVING
1.0

GENERAL

the bar of a weighted line to plunge to this depth and

Divers have penetrated the oceans through the centuries for

held his breath for 3 minutes and 39 seconds.

The obvious advantage

purposes identical to those of modern diving: to

acquire food, search for treasure, carry out military

of free diving as a work

(and as a recreational method)

is

operations, perform scientific research and explora-

freedom of the breath-hold diver

and enjoy the aquatic environment. In a brief
history of diving, Bachrach (1982) identified five
principal periods in the history of diving, from free (or

obvious disadvantage

tion,

breath-hold) diving, to bell diving, surface support or

helmet (hard hat) diving, scuba diving, and, finally,
saturation diving. (Atmospheric diving, another div-

mode, is discussed in Section 17.5.) All of these
diving modes are still currently in use.
ing

limited to the

maintain

FREE (BREATH-HOLD) DIVING

Free diving, or breath-hold diving,
diving techniques, and

it

snorkel

book,

all

in

The Hae-Nyu and

Korea and Japan (Figure

pearl divers of

among

1-1) are

the better-known breath-hold divers. In his

Half Mile Down, Beebe (1934)

is

an aid

reports finding

in

it fills

necessarily

is

can take

air the diver

and

in

breath or can obtain by means of a

The modern

breath-hold diving but

is

not used

because on descent

to provide a continuous supply of air,

with water that must then be exhaled on surfacing.

DIVING BELLS

The second

the earliest of

has played an historic role

the search for food and treasure.

Ama

is

amount of

in a single

maneuver; the

to

that the air supply

snorkel-type reed or tube to the surface.

1.2
1.1

is

method

mobility and the

its

diving.

One

principal historical

mode

of diving

bell

is

of the earliest reports of the use of a device

some

that enabled a diver to enter the water with

degree of protection and a supply of air involved the

Colimpha used in Alexander the Great's
approximately 330 B.C., depicted by an
Indian artist in a 1575 miniature (Figure 1-2). An

diving bell

descent

in

several mother-of-pearl inlays in the course of con-

account of

ducting an archeological dig at a Mesopotamia site

manuscript, The True History of Alexander. In his
Problemata, Aristotle described diving systems in use

that dated

back

to

4500 B.C.; these

shells

must have

been gathered by divers and then fashioned into inlays

in

by artisans of the period. Beebe also describes the
extensive use of pearl shells among people from other

divers,

ancient cultures.

The Emperor

of China, for example,

this dive

his time:

appeared

"they contrive a means of respiration for

by means of

a container sent

naturally the container

which constantly

received an oyster pearl tribute around 2250 B.C. Free

In the

Greek historian Thucydides

that

in

According

to

an Athenian attack

which the Athenian divers cut through
underwater barriers that the Syracusans had built to

on Syracuse

in

obstruct and

damage

Greek

Rome
on

his shoulders

hold divers sometimes used hollow reeds as breathing

by

slings.

remain submerged for
type of primitive snorkel was use-

tubes, which allowed

longer periods; this
ful in military

them

to

operations (Larson 1959).

Free diving continues to be a major diving method.
set in 1969 by a U.S. Navy diver,
Robert Croft, who made a breath-hold dive to 247 feet

World records were

(75 meters), a record broken in 1976 by a French diver,

Jacques Mayol, who

set

the current world's breath-

hold dive record at 325 feet (99 meters).

October 1991

— NOAA

Diving Manual

Mayol grasped

was not

bell.

a

until

device that can

Davis (1962)

about an hour

1535
of a

tells

in a lake

near

using de Lorena's diving apparatus, which rested

ships. Free or breath-

the

for

air,

few

this period, very

Guglielmo de Lorena developed

who worked

them;

to

submerged man."

in diving. It

be considered a true diving
diver

down

not filled with water, but

1000 years following

developments occurred

reports.

is

assists the

divers were also used in military operations, as the

Thucydides, divers participated

13th century French

in the

De

and had much of

its

weight supported

Lorena's "bell" thus provided a

finite

but

reliable air supply.

In

1691, the British astronomer Sir

Edmund

Halley

(who was then Secretary of the Royal Society) built
and patented a forerunner of the modern diving bell,
which he later described in a report to the Society. As
Sir Edmund described it, the bell was made of wood
coated with lead, was approximately 60 cubic feet
(1.7 cubic meters) in volume, and had glass at the
top to allow light to enter; there was also a valve to
1-1

Section

1

Figure 1-1

Breath-Hold Pearl Divers

Photos courtesy Suk

1.3

(Figure 1-3). In his history of diving, Davis (1962)
suggests that Halley undoubtedly knew of a develop-

Although these early diving

to provide air

from the surface

to a diving bell

pressure. Papin proposed to use force
to

pumps

under

or bellows

provide air and to maintain a constant pressure
bell. Davis speculates that Halley's choice

within the

of the barrel rather than forced air method of replenishment may have reflected Halley's concern that Papin
(who was also a Fellow of the Royal Society) would
accuse him of stealing his concept. Halley's method
was used for over a century until Smeaton introduced
a successful forcing pump in 1788. In 1799, Smeaton
dived with his "diving chests," which used a forcing

pump

to replenish the air supply

Diving bells continue to be used today as part of

modern diving systems, providing a method of transporting divers to their work sites while under pressure
and, once at the

site,

of supplying breathing gas while

the diver works. Both modern-day open (or "wet")

and

bells

provided some

protection and an air supply, they limited the mobility

and 18th centuries, a number of
of leather) were developed to
provide air to divers and to afford greater mobility.
However, most of these devices were not successful,
because they relied on long tubes from the surface to
provide air to the diver and thus did not deal with the
problem of equalizing pressure at depth.
The first real step toward the development of a surfacesupported diving technique occurred when the French
scientist Freminet devised a system in which air was
of the diver. In the I7th

devices (usually

pumped from

made

the surface with a bellows, allowing a

constant flow of air to pass through a hose to the diver
in the water.

(Larson 1959).

Hong

HELMET (HARD-HAT) DIVING

vent the air and a barrel to provide replenished air

ment reported by the French physicist Denis Papin,
who in 1689 had proposed a plan (apparently the first)

Ki

the

first

This system

is

considered by

many

to

be

true helmet-hose diving apparatus. Freminet

has been credited with diving in 1774 with this device
to a

depth of 50 feet (15 meters), where he remained

for a period of

The

first

1

hour.

major breakthrough

in

surface-support

closed bells are clearly the successors of these ancient

diving systems occurred with Augustus Siebe's inven-

systems.

tion of the diving dress in 1819.

1-2

NOAA

Around the same

Diving Manual

time,

— October 1991

History of Diving

Figure 1-2

Figure 1-3
Halley's Diving

Alexander the Great's Descent Into The Sea

Courtesy National

Academy

of

suit that

would

allow firefighters to work in a burning building. They

received a patent for this system in 1823, and later
modified

it

to

1690

Sciences

Deane Brothers, John and Charles, were working

the

on a design for a "smoke apparatus," a

Bell,

"Deane's Patent Diving Dress," consisting

Courtesy National

particular helium-oxygen, were developed.

Sciences

The

first

the

USS

Squalus,

in

The breathing

1939.

of mixed

gases such as helium-oxygen permitted divers to dive

depths for longer periods than had been

to greater

with ports and hose connections for surface-supplied

possible with air mixtures.

Siebe's diving dress consisted of a waist-length

of

major open-sea use of helium and oxygen as a breathing mixture occurred in the salvage of the submarine,

of a protective suit equipped with a separate helmet

air.

Academy

supported diving technique

is

The hard-hat surfaceprobably

still

the most

received air under pressure from the surface by force

widely used commercial diving method; the use of
heliox mixtures and the development of improved decom-

pump;

pression tables have extended the diver's capability to

jacket with a metal helmet sealed to the collar. Divers

the air subsequently escaped freely at the diver's

waist. In

1837, Siebe modified this open dress, which

work

in this

diving dress at depth. Although surface-

allowed the air to escape, into the closed type of dress.

supported diving has several advantages

The closed

stability, air supply,

suit retained the

attached helmet but, by

venting the air via a valve, provided the diver with a
full-body air-tight suit. This suit served as the basis
for

modern hard-hat diving

was tested and found

to

gear. Siebe's diving suit

be successful

in

1839 when

the British started the salvage of the ship
George, which had sunk

in

1782

to a

until

— NOAA

contained underwater breathing apparatus (scuba).

depth of 65 feet

major developments occurred in hard-hat gear
the 20th century, when mixed breathing gases, in

October 1991

certain dive situations by the development of self-

Royal

(19.8 meters) (Larson 1959).

No

in terms of
and length of work period, a major
problem with hard-hat gear is that it severely limits
the diver's mobility. This limitation has been overcome in

Diving Manual

1.4

SCUBA DIVING

The development

of self-contained underwater breathing

apparatus provided the free moving diver with a portable

1-3

Section

1

Figure 1-4
Triton Diving Apparatus
supply which, although finite

air

in

comparison with

the unlimited air supply available to the helmet diver,

allowed for mobility. Scuba diving
quently used

ous forms,

work

mode

is

is

the most fre-

in recreational diving and, in vari-

perform underwater
and commercial purposes.

also widely used to

for military, scientific,

There were many steps
cessful self-contained

in the

development of a suc-

underwater system. In 1808,

Freiderich von Drieberg invented a bellows-in-a-box
device (Figure 1-4) that was worn on the diver's back

from the surface. This
work but it did
serve to suggest that compressed air could be used in
diving, an idea initially conceived of by Halley in
1716. In 1865, two French inventors, Rouquayrol and
Denayrouse, developed a suit (Figure 1-5) that they
described as "self-contained." In fact, their suit was
not self contained but consisted of a helmet-using
surface-supported system that had an air reservoir
that was carried on the diver's back and was sufficient
to provide one breathing cycle on demand. The demand
valve regulator was used with surface supply largely
and delivered compressed
device,

named

air

Triton, did not actually

because tanks of adequate strength were not then available to handle air at high pressure. This system's

demand

which was automatically controlled, represented a
major breakthrough because it permitted the diver to
valve,

air when needed in an emergency. The
Rouquayrol and Denayrouse apparatus was described
with remarkable accuracy in Jules Verne's classic,
Twenty Thousand Leagues Under The Sea, which was
written in 1869, only 4 years after the inventors had

have a breath of

made

their device public (Larson 1959).

The demand valve played

a critical part in the later

development of one form of scuba apparatus. However,

since divers using scuba gear exhaled directly into

the surrounding water,

much

air

was wasted. One

solution

problem was advanced by Henry Fleuss, an
English merchant seaman who invented a closed-circuit
breathing apparatus in 1879 that used pure oxygen
compressed to 450 psig for the breathing gas supply
to this

and caustic potash

to purify the exhaled oxygen. Fleuss'

"closed circuit oxygen-rebreather

when

SCUBA"

passed a

was used successfully in 1880 by
the English diver Alexander Lambert to enter a flooded
tunnel beneath the Severn River to secure an iron door
that had jammed open and to make needed repairs in
the tunnel. Although Fleuss' rebreather was successful
in this limited application, the depth limitations
associated with the use of pure oxygen directed most
attention to compressed air as a breathing mixture.
crucial test

it

In the 1920's, a French naval officer, Captain Yves

Le

Prieur,

1-4

began work on a self-contained

air diving

Courtesy National

Academy

of

Sciences

apparatus that resulted in 1926 in the award of a
patent, shared with his countryman Fernez. This device
(Figure 1-6) was a steel cylinder containing compressed
air that was worn on the diver's back and had an air
hose connected to a mouthpiece; the diver wore a nose
clip and air-tight goggles that undoubtedly were
protective and an aid to vision but did not permit
pressure equalization. The cylinder on the first FernezLe Prieur model contained around 2000 psi of air and
permitted the wearer to remain less than 15 minutes in
the water. Improved models later supplied sufficient
air to permit the diver to remain for 30 minutes at
23 feet (7 meters) or 10 minutes at 40 feet (12 meters).
The major problem with Le Prieur's apparatus was the
lack of a demand valve, which necessitated a continuous flow (and thus waste) of gas. In 1943, almost
20 years after Fernez and Le Prieur patented their
apparatus, two other French inventors, Emile Gagnan
and Captain Jacques-Yves Cousteau, demonstrated their
"Aqua Lung." This apparatus used a demand intake
valve drawing from two or three cylinders, each
containing over 2500 psig. Thus it was that the demand
regulator, invented over 70 years earlier by Rouquayrol
and Denayrouse and extensively used in aviation, came
into use in a self-contained breathing apparatus that
did not emit a wasteful flow of air during inhalation

NOAA

Diving Manual

— October 1991

History of Diving

Figure 1-5

Rouquayrol-Denayrouse Semi-Self-Contained

Figure 1-6

Diving Suit

Fernez-Le Prieur Self-Contained Diving Apparatus

Courtesy National

Academy

Sciences

of

Equivalent self-contained apparatus was used by the
military forces of Italy, the United States, and Great

World War II and continues in active
The rebreathing principle, which avoids

Britain during

use today.

waste of gas supply, has been extended to include
forms of scuba that allow the use of mixed gas (nitrogen or
helium-oxygen mixtures)
tion

depth and dura-

to increase

beyond the practical

oxygen

limits of air or pure

breathing (Larson 1959).

A

major development

occurred

in

in

regard to mobility

France during the 1930's:

Carlieu developed a set of swim
Courtesy National

(although

it

Academy

Sciences

of

continued to lose exhaled gas into the
made possible the develop-

water). This application

ment of modern open-circuit

air

scuba gear (Larson

In 1939, Dr. Christian Lambertsen began the devel-

opment of

a series of three patented forms of

oxygen

rebreathing equipment for neutral buoyancy underwater

swimming, which became the

first

self-contained under-

water breathing apparatus successfully used by a large

number

of divers.

piratory Unit

The Lambertsen Amphibious Res-

(LARU)

(Figure 1-7) formed the basis

for the establishment of U.S. military self-contained

diving (Larson 1959).

This apparatus was designated scuba (for
contained underwater breathing apparatus) by

October 1991

— NOAA

Diving Manual

its

selfusers.

diving

de

the first to be

produced since Borelli designed a pair of claw-like
fins in 1680. When used with Le Prieur's tanks, goggles, and nose clip, de Carlieu's fins enabled divers to
move horizontally through the water like true swimmers,
instead of being lowered vertically in a diving bell or in

hard-hat gear.

1959).

fins,

in

Commander

The

later use of a single-lens face

which allowed better

visibility as well

zation, also increased the

mask,

as pressure equali-

comfort and depth range of

diving equipment.

Thus

the development of scuba

added a major work-

ing tool to the systems available to divers; the

mode allowed

new

freedom of movement and
access to greater depths for extended times and required
much less burdensome support equipment. Scuba also
enriched the world of sport diving by permitting
recreational divers to go beyond goggles and breathhold diving to more extended dives at greater depths.
divers greater

1-5

Section

1

Figure 1-7

World War Military Swimmer Dressed in
Lambertsen Amphibious Respiratory Unit
II

decompression obligation in the course of such
The initial development of saturation diving by
the U.S. Navy in the late 1950's and its extension by
naval, civilian government, university, and commertial

dives.

cial

laboratories revolutionized scientific, commercial,

and military diving by providing a method that permits
divers to remain at pressures equivalent to depths of

up
2000 feet (610 meters) for periods of weeks or
months without incurring a proportional decompres-

to

sion obligation.

Saturation diving takes advantage of the fact that a
diver's tissues

become saturated once they have absorbed

the nitrogen or other inert gas they can hold at that

all

particular depth; that
tional gas.

Once

is,

they cannot absorb any addi-

a diver's tissues are saturated, the

diver can remain at the saturation depth (or a depth

within an allowable excursion range up or

down from

the saturation depth) as long as necessary without
proportionately increasing the

amount of time required

for decompression.

mode work

Divers operating in the saturation

out of

a pressurized facility, such as a diving bell, seafloor

habitat, or diver lockout submersible.
facilities

These subsea

are maintained at the pressure of the depth at

which the diver

be working; this depth

will

termed

is

the saturation or storage depth.

The

historical

development of saturation diving

depended both on technological and

scientific advances.

Engineers developed the technology essential to support the saturated diver,

and physiologists and other

scientists defined the respiratory

capabilities

and

limits of this

and other physiological

mode.

Many

researchers

played essential roles in the development of the saturation

Navy team working at
Submarine Medical Research Laboratory

concept, but the U.S.

London, Connecticut,

is

the U.S.
in

generally given credit for

New

making

team
was led by two Navy diving medical officers, George
Bond and Robert Workman, who, in the period from
the mid-1 950's to 1962, supervised the painstaking
animal tests and volunteer human dives that provided

the major initial breakthroughs in this field. This

the scientific evidence necessary to confirm the valid-

Courtesy C.

J.

Lambertsen

ity of

the saturation concept (Lambertsen 1967).

1.5.1

Saturation Diving Systems

The
1.5

SATURATION DIVING

Although the development of surface-supplied diving
permitted divers to spend a considerable amount of

earliest saturation dive

performed

in the

open

sea was conducted by the Link group and involved the

use of a diving bell for diving and for decompression.
Initial

Navy

efforts involved placing a saturation hab-

working time under water, divers using surface-supplied

on the seafloor. In 1964, Edwin Link, Christian
Lambertsen, and James Lawrie developed the first

systems for deep and/or long dives incurred a substan-

deck decompression chamber, which allowed divers

1-6

itat

NOAA

Diving Manual

in

— October 1991

History of Diving

a sealed bell to be locked into a pressurized environ-

ment

at the surface for the

slow decompression from

The first commercial application of this
form of saturation diving took place on the Smith
Mountain Dam project in 1965 and involved the use of
a personnel transfer capsule. The techniques pioneered at
Smith Mountain have since become standard in comsaturation.

mercial diving operations: saturated divers
pressure, in the deck decompression

live,

a surface vessel and are then transferred to the under-

water worksite

in

a pressurized personnel transfer cham-

ber (also called a surface decompression chamber)

(Lambertsen 1967). Although saturation diving systems are the most widely used saturation systems in
commercial diving today, two other diving technologies
also take advantage of the principle of saturation: habitats

technologically advanced habitat system, has replaced
the

Hydrolab

and lockout submersibles.

as

NOAA's

principal seafloor research

1.5.3

Lockout Submersibles

Lockout submersibles provide an alternative method
for diver/scientists to gain access to the underwater
environment. Lockout submersibles are dual-purpose
vehicles that permit the submersible's pilot/driver

crew to remain at surface pressure
1

at

which saturated diver-scientists live and work under
pressure for extended periods of time. Habitat divers
dive from the surface and enter the habitat, or they
may be compressed in a pressure vessel on the surface
to the pressure of the habitat's storage depth and then
be transferred to the habitat. Decompression may take
place on the seafloor or in a surface decompression
chamber after the completion of the divers' work. The
most famous and widely used habitat was NOAA's
Hydrolab, which was based in the Bahamas and Caribbean from 1972 to 1985 and provided a base for more
than 600 researchers from 9 countries during that
time. In 1985, the Hydrolab was retired from service
and now resides permanently in the Smithsonian Insti-

— NOAA

and

at a pressure of
is

pressurized

separate compartment to the pressure of the depth

which he or she

will

be working. The lockout com-

in effect as a

personnel transfer

and from the

seafloor.

The Johnson Sea-Link, which can be pressurized

Habitats are seafloor laboratory/living quarters in

October 1991

(i.e.,

atmosphere), while the diver-scientist

in a

capsule, transporting the diver to

Habitats

discus-

sion of habitat-based in-situ research programs.)

partment thus serves
1.5.2

more detailed

laboratory. (See Section 17 for a

under

chamber on board

Museum of Natural History in WashThe Aquarius, a more flexible and

tution's National

ington, D.C.

Diving Manual

2000 fsw (610 msw), has played a central

role in

undersea research program for years, particularly
pollution

1.6

and

to

NOAA's
in

fisheries research off the Atlantic coast.

SUMMARY

Humans have

explored the ocean depths at least since

the fifth millennium B.C., and the development of the

diving techniques and systems described in this section reflects

mankind's drive for mastery over

The search

all

aspects

methods that will
allow humans to live comfortably in the marine biosphere for long periods of time continues today, as
engineers and scientists work together to make access
to the sea safer, easier, and more economical.

of the environment.

for

1-7

(

(

1

Page

SECTION 2
PHYSICS
OF

2.0

General

2-1

2.1

Definitions

2-1

DIVING

2.2

2.3
2.4

2.1.1

Pressure

2-1

2.1.2

Temperature

2-1

2.1.3

Density

2-1

2.1.4

Specific Gravity

2-1

2.1.5

Seawater

2-1

2-2

Pressure
2.2.1

Atmospheric Pressure

2-2

2.2.2

Hydrostatic Pressure

2-2

2.2.3

Absolute Pressure

2-2

2.2.4

Gauge Pressure

2-3

2.2.5

Partial Pressure

2-3

Buoyancy
Gases Used

2-3
in

2-6

Diving

2.4.1

Air

2-6

2.4.2

Oxygen

2-6

2.4.3

Nitrogen

2-6

Helium
2.4.5
Carbon Dioxide
2.4.6
Carbon Monoxide
2.4.7
Argon, Neon, Hydrogen
Gas Laws

2-6

2.4.4

2.5

2-7

2-7

2-8

2.5.4

Law
Law
Charles' Law
Henry's Law

2-7

Boyle's

2.5.5

The General Gas Law

2-11

2.5.2
2.5.3

2.6

Gas Flow

(Viscosity)

2.7

Moisture

in

2-10
2-1

2-12

Breathing Gas

2.7.1

Condensation

2.7.2

Fogging of the

in

2-12

Breathing Tubes or

Mask

Mask

The Physics

of Light

Consequences

2-13

2-13

Light and Vision Under Water
2.8.1

2.9

2-6

Dalton's

2.5.1

2.8

2-6

Under Water and

for Vision

2-13
the

2-13

2.8.1.1

Refraction

2-13

2.8.1.2

Scatter

2-14

2.8.1.3

Absorption

2-14

2.8.1.4

Insufficient Light

2-15

Acoustics

2-16

(

(

(

F

PHYSICS

OF
DIVING
2.0

GENERAL

Rankine (R)

This section describes the laws of physics as they affect

humans

the water.

in

A

thorough understanding of the

physical principles set forth in the following paragraphs

is

Temperatures measured
to

=

°F
2.1

to

may

centigrade

in

X X) +

(1.8

Temperatures measured

DEFINITIONS

plus 273.15

°F plus 459.67
be converted

Fahrenheit using the following formula:

and effective diving performance.

essential to safe

X

=
=

Kelvin (K)

32

may

Fahrenheit

in

be converted

centigrade using the following formula:

This paragraph defines the basic principles necessary
to

an understanding of the underwater environment.

The most important

2.1.1

(°F

-

C

of these are listed below.

32)

Pressure

Pressure

is

force acting on a unit area. Expressed

2.1.3

Density

Density

mathematically:

mass per unit volume. Expressed mathe-

is

matically:

Pressure

=

Force

P

or

=

Area

Density (D)

=

Mass

Volume
Pressure
(psi) or

usually expressed in pounds per square inch

is

Density

kilograms per square centimeter (kg/cm 2 ).

meter (gm/cm 3 )

Temperature

form of energy that increases the temperawhich it is added and
decreases the temperature of the matter from which it
is removed, providing that the matter does not change
state during the process. Quantities of heat are measured

Heat

is

in the

in

grams per cubic

centi-

metric system.

a

ture of the substance or matter to

in calories or British

The temperature
Temperature

is

thermal units (Btu).
of a

body

is

measure of

a

thermometer and expressed
or Fahrenheit (°F).

in

it

is

its

heat.

measured by a

degrees centigrade (°C)

The quantity

equal to the total kinetic energy of

of heat in the
all

of

its

Temperature values must be converted

body

is

Specific gravity

is

the ratio of the density of a sub-

stance to the density of fresh water at 39.2 °F (4°C).

Fresh water has a specific gravity of 1.0 at 39.2°
cific gravities

greater than 1.0, and substances lighter

than fresh water have specific gravities

human body
1.0,

less

than

1.0.

The

has a specific gravity of approximately

although this varies slightly from one person

to

another.

molecules.
to absolute

values for use with the Gas Laws. Both the Kelvin and
Rankine scales are absolute temperature scales. Absois

2.1.4 Specific Gravity

(4°C); substances heavier than fresh water have spe-

produced by the average kinetic energy or

speed of the body's molecules, and

lute zero

usually stated in pounds per cubic foot (lb/ft 3 )

English system and

in the

2.1.2

is

the hypothetical temperature characterized

2.1.5

Seawater

Seawater

is

known

that occur in nature.

to contain at least 75

The

elements

four most abundant elements in

by the complete absence of heat; it is equivalent to
approximately -273 °C or -460 'F. Conversion to the
Kelvin or Rankine scales is done by adding 273 units to
the temperature value expressed in centigrade or 460

seawater are oxygen, hydrogen, chlorine, and sodium.

units to the temperature value expressed in Fahrenheit,

ture of seawater varies

respectively.

30°C).

October 1991

— NOAA

Diving Manual

Seawater

is

always slightly alkaline because

it

con-

tains several alkaline earth minerals, principally sodi-

um, calcium, magnesium, and potassium. The temperafrom 30.2T

to

86.0°F

(-IX

to

2-1

Section 2

Table 2-1
Conversion Factors, Metric to English Units

The

specific gravity of seawater

is

affected both by

and temperature, and these effects are interrelated. For example, water with a high enough
salt content to sink toward the bottom will float at the
surface if the water is sufficiently warm. Conversely,
salinity

water with a relatively low

salt

content will sink

if it is

Seawater also is an excellent electrical conductor, an interaction that causes corrosion
problems when equipment is used in or near the ocean.

To Convert
From
Metric Units

To

English Units

Multiply

By

PRESSURE

sufficiently chilled.

gm/cm 2

inch of fresh water

pounds/square inch

1

kg/cm 2
kg/cm 2
kg/cm 2
cm Hg
cm Hg
cm Hg
cm Hg

1

cm

1
1

The

viscosity of seawater varies inversely with tem-

perature and
as at 89.6

nearly twice as great at 33.8 °F (1°C)

is

°F (32 °C). The impact of

be seen when the same sailboat
higher speeds in warm water than in

many

In

1

able to achieve

1
1

cold.

parts of the world the metric system of

measurement
still

is

1

property can

this

is

1

of fresh water

feet of fresh

0.394

water

inches of mercury

14.22

(psi)

(ffw)

Hg)

(in.

32.8

28.96

pound/square inch

0.193

foot of fresh water

0.447

foot of seawater (fsw)

0.434

inch of mercury

0.394

inch of fresh water

0.394

used rather than the English system

widely used in the United States. Table 2-1 pres-

VOLUME AND CAPACITY

ents factors for converting metric to English units.

2.2

PRESSURE

The pressure on
forces: the

a diver under water

is

the result of two

weight of the water over him or her and the

weight of the atmosphere over the water. Table 2-2

1

cc or ml

cubic inch (cu

1

m3

cubic feet (cu

1

liter

cubic inches

1

liter

cubic foot

1

liter

fluid

1

liter

quarts (qt)

ounces

0.061

in.)

35.31

ft)

61.02

0.035
(fl

33.81

oz)

1.057

provides factors for converting various barometric pressure units into other pressure units.

The

various types

WEIGHT

of pressure experienced by divers are discussed in the
following sections.

ounce (oz)
ounces
pounds (lb)

gram
1kg
1kg
1

2.2.1

Atmospheric Pressure

Atmospheric pressure acts on all bodies and strucatmosphere and is produced by the weight
of atmospheric gases. Atmospheric pressure acts in all
directions at any specific point. Since it is equal in all

0.035
35.27
2.205

LENGTH

tures in the

directions,

its

effects are usually neutralized.

At sea

atmospheric pressure is equal to 14.7 psi or
1.03 kg/cm 2 At higher elevations, this value decreases.
Pressures above 14.7 psi (1.03 kg/cm 2 ) are often
level,

1

cm

inch

1

meter

inches

1

meter

feet

3.28

1

km

mile

0.621

0.394
39.37

.

AREA

expressed in atmospheres. For example, one atmosphere

equal to 14.7 psi, 10 atmospheres is equal to 147 psi,
and 100 atmospheres is equal to 1470 psi. Figure 2-1
shows equivalent pressures in the most commonly used
units for measuring pressure at both altitude and depth.
is

1

cm 2

square inch

1

m2

square feet

1

km 2

square mile

0.155
10.76

0.386

Adapted from

2.2.2

produced by the weight of
and acts on all bodies and struc-

water (or any fluid)

immersed

in the

is

water (or

pressure, hydrostatic pressure
at a specific depth.

sure to divers

is

is

fluid).

Like atmospheric

equal

hydrostatic pressure.

descent in seawater and 0.432 psi per foot

(1

kg/cm 2

per 10 meters) of descent in fresh water. This relationship

is

shown graphically

in

Figure 2-2.

in all directions

The most important form

rate of 0.445 psi per foot (1

2-2

(1979)

Hydrostatic Pressure

Hydrostatic pressure
tures

NOAA

It

kg/cm 2 per

of pres-

increases at a

9.75 meters) of

2.2.3

Absolute Pressure

Absolute pressure

is

the

sum

of the atmospheric

pressure and the hydrostatic pressure exerted on a

NOAA

Diving Manual

— October 1991

Physics of Diving

Table 2-2
Conversion Table for Barometric Pressure Units

N/m 2

atmosphere

1

Newton (N)/m 2 or

2

Hg

lb/in

("Hg)

(psi)

760

29.92

14.70

.0102

.0075

2953X10" 3

.1451X10" 3

Pa

bars

mb

kg/cm 2

(cm H 2 0)

1

1.013X10 5

1.013

1013

1.033

1033

.01

1.02X10' 5

=

1

gm/cm 2

or

atm

in.

mm

Hg

Pascal (Pa)

=

9869X10" 5

1

bar

=

.9869

10 5

1

1000

1.02

1020

750.1

29.53

14.51

1

millibar

(mb)

=

9869X10" 3

100

.001

1

.00102

1.02

.7501

.02953

.01451

1

kg/cm 2

=

.9681

9807X10 5

.9807

980.7

1

1000

735

28.94

14.22

1

gm/cm 2

=

968.1

98.07

9807X10' 3

.9807

.001

1

.735

.02894

.01422

=

.001316

133.3

.001333

1.333

.00136

1.36

1

.03937

.01934

.0334

3386

.03386

33.86

.03453

34.53

25.4

1

.4910

.06804

6895

.06895

68.95

.0703

70.3

51.70

2.035

1

(1

1

cm H 2 0)

mm

Hg

1

in.

Hg

=

1

2
lb/in

=

(psi)

10

1

5

Adapted from

submerged body. Absolute pressure

is

measured

in

pounds per square inch absolute (psia) or kilograms
per square centimeter absolute (kg/cm 2 absolute).

submerged body can be calculated by

subtracting the weight of the submerged body from the

ment, that

Gauge Pressure

Gauge pressure
pressure

and

a

being

pressure

specific

measured.

Pressures are usually measured with gauges that are

balanced to read zero
to the air.

at sea level

Gauge pressure

is

reads in

when they

are open

therefore converted to

absolute pressure by adding 14.7
psi or 1.03 if the dial

is,

the dial reads in

if

kg/cm 2

.

that of the displaced liquid, the

and the body

Pressure

density, that

In a mixture of gases, the proportion of the total

pressure contributed by a single gas in the mixture
called the partial pressure.

tributed by a single gas

is

buoyancy will be positive and the body will float or be
buoyed upward. If the weight of the body is equal to
that of the displaced liquid, the buoyancy will be neutral and the body will remain suspended in the liquid.
If the weight of the submerged body is greater than

is

The

is

partial pressure con-

in direct

proportion to

its

percentage of the total volume of the mixture (see
Section 2.5.1).

buoyancy

will

be negative

will sink.

The buoyant
2.2.5 Partial

If the total displace-

the weight of the displaced liquid,

greater than the weight of the submerged body, the

the difference between absolute

is

(1979)

Using Archimedes' Principle, the buoyancy or buoyant
force of a

weight of the displaced liquid.
2.2.4

NOAA

is,

force of a liquid
its

is

dependent on

its

weight per unit volume. Fresh water

has a density of 62.4 pounds per cubic foot (28.3 kg/

m3

). Seawater is heavier, having a density of 64.0
pounds per cubic foot (29 kg/0.03 m 3 ). Therefore, a
body in seawater will be buoyed up by a greater force
than a body in fresh water, which accounts for the fact
that it is easier to float in the ocean than in a fresh

0.03

water lake.

2.3

BUOYANCY

Archimedes' Principle explains the nature of buoyancy.

A

body immersed in a liquid, either wholly
is buoyed up by a force equal
the weight of the liquid displaced by

or partially,
to

the body.

October 1991

Lung capacity can have a significant effect on the
buoyancy of a submerged person. A diver with full
lungs displaces a greater volume of water and therefore is more buoyant than a diver with deflated lungs.
Other individual differences that may affect buoyancy
include bone structure, bone weight, and relative amount
of body fat. These differences help to explain why
certain individuals float easily

— NOAA

Diving Manual

and others do

not.

2-3

m
nn

i

Section 2

Figure 2-1
Equivalent Pressures, Altitudes, and Depths

Atmospheres (atm)
I

1

1

.0

1

1

1

1

1

.2

.1

Pounds Per Square Inch

1

1

.3

1

.4

1

1

.5

1

1

.6

1

1

.7

1

1

1

.8

1

1.0

.9

— — — — — — — — — — — — — — — — — — — — — — — — — — — — —i—
I

I

I

I

I

(psi)

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

2

4

Inches of Mercury

(in

i

i

i

i

12

14

14.7

Hg)
i

i

i

i

i

5

i

i

i

i

i

10

i

i

i

i

i

i

i

i

i

20

15

i

i

i

i

i

25

29.92

— — — — — — —(mm
———————————————————————

Millimeters of Mercury
i

i

i

10

——————————————————————————————
i

i

8

6

i

i

i

Hg)

i

i

i

i

i

i

200

100

i

i

i

i

i

i

i

i

i

400

300

i

i

i

i

500

i

i

i

i

i

700

600

760

+
Millibars (mb)
1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

P

1

I

200

100

400

300

600

500

700

800

900

0123456789
Newtons Per Square Meter x104 (n/m 2 x10

4

I

1

1

1

1

1

1

1

1

i

i i

i

i

60

100

30

m

i

i

i

i

i

i

i

i

15

i

i

i

8

I

1

1

1

I

I

1

I

I

P

1

1

i

i

i

I

10

5

2
I

of Feet

i

i

10

I

1

10.13

—n— — — —
i

i

3

I

I

1

Thousands

1

6

I

1

i

i

i

20

10

Ll_l

1

i

30

40

1

1

i

i

i

50

20

)

———————

Pressure Altitude

1

1013.2

I

I

I

I

I

Thousands of Meters

0123456789
Atmospheres Absolute (ATA)

I

1

Depth

1

in

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

10

Seawater
I

Meters
1

1

1

1

1

1

40

20

I

I

200

150
I

I

I

1

I

I

I

1

80

60

100

50

1

250

300
I

I

Feet

Adapted from National Aeronautics and Space Administration (1973)

2-4

NOAA

Diving Manual

— October 1991

'

Physics of Diving

Figure 2-2
Effects of Hydrostatic Pressure

>

At the Surface
Atmosphere Absolute, 14.7 psi
The flotation device is fully expanded.

in
At 33 Feet
{Vi

2 Atmospheres Absolute, 29.4 psi
Surface Volume) Because of hydrosta tic
pressure, the same volume of air in the
flotation device is reduced to only Vi its
surface lifting capacity

At 1 32 Feet
5 Atmospheres Absolute, 73.5 psi
A Surface Volume) Because of hydrostatic
X

pressure, the

same volume

flotation device

surface

lifting

is

of air

in

reduced to only

the

Vi

its

capacity.

Adapted from

October 1991

— NOAA

Diving Manual

NOAA

(1979)

2-5

Section 2

Divers wearing wet suits usually must add diving

some other diving

the diver should adjust his or her

gases. For example, when nitrogen is
breathed at increased partial pressures, it has a distinct anesthetic effect called "nitrogen narcosis," a
condition characterized by loss of judgment and

neutral state so that

disorientation (see Section 3.2.3.5).

weights to their weight belts to provide the negative

buoyancy that allows normal descent. At working depth,

buoyancy to achieve a
work can be accomplished without

the additional physical effort of counteracting positive

(upward) or negative (downward) buoyancy.
2.4.4

Helium

Helium
2.4

GASES USED

IN

DIVING

While under water, a diver

is

amounts.

totally

dependent on a

Two methods of providing
used. The diver may be supplied

is

It

breathing gases can be

diluent for

or he or she

may

The second method

gas supply.

Many

air

is

in

and

is

is

color-

used extensively as a

deep diving gas mixtures. Helium

has some disadvantages but none as serious as those
associated with nitrogen. For example, breathing helium-

called scuba, an

is

combinations of breathing gases are used

Compressed

tasteless

oxygen mixtures causes a temporary distortion of speech
(producing a Donald Duck-like voice), which hinders

Apparatus."
diving.

the atmosphere only in trace

carry the breathing

Underwater Breathing

initialism for "Self-Contained

and
oxygen

odorless,

less,

merged source,

in

substance, -452.02°F (-268. 9°C). Helium

supply of breathing gas.

with gas via an umbilical from the surface or a sub-

found

has the lowest boiling point of any known

the most

common, but

use of other mixtures for special diving situations

The following paragraphs describe
most commonly found in diving operations.
increasing.

in

the
is

the gases

communication. Helium also has high thermal conductivity, which causes rapid loss of body heat in divers
breathing a helium mixture. Helium is used in breathing mixtures at depth because of its lower density and
lack of narcotic effect. However, helium should never
be used

in diving or

standing of

its

treatment without a

full

under-

physiological implications.

2.4.1 Air

Air

is

a mixture of gases (and vapors) containing

nitrogen (78.084%), oxygen (20.946%), argon (0.934%),

carbon dioxide (0.033%), and other gases (0.003%).
Compressed air is the most commonly used breathing
gas for diving (see Section

2.4.2

is

is

4).

a colorless, odorless, and tasteless gas that

only slightly soluble in water.

It

can be liquefied at

-297. 4°F (-183°C) at atmospheric pressure

when cooled

T

and

will

Oxygen
is the only gas used by the human body, and it is
essential to life. The other gases breathed from the
solidify

to -361.1

atmosphere or breathed by divers
serve only as vehicles and diluents

oxygen

is

(-218.4°C).

in their

gas mixtures

for oxygen.

However,

dangerous when excessive amounts are

breathed under pressure; this harmful effect

oxygen poisoning (see Section

is

is

and fermentation. It is colorless, odorless, and
Although carbon dioxide generally is not
considered poisonous, in excessive amounts it is harmful to divers and can even cause convulsions. Breathing
C0 2 at increased partial pressure may cause unconsciousness (see Sections 3.1.3.2 and 20.4.1). For example,
a person should not breathe air containing more than
0.10 percent C0 2 by volume (see Table 15-3); divers
must therefore be concerned with the partial pressure
tion,

of the carbon dioxide in their

systems,

point

is

is

and

tasteless gas. It

incapable of supporting

life.

-320. 8°F (-196°C). Nitrogen

is

oxygen in diving gas
mixtures but has several disadvantages compared with

2-6

the removal of the excess

the diver's breathing
(see Sections 15.5.1.2

and

C0 2

generated by

essential to diving safety

is

15.5.1.3).

3.3).

a colorless, odorless,

commonly used

breathing gases. In the

case of closed- and semi-closed-circuit breathing

Carbon Monoxide

Carbon monoxide (CO) is a poisonous gas. It is colorand tasteless and therefore difficult to
detect. Carbon monoxide is produced by the incomplete combustion of hydrocarbons, which occurs in the
exhaust systems of internal combustion engines. Carbon monoxide may also be produced by over-heated
less, odorless,

chemically inert and

Its boiling

produced by various

called

Nitrogen

Nitrogen
is

a gas

is

natural processes such as animal metabolism, combus-

2.4.6
2.4.3

Carbon Dioxide

Carbon dioxide (C0 2 )

tasteless.

Oxygen

Oxygen

2.4.5

as a diluent for

oil-lubricated compressors.

NOAA

A

level of

Diving Manual

20 parts per

— October 1991

Physics of Diving

CO

million of

should not be exceeded

breathing systems (see Table 15-3).

in

When

pressurized

scuba

cyl-

container were filled with oxygen alone, the partial
pressure of the oxygen would be

atmosphere.

l

If

the

inders are filled, care should be taken not to introduce

same container were

CO

sures of each of the gases comprising air would con-

from the exhaust system of the

compressor into

air

the breathing gases. Proper precautions

must be taken

where cylinders are filled are
adequately ventilated. The compressor's air intake must
draw from an area where the atmosphere is free of
to ensure that all areas

with

filled

tribute to the total pressure, as

shown

in

the following

tabulation:

Percent of

Component x

=

contamination, such as automobile exhaust fumes.

Total Pressure (Absolute)

Partial

Pressure

Atmospheres

Percent of

Argon, Neon, Hydrogen

2.4.7

the partial pres-

air,

component

Gas

partial

pressure

Argon, neon, and hydrogen have been used experimentally as diluents for oxygen

in

breathing gas mix-

although these gases are not used routinely

tures,

in

diving operations. However, the results of recent research

N2

78.08

0.7808

o2

20.95

.2095

co 2

.03

.0003

Other

.94

.0094

100.00

1.0000

suggest that hydrogen-oxygen and helium-hydrogen-

oxygen breathing mixtures may be used within the
next decade in deep diving operations (Peter Edel,

Total

personal communication).

2.5

Example

GAS LAWS

The behavior

If the

of

gases

all

is

affected by three factors:

the temperature of the gas, the pressure of the gas,
the

volume of the

gas.

The

among

relationships

and

these

what are called the
Gas Laws. Five of these, Dalton's Law, Boyle's Law,
Charles' Law, Henry's Law, and the General Gas Law,
three factors have been defined in

are of special importance to the diver.

were

Dalton's

Law

Dalton's

The
that
if

it

total

is

for

example a scuba cylinder,

with air to 2000

psi,

the following steps

table.

Step

1

— Dalton's Law
X

Percent of component gas

Law

=

total pressure (abso-

partial pressure

Percent of

com ponents:

states:

total pressure

gases

same container,

filled

would be necessary to calculate the partial pressures
(in ATA's) of the same components listed in the above

lute)

2.5.1

1

exerted by a mixture of

equal to the

sum

78.08%

N2

.7808

of the pressures

N2

100

would be exerted by each of the gases
alone were present and occupied the

20.95%

o2

volume.

.2095

2

100

In a gas mixture, the portion of the total pressure

contributed by a single gas

is

called the partial pres-

P Total

=

PPl

+

PP2

+

PPn

C0 2

00.94%
.0094 Other

Other
100

=

total pressure of that

Ppi

=

partial pressure of gas

Pp 2

=

partial pressure of gas

Pp n

=

partial pressure of other gas

P Tola

An

.0003

100

where

at

00.03%

co 2

sure of that gas. Stated mathematically:

gas

l

component

Step

2

l

— Convert

2000

psi to

atmospheres absolute

(ATA)

easily understood

example

atmospheric pressure, 14.7

October 1991

— NOAA

component

2

components.

(2000

psi)

+

1

= ATA

14.7 psi
is

psi

that of a container
(l

kg/cm 2 ).

Diving Manual

If the

136

+

1

=

137

ATA
2-7

Section 2

Step

3

—

ATA

Partial pressure of constituents at 137

Pp N

=

0.7808

X

137

=

106.97

Pp

=

0.2095

X

137

=

28.70

Pp co

=

0.0003

X

137

=

0.04

ATA

p P0ther

= 00094 X

137

=

1.29

ATA

Step 2

— Boyle's Law

ATA

C0 2

nents of the gas, particularly

,

33 feet of water):

=K

P2 V 2
P2

ATA

Step

3

=

pressure at 33 feet in

V2 =

volume

K =

constant.

— Equating

increased significantly

higher pressures, although they were fairly low at

ATA

at 33 feet in ft 3

the constant, K, at the surface and

at 33 feet,

we have
P.V,

Observe that the partial pressures of some compoat

(
(at

the following equation:

=

p2v2

Transposing to determine the volume at 33

atmospheric pressure. As these examples show, the
implications of Dalton's Law are important and should
be understood by all divers.

feet:

P.V,

where

Law

2.5.2 Boyle's
Boyle's

Law

P

1

=

states:

At constant temperature, the volume of

V,

a

gas varies inversely with absolute pressure,

=

v2 =

1

atmosphere (ATA)

2

ATA

24
1

while the density of a gas varies directly

V2 =

with absolute pressure (Figure 2-3).

For any gas at a constant temperature, Boyle's

Law

ft

3

ATA X 24
2 ATA

12

ft

3

ft

3
.

(

is:

Note that the volume of air in the open bell has been
compressed from 24 to 12 cubic feet in the first 33

PV = K

feet of seawater.

where

=

P

Law

Boyle's

changes

in the

absolute pressure

V =

volume

K=

constant.

Step 4

— Using

the

mine the

method illustrated above
volume at 66 feet:

to deter-

air

P]V,
is

important to divers because

volume of a gas

to

changes

it

relates

in pressure

(depth) and defines the relationship between pressure

and volume in breathing gas supplies. The following
example illustrates Boyle's Law.

Example

1

An open

(Boyle's

where
P,

Law)

v3 -

diving bell with a volume of 24 cubic feet

is

V3 =

be lowered into the sea from a surface support ship.
No air is supplied to or lost from the bell, and the
to

is

the

same

volume of the

air

space

temperature
66-foot,

Step

1

at all depths. Calculate the
in

Step

the bell at the 33-foot,

5

— For

1

ATA
ATA X 24
3 ATA

8

ft

3

ft

3

3
.

method illusvolume would be:

a 99-foot depth, using the

trated previously, the air

and 99-foot depths.

— Boyle's Law
=
V, =
K =
P

v4 =

(at surface):

P,V,

2-8

=

=K

pressure at surface in

(

volume

ATA

3
at surface in ft

constant.

PlV,

where

p4
V,

NOAA

<

= 4 ATA
= 6 ft 3
.

Diving Manual

— October 1991

>

Physics of Diving

Figure 2-3
Boyle's Law

Adapted from

October 1991

— NOAA

Diving Manual

NOAA

(1979)

2-9

Section 2

As depth increased from the surface
volume of

open

air in the

24 cubic feet to 6 cubic
In this

bell

to

99

Because the volume of the closed

feet, the

was compressed from

surface as

at

it is

99

feet, the

bell is the

decrease

in the

same

at the

pressure

is

a result of the change in temperature. Therefore, using

feet.

example of Boyle's Law, the temperature of

Charles' Law:

the gas was considered a constant value. However,

temperature significantly affects the pressure and volume
of a gas;

is

it

therefore essential to have a

method of

(volume constant)

including this effect in calculations of pressure and

volume.
is

To

because the temperature of the water deep

oceans or

in the

knowing the effect of temperature

a diver,

essential,

in lakes

is

from the temperature of the

where

often significantly different
air at the surface.

The gas

=
=
T7 =

law that describes the physical effects of temperature

on pressure and volume

At

Law

Charles' Law.

14.7 psia (atmospheric pressure)

T,

80°F
33 °F

+
+

460°F
460° F

=
=

540 Rankine
493 Rankine.

Transposing:

Law

2.5.3 Charles'
Charles'

is

Pj

states:

a constant pressure, the

P2

volume of a

=

P.T 2
T,

gas varies directly with absolute temperature. For any gas at a constant volume,

the pressure of a gas varies directly with

P,
r
2

absolute temperature.

_
—

X

14.7

493

540

Stated mathematically:

P2
(volume constant)

=

13.42 psia.

Note that the

final pressure

is

below atmospheric

pressure (14.7 psia) because of the drop in temperature.

—=—
V,

T,

Example 3

(pressure constant)

To

(Charles'

Law)

illustrate Charles'

Law

further, consider the fol-

lowing example:

where

An

=
P2 =
Tj =
T2 =
V, =
V2 =
P(

To

initial

initial

final

one given for Boyle's

A

(Charles'

is

45 ° F.

What

is

is

feet.

At the

80 °F; at depth, the temper-

the volume of the gas in the bell at

99 feet?

Law, we know
compressed
to 6 cubic
that the volume of the gas was
level.
99-foot
feet when the bell was lowered to the

From Example

volume

volume.

Law, an example similar

Law

lowered into the ocean to a depth of 99

ature

pressure (absolute)

final pressure (absolute)
initial

having a capacity of 24 cubic feet

bell

surface, the temperature

final pressure (absolute)

illustrate Charles'

Example 2

is

pressure (absolute)

open diving

to the

can be used.

1

illustrating Boyle's

Applying Charles' Law then illustrates the additional
reduction in volume caused by temperature effects:

Law)

closed diving bell at atmospheric pressure and

having a capacity of 24 cubic feet

is

lowered from the

surface to a depth of 99 feet in the ocean. At the
surface, the temperature

perature

when
33°F.

2-10

it

is
is

is

80 °F;

at

99

feet,

33 °F. Calculate the pressure on the bell
at the 99-foot level

where

the tem-

and the temperature

is

=
=
T2 =
Vj

volume

T,

80 °F
45 °F

at depth, 6 ft 3

+
+

NOAA

460 °F
460 °F

=
=

540 Rankine
505 Rankine.

Diving Manual

— October 1991

Physics of Diving

Transposing:

2.5.5

The General Gas Law
comGeneral Gas Law,

Boyle's and Charles' laws can be conveniently

Vv 2 —

V,T 2

bined into what

X

6

as the

expressed mathematically as follows:

T,

V —

known

is

P,V,

P.V,

505

540

=

V,

5.61 ft 3

T|

P2

=

V,

Law

Henry's

=
=
=

P,

Law

Henry's

2.5.4

where

.

states:

The amount

of any given gas

that

initial

pressure (absolute)

initial

volume

initial

temperature (absolute)

will

dissolve in a liquid at a given temperature

and

a function of the partial pressure of the

is

gas that

is

contact with the liquid and the

in

coefficient

solubility

gas

the

of

in

the

particular liquid.

final pressure (absolute)

V2 =

final

volume

=

final

temperature (absolute).

Tt

This law simply states that, because a large percentage
of the

human body

is

more gas

water,

will dissolve into

Example 4 (General Gas Law)

the blood and body tissues as depth increases, until
the point of saturation
gas, saturation takes

long as the pressure

reached. Depending on the

is

from
is

24 hours or longer. As

8 to

maintained, and regardless of

the quantity of gas that has dissolved into the diver's
tissues, the

A

gas will remain

way

in

99 feet

which Henry's Law

works can be seen when a bottle of carbonated soda
suddenly, causing the gases in solution to

happens
rate

is

form bubbles. This

in a diver's tissues if the

is

developed fully

is

VG

for

=

Henry's

come out

The General Gas Law

states:

p2v 2

P,V,

of

T,

prescribed ascent

in the discussion of

decom-

where

=
V, =
T, =
P2 =
T2 =
P,

Law

Determine the volume of

similar to what

pression (see Section 3.2.3.2).

The formula

being lowered to

is

exceeded. The significance of this phenomenon

for divers

is

seawater from a surface temperature of 80 °F to

a depth temperature of 45 °F.

opened. Opening the container releases the pressure
solution and to

in

the gas in the bell at depth.

in solution.

simple example of the

Let us again consider an open diving bell having a

capacity of 24 cubic feet that

is:

aP,

VL

14.7 psia

24

3

ft

80°F

+

460°F

=

540 Rankine

460 °F

=

505 Rankine.

58.8 psia

45 °F

+

Transposing:

where

VG =

volume of gas dissolved at STP
(standard temperature and pressure)

V,

=

PiV.T 2
T,P,

VL =
a

=

volume of the
Bunson

liquid

solubility coefficient at specified

(14.7X24X505)

V,

temperatures

(540)(58.8)
P|

=

partial pressure in

atmospheres of that

gas above the liquid.

October 1991

— NOAA

Diving Manual

V,

=

5.61

ft

3
.

2-11

3

Section 2

Figure 2-4

Gas Laws

(

same answer as that derived from a combination of Example 1 and Example 3, which were used
This

to

is

the

demonstrate Boyle's and Charles' Laws. Figure 2-4

among

illustrates the interrelationships

Charles' Law, and the General

Boyle's Law,

Gas Law.
Note: Effects of gravity

2.6

and water vapor are

GAS FLOW (VISCOSITY)

considered

There are occasions when it is desirable to determine
the rate at which gas flows through orifices, hoses, and
other limiting enclosures. This can be approximated

by employing Poiseuille's equation
expressed mathematically as:

for a given gas

gases,

which

V =

is

for

in

not

the illustration

because they are so sma

I

ATM 80°F

40°F

60°F

3

2

l

APr 4 7r
8Lt7

where

20-0

V

=

AP =

gas flow, in

cm 3 sec

2

1

•

ATM
4

•

6

cm-2

r

=

radius of tube, in

cm

L

=

length of tube, in

cm

t]

=

viscosity, in poise.

(

r

This equation can be used only in relatively simple

3

9.6

10.0

9.3

ATM
7

systems that involve laminar flow and do not include a

9

8

of valves or restrictions. For practical applica-

tions, the diver

should note that, as resistance increases,

flow decreases in direct proportion. Therefore,

length of a line

if

the

increased, the pressure must be

is

increased to maintain the

same

flow.

Nomograms

for

flow resistance through diving hoses can be found in

Volume

5

pressure gradient between 2 ends of
tube, in dynes

number

18.5

19.

2 of the

US Navy

Diving

Manual

6.6

6.4

(1987).

1

r

6.2

Instructions:

2.7

MOISTURE

IN

(1)

BREATHING GAS

Breathing gas must have sufficient moisture to be comfortable for the diver to breathe.

Too much moisture in
and pro-

a system can increase breathing resistance

duce congestion; too

little

(2)

can cause an uncomfortable

sensation of dehydration in the diver's mouth, throat,

nasal passages,

and sinus

cavities (U.S.

Navy

1988).

(3)

Air or other breathing gases supplied from surface
compressors or tanks can be assumed to be dry. This
dryness can be reduced by removing the mouthpiece

and rinsing the mouth with water or by having the
diver introduce a small amount of water into his or her
throat inside a full face mask. The use of gum or candy

2-12

(4)

A

uniform bore sealed-end tube with 20 divisions is inverted in a container of water at 80 degrees F and
one atmosphere pressure. The conditions of
temperature and pressure are then changed as illustrated to explain the three gas laws.
Steps 1,2,3; 4,5,6; 7,8,9 (horizontally) illustrate Charles'
Law, i.e., the reduction of volume with reduction in
temperature at a constant pressure.
Steps 1,4,7; 2,5,8; 3,6,9 (vertically) illustrate Boyle's Law,
i.e., at a constant temperature the volume is inversely
related to the pressure.
Steps 1,5,9; 3,5,7 (diagonally) illustrate the General
Gas Law i.e., a combination of Charles's and Boyle's
Laws.

Adapted from

NOAA

Diving Manual

NO A A

(1979)

— October 1991

(

Physics of Diving

Figure 2-5
Objects Under Water Appear Closer
can be dangerous, because

to reduce dryness while diving

these items

may become

The mouthpiece should

may

lodged

not be

be polluted (see Section

Condensation

2.7.1

in

1

in the diver's throat.

removed

in

water that

1).

Breathing Tubes or

Expired gas contains moisture that

Mask

may condense

the breathing tubes or mask. This water

is

easily

in

blown

out through the exhaust valve and generally presents
no problem. However,

may

freeze;

if

in

very cold water the condensate

this freezing

becomes serious enough

to

block the regulator mechanism, the dive should be
aborted.

2.7.2

Fogging of the Mask

Condensation of expired moisture or evaporation
from the skin may cause fogging of the face mask glass.
Moistening the glass with saliva, liquid soap, or
commercially available anti-fog compounds will reduce
or prevent this difficulty. However, it should be noted
that some of the ingredients in chemical defogging
agents can cause keratitis (inflammation of the cornea) if improperly used. Wright (1982) has described
two such cases; symptoms included severe burning,
photophobia, tearing, and loss of vision, which Wright
attributed to the use of excessive quantities of the

Rays passing from water

into air are retracted

normal, since the refractive index of water

The

is

away from

the

1.33 times that of

system of the eye (omitted for simplicity) forms a
image on the retina, corresponding to that of an
object at about three-quarters of its physical distance from the
air-water interface. The angle subtended by the image is thus 4/3
air.

real

lens

inverted

larger than

Source:

in air.

NOAA

(1979)

defogging solution and inadequate rinsing of the mask.

2.8

LIGHT

AND VISION UNDER WATER

diving, the refraction occurs at the interface

mask and the water. The
image of an underwater object (see Figure 2-5) is
magnified, appears larger than the real image, and
the air in the diver's

2.8.1

The Physics of Light Under Water and
the Consequences for Vision

To function

effectively under water, divers

understand the changes that occur
ception under water.

Many

simply by the fact that

must

in their visual per-

of these changes are caused

light, the stimulus for vision,

travels through water rather than air; consequently

it

between
refracted

seems

to be positioned at a point three-fourths of the

actual distance between the object and the diver's
faceplate.

This displacement of the optical image might be
expected to cause objects to appear closer to the diver

than they actually are and, under some conditions,

and scattered differently than
Refraction, absorption, and scatter all follow

objects do indeed appear to be located at a point three-

physical laws and their effects on light can be predicted;

fourths of their actual distance from the diver. This

is

refracted, absorbed,

in air.

changed physical stimulus can in turn have pronounced effects on our perception of the underwater
world. Both the physical changes and their effects on
vision are described in detail in Kinney (1985) and are
only summarized here.

this

distortion interferes with hand-eye coordination

and

accounts for the difficulty often experienced by novice

At
phenomenon may reverse
objects appearing farther away than

divers attempting to grasp objects under water.
greater distances, however, this
itself,

with distant

they actually are.

The

clarity of the

water has a pro-

found influence on judgments of depth: the more tur2.8.1.1

Refraction

bid the water, the shorter the distance at which the

In refraction, the light rays are bent as they pass

from one medium

October 1991

to

another of different density. In

— NOAA

Diving Manual

reversal

from underestimation

to overestimation

occurs

(Ferris 1972). For example, in highly turbid water, the

2-13

Section 2

distance of objects at 3 or 4 feet (0.9 or 1.2

m) may be

overestimated; in moderately turbid water, the change

might occur

20 to 25 feet

at

away

clear water, objects as far

22.9

(6.1 to 7.6

m); and in very

as 50 to 75 feet (15.2 to

m) might be wmferestimated.

It

is

20/200) on the surface (Luria and Kinney 1969). While

myopes (near-sighted

much

as

loss in

individuals with

individuals) do not suffer quite

acuity

if

their face

masks are

lost as

20/20
myopes and normals, were found

vision do, the average acuities

of the two groups,

important for the diver to realize that judgments

of depth and distance are probably inaccurate.

As a
more

be 20/2372 and 20/4396, respectively,

in

to

one study of

underwater acuity without a mask (Cramer 1975).

rough rule of thumb, the closer the object, the
likely it will appear too close, and the more turbid the
water, the greater the tendency to see

it

as too far away.

Scatter occurs

Training to overcome inaccurate distance judgments

can be effective, but

it

is

important that

it

be carried

out in water similar to that of the proposed dive or
in a variety of different

In addition, training

types of water

(Ferris 1973).

must be repeated periodically

to

in the optical

image

result in a

number

other distortions in visual perception. Mistakes in

of

esti-

mates of size and shape occur. In general, objects
under water appear to be larger by about 33 percent
than they actually are. This often

pointment

to sport divers,

who

is

a cause of disap-

find, after bringing

catches to the surface, that they are smaller than they

appeared under water. Since refraction effects are greater
for objects off to the side of the field of view, distortion

perceived shape of objects

is

in air,

light

an object appears to cross the

distortions; if

view,

its

speed

will

apparent distance

These errors

it

be increased because of the greater
travels (Ross

in visual

and Rejman 1972).

perception and misinterpreta-

refraction can be overcome, to

and speed caused by
some extent, with experi-

ence and training. In general, experienced divers
fewer errors

diffused and scattered by the water molecules

is

all

divers are influ-

to

respond more accurately have met

organisms. Normally, scatter interferes with vision
and underwater photography because it reduces the
contrast between the object and its background. This

these undesirable effects, air itself
if

the face

in water,

mask

is

is

essential for vision.

lost,

the diver's eyes

which has about the same refrac-

Consequently, no normal focusand the diver's vision is impaired
immensely. The major deterioration is in visual acuity;
other visual functions such as the perception of size
and distance are not degraded as long as the object can
be seen (Luria and Kinney 1974). The loss of acuity,
however, is dramatic, and acuity may fall to a level
that would be classified as legally blind (generally

tive index as the eyes.

ing of light occurs

2-14

major reason why vision

loss of contrast is the

much more

is

so

restricted in water than in air (Duntley

1963, Jerlov 1976); it also accounts for the fact that
even large objects can be invisible at short viewing
distances. In addition, acuity or perception of small

much

generally

is

poorer in water than in

air,

despite the fact that the optical image of an object

The

magnified by refraction (Baddeley 1968).

is

deterioration increases greatly with the distance

the light travels through the water, largely because the

image-forming light is further interfered with as it
passes through the nearly transparent bodies of the
biomass, which is composed of organisms ranging from
bacteria to jellyfish (Duntley 1976).

2.8.1.3

Absorption

Light

much
tral

Although the refraction that occurs between the
water and the air in the diver's face mask produces

immersed

kinds of particulate matter held in

make

with some, but not complete, success.

For example,

all

suspension in the water, and by transparent biological

enced to some extent by the optical image, and attempts

them

greater concern under water because

judging the underwater world than do

in

novice divers. However, almost

are

much

of

under water
field of

tions of size, distance, shape,

to train

is

it

frequent. Similarly,

the perception of speed can be influenced by these

Although scattering also occurs

particles in the water.

details
in the

when individual photons of light are
when they encounter suspended

deflected or diverted

themselves, by

be effective

Changes

Scatter

2.8.1.2

to

of

is
it

absorbed as
is

lost in

components of

it

passes through the water, and

the process. In addition, the spec-

light, the

wavelengths that give

rise

our perception of color, are differentially absorbed.

Transmission of light through air does not appreciably

change its spectral composition, but transmitting light
through water, even through the clearest water, does,
and this can change the resulting color appearance
beyond recognition. In clearest water, long wavelength
or red light is lost first, being absorbed at relatively
shallow depths. Orange

is

filtered out next, followed

by yellow, green, and then blue. Other waters, particusilt, decomposing plant
and animal material, and plankton and a variety of
possible pollutants, which add their specific absorp-

larly coastal waters, contain

tions to that of the water. Plankton, for

NOAA

Diving Manual

example, absorb

—October 1991

Physics of Diving

violets

and blues, the colors transmitted best by clear
of material suspended in some harbor

ous under water because fluorescent materials convert

frequently sufficient to alter the transmission

are rarely present under water, which increases the

water.

The amount

water

is

curve completely; not only
ted, but the long

is

wavelengths

very

may

little

light transmit-

in clear

water (Jerlov 1976, Kinney

et al.

1967, Mertens

1970).

Color vision under water, whether for the
of colors, color appearances, or legibility,

more complicated than

is

visibility

thus

much

Accurate underwater
know the colors involved,

in air.

color vision requires that divers

understand the sensitivity of the eye to different col-

know

ors,

color contrast.

be transmitted bet-

than the short, a complete reversal of the situation

ter

short wavelength light into long wavelength colors that

the depth and underwater viewing distance,

The use

of color coding under water

by these changes

in

they are equally bright, but

equally visible

the characteristics of the specific waters involved. Infor-

turbid harbor waters, red

mation is available from several investigations about
which colors can be seen best and which will be invisi-

green

under water (Kinney

et al.

is

a

summary

in

the appearance of colors under

water. For example, red objects frequently appear black

under water. This

is

readily understandable

when one

considers that red objects appear red on the surface
because of reflected red

light.

in

Since clear water absorbs

the red light preferentially, at depth no red light reaches

best for peripheral or off-center viewing.

Attenuation and scatter dramatically reduce the

amount of

natural light available under water, restricting

natural daylight vision to a few hundred feet under the

and to
to 2 feet (0.30 to 0.61 m) or
under the worst or highly turbid conditions. If
there is not enough light (without an auxiliary dive
best of conditions

l

less

light) for daylight vision,

we take

many

visual capabilities that

for granted in air will be greatly different; this

includes good acuity, color vision, and good central or

the object to be reflected, and therefore the object

direct vision. In a low-light situation, acuity

appears unlighted or black. In the same way, a blue

poor and the diver

object in yellowish-green water near the coast could

appear black. Substances that have more than one
peak in their reflectance curve may appear quite different on land and in the sea. Blood is a good example;

maximum in the green is
a much larger one in the
red. At depth, the water may absorb the long wavelength light and blood may appear green. The ghostly
at the surface a reflectance

not noticeable because there

appearance of divers
clear water

is

in

20 to 30

feet (6.1 to 9.1

and

less color

is

m)

of

loss of red light.

perceived as the

depth and viewing distance under water are increased,

and

all

objects tend to look as though they are the

color (the color that
ular

is

same

best transmitted by that partic-

body of water). Objects must then be distinguished

by their relative brightness or darkness. In Table

many

2-3,

of the most visible colors are light, bright colors

that give good brightness contrast with the dark water
If the background were different (for examwere white sand), darker colors would have
increased visibility. Fluorescent colors are conspicuit

October 1991

— NOAA

Diving Manual

is

very

be unable to read; he or she will

have no clear vision, because

objects will appear

all

center to see rather than looking directly at an object.

Moreover,

in

order to see at

all,

the diver must dark-

adapt.
In air, an individual

can gradually adapt to night-

time light levels during twilight and probably not notice

may go directly
from bright sunlight on the boat into a dark underwater world and be completely blind. To function effectively,

the change in vision; however, a diver

the diver's eyes

light.

must adjust

30 minutes

as long as

Some

if

to the

dim illumination

he or she has been

for

in bright

adaptation will take place while the diver

descends, but the rate of descent cannot be slow enough to

make

this a practical solution,

are required. This
in

is

and other techniques

especially important during dives

which the bottom time

is

short

and

visual observa-

tion important.

The most

background.
ple, if

will

white, gray, or black; the diver will have to look off-

is

another example of the

In general, less

highly

best for direct viewing and

is

2.8.1.4 Insufficient Light

of the results of these experi-

ments and shows the colors that were most visible when
viewed by a diver against a water background.

Changes occur too

is

if

1967, 1969; Kinney and

Miller 1974; Luria and Kinney 1974; Kinney 1985).

Table 2-3

complicated

colors can be employed without risk of confusion. Green
and orange are good choices, since they are not confused in any type of water. Another practical question
concerns the most legible color for viewing instruments
under water; the answer depends on many conditions,
which are specified in Human Engineering Guidelines
for Underwater Applications (Vaughan and Kinney
1980, 1981). In clear ocean water, most colors are

and are familiar with the general nature of water and

ble

is

color appearance, and only a few

to

remain

dive.

in

effective

way

to

become dark-adapted

is

the dark for 15 to 30 minutes before the

If this is impossible,

red goggles are recommended.

2-15

Section 2

Table 2-3
Colors That Give Best Visibility
Against a Water Background

Water Condition

Murky, turbid water of low
(rivers,

visibility

Natural Illumination

Incandescent Illumination

Fluorescent yellow, orange,

Yellow, orange, red, white

(no advantage

and red

harbors,

in

Mercury Light

Fluorescent

fluorescent

yellow-orange

paint)

etc.)

yellow-green and

Regular yellow, orange, and

Regular yellow, white

white

Moderately turbid water

Any fluorescence

(sounds, bays, coastal

yellows, oranges, or reds

the

in

Any fluorescence

Fluorescent

the

in

yellows, oranges, or reds

yellow-green or

yellow-orange

water)

Clear water (Southern
water,

deep water

Regular paint of yellow,

Regular paint of yellow,

orange, white

orange, white

Fluorescent paint

Fluorescent paint

Regular yellow, white

Fluorescent paint

offshore,

etc.)

Note: With any type of illumination, fluorescent paints are superior.
a.

With long viewing distances, fluorescent green and yellow-green are excellent.

b.

With short viewing distances, fluorescent orange

is

also excellent

Adapted from

The

night vision system of the eye

is

relatively insensi-

tive to red light; consequently, if a red filter

is

worn

colder a layer of water, the greater

its

that a sound heard 164 feet (50 meters)

light

day vision system to continue to function. The
red filter should be worn for 10 to 15 minutes and must
be removed before the dive. Because high visual sensitivity is reached sooner when this procedure is used,
visual underwater tasks can be performed at the beginning of the dive instead of 20 to 30 minutes later. If it is
necessary to return to the surface even momentarily,
the red filter should be put on again, because exposure
for the

to bright light quickly destroys the

dark-adapted state

of the eye.

is

within one layer

source

if

may

the diver

is

in

is

a periodic motion of pressure change transmitted
(air),

Since liquid

a denser

required

is

to

a liquid (water), or a solid (rock).

medium than

disturb

its

gas,

equilibrium.

more energy

Once

this

disturbance takes place, sound travels farther and faster
in the

denser medium. Several aspects of underwater

sound are of interest

to the

working diver.

may be two or more
water at different tem-

During diving operations, there
distinct contiguous layers of

peratures; these layers are

2-16

source
its

In shallow water or in enclosed spaces, reflections
and reverberations from the air/water and object/water

interfaces will produce anomalies in the sound field,
i.e.,
is

echoes, dead spots, and sound nodes.

swimming

shallow water,

in

among

When

a diver

coral heads, or in

enclosed spaces, periodic losses in acoustic communication signals and disruption of signals from acoustic

The problem

as the frequency of the

signal increases.

through a gas

is

its

another layer.

navigation beacons are to be expected.

ACOUSTICS

Sound

from

be inaudible a few meters from

becomes more pronounced
2.9

density; as the

transmitted between them. This means

sound energy

adapt and at the same time there

be enough

(1979)

difference in density between layers increases, less

over the face plate before diving, the eyes will partially
will

NOAA

known

as thermoclines.

The

The use

of open-circuit scuba affects sound recep-

by producing high noise levels at the diver's head
and by creating a screen of bubbles that reduces the
effective sound pressure level (SPL). If several divers
are working in the same area, the noise and bubbles
tion

communication signals more for some divers
than for others, depending on the position of the divers
in relation to the communicator and to each other.
will affect

A

suit is an effective barrier to sound
above 1000 Hz, and it becomes more of

neoprene wet

at frequencies

NOAA

Diving Manual

—October 1991

Physics of Diving

a barrier as frequency increases. This problem can be
overcome by exposing a small area of the head cither
by cutting holes 0.79 to 1.18 in. (2 to 3 cm) at the
temples or above the ears of the hood.
The human ear is an extremely sensitive pressure
detector in air, but it is less efficient in water. A sound
must therefore be more intense in water ( + 20 dB to
60 dB, SPL) to be heard. Hearing under water is very

to localize

and navigate

conditions.

In general,

similar to trying to hear with a conductive hearing loss

correspondingly high intensity pressure waves.

under surface conditions: a smaller

may

shift in pressure

is

to

sound beacons under

all

successful sound localization

and navigation depend on clearly audible pulsed signals of short duration that have frequency components
below 1500 Hz and above 35,000 Hz and are pulsed
with a fast rise/decay time.

Sound

is

transmitted through water as a series of

pressure waves. High intensity sound

is

transmitted by

A

diver

be affected by a high intensity pressure wave that

transmitted from the surrounding water to the open

required to hear sounds at the extreme high and low

is

frequencies, because the ear

The preswave may create increased pressure within these
open spaces, which could result in injury.
The sources of high intensity sound or pressure waves
include underwater explosions and, in some cases, sonar.
Low intensity sonars such as depth finders and fish
finders do not produce pressure waves of an intensity
dangerous to a diver. However, some military antisubmarine sonar-equipped ships do pulse high intensity pressure waves dangerous to a diver. It is prudent

frequencies.

is

not as sensitive at these

The SPL necessary

nication and navigation

for effective

a function of the

is

commu-

maximum
dB SPL

distance between the diver and the source (-3
for every doubling of the distance

and the measurement

point), the

between the source

frequency of the signal,

the ambient noise level and frequency spectrum, type of

head covering, experience with diver-communication
equipment, and the diver's stress level.
The use of sound as a navigation aid or as a means of
locating an object in the environment depends primarily

on the difference

in

the time of arrival of the sound

two ears as a function of the azimuth of the
source. Recent experiments have shown that auditory
at the

localization cues are sufficient to allow relatively pre-

sound localization under water. Moreover, it has
been demonstrated that under controlled conditions

cise

divers are able to localize

and navigate

to

sound bea-

cons (Hollien and Hicks 1983). This research and practical experience

have shown that not every diver

October 1991

— NOAA

Diving Manual

is

able

spaces within the body (ears, sinuses, lungs).
sure

to

suspend diving operations

transponder

is

being operated

a diver-held pinger system,

it

if

a high-powered sonar

in the area.
is

When

using

advisable for the diver

wear the standard 1/4-inch (0.64-cm) neoprene
for ear protection. Experiments have shown that
such a hood offers adequate protection when the ultrasonic pulses are of 4-ms duration, are repeated once
per second for acoustic source levels up to 100 watts,
to

hood

and are

at head-to-source distances as short as

4 inches

(10 cm).

2-17

(

(

(

Page

SECTION

3

DIVING

3.0

General

3-1

3.1

Circulation and Respiration

3-1

PHYSIOLOGY

3.1.1

Circulatory System

3-1

3.1.2

Mechanism

3-2

3.1.3

3.1.2.1

Pulmonary Ventilation

3-2

3.1.2.2

Blood Transport of Oxygen and Carbon Dioxide

3-2

3.1.2.3

Gas Exchange

3-4

3.1.2.4

Tissue

3.1.2.5

Summary

Need

in the

for

Tissues

Oxygen

of Respiration Process

Respiratory Problems

3.1.3.4

Smoking

3-7

3.1.3.5

Excessive Resistance to Breathing

3.1.3.6

Excessive

3.1.3.7

Hyperventilation and Breath-holding

Dead Space

3.2.1.2
3.2.1.3
3 2.1.4

The
The
The
The

3-5

3-6

3-8

3-8
3-8

3-10

Direct Effects of Pressure During Descent
3.2.1.1

3.2.3

3-5

3.1.3.3

Effects of Pressure

3.2.2

3-4

3-5

3.1.3.2

3.2.1

3-4

Hypoxia
Carbon Dioxide Excess (Hypercapnia)
Carbon Monoxide Poisoning

3.1.3.1

3.2

of Respiration

3-10

Ears

3-10

Sinuses

3-12

Lungs

3-13

Teeth

3-14

Direct Effects of Pressure During Ascent

3-14

3.2.2.1

Pneumothorax

3-14

3.2.2.2

3-14

3.2.2.3

Emphysema
Subcutaneous Emphysema

3.2.2.4

Gas Embolism

3-15

3.2.2.5

Overexpansion of the Stomach and Intestine

3-16

3.2.2.6

Bubble Formation and Contact Lenses

Mediastinal

Indirect Effects of Pressure

3-15

3-16

3-16

3.2.3.2

Gas Absorption and Elimination
Decompression Sickness

3.2.3.3

Counterdiffusion

3-19

3.2.3.4

Aseptic Bone Necrosis (Dysbaric Osteonecrosis)

3-20

3.2.3.5

Inert

3.2.3.6

High Pressure Nervous Syndrome (HPNS)

Inert

3.2.3.1

Gas Narcosis

3.3

Oxygen Poisoning

3.4

Effects of Cold (Hypothermia)

3-16
3-17

3-20
3-22

3-22
3-24
3-25

3.4.3

Thermal Protection
Symptoms of Hypothermia
Survival in Cold Water

3.4.4

Rewarming

3-27

3.4.1

3.4.2

3-25

3-26

3.5

Effects of Heat (Hyperthermia)

3-27

3.6

Drugs and Diving

3-28

3.6.1

3.6.2

Prescription Drugs

3-28

Drugs

3-28

Illicit

(

(

<

DIVING

PHYSIOLOGY
3.0

GENERAL

Figure 3-1

This section provides divers with basic information
about how the body reacts to physiological stresses
that are

imposed by diving and how

to

compensate

The Process

of Respiration

for

these stresses and other physical limitations. Divers
Conchae

should become familiar with the terminology used in
this

Sphenoidal Sinus

chapter to understand and be able to describe any

symptoms or physical problems they
Commonly used diving medical terms are

diving-related
experience.

Septum

Adenoid
(Naso-Pharyngeal Tonsil)

defined in the glossary of this manual (Appendix E).

3.1

The

CIRCULATION AND RESPIRATION
each

activity of

cell

Hairs

Soft Palate

Hard Palate

Tonsil

Tongue

of the body involves several

delicate reactions that can take place only under well-

defined chemical and physiological conditions.
chief function of the circulatory system

is

to

conditions around the cells at the level that
for their functioning.

The

Esophagus (Food Tube)

The
Larynx (Voice Box)

maintain

is

Trachea (Windpipe)

optimal

regulation of cardiac output

and the distribution of the blood are central

Alveoli

is

Lung

Bronchus

to the

Pulmonary
Vein

the process by which gases, oxygen,

Pulmonary

and carbon dioxide are interchanged among the tissues
and the atmosphere. During respiration, air enters the
lungs via the nose or

Right

Bronchial

physiology of circulation.

Respiration

Pharynx

mouth and then

Artery

Cut Edge
of Pleura

traverses the

(Hilus)

Bronchiole

pharynx, larynx, trachea, and bronchi. Air being exhaled

follows this path in reverse.

The bronchi enter the

lungs and divide and re-divide into a branching net-

Pulmonary
Venule

Cut Edge of
Diaphragm

work, ending in the terminal air sacs (alveoli), which
are

approximately one ten-thousandth of an inch

(0.003 millimeter) in diameter.

The

Pulmonary
Arteriole

Stomach

alveoli are sur-

rounded by a thin membrane, and the interchange of
membrane, where the blood

gases takes place across this

Source:

NOAA

(1979)

pulmonary capillaries takes up oxygen and
gives off carbon dioxide. This process is shown schein the tiny

Before discussing diving physiology, a basic understanding of circulation, respiration, and certain prob-

lems associated with the air-containing compartments
of the

body

is

necessary. These topics are discussed in

the following paragraphs.

3.1.1

Circulatory

The heart
sides,

is

System

divided vertically into the right and

left

each consisting of two communicating chambers,

October 1991

— NOAA

is pumped by the
pulmonary artery, through the
pulmonary capillaries, and back to the left side of the
heart through the pulmonary veins. The left ventricle
pumps the blood into the aorta, which distributes it to
the body. This distribution is accomplished by a continual branching of arteries, which become smaller
until they become capillaries. The capillaries have a
thin wall through which gases and other substances are
interchanged between the blood and the tissues. Blood
from the capillaries flows into the venules, the veins,

the auricles and ventricles. Blood

matically in Figure 3-1.

Diving Manual

right ventricle into the

3-1

Section 3

is returned to the heart. In this way,
carbon dioxide produced in the tissues is removed,
transported to the lungs, and discharged. This process
is shown schematically in Figure 3-2.
During exercise, there is an increase in the frequency
and force of the heart beat as well as a constriction of
the vessels of the skin, alimentary canal, and quiescent
muscle. Peripheral resistance is increased and arterial
pressure rises. Blood is expelled from the spleen, liver,
skin, and other organs, which increases circulatory
blood volume. The net result of this process is an increase
in the rate of blood flow to the body organs having a
high demand for oxygen
the brain, the heart, and any

and, finally,

—

adequately to a demand for increased ventilation during exercise. Because diving often requires strenuous
exercise, cardiovascular or respiratory disorders

participating in this activity.

3.1.2.1

Pulmonary Ventilation

Air drawn into the lungs
passages until

air

it

is

distributed through smaller

reaches the honeycomb-like alveoli or

through which the exchange of respiratory
The rates at which

air sacs

gases takes place (see Figure 3-1).

oxygen

active muscles.

may

from actively

seriously limit or prevent an individual

is

supplied and carbon dioxide removed from

the lungs depend on several factors: (1) the composi-

and volume of the

tion

3.1.2

Mechanism

The

of Respiration
is

and relaxation of
muscles. This thoracic cavity contains the lungs, which
are connected with the outside environment through
the bronchi, the trachea, and the upper respiratory
passages and the heart and great vessels. When the
volume of the thoracic cavity changes, a decrease or
altered by the rhythmic contraction

increase in pressure occurs within the internal

cham-

bers and passages of the lungs. This change causes air

passageways
is

until the pressure

through the respiratory

everywhere

in

the lungs

equalized with the external pressure. Respiratory

ventilation consists of rhythmic changes of this sort.

Respiration is affected by the muscular action of the
diaphragm and chest wall and is under the control of
the nervous system, which itself
in

is

through the

res-

gases in the blood; and (3) the duration for which a

chest wall encloses a cavity, the volume of which

to flow into or out of the lungs

air supplied

piratory passages; (2) the partial pressures of respiratory

responding to changes

blood oxygen and carbon dioxide levels. The normal

respiratory rate at rest varies from about 12 to 16

given volume of blood

is

exposed to alveolar

air.

In a

good physical condition, other facinfluencing respiratory exchange are not likely to

normal person
tors

in

be significant.
liter of oxygen is used by the
During exercise, an exchange of
about 3.5 liters or more of oxygen per minute may take
place. This flexibility is accomplished by increased

At

rest,

about 0.3

tissues per minute.

frequency of breathing, increased heart action propelling blood

through the pulmonary capillaries, and

increased differences in the partial pressures of oxy-

gen and carbon dioxide during exercise. Figure 3-3
depicts oxygen consumption as a function of work rate.
Normally, despite wide differences in the rates of gaseous exchange in the resting and heavy exercise condiblood leaving the lungs is almost completely
saturated with oxygen and in equilibrium with the
tions, the

alveolar carbon dioxide pressure.

breaths a minute. During and after heavy exertion, this
rate increases severalfold.

In the chest wall's normal resting position, that

is,

at

the end of natural expiration, the lungs contain about

Even when one voluntarily expels all
the air possible, there still remain about 1.5 liters of
residual air. The volume of air that is inspired and
expired during rest is referred to as tidal air and averages about 0.5 liter per cycle. The additional volume
2.5 liters of air.

3.1.2.2

Blood Transport of Oxygen and

Carbon Dioxide
Blood can take up a much

from the resting expiratory position of 2.5 liters that
can be taken in during a maximal inspiration varies

greater quantity of oxygen
and carbon dioxide than can be carried in simple solution. Hemoglobin, which is the principal constituent in
red blood cells and gives the red color to blood, has a
chemical property of combining with oxygen and with
carbon dioxide and carbon monoxide. The normal hemo-

greatly from individual to individual, ranging from

globin content of the blood increases the blood's oxygen-

about 2 to 6

liters.

The

total

breathable volume of

air,

carrying capacity by about 50 times.

The reaction

governed primarily

called the vital capacity, depends on the size, develop-

between oxygen and hemoglobin

ment, age, and physical condition of the individual.

by the partial pressure of oxygen. At sea level, where
there is normally an inspired oxygen partial pressure

Vital capacity

is

defined as the maximal volume that

can be expired after maximal inspiration.
in vital

3-2

A

reduction

capacity limits the ability of a person to respond

is

of 150 millimeters of mercury, the alveolar hemoglobin

becomes about 98 percent saturated

NOAA

Diving Manual

in

terms of

its

—October 1991

Diving Physiology

Figure 3-2

The Circulatory System

Right
auricle

Lung

capillaries

Tricuspid -f^lt
valve

Bicuspid valve

Veins
Arteries

Body

capillaries

Source:

capacity to form oxy-hemoglobin. In the tissues, where

the partial pressure of oxygen

normally about
20 millimeters of mercury, between one-third and
one-half of this oxygen is given up by hemoglobin and

made

available to the tissues.

It

is

is

apparent that the

blood of persons lacking a sufficiency of hemoglobin,
i.e.,

anemic persons,

to carry oxygen.

generally less

fit

As

will

be deficient

a consequence,

in its

anemic people are

for diving than people

anemic.

October 1991

capacity

who

are not

The blood contains
in

Shilling.

a small

Werts. and Schandelmeier (1976)

amount of carbon dioxide

simple solution, but a greater amount

is

found

in

chemical combinations such as carbonic acid, bicarbonate, or bound to hemoglobin. All the forms of carbon dioxide tend toward chemical equilibrium with
each other. The taking up of oxygen by the hemoglobin
in the lung capillaries favors the unloading of carbon
dioxide at the

same time

dioxide into the blood

in

that the absorption of carbon

the tissues favors the release

of oxygen.

— NOAA

Diving Manual

3-3

Section 3
Figure 3-3

Oxygen Consumption and
Respiratory Minute Volume
as a Function of

Work Rate
S

Sitting

S.

Rest

Light

Moderate

Work

Work

Heavy Work

Severe Work

Quietly!*

Swim,

0.71

I

(Slow)H^

0.5 Knot

(20)

.E

E
Swim, 0.85 Knot (Average
"5

^

= c

1.4

I

(40)

8

SpeeoV^^
Swim,

1

Knot

»s
E *

2

°

il

Swim,

2.1

1.2

Knots^^

\^

(60)

o

0)

\^

2.8

cc

(80)

"\
\

I

I

I

I

i

I

I

Oxygen Consumption, standard

i

liters/min
Derived from

Gas Exchange

3.1.2.3

in

the Tissues

3.1.2.4

NOAA

(1979)

Tissue Need for Oxygen

of oxygen and carbon dioxide between

All living tissues need oxygen, but tissues that are

the blood and body cells occurs in opposite directions.

especially active during exertion, such as skeletal muscle,

Oxygen, which

need greater amounts of oxygen. The brain, however,

The exchange

is

continuously used in the tissues,

exists there at a lower partial pressure than in the

made up

is

of tissue that has an extraordinarily high and

produced inside the tissue

nearly steady requirement for oxygen. Although the

which increases its concentration relative to that
of the blood reaching the tissues. Therefore, blood
supplied by the arteries gives up oxygen and receives

nervous system represents only about 2 percent of the

Carbon dioxide

blood.

is

cells,

transit through the tissue
exchange of these respiratory
amount of gas movement depend on

carbon dioxide during
capillaries.

The

its

rate of

gases and the total

their respective partial pressure differences, since the

exposure time of blood

in the tissue capillaries is

ade-

body weight,

it

requires about 20 percent of the total

circulation and 20 percent of the total oxygen used by

the body per minute at work or at rest. If circulation

completely cut

off,

consciousness

may be

one-quarter of a minute and irreparable

higher centers of the brain
5

minutes (see Section

is

lost in

about

damage

to the

may occur

within

3

to

3.1.3.1).

quate for nearly complete equilibration to be achieved.

When

more active, the need for oxygen is
The increased oxygen is supplied not from an

tissues are

greater.

increase in the oxygen content of the arterial blood but

by the larger volume of blood that flows through the
tissues and by a more complete release of oxygen from
a given volume of the blood. There can be as

much

ninefold increase in the rate at which oxygen
plied to active tissues.

3-4

is

as a

3.1.2.5

Summary

The process

of Respiration Process

of respiration includes six important

phases:
(1)
(2)

sup-

Breathing or ventilation of the lungs;

Exchange of gases between blood and

air in the

lungs;
(3)

The

transport of gases carried by the blood;

NOAA

Diving Manual

— October 1991

Diving Physiology

(4)

(5)

Exchange of gases between blood and body tissues;
Exchange of gases between the tissue fluids and

and
Use and production of gases by the

cells.

Each phase of this process is important to the life of the
and the process must be maintained constantly
by the respiratory and circulatory systems.

cells,

so that spontaneous breathing will resume.
cult to

know when

It

is

diffi-

the heart action has stopped com-

pletely, so efforts at resuscitation
until

3.1.3

will

If breathing has stopped but heart action continues,
cardiopulmonary resuscitation may enable oxygen to
reach the brain and revive the breathing control center

cells;

(6)

promptly before breathing stops, the diver usually

regain consciousness shortly and recover completely.

must be continued

medical attendants pronounce a victim dead.

Respiratory Problems

Although most physiological problems associated

WARNING

with diving are related to the breathing of gases at the

high pressures encountered under water, respiratory
problems may occur at the surface as well. These problems are generally related to the inadequate transport

Is

Onset

of oxygen to the cells and to the inadequate removal of

Some

carbon dioxide.

of the

common

respiratory prob-

3.1.3.2

An

lems are hypoxia, hypercapnia, and carbon monoxide

Each of these

poisoning.

is

discussed in the following

if

Natural Warning That Tells a Diver
of

Hypoxia

Carbon Dioxide Excess (Hypercapnia)

excess of carbon dioxide in the tissues can occur

the process of carbon dioxide transport and elimina-

tion

paragraphs.

No

There
of the

is

interrupted or modified. In diving, carbon diox-

because there is too much
carbon dioxide in the diver's breathing medium or
because the carbon dioxide that is produced is not
eliminated properly. The diver's own metabolic processes
are generally the source of any excess carbon dioxide.
The proper carbon dioxide level is maintained in the
body by respiration rapid enough to exhale the carbon
ide excess occurs either

Hypoxia
The term hypoxia, or oxygen shortage, is used to
mean any situation in which tissue cells fail to receive
or are unable to obtain enough oxygen to maintain
3.1.3.1

their

normal functioning. Hypoxia can occur as a result of

interference with any phase of the oxygen transport

dioxide produced and delivered to the lungs. For breath-

process.

ing to be effective, the air inhaled

Hypoxia stops the normal function of
tissue cells are the

most susceptible of

all

Brain

cells.

body

cells to

minimum

must contain

a

mask
mouthpiece or

of carbon dioxide. Inadequate helmet or

ventilation, too large a

dead space

in

hypoxia; unconsciousness and death can occur before

tubing, or failure of the carbon dioxide absorption

the effects of hypoxia are apparent on other cells.

system of closed- or semi-closed-circuit breathing
systems may produce an excess of carbon dioxide in

Hypoxia may cause sudden unconsciousness
is

gradual,

may

or,

if

onset

decrease the ability to think clearly,

orient oneself, or to perform certain tasks. Confusion

and difficulty

standing, walking, and maintaining

in

may

the gas breathed.
All tissues are affected by an excess of carbon dioxide,

but the brain

the most susceptible organ to

is

be

hypercapnia. Figure 3-4 shows the physiological effects

unaware of impending trouble even though they become

of different concentrations of carbon dioxide for vari-

coordination often follow. Victims of hypoxia

drowsy and weak.
that as

A

particular danger of hypoxia

progresses,

it

may

being that

it

is

causes a false sense of well-

prevent the diver from taking correc-

ous exposure periods. At the concentrations and durations represented

effects have

by Zone

I,

no perceptible physiological

been observed. In Zone

II,

small threshold

severe and sud-

hearing losses have been found and there

den, unconsciousness develops almost at once; un-

ble doubling in the depth of respiration.

tive action soon

enough.

If

consciousness usually occurs
pressure of oxygen
lent to the

falls

hypoxia

when

to 0.10

is

the inspired partial

atmosphere,

i.e.,

oxygen pressure prevailing when

equiva-

a person

breathes a 10 percent oxygen mixture at atmospheric
pressure.

Below

this level,

permanent brain damage

and death occur quickly (US Navy 1985).
If a diver suffering from severe hypoxia

not res-

October 1991

— NOAA

If

will

given fresh air

Diving Manual

a percepti-

Zone
symptoms
In

III,

are

mental depression, headache, dizziness, nausea, 'air
hunger,' and a decrease in visual discrimination. Zone
IV represents marked physical distress associated with
dizziness and stupor, which is accompanied by an inability to take steps for self-preservation.

is

cued quickly, the interference with brain function
cause failure of breathing control.

the zone of distracting discomfort, the

is

stage of the

Zone IV

state

CO., partial pressure

is

The

final

Above a
of 0.15 ATA, muscle

unconsciousness.

(PCOJ

spasms, rigidity, and death can occur.

If

an excess of

3-5

Section 3

Figure 3-4
Relation of Physiological Effects to Carbon
Dioxide Concentration and Exposure Period

<
<

10

10

\

Zone

IV Dizziness, stupor,

unconsciousness

o
0.08

0.06

\

Zone

III

8

<
5

6

.£

Distracting discomfort

c

A

0.04

^^^^

Zone

II

Zone

I

No

3

o
CM
O
O

2

.o

"""""""——««»,

Minor perceptible changes

0.02

o
«
c
•
c
o

effect

0.5
I

0.00

I

I

I

I

I

30

40

50

60

70

I

20

10

PC0 2 ATA

40 Days

Exposure Time, minutes

Derived from

NOAA

(1979)

carbon dioxide causes a diver to lose consciousness, he

differences in individual responses to increases in car-

or she can be revived quickly

bon dioxide. The amount of work, the depth, and the

with fresh

air.

The

if

the lungs are ventilated

aftereffects of hypercapnia include

headache, nausea, dizziness, and sore chest muscles.

The bar graph

at the right of

Figure 3-4 extends the

period of exposure shown to 40 days.
for exposures of

It

illustrates that,

40 days, concentrations of carbon

dioxide in air of less than 0.5 percent (0.005

ATA

breathing

medium

are factors that will also alter the

effect of an increase in carbon dioxide on breathing.

Deliberately reducing one's breathing rate will cause a

carbon dioxide buildup; maintaining an adequate ventilation rate

necessary to remove carbon dioxide

is

from the lungs

effectively.

Other conditions that increase

(Zone A) cause no biochemical or

the likelihood of carbon dioxide poisoning include severe

other effects; concentrations between 0.5 and 3.0 per-

exertion, high partial pressures of oxygen, high gas

partial pressure)

cent (0.005-0.03

ATA

partial pressure)

adaptive biochemical changes, which

(Zone B) cause

may

be consid-

and the use of breathing apparatus that has
excessive dead space or high breathing resistance.
density,

ered a mild physiological strain; and concentrations

above 3.0 percent (0.03 ATA partial pressure) (Zone
C) cause pathological changes in basic physiological
functions. For normal diving operations, ventilation
rates should be
tial

maintained so that carbon dioxide par-

pressures are maintained in Zones

short-term exposures and in Zones

A

I and II for
and B for long-

WARNING
Skip-Breathing Is Not a Safe Procedure
Because Carbon Dioxide Buildup Can Occur
With Little or No Warning

term exposures.
Increased carbon dioxide

in the

breathing-mixture

stimulates the respiratory center to increase the breathing
rate.

Carbon dioxide

at a partial pressure of 0.02

the carbon dioxide level reaches a partial

pressure of 0.05 atmosphere, an uncomfortable sensation of shortness of breath occurs.

3-6

There are large

Carbon Monoxide Poisoning

Inspired carbon monoxide

atmo-

sphere generally increases breathing noticeably.

When

3.1.3.3

(CO) combines with hemothem incapable

globin in the red blood cells, rendering
of carrying oxygen to the tissues.

bound

When

carbon monoxide

hemoglobin, a person experiences tissue
hypoxia (oxygen deficiency in the tissues) even though

is

to

NOAA

Diving Manual

— October 1991

Diving Physiology

the air being breathed has sufficient oxygen. This con-

CO

monoxide (40,000 ppm). The average carbon monoxide

Hemoglobin combines with carbon monoxide about 210 times more

concentration inhaled during the smoking of one cigarette

readily than with oxygen, so very small concentrations

7.0 percent

dition

known

is

as

poisoning.

monoxide can be dangerous to life (US Navy
The hemoglobin-carbon monoxide combination is

400-500 ppm, which produces anywhere from 3.8 to
carboxyhemoglobin (HbCO) in the blood;

is

of carbon

in

1985).

cent.

red in color and

may

cause an unnatural redness of the

However, since this redness may not
occur, carbon monoxide poisoning cannot be ruled out

lips

and

skin.

non-smokers, the

The percentage

HbCO level is generally 0.5
of HbCO blood levels after

per-

con-

tinuous exposure to carbon monoxide for 12 hours or
after reaching equilibrium are

summarized

in the table

below.

simply because a person has normal coloring. In addition to

its

oxidase a

>

monoxide
enzyme (cytochrome

effects on hemoglobin, carbon

combines with the

final respiratory

Continuous Exposure

as well.

level

Because carbon monoxide poisoning

feres with the delivery of

symptoms
oxia.

to

is

50
40

may

8.4
6.7

30
20

high

cause rapid poisoning without the diver's

awareness, he or she

Blood

inter-

are identical to those of other types of hyp-

monoxide

in

%

ppm

CO,

to the tissues, the

the concentration of carbon

If

enough
If

oxygen

HbCO

Level of

causing hypoxia at the tissue

in the tissues,

f

5.0
3.3

10

1.7

—

lose consciousness suddenly.

0.5 (non-smoker)

monoxide poisoning is more gradual in
pounding headache, nausea, and vomiting may

the carbon

onset,

Source:

NOAA

(1979)

occur.

A

diver's breathing gas can be

carbon monoxide

if

contaminated by

the compressor supplying the breath-

draws from an area where the

ing gas

air

is

contami-

nated by the exhaust from a gasoline or diesel engine or
if

vapor from the

oil

used to lubricate the compressor

gets into the air supply.

It

is

essential that the air

intakes on compressors be protected to avoid this source

of carbon monoxide contamination and that

appropriate flash point

is

used

in

oil

with an

any oil-lubricated

compressor that supplies divers' breathing

air (see Sec-

a diver loses consciousness,

it

is

routine to

administer recompression treatment because of fear
that either decompression sickness or an arterial gas
embolism has caused the loss of consciousness. Occasionally, carbon monoxide poisoning is the cause of
unconsciousness, and recompression treatment, using
either USN Treatment Table 5 (Oxygen Treatment of
Type I Decompression Sickness; US Navy 1985) or a
hyperbaric oxygen treatment table designed specifically to treat carbon monoxide poisoning, is the treatment of choice in these cases as well. Carbon monoxide
poisoning victims who resume breathing and regain
consciousness quickly have a good chance of complete

recovery.

3.1.3.4

Smoking

Smoking

20

ppm

directly affects the oxygen-carrying capabil-

ity of the red

blood

cells.

The smoke

of a typical

American cigarette contains about 4 percent carbon

October 1991

— NOAA

Diving Manual

carbon monoxide for 12 hours (equivalent

to the

maximum

carbon monoxide level allowed in divers'
breathing air by the U.S. Navy (see Table 15-6)).
Considering that it takes a heavy smoker approximately
8

hours to eliminate 75 percent of the carbon monoxide

inhaled,

it

is

clear that the

HbCO

level (0.95 percent)

smoker diving 8 hours after the last
cigarette is almost twice that of a non-smoker
(0.50 percent). The carboxyhemoglobin blood level of
a passive smoker (i.e., a person who does not smoke but
who is exposed to the smoke of others) can rise to
even for

tion 4.2.2).

When

Table 3-1 shows the relationship between smoking
and HbCO blood levels. This table shows that the
HbCO level in the blood of divers who smoke is higher
than it would be if the divers had been exposed to

5

a light

percent after exposure to a smoke-filled environment

(Surgeon General 1986).

The dose
smoking

is

of carbon
toxic;

psychomotor

it

test

monoxide

a

causes changes
results,

smoker receives from
in

neurologic reflexes,

sensory discrimination, and

electrocardiograms, as well as fatigue, headache,

irri-

and disturbed sleep. Other shortterm effects of smoking may also adversely affect the
diver. For example, in addition to accelerating the
atherosclerotic changes in blood vessels, cigarette smoke
also raises blood pressure and increases heart rate.
Smokers have trouble eliminating respiratory tract
secretions, and the accumulation of these secretions
can make equalizing pressure in the ears and sinuses
difficult (Shilling, Carlston, and Mathias 1984). The
irritants in inhaled tobacco smoke can cause an increase
tability, dizziness,

3-7

Section 3

Table 3-1

Carboxyhemoglobin as a
Function of Smoking
ence the amount of breathing resistance encountered
Median

HbCO
Smoking Habits

Level,

Expired

%

CO, ppm

by a diver using the equipment. Gases moving through
tubes of optimal design will flow 'in line' or in laminar
flow until restrictions in or the dimensions of the tube

Light

smoker

cause the air molecules to begin moving

pack/

(less than Vz

day)

3.8

Moderate smoker (more than Vz
pack/day and less than 2
packs/day)
Heavy smoker (2 packs or more/

17.1

fashion {turbulent flow).

5.9

27.5

laminar flow

6.9

32.4

required to

day)

Source:

NOAA

(1979)

move gas
is

that

in a

The increase
in

is

disordered

in the effort

turbulent rather than

significant: the resistance increases in

relation to the square of the increased flow rate; that

is,

doubling the flow rate causes a fourfold increase

in

resistance (see Section 2.6). This

may

be a problem

with small-bore snorkels, small-diameter exhaust valves,

mucus and a chronic inflammatory change in
Over a prolonged period, these
conditions may result in structural weakness of the
lung, such as emphysematous bullae, alveoli enlarged
in bronchial

the bronchial lining.

with

air,

Lung

or obstructive lung disease.

cysts can

enlarge because of gas trapped by bronchial obstruc-

and may then rupture. The resulting tears can
open into pulmonary veins, permitting gas embolism.
Furthermore, nicotine and carbon monoxide increase
tion

the 'stickiness' of blood platelets, causing a clumping
that can interfere with the flow of blood in the small
vessels; this condition
tibility to

Navy

may

increase a person's suscep-

decompression sickness. In

divers, cigarette

a study of 93

smoking was found

to

be

associated with lung function decrement and to have

an important and adverse effect on divers' health
(Dembert et al. 1984). Other Navy research reported
by Dembert and co-authors suggests that there is an
association between smoking and the risk of decompression sickness.

The

or inadequate breathing tubes and mouthpieces. Thus,
snorkels should have diameters approximately 3/4 inch
(1.9 centimeters) with

no unnecessary bends, corruga-

tions, or obstructions,

and exhaust valves should be

enough

large

to

keep the exhalation resistance as low

as possible (see Sections 5.1.1.4

The

position of the

demand

and

relation to the internal pressure in the lungs
in closed-circuit

spiratory system clearly indicate that divers should

smoking altoavoid smoking for several

(Figure 3-5).

As the work-of-breathing

level in the tissues

(US Navy

1985).

Excessive Dead Space
Dead space in a diving system

3.1.3.6

residual exhaled air remains.

some

A

is

A

A

of

well-designed system has

work-of-breathing
in

(i.e.,

ume by

the

amount

breathing) to some extent. If the

breathing resistance of the apparatus
difficult to breathe

is

high,

it

will

be

adequately even during ordinary

exertion and breathing will

become impossible during

hard work. Resistance to the flow of breathing gas

is

caused by demand regulators, valves, hoses, and other

appurtenances of a life-support system. Well-designed

equipment minimizes the amount of resistance
flow of breathing gas (see Section

The

5.

1

.

1

.

determining how

must

this ineffective vol-

much exhaled

gas

is

actually

rebreathed.

Full-face

dead space;
breath

masks may add as much as 0.5 liter of
this excess must be ventilated with each

(US Navy

1985). Because of carbon dioxide

buildup, the excess can seriously limit a diver's ability
to do work. Free-flow helmets do not have this dead
space problem. The use of oral-nasal masks inside
full-face masks is effective in reducing the amount of

dead space (see Section

5.2.1).

to the

3.1.3.7 Hyperventilation

1 ).

characteristics of the breathing gases flowing

through tubes of various sizes and configurations

3-8

minimum dead

not reveal dead space volume; special equipment

breathing apparatus used by a diver under water

work involved

mask may return
amount

casual examination of diving equipment will

be used to measure the extent of

Excessive Resistance to Breathing

which

returned depends on the dead space volume within the

space.

Any

that space in

diver exhaling into a

of this exhaled gas to the lungs; the

gether, they should at least

will increase the

increases, the

body reaches a point where it will accept increased
carbon dioxide rather than perform the respiratory
work required to maintain a normal carbon dioxide

system.

3.1.3.5

critical

pressure causing an increase in breathing resistance

not smoke. If divers are not able to stop

hours before diving.

is

scuba to avoid unbalanced hydrostatic

snorkel, mouthpiece, or full-face

deleterious effects of smoking on the cardiore-

5.6.1).

valve or breathing bag in

influ-

The

(C0

)
2

and Breath-holding

respiratory system utilizes both carbon dioxide

and oxygen (0 2 ) tensions

NOAA

(partial pressures) in

Diving Manual

— October 1991

Diving Physiology

Figure 3-5

on Location
Bags Within a Closed-Circuit Scuba

Effects of Hydrostatic Pressure
of Breathing

Breathing bag
subject to

is

more

deeper than the lungs.

It

is

hydrostatic pressure,

increasing breathing resistance on

exhalation.

Breathing bag is at the same level as the
lungs. Breathing resistance is the same as
on the surface.

Breathing bag is shallower than the lungs.
It is subject to less hydrostatic pressure,
increasing breathing resistance on
inhalation.

Source:

the body to regulate the process of breathing. Rising

CO,

tension and falling O, tension are monitored by

biological sensors in the body,

the breathing response

when

which normally trigger

the appropriate levels are

reached. Hyperventilation (rapid, unusually deep breath-

ing in excess of the necessary rate for the level of

normal operation of the
mechanism. Hyperventilation lowers the CO, level in body tissues to levels below normal, a condition known as hypocapnia, which initially
causes a feeling of lightheadedness and may cause
weakness, faintness, headache, and blurring of vision
activity) interferes with the

respiratory control

over a longer period.

Hyperventilation

in

distance

underwater swimming or breath-holding competitions,

is

or

spasm occurs

Some

unconsciousness before the

CO,

fall

may drown.

tion.

Divers

who

notice that they are hyperventilating

should take immediate steps to slow their breathing

ly.

and,

if

feasible,

ascend prompt-

After reaching the surface, they should inflate their

buoyancy compensators. Hyperventilating divers should
because they

hyperventilation, oxygen levels can

water, the diver

more susceptible to hyperventilation-induced hypocapnia than others; however, sufficiently prolonged hyperventilation induces unconsciousness or muscle spasms in most individuals.
Both scuba and surface-supplied divers should be
aware of the problems associated with hyperventila-

dioxide level without significantly increasing the oxy-

in

in the

individuals are

not attempt to

breath-holding after

and may cause uncon-

sciousness or muscle spasms. If either unconsciousness

a dangerous practice. Hyperventilation lowers the carbon

When

(1979)

often initiated by anxiety or physi-

cal stress or outright panic

rate, notify their buddies,

Voluntary hyperventilation, which occurs

gen level of the blood.

is

NOAA

swim

may

to a

boat or the shore unaided

lose consciousness in the attempt.

During surface-supplied diving, the tender should

to levels resulting

continuously monitor the diver's breathing for signs of

high enough

hyperventilation. Divers starting to hyperventilate should

level

is

As a consequence, competiunderwater breath-holding events should be discouraged (Bove 1985).

Once on

to stimulate respiration.

be asked to stop work and

tive

ing the breath for short periods will aid in replenishing

October 1991

— NOAA

Diving Manual

low

CO,

levels

rest.

the surface, hold-

and may avert further complications.

3-9

Section 3

3.2

EFFECTS OF PRESSURE

The

effects of pressure on divers

may

be divided into

two principal categories: (1) those that are direct and
mechanical; and (2) those that come about because of

changes

in

With

the partial pressure of inspired gases.

each 2-foot (0.61 meter) increase

depth of sea-

in the

water, the pressure increases by almost

Each

psi.

1

The many changes in pressure regularly involved in
diving make a pressure-sensitive middle ear a liability
for a diver.

The

immersion on the human ear causes it
under water than it does in air.

effect of

to function differently

Normally, sound

is

compressed)

high-amplitude

in a

transmitted in air (which

(HA) low

is

easily

force mode.

33 feet (10 meters) of descent in seawater increases the

In liquid (which

pressure by an additional atmosphere (14.7

transmitted in a low-amplitude (LA) high force mode.

The lungs and

psi).

respiratory passages contain air at

times. In addition to the major air channels,

all

which

include the nose, mouth, throat, larynx, and trachea,
there are a

number

of side compartments issuing from

The human ear

difficult to compress),

is

designed to convert

is

HA

of sound in the external

and middle

however, sound arrives at the ear

the upper respiratory passages that are important in

back

When

occur

the

exposed to pressure changes, such as those that

is

in diving, air

contained

in these cavities

compression because the pressure of the

undergoes

to

LA

is

As

not efficient.

ear.

In water,

LA mode,
LA to HA

and
and

a result, the external/

middle ear mechanisms are functionally bypassed under
water and hearing

primarily achieved by bone (skull)

is

conduction.

When

air delivered

by the breathing supply must be equilibrated with the
pressure of the surrounding environment. The pressure

LA

energy to

in the

diving physiology. These include the eustachian tubes,

body

is

energy (see Figure 3-6) by the mechanical processing

the process of converting sound from

the middle ear, and the paranasal sinuses.

sound

divers experience extreme changes in ambient

may

pressure, the ears

be injured unless the pressure

of air breathed into and out of the lungs and respiratory

between the air-containing cavity and the ambient
atmosphere is equalized. Barotitis media (middle ear

accordance with changes

squeeze) resulting from inadequate pressure equaliza-

passages thus also changes

in

the surrounding hydrostatic pressure.

in

between the middle ear and the ambient pressure
common problem among divers. Although
occasionally disabling, it is usually reversible. Because
more people are diving to deeper depths, there have
tion
is

3.2.1

Direct Effects of Pressure During Descent

Humans can

tolerate increased pressures

if

they are

uniformly distributed throughout the body. However,

when

the outside pressure

is

different

from that inside

the body's air spaces, this difference in pressure

shape of the involved

distort the

This

ry.

is

may

causing inju-

tissues,

in

been more serious and disabling problems involving
the inner ear.
In terrestrial environments, balance

and

such spaces as the sinuses and the

middle ear must be equalized on descent, or pressure

spatial ori-

entation depend on input to the central nervous system

from the

visual, proprioceptive (sense of touch),

vestibular (sense of balance) systems.

called barotrauma.

The pressure

a fairly

work beneath the

sea, visual

When

and

people

and proprioceptive cues

are frequently distorted; thus, spatial orientation and

differences will develop across the walls of these spaces.

balance become more dependent on information received

Once

from the vestibular system. Vestibular system dysfunc-

it

the pressure at a given depth has been equalized,

must be allowed

to

decrease

if

decreases, as occurs during ascent.

the external pressure

The

effects of pressure

on various parts of the body are discussed

in

the following

paragraphs.

tion

may occur

in

many phases

of diving, and the

subsequent vertigo, nausea (and, occasionally, vomiting)

can be

life

threatening.

The middle ear space (Figure
cell

systems

in the skull

3-6) connects with air

bone containing the

ear.

With

an intact eardrum membrane, the only communication
3.2.1.1

The Ears

between

this

system and the ambient atmosphere

is

The air-containing external and middle ear gives
humans a device that efficiently transforms airborne

through the eustachian tube. This tube

sound energy

leads from the middle ear to the nasopharynx (or upper

this

energy

is

to the fluid-containing inner ear,

where

transduced into electrical signals. Proper

functioning of this

mechanism requires

that both the

external ear canal and the middle ear contain air and
that differences in pressure be avoided

between these

structures and the ambient atmosphere or inner ear.

3-10

1.4 to 1.5 inches (3.5 to 3.8

cm) long

is

approximately

in the

adult and

expanded portion of the throat) behind the nasal caviThe nasopharyngeal opening normally is closed
by positive middle ear pressure, or, when opened during swallowing, by muscular action on the surrounding

ties.

cartilage.

NOAA

Diving Manual

— October 1991

Diving Physiology

Figure 3-6
Principal Parts
of the Ear

drum
Semicircular canals

or inner ear

may occur

with as

as 3 pounds
and they may

little

(1.3 kilograms) of pressure differential,

happen anywhere

in

the water column.

WARNING
Because Of The Danger Of Round Window
Rupture,

A

Maneuver Should

Forceful Valsalva

Not Be Performed During Descent

The inner ear consists of a system of fluid-filled
bony channels within the temporal bone (Figure 3-6).
Membranous

structures that are divided into two parts,

the vestibular system containing the semi-circular canals

and the auditory system, are located

in

these channels.

These two systems are interconnected and have a

common

blood supply. Changes in cerebrospinal fluid pressure

EAR

can be transmitted directly to the inner ear compartments, and therefore any maneuver such as straining,
The

air-containing external auditory canal, middle ear,

chian tube are noted. The
the perilymphatic

fluid-filled

inner ear

and eusta-

subdivided into

is

and endolymphatic spaces, which connect

to

the subarachnoid space by the cochlear duct and endolymphatic
duct, respectively.

Source: Bennett and Elliott (1982) with the
permission of Bailliere Tindall, Ltd.

or trying to clear the ears against closed nasal

lifting,

passages can cause increased pressure in the ear's fluidfilled

compartments. Marked pressure changes may

cause ruptures between the inner and middle ear, leading

.

to vertigo

and hearing

loss;

this

may happen even

in

shallow exposures.

The eustachian tube

In general,
is

lined by epithelium that

similar to the lining of the nose, sinuses,

ynx.

Abnormal

is

and nasophar-

nasal function can be caused by acute

or chronic inflammatory diseases, allergy, chronic

irrita-

from excessive smoking or prolonged use of nose
drops, or chronic obstruction from internal or external

tion

nasal deformities or lesions. Nasal dysfunction

may

contribute to inadequate eustachian tube function, which

may

cause middle or inner ear barotrauma

in divers

(Sections 20.3.2 and 20.3.3).

Descent usually causes greater difficulty

in

equalizing

the ear than ascent because the air passes from the

middle ear more easily than into the middle ear from
As descent or compression proceeds,

the nasopharynx.

middle ear pressure must be equalized constantly to
prevent middle ear barotrauma with possible eardrum

rupture or inner ear injury caused by rupture of the

round window (see Figure 20-1). Successful methods
of equalizing middle ear pressure are swallowing,

yawning, or gently blowing against a closed mouth and
nostrils. Forceful blowing (valsalva maneuver) should
never be done because, if the middle ear pressure is
already negative, forceful blowing, which causes an

any individual who has difficulty with

middle ear ventilation at the surface should not dive.

Furthermore, individuals who have chronic nasal
obstruction or a history of frequent upper respiratory

infections, nasal allergies, mastoid or ear disease,

or chronic sinus trouble should have a

complete

otolaryngological evaluation before diving. Also, individuals

who have an upper

respiratory infection of any

kind should not dive until the infection has cleared.

Systemic and topical drugs may improve nasal function
and sinus and middle ear ventilation. However, divers
should use such agents cautiously because the rebound
phenomenon that occurs after the drug, and especially
topical nose drops, wears off may lead to greater nasal
congestion and even greater equalization problems in
the ears and sinuses. Prolonged use of topical nasal

medications can cause chronic nasal

irritation.

For safe diving, equalization problems must be
avoided. For example,

if

a diver cannot clear his or her

ears on the surface, he or she should not dive.

Some

steps to be followed during descent are:
•

Descend

feet first, preferably

line or a

drop

line.

It

is

down

the anchor

easier to equalize middle

increase in cerebrospinal fluid and inner ear pressure,

ear pressure in the upright position because drain-

may

age

rupture the round window. Injuries to the ear-

October 1991

— NOAA

Diving Manual

is

more

effective in this orientation.

3-11

Section 3

Figure 3-7
Location of
Sinus Cavities
•

Clear the middle ear early, actively, and conscientiously during descent. Clearing by forceful
blowing against a closed mouth and nose should be

•

Stop the descent

avoided,

if

(

possible.
if

ear blockage or fullness devel-

symptoms

ops; the diver should ascend until these

have cleared, even

if

return to the surface

Descent should not be continued

is

required.

until ear pain

develops.

Inner-ear decompression sickness (also called vestibular decompression sickness) has occurred with no

symptoms other than

vertigo, ringing in the ears, or

nausea (Farmer 1976). Vestibular decompression sickness

commonly

seen more

is

after

deep helium-oxygen

dives, particularly after a switch to air in the later

stages of decompression, although

shallower air diving.

in

Any

also has occurred

it

diver with such

symptoms
Orbit Of Eye

during descent or compression should be considered as

having inner ear barotrauma, including possible rupture of the oval and round windows,

and should not be

recompressed. Recompression would again subject the
diver to unequal middle ear pressures. However, even
if

Maxillary
Sinus

these precautions are heeded, hearing impairment

can develop as a result of diving. For

this reason, divers

should have annual audiometric examinations.

(

NOTE
Any

diver with ringing or roaring in the ears,
loss of hearing, vertigo or dizziness, or nausea or vomiting during or shortly after decompression from a dive should be treated as
having inner-ear decompression sickness.

The Sinuses

3.2.1.2

The

sinus cavities are

shown

in

Figure 3-7. Although

paranasal sinus barotrauma occurs only rarely in divers,

inflammation and congestion of the nose, nasal deformities,

or masses can cause blockage of the sinus opening.

This blockage leads to a series of changes within the
cavities, consisting of absorption of pre-existing gas,

vacuum formation,

Maxillary
Sinus

swelling, engorgement, inflamma-

tion of the sinus lining, or collection of fluid in the
sinus cavity.

When

such blockage occurs during descent

in diving or flying, the intra-sinus

vacuum becomes

greater and the resulting pathological changes are
severe; there
in

some

may

more

Opening To

Pharynx

Eustachian

Tube

be actual hemorrhage into the sinus

instances.

Paranasal sinus barotrauma also occurs during ascent;
the

mechanism of

this

trauma appears

to be a

blockage

(

of a one-way valve of the sinus by inflamed mucosa,
cysts, or polyps,

3-12

which permits pressure equalization

Source:

NOAA

Diving Manual

NOAA

(1979)

—October 1991

Diving Physiology

Figure 3-8

Pressure Effects

on Lung Volume
during descent but impairs it during ascent. The symptoms and management of paranasal sinus barotrauma
are discussed in Sections 20.2.1 and 20.3.

The Lungs
As long as normal breathing takes place and

the

ample, the lungs and airways

will

3.2.1.3

breathing supply

is

equalize pressure without difficulty. If divers hold
their breath during a pressure increase, no difficulty
arises until the total

compressed

to less

volume of

air in the lungs

is

than the residual volume. Once the

in the lungs becomes less than the residual
volume, pulmonary congestion, swelling, and hemor-

volume

rhage of the lung tissue occurs; this condition is called
thoracic squeeze. Figure 3-8 graphically illustrates
the effects of pressure on lung volume.
In breath-hold diving, no high-pressure air

able to the lungs. Pressure compresses

and

Law

(P

fall in

lung volume,

the effects of Boyle's

i.e.,

V =P,VJ. Lung volume

tolerable compression.
will

avail-

diaphragm; pressure equalization results

raises the

from the

is

the diver's chest

Descending

limits the extent of

to

33 feet (10 meters)

reduce lung volume by one-half. Compression down

volume (the amount of air in the lungs after
forceful expiration) can be tolerated; however, when
chest compression exceeds this limit, tissue trauma
occurs. Fluid from the capillaries and tissues then
enters the alveoli and the air passageways and may
to residual

At the surface

Atmosphere Absolute, 4.7 psi. The lungs are
expanded with a full breath of air.
1

1

fully

cause gross hemorrhaging. Mild lung barotrauma causes

only pain and a slight exudation, which

reabsorbed, but

is

the lungs

quickly

may

be
damaged. This form of trauma generally responds well
in serious cases,

to conservative treatment consisting of general supportive

care, prevention of infection,

and intermittent

positive-

pressure inhalation therapy. Spraying with bronchodilators

may

and aerosols and inducing gravitational drainage
prove beneficial

if

hemorrhage

or bruising has

been severe.

The use of

a breathing

inspiratory resistance

apparatus that has a high

may cause pulmonary edema

(increased fluid in the tissues of the lungs). In an effort
to

maintain adequate lung ventilation during moder-

ate activity, the small veins of the lungs

aged, fluid

may

may

be dam-

seep through the membranes, and the

may rupture. In addition, gas exchange can be
hampered, which increases the risk of decompression
sickness. Coughing and shortness of breath are symptoms of this condition, and x rays of the chest may show
patchy pulmonary infiltration, which usually clears
alveoli

At 33 Feet
2

Atmospheres Absolute. 29.4

hydrostatic pressure, the

lungs

is

reduced

to only

Vi

psi.

Because

same volume
its

of

of air in the

surface volume.

within 24 hours without specific therapy.

The lungs can be traumatized during the compression phase of a dive or treatment

October 1991

— NOAA

if

an individual stops

Diving Manual

Source:

NOAA

(1979)

3-13

Section 3

may

breathing, either voluntarily by breath-holding or invol-

overexpansion and overpressurization of the lungs

untarily because of windpipe or tracheal obstruction

cause progressive distension of the alveoli. This over-

or convulsions.

distension

may be

general, which occurs with breath-

holding or insufficient exhalation, or localized, which
3.2.1.4

happens with partial or complete bronchial obstruc-

The Teeth

tion

Pain

in the teeth (harodontalgia)

can occur

in diving

and may be caused either by referred pain from the
paranasal sinuses or by tooth squeeze. This latter condition, athough uncommon, is caused by a variety of
dental conditions, such as

new

lesions or a lesion that

has developed around the edge of an old

filling (recur-

(Rottman 1982). Tooth squeeze is not caused
trapped in a filling. Other causes of tooth squeeze

rent decay)

by

air

include recent extractions,

gum

infections that have

formed periodontal pockets, large areas of decay where
is infected, and recent fillings. Tooth squeeze

the pulp

can also occur

if

is

mucus,

of any type. Problems of lung overinflation can occur

during ascent from depths as shallow as 4-6 feet
(1.2-1.8 meters)

if

the breath

is

held. Several of the

most commonly encountered physiological

difficulties

associated with pressure during ascent are described

paragraphs; each may be prevented by
breathing normally during ascent, providing there is
no localized airway obstruction. Figure 3-9 shows the
in the following

possible consequences of overinflation of the lungs.

to

dry and seal the canal between treatments with a material
is

lesions,

a person dives while undergoing root

canal therapy. Part of the root canal procedure

that

caused by the presence of bronchial

bronchospasm. For this reason, individuals with
bronchial asthma should not do compressed gas diving

or

WARNING

designed to be adequate at a pressure of one

atmosphere. Exposure to higher pressures, however,
can produce small leaks

in this

Do Not Hold Breath While Ascending

material that are not

able to release air fast enough during subsequent ascent.

Like other squeezes, tooth squeeze usually subsides

3.2.2.1

Pneumothorax

Distended alveoli or

(emphysematous

sphere. This

when the ambient pressure is reduced to one atmomechanism also may be the explanation

blebs)

for tooth explosion (Rottman 1982). Gas that has accumulated slowly during a saturation dive can cause

is

tooth explosion during or after decompression.

gas expands as the diver surfaces, causing increased

may

(pleura),

air-filled blisters

membrane lining of the chest
causing pneumothorax. Under pressure, this
rupture the

extremely dangerous because trapped intrapleural

pressure in the chest cavity.

The lungs may be

lapsed by this pressure, and the heart
3.2.2 Direct Effects of

Pressure During Ascent

is

if

the breath

is

held or there

a localized airway obstruction, the expanding air

retained, causing overinflation

col-

be pushed

its normal position. Symptoms and signs include
sudden severe pain, reduction of breathing capability,
and, rarely, coughing of frothy blood.
The rapid onset of pneumothorax can cause sudden

out of

During a pressure decrease (e.g., during ascent), the
air in the body cavities expands. Normally, this air
vents freely and there are no difficulties. If breathing
is normal during ascent, the expanding lung air is
exhaled freely. However,

may

is

and overpressurization

of the lungs. For example, the air in the lungs at a

depth of 66 feet (20.1 meters) gradually expands to

respiratory and circulatory difficulty, impaired car-

diac function, or death from shock. Early diagnosis

and prompt treatment with thoracentesis (chest puncture) are essential. If recompression is required for
concomitant conditions, the pneumothorax must be
vented or released by a chest tube or other device
before ascent

is

accomplished.

WARNING
3.2.2.2

A

Who Has

Experienced Blowup (or an
Overpressure Accident) Must Immediately
Be Examined by a Physician
Diver

Mediastinal

Emphysema

Mediastinal emphysema

is

the result of air being

forced into the tissues about the heart, the major blood
vessels,

and the trachea (windpipe)

in the

middle of the

Gas trapped in the spaces between tissues may
expand rapidly with continuing decompression, causing impaired venous return. The symptoms of mediastinal emphysema are pain under the sternum (breastbone) and, in extreme cases, shortness of breath or
chest.

volume during ascent to the surface (see
air volume can expand safely to the
point of maximum inspiration, assuming there is no
three times

Figure 3-8).

its

The

airway obstruction.

3-14

If the

pressure decreases further,

NOAA

Diving Manual

— October 1991

Diving Physiology

Figure 3-9
Complications From Expansion
of Air in the Lungs During Ascent
fainting caused by circulatory interference resulting
vessels. The
emphysema is

from direct pressure on the heart and large
treatment for mild cases of mediastinal

symptomatic. In more severe cases, oxygen inhalation

may aid resolution of the trapped gas. For severe,
massive mediastinal emphysema, recompression is

Cerebral Gas Embolism

required.

Air Passes Via

Carotid Arteries
To Brain

Subcutaneous Emphysema
may be associated
mediastinal emphysema, is caused by air being

3.2.2.3

Subcutaneous emphysema, which
with

Mediastinal

forced into the tissues beneath the skin of the neck

Emphysema

extending along the facial planes from the mediasti-

num. Unless

it

is

extreme (characterized by a crack-

ling of the skin to the touch), the only

symptoms of

subcutaneous emphysema are a feeling of fullness

in

the neck and, perhaps, a change in the sound of the
voice.

Having the victim breathe oxygen

will

acceler-

ate the absorption of this subcutaneous air.

Gas Embolism

3.2.2.4

The most
tion

serious result of

nary venous system. This gas

Air Passes Along

Air Enters-

Bronchi To

Pleural Cavity

Mediastinum

(Pneumothorax)

Air Enters

Blood Vessel

pulmonary overpressuriza-

the dispersion of alveolar gas into the pulmo-

is

is

carried to the heart and

then into the arterial systemic circulation, causing gas

emboli (gas bubbles)

in the

coronary, cerebral, and

other systemic arterioles. These gas bubbles continue

expand as the pressure decreases, which in turn
makes the clinical signs more severe. (Section 20.4.2
describes the symptoms of arterial gas embolism in
to

detail.)

The
Alveoli

lism

Expanded

clinical features of

may

traumatic arterial gas embo-

occur suddenly or be preceded by dizziness,

headache, or a feeling of great anxiety. Unconsciousness,

and convulsions follow quickly. Motor
and in
different combinations. Death is caused by coronary

cyanosis, shock,

and sensory

deficits occur in various degrees

or cerebral occlusion with cardiac arrhythmia, respiratory failure, circulatory collapse,

examination of a person with

and shock. Physical

a gas

embolism may

reveal: (1) focal or generalized convulsions; (2) other

neurological abnormalities; (3) marbling of the skin;
Alveoli

Normal

bubbles

(4) air

j^

in the retinal vessels of the eye;

(5) hemoptysis; or (6) Liebermeister's sign (a sharply

defined area of pallor in the tongue). Temporary obstruction of

an air passage, which can occur with a cold or

bronchitis, increases the risk of gas embolism,

and

diving with a respiratory infection should therefore be

avoided.

A

person with bronchial asthma has hyper-

reactive small airways in the lung. Breathing dry

compressed
Source:

October 1991

— NOAA

Diving Manual

NOAA

(1979)

air,

aspiring salt water or cold water,

exercising, or being anxious can all cause a

bronchospasm

3-15

Section 3

under water. Ascent with local

air

trapped

in the alveoli

could cause a pressure imbalance and rupture, resulting
in

gas embolism. For this reason, bronchial asthma

is

a

contraindication for compressed gas diving,
regardless of how well the asthma is controlled by
medication. Coughing or sneezing while in a recom-

strict

pression

chamber

or while ascending during a dive can

embolism. Divers should stop their
they feel a cough or a sneeze coming on, and

ascent to expel gas by belching or passing

An

tum.

may

during ascent

cause marked discomfort and vaso-

foods before diving is not recommended. If a diver
swallows enough air, he or she may have difficulty

may

breathing and

then panic. Accordingly, activities

that cause air swallowing, such as

ascents

avoided during diving.

chamber operators should stop the chamber ascent
they are notified that an occupant of the chamber

The only

effective treatment for gas

A

is

patient should be kept in the

which may help

to

keep bubbles

embolism

Bubble Formation and Contact Lenses
The use of contact lenses by divers has increased

3.2.2.6

is

significantly in recent years. For this reason, studies

position,

in the circulation

reaching the brain. Placing the patient on the
helps to maintain cardiac output, which

may

from

left side

be impaired

because the gas bubbles have decreased the efficiency
of the

pumping action

of the heart (see Figure 19-9).

In non-fatal cases, residual paralysis, myocardial necrosis,

may occur

recomnot carried out immediately and may even

and other ischemic

injuries

pression

is

occur

adequately treated patients

in

in

initiating therapy.

if

there

if

is

a delay

Hyperbaric chambers that can-

not be pressurized to 6

ATA

chewing, should be

if

merely symptomatic.

head-down

gum

is

about to cough or sneeze.
recompression; other treatment

per rec-

vagal effects. Eating large amounts of gas-producing

also cause a gas
if

it

excess of gas in the stomach or intestine

are not as effective for

embolism treatment as those with this capacity, but
recompression to 2 or 3 ATA is far better for the
embolism patient than no recompression.

have been done to determine the inherent dangers of
using them, especially during decompression (Simon
and Bradley 1981). Three types of contact lenses were

compared, membrane (soft) lenses and two types of
polymethylmethacrylate (hard) lenses. One type of
hard lens (fenestrated) had a 0.016 inch (0.4 millimeter)
hole in the center, while the other type (non-fenestrated)

was
sions

solid throughout.

from 149

During controlled decompres-

feet (45.5 meters) in a hyperbaric

cham-

wearing the non-fenestrated hard lenses

ber, subjects

developed small bubbles in the precorneal tear film
under the contact lens. These bubbles, first observed at
70 feet (21.3 meters), increased both in number and

decompression progressed. The divers wearing

size as

these hard lenses experienced soreness, decreased vis-

ual acuity, and reported seeing halos

when viewing

These symptoms were noted at the time of bubble formation and persisted for about 2 hours after
return to sea level (Simon and Bradley 1981). No bubbles were noted under the same decompression conditions when the divers wore the fenestrated hard lens,
lights.

WARNING
Central Nervous System Decompression
Sickness Is Clinically Similar to Gas Embolism and the Treatment of Either Requires a
Recompression Chamber

membrane lens, or no lens at all.
The authors of this study concluded that

the soft

the bubble

formation was caused by the lack of permeability of
the hard non-fenestrated lens (Simon and Bradley
In cases of gas embolism, administering

oxygen and

positioning the body (head-down at a 15 degree angle)

are only partially effective; drugs and fluids also

be helpful. These measures should be used
val before the patient reaches a

may

It is recommended, therefore, that divers electing
wear contact lenses use either soft membrane lenses

1981).
to

or hard fenestrated lenses.

in the inter-

recompression cham-

3.2.3 Indirect Effects of

ber (see Section 20.4.2).

The

in the partial

3.2.2.5

Overexpansion of the Stomach and Intestine

The stomach and

large intestine ordinarily contain

1.06 quarts (1 liter) or

more

of entrapped gas. Since

Pressure

indirect effects of pressure are caused

by changes

pressures of the gases in the breathing

medium. These

effects include saturation

and desat-

uration of body tissues with dissolved gas and changes
in

body functions caused by abnormal gas

tensions.

the intestines are surrounded by soft tissues, the com-

pression and re-expansion of these air bubbles are
ordinarily neither hazardous nor noticeable. If one

swallows air while diving,

3-16

it

may

be necessary during

3.2.3.1 Inert

Gas Absorption and Elimination

While breathing

air at sea level,

body

tissues are

equilibrated with dissolved nitrogen at a pressure equal to

NOAA

Diving Manual

— October 1991

Diving Physiology

the partial pressure of nitrogen in the lungs. During

and thus causes

exposures to altitude (low pressure) or

tissues;

in

diving (high

inert gas to be eliminated

after a sufficient time,

enough gas

from body
will have

pressure), the partial pressure of nitrogen in the lungs

been eliminated

to

change and the tissues will either lose or gain
nitrogen to reach a new equilibrium with the nitrogen
pressure in the lungs. The taking up of nitrogen by the
tissues is called absorption or uptake; giving up nitrogen from the tissues is termed elimination. In air diving, nitrogen absorption occurs when a diver is exposed
to an increased nitrogen partial pressure, and elimination occurs when pressure decreases. This process occurs
when any inert gas is breathed.

This process

continued until the diver reaches the

will

Absorption consists of several phases, including the
transfer of inert gas

from the lungs

and

to the blood

then from the blood to the various tissues through

which

The gradient

flows.

it

for gas transfer

partial pressure difference of the gas

is

the

between the lungs

and blood and the blood and the tissues. The volume of
blood flowing through the tissues is usually small com-

is

surface safely.

permit the diver to ascend further.

On

surfacing, the diver's body

contains inert gas in supersaturated solution
tissues,

but this

is

normally safe

if

kept within proper

decompression limits and if further pressure reduction, such as ascent to altitude, does not occur (see
Section 14.8).

The basic principles
same for any

are the

of absorption and elimination
inert gas breathed.

However,

there are differences in the solubility and rates of gas
diffusion in water
in tissues

and

fat.

Helium

than nitrogen and diffuses

equilibration occurs
the case for nitrogen.

is

much

less soluble

Thus, helium

faster.

somewhat more rapidly than is
The advantages in using helium-

oxygen rather than nitrogen-oxygen mixtures are

pared to the mass of the tissue, but over a period of

dom from narcosis and a decrease in breathing
To develop mathematical models of gas

time the gas delivered to the tissue will cause

tissues,

physiological theory postulates that the

body

composed of

it

to

become equilibrated with that carried in solution by
the blood. The rate of equilibration with the blood gas
depends on the volume of blood flow and the respective
capacities of blood and tissues to absorb the dissolved

still

some

in

is

free-

resistance.

solubility in

human

several 'tissue compartments,' each

having a different 'half time.' For example, a compartment with a half time of 10 minutes is one in which
the tissues are 50 percent saturated with gas after

For example, fatty tissues hold significantly more

exposure to pressure for 10 minutes, while a 20-minute

gas than watery tissues and will thus take longer than

compartment would be 50 percent saturated in 20 minutes, and so on. Various characteristics of these theoretical compartments, such as their relative fattiness,

gas.

watery tissues to saturate or desaturate excess inert
gas.

The process
tion.

of elimination

is

the reverse of absorp-

During ascent and after surfacing, the

tissues lose

are believed to account for these differences in tissue
half times.

excess inert gas to the circulating blood by diffusion,
the gradient being the difference
partial pressure in

between the

inert gas

of inert gas that can be

Decompression Sickness
Decompression sickness (DCS) refers to the illness
that may occur after a reduction in barometric pres-

limited, so the tissue inert gas

sure; such a reduction in pressure can occur either

each tissue and that

in the

blood

after the blood has equilibrated to the pressure of the

gas in the lungs.

taken up

in the

The amount

blood

is

tension falls gradually.

As

blood flow, the difference

amount

in

absorption, the rate of

in partial

and the
and blood

pressures,

of inert gas dissolved in the tissues

determine the rate of elimination. After decompressing to
the surface or ascending to a shallower level, equilibration

new level may require 24 hours or more.
is assumed that, during decompression,

at the
It

and

tissues

can to some degree hold gas

solution without bubbles being formed.

to

the blood

in

supersaturated

A

supersaturated

is

become supersaturated

when returning from

the depth of a dive to the atmo-

sphere at sea level or when going from the atmosphere
at sea level to the

atmosphere

decompression sickness

from solution

in

is

for short periods of time, a

bubbles are the cause of

DCS

October 1991

— NOAA

Diving Manual

borne out by the facts

DCS (as well
DCS symptoms

incidents of

as during decompressions in

occurred), and (2) no other

explanation accounts so well for the success of

re-

compression therapy as a treatment for DCS.

These bubbles can cause the symptoms and signs of
through various mechanisms: Intracellular bub-

bles can disrupt the cells

without bubble

establishes an outward gradient

is

which no

depth and duration of

his or her dive,

of

that (1) bubbles have been seen and recorded during

DCS

The ascent

The cause

the tissues and blood of the body and

diver can ascend a certain distance, depending on the

formation.

at altitude.

the release of dissolved gas

the consequent formation of bubbles in the body. That

one that holds more gas than would be
possible at equilibrium at the same temperature and
pressure. Because of the ability of the blood and tissue

solution

3.2.3.2

and cause

loss of function;

intravascular bubbles can act as emboli and block

3-17

Section 3

many

circulation either to a few or

tissues,

The most common symptom

depending

DCS

of

is

which

pain,

is

on where these bubbles lodge; and extravascular bubbles can cause compression and stretching of the blood

usually localized at a joint. Pain

and nerves. In addition, the blood-bubble interface acts as a foreign surface and activates the early
phases of blood coagulation and the release of vasoactive

often described as a dull, throbbing pain deep in the
joint or tissue.

substances from the cells lining the blood vessels.

the pain as being related to

vessels

The causes

of

DCS

include inadequate decompres-

decompression table used was

sion (either because the

inadequate or was not followed properly), individual
physiological differences, or environmental factors.
Inadequate decompression

is

an obvious cause of

DCS,

70

to

DCS

75 percent of

The

reported to occur in

is

cases.

The pain

onset of this pain

and, in the early stages, the diver

DCS

of

is

usually gradual

is

may

not recognize

DCS. However,

the pain

more intense and, in some cases, it may
become severe enough to interfere with the strength of

slowly becomes

the limb. In divers, the upper limbs are affected about

three times as often as the lower limbs. Before

decided that the case involves Type

DCS

I

it

is

only, the

symptoms occur even when the decom-

diver should be given a careful examination for any

obviously inadequate. In addition, decom-

as obesity, fatigue, age, poor physical condition, being

may be masking
symptoms. However, if pain is truly the
only symptom, the case falls into the Type I category
and should be treated as such.
Although pain is reported as a symptom in 30 percent of cases of Type II DCS, this form of DCS includes
all cases that have respiratory problems, hypovolemic
shock, or more serious symptoms or signs of central or
peripheral nervous system involvement. Because of the

dehydrated, or having an illness that affects the lung

involvement of the nervous system, Type

or circulatory efficiency. Environmental factors that

be associated with

but frequently no

pression

is

may occur even

pression sickness

tables used are adequate

Moreover,

it

common

is

if

the decompression

and are
assume

strictly observed.

to

that

DCS

cannot

occur on a 'no-decompression' dive; however, although
is

uncommon

dives,

it

DCS

for

to

it

occur on no-decompression

can happen. Differences

in individual physi-

DCS

include factors such

ology that

may

predispose to

have been implicated

in the

DCS

development of

cold water, heavy work, rough sea conditions,

are

and the

Decompression sickness (colloquially termed 'the
may be divided into two general categories,
Type I and Type II. Type I DCS includes those cases in
which pain, skin itching or marbling, or lymphatic
involvement are the only symptoms. The mildest cases
bends')

DCS

are those involving the skin or the lymphatics.

Skin bends are characterized by itching of the skin and
a burning sensation,

which may also be accompanied

by the appearance of a mottled rash or marbling of the
skin. Lymphatic involvement is usually signaled by

many

These usually have their
after a dive but, as

is

II

DCS may

and symptoms.
onset during or immediately

different signs

Type

the case with

I

DCS, may

experts also consider the

and excessive fatigue that

DCS.

may

common

site for

Type

II

DCS

common symptoms

in spinal

cord trauma; these include paralysis, loss of

are similar to those seen

sensation, muscular weakness, loss of sphincter control,

and girdle pain of the trunk. Often the symptoms

or signs of either spinal cord

DCS

or peripheral nerve

DCS

do not follow a typical nerve distribution, and
care must be taken not to dismiss strange neurological
complaints or findings as hysterical

may

toms

be unstable

in position

is

uncommon.

early stage of spinal or peripheral

of anorexia

symptoms

follow a dive manifes-

the spinal cord, and

is

the most

symptoms

painless swelling, but such involvement

Some

serious

occur as long as 36 hours after surfacing. The most

use of heated suits.

of

neurological signs, because the pain

more

is

matic nerve

different

in origin.

Symp-

and type during the

DCS;

this shifting in

from the usual history of

trau-

injuries.

which are

Cerebral decompression sickness can be manifested

mild pains that begin to resolve within 10 minutes of

form of almost any symptom. Common ones are
headaches or visual disturbances, and others include
dizziness, tunnel vision, confusion, disorientation,
psychotic symptoms, and unconsciousness. The combination of nausea, vomiting, vertigo, and nystagmus
is characteristic of labyrinthine DCS, which is known
as the 'staggers' because its victims have difficulty

tations of

Type

I

onset, are considered

mild cases of Type

In addition, 'niggles,'

symptoms
I

involvement, or niggles)

DCS

of

Type

I

DCS. These

(skin bends, lymphatic

do not require treatment other

than breathing pure oxygen at
of time, and often even this

1

is

ATA

for a short period

not required. However,

any diver with niggles, skin bends, or lymphatic
involvement should be watched closely, because these
symptoms may presage the onset of more serious problems that

will require

recompression.

ply be assumed that these symptoms
to more severe ones.

3-18

It

should not sim-

in the

walking or maintaining their balance. Tinnitus and
partial deafness may also occur as part of this complex
of symptoms.

Pulmonary

will not progress
It

is

DCS

is

commonly known

as the 'chokes.'

characterized by substernal distress on inhala-

NOAA

Diving Manual

— October 1991

Diving Physiology

Figure 3-10
Isobaric Counterdiffusion
tion,

coughing that can become paroxysmal, and severe

respiratory distress that can end in death. This form of

DCS has been
DCS cases.

reported to occur

(A) Steady

(

about 2 percent of

in

if

°

o

Hypovolemic shock may occur as the sole symptom
of Type II DCS, but it is more commonly associated
with other symptoms. The symptoms of rapid pulse
rate, postural hypotension, etc., are no different from
those found in hypovolemic shock occurring for other
reasons and should be treated in the same manner, that
Rehydration should be performed
is, by rehydration.
orally

o

o

o

all

the patient

conscious

is

intravenously. Mild hypovolemia

or, if

may

State-

o

1

°

o

o

o
°n\°
o
^-^

o

£Jftt&CQ

°y^M
\.
r

o

r

/•JZWv

o
o

O
•

o

•V

Gas

1

Gas

2

o

V

mpJTSt\\

o

o

)

I

o \

o

&&**•*
•*

°

0-**°

o

unconscious,

be more com(B) Transient

mon

in

diving than

is

generally realized because of the

'•

while dressed in a diving

suit,

/No
\

limited access to fluids,

*f

symptoms of

more complete discussion

DCS may

be found

in Elliott

1

I

always be identified and treated, because the treatment of DCS is less effective if the shock condition has

A

•

•

pressure or cold diuresis, etc. Hypovolemic shock should

not been corrected.

•

•

increased heat load that results from working hard

'W°
•y Rx\.

*
•

of the

and Kindwall

Jfe
L-^O/fcr^

•

(1982).

!•

Q¥sV\

•

•

•
•

1

•
cs*r°*

Source: Bennett and Elliott 1982) with the
permission of Bailliere Tmdall, Ltd.
(

3.2.3.3

Counterdiffusion

Experiments dating back

.

1962 have demonstrated

to

that the sequential use of different breathing gases in a

particular order, determined by their physical properties,

could increase dive time at depth without increas-

During some of
was discovered that a
diver breathing one gas mixture while surrounded by
ing a diver's decompression obligation.

these experiments, however,

it

another could develop serious gas lesions even when
the ambient pressure
level

was maintained at a constant
(D'Aoust and Lambertsen 1982).

For example, experimental subjects breathing neon

at the skin,

where a gradient sloping to the exterior
approaches satu-

exists; note that the superficial skin

ration with gas

1

(°),

except for a gradient

ies.

The process depicted

deep

counterdiffusion occurs
is

in

Figure 3-1

tissue isobaric gas exchange.

suddenly changed

to

if

environment developed skin lesions, severe nausea,
vomiting, and vestibular derangement. Because this
phenomenon involves the passage of gases at the same
ambient pressure through tissue fluids in opposing

skin,

has been termed isobaric counterdiffusion or

isobaric counterexchange.

saturation or subsaturation) can occur in the skin or

between internal

tissues

and

their capillaries. This

can

lead not only to serious lesions but also to the formation of gas

constant.

emboli even when ambient pressures are

The process

is

shown

in

situation depicted in Figure 3-1

'steady state' and occurs

when

0A

Figure 3-10. The
is

referred to as

the superficial tissues

of the subject approach saturation with gas 2

October 1991

is

— NOAA

Diving Manual

(•)

except

OB occurs

different

and gas

2 (•) will be

initially

in

from the
1

c
(

)

will

through the

taken up again via the

lungs and through the skin. Unlike the situation

in

Figure 3-1 0A, this latter process must be considered
transient, since gas
to a negligible level

1

(°) eventually will be

and gas 2

(•)

will

the subject at a final pressure that

Depending on circumstances, counterdiffusion (super-

that

1

Deep-tissue isobaric

one being breathed. In such a situation, gas

be eliminated via the lungs and

it

gas

the gas surrounding a diver

one that

or nitrogen mixtures while surrounded by a helium

directions,

in

slopes from the exterior to the interior blood capillar-

reduced

eventually saturate
is

no greater than

ambient (D'Aoust and Lambertsen 1982).

Depending on depth and the breathing gases being
used, the total gas tensions produced during the transient

can reach levels sufficiently high

to

formation and decompression sickness.

cause bubble

Work

in this

complex field is continuing and should lead to the use
of improved gas sequences and improvement in the
efficiency of deep diving and the development of safer
decompression procedures.

3-19

Section 3

3.2.3.4

Aseptic Bone Necrosis
(Dysbaric Osteonecrosis)

Exposure
pressure

is

to

compressed

which may have been a factor in the destrucBone lesions may not become
apparent on x rays for 4 months to 5 years after the
crystals,

tion of the joint surface.

air at elevated

atmospheric

sometimes associated with the death of

necrosis

This condition

(1982).

is

referred to as avascular necrosis of

bone, caisson disease of bone, or aseptic or dysbaric

bone necrosis. These changes are not of infectious

ori-

A

initiating insult.

portions of the long bones of the exposed individual.

A

detailed review of aseptic bone

may be found

McCallum and Harrison

in

3-year survey of 350 full-time divers in the British

Navy showed

bone
had shown no

a 5-percent incidence of aseptic

and they have been seen in patients suffering from
many conditions, such as chronic alcoholism, pancreatitis, and sickle-cell anemia, in patients using sys-

evidence of having experienced decompression sick-

temic steroids, and

survey of 934 U.S.

gin,

in caisson

(compressed

air tunnel)

workers and divers. The development of changes

in the

accompabreakdown,

necrosis; half of the affected divers

ness

(Workman, personal communication).

Navy

divers,

aseptic bone necrosis were found by standard radio-

hip and shoulder joints of caisson workers,

graphic techniques; another

nied by crippling effects caused by joint

as doubtful (Hunter et

was

first

noted

in

1888, but the disease has not been

who

In a recent

16 positive cases of

1.71

al.

1 1

cases were interpreted

1978).

The data revealed

a

percent incidence overall and a 6.7 percent inci-

more conservative decompression procedures than com-

dence for divers over the age of 35. Although the
relationship between aseptic bone necrosis and decom-

pressed air tunnel workers do.

pression sickness

particularly prevalent in divers,

generally observe

is

not clear, the incidence of oste-

of aseptic bone necrosis occur in the

onecrosis in the subjects of this study was found to be

head of such bones as the femur (long leg bone) or
humerus (bone of the upper arm), the weakened underlying bone that supports the cartilage covering the bone
will collapse under weight-bearing and activity, causing the joint surface to break down and become irregular. Pain occurs with movement of these joints and is
accompanied by muscle spasms around the joint and
the inability to use the joint in a normal manner. Since
the lesions often are bilateral and symmetrical, both

and number of months of diving.
Navy, the
long-bone radiographs of a group of 177 non-diving
enlisted men were compared to the long-bone radiographs of 93 enlisted divers 35 years of age or over
(Hunter and Biersner 1982). It was found that diving,
as practiced by the U.S. Navy, contributes independently
to the development of aseptic bone necrosis and bone

If the lesions

may collapse,
Lesions may also occur

femoral heads

causing severe disability.
in

the shafts of the long

bones, but these almost never cause
bility;

symptoms

or disa-

however, bony scars that indicate increased density

may appear on

x ray after

elbows, wrists,

new bone

Bone necrosis

is

deposited during

seldom seen in the
or ankles of divers or caisson workers

the healing process.

is

(Kindwall 1972).

Factors that

may

be related to the likelihood of

developing bone lesions are frequency of exposure to
pressure,

number

of cases of bends,

adequacy and

promptness of recompression treatment, and the

total

amount of exposure to pressure. According to McCallum
and Harrison (1982), "The whole process from the
first radiographic appearance of the lesions to loss of
continuity in the joint surface may take only from 3 or
4 months to 2 or 3 years or perhaps longer."
The cause of aseptic bone necrosis has still not been
demonstrated beyond doubt. There is some evidence
that fat emboli may occlude circulation in the blood
vessels in bone and other tissues and thus may be a
factor in the development of hip lesions in the chronic
alcoholic with a fatty liver. In patients with gout,
lesions of the hip joints have contained sodium urate

3-20

related both to age

In another study conducted by the U.S.

cysts, as

evidenced among divers

in the tested group.

This conclusion was qualified by the statement that
the results must be viewed with caution 'because of the
larger

number

group

than for the diver group, the small

of doubtful films found for the nondiver

number

of

and doubtful cases found in either group, the
age of the samples used (35 years of age or older), and
the substantial degree of unreliability demonstrated in
the classification of the films' (Hunter and Biersner
1982). A subsequent study, also by the U.S. Navy,
concluded that the prevalence of bone cysts among
Navy divers is probably related to one or more of
several conditions, including hyperbaric exposure,
positive

genetic predisposition, and increased exposure to adverse

environmental or hazardous conditions (Biersner and

Hunter 1983).

3.2.3.5 Inert

Gas Narcosis

Inert gas narcosis is caused by the raised partial
pressure of the inert gas in compressed air (see
Section 20.1.6). In diving, the most common type of
inert gas narcosis

and other

is

nitrogen narcosis. Although nitrogen

inert gases are physiologically inert

mal conditions, they are able

NOAA

to

under nor-

induce signs and symp-

Diving Manual

— October 1991

Diving Physiology

toms of narcosis or anesthesia at sufficiently raised
pressures. Other inert gases, such as those in the noble
gas series, range

narcotic potency from helium through

in

neon, nitrogen, argon, and krypton to the surgical anesthetic xenon.

Recent analyses have demonstrated that

the qualitative behavioral effects are equivalent regardless of the specific
al.

Neon

1985).

gas causing the narcosis (Fowler et

has been used satisfactorily for exper-

imental diving procedures but

Helium

is

not used in diving

widely used

The onset of narcosis is rapid. The condition is often
when a diver first reaches depth and may there-

severe

Recovery

after stabilize.

equally rapid and

is

accom-

is

plished by ascending to a shallower depth so that the
narcotic effect of the inert gas

who
remember

reduced. Divers

is

may

have experienced narcosis on a dive

not

events occurring at depth.

High alveolar pressures of
in their effects

N

and CO, are additive

on performance, but

CO,

has no signif-

diving as a

icant effect on nitrogen narcosis (Hesser, Adolfson,

substitute for nitrogen and to prevent narcosis (see

and Fagraeus 1971). Factors that can increase the

such a weak narcotic that

susceptibility to narcosis include alcohol or the after-

today.

is

a gas

Section 15.1.3). Helium

is

in

helium narcosis has not been demonstrated.

that

is

it

caused by the physiochemical interaction of

the inert gas with the nerve cell

A

body.
rect

is

membranes

of the

theory widely held that has been proved incorthat the signs and

symptoms

of narcosis are

caused by carbon dioxide retention resulting from
respiratory embarrassment occasioned by the breathing of dense inert gas mixtures at raised pressures.

signs and symptoms of narcosis are noticed first
approximately 100 feet (30.5 meters) during com-

The
at

pressed air breathing and are similar to those of alcoholic intoxication or the early stages of hypoxia; there
is

a wide variation in individual susceptibility. However,

depths the majority of compressed air divers

at greater

show impairment of thought, time perception, judgment, reasoning, memory, ability to perform mental or
motor

tasks,

and increased reaction time (see Table

Many measures

3-2).

have been used to assess the perform-

ance decrement resulting from inert gas narcosis.
Cognitive tests are more sensitive measures of narcotic
effects than manual dexterity tests (Fowler et al. 1985).
Intellectual capacities such as short-term

memory

are

affected to a greater extent than manual dexterity. If

become

where they are

dives

air

depths

to

symptoms

of nar-

et al. 1960).

greater

100

than

feet

(30.5 meters), special precautions should be taken;

only experienced,

many

be used. As

fit,

and well-trained divers should

decisions as possible should be

made

before the dive, including length of bottom time, duration of ascent,

and actions

to be taken in

an emergency.

Experience, frequent exposure to deep diving, and a
high degree of training

may

permit divers to dive as

deep as 180-200 feet (54.9-61 meters) on

air,

but

novices or susceptible individuals are advised to remain
at shallower depths.

At depths greater than 180

feet

(54.9 meters), the performance or efficiency of divers

breathing compressed air will be impaired. At 300 feet
(91.5 meters) or deeper, the signs and
narcosis are severe and there

is

symptoms

of

the possibility of hallu-

cinations, bizarre behavior, or loss of consciousness.

Furthermore, because of the associated increased oxygen
partial pressure at such depths,

may

oxygen convulsions

occur.

oxygen tend

may have

feel-

and well-being (euphoria) and a sense
accompanied by

of detachment from the environment,

dangerous overconfidence, an uncontrollable desire

and

a tingling

gums, and

correct

For

Frankenhaeuser

Experimental work has suggested that divers satu-

ings of elation

lips,

pressure increase the signs and

cosis (Hesser 1963;

rated on compressed air or a mixture of nitrogen and

Divers experiencing nitrogen narcosis

to laugh,

nitrogen partial pressure, increases in the oxygen partial

likely

tasks well before diving.

a

motion sickness remedies and sedatives. At a constant

narcotic, they should practice anticipated

divers expect to dive in situations
to

and the effects of

effects of alcohol, fatigue, anxiety, cold,

Although many theories have been developed to
explain the mechanism of inert gas narcosis, it is clear

legs.

and vague numbness of the

There may be an

and rapid decisions or

on a task. Errors

may

be

inability to

make

to concentrate effectively

made

in

recording or compil-

some

to adjust to

of the narcotic effects of

nitrogen, thus permitting deeper air breathing excur-

made (Hamilton

et al. 1973, Schmidt et al.
and Hamilton 1975, Miller 1976).
However, divers must have demonstrated their ability

sions to be

1974,

Langley

to adjust to elevated partial pressures of nitrogen before

procedures relying on

it

can be used without taking

extra care and providing additional supervision (Bennett

1976, 1982). Various efforts have been

made

to use

ing data or computations. Novices, especially, may-

drugs and other methods to reduce the effects of nar-

develop terror rather than euphoria. Narcosis

cosis.

nificant

danger

to divers

because

it

is

a sig-

increases the risk

of an accident and simultaneously diminishes their
ability to

cope with an emergency.

October 1991

— NOAA

Diving Manual

In general, 'the

weight of evidence favors the

conclusion that ethanol (alcohol) exacerbates narcosis

and amphetamine ameliorates

it.

This

with the view that narcosis depresses the

is

consistent

CNS

(central

3-21

Section 3

Table 3-2
Narcotic Effects of
Air Diving

Compressed

Depth

Feet

Meters

Effect

30-100

9.1-30.5

Mild impairment of performance on unpracticed tasks
Mild euphoria

100

Reasoning and immediate memory affected more than motor coordination and

30.5

choice reactions. Delayed response to visual and auditory stimuli

100-165

Laughter and loquacity

30.5-50.3

may be overcome by

self control

Idea fixation and overconfidence
Calculation errors

165

50.3

Sleepiness, hallucinations, impaired judgment

165-230

50.3-70.1

Convivial group atmosphere.

May be

terror reaction in

some

Talkative. Dizziness reported occasionally

Uncontrolled laughter approaching hysteria

230

70.1

Severe impairment

230-300

70.1-91.5

Gross delay

in

of intellectual

response to

some

performance. Manual dexterity less affected

stimuli.

Diminished concentration

Mental confusion. Increased auditory

300

in

sensitivity,

i.e.,

sounds seem louder

Stupefaction. Severe impairment of practical activity and judgment

91.5

Mental abnormalities and

memory

defects. Deterioration

in

handwriting,

euphoria, hyperexcitability

Almost

300

total loss of intellectual

and perceptive

faculties

Hallucinations (similar to those caused by hallucinogenic drugs rather than alcohol)

91.5

Derived from Edmonds, Lowry, and Pennefather (1976)

nervous system)' (Fowler et

al.

1985). (Readers are

referred to Bennett (1982) and Fowler et

more complete discussions of

3.2.3.6

al.

(1985) for

High Pressure Nervous Syndrome (HPNS)

At diving depths greater than 600 fsw (183 msw),
signs and symptoms of a condition known as the high
pressure nervous syndrome (HPNS) appear and become
worse the faster the rate of compression used and the
acterized in
postural

humans by

compresemploying

exponential compression rates, adding other inert gases

inert gas narcosis.)

greater the depth or pressure attained.

rate of compression to depth, using a stage
sion with long pauses at selected intervals,

HPNS

is

such as nitrogen to helium/oxygen mixtures, and
selecting personnel carefully. At present, the data suggest
that adding 10 percent nitrogen to a helium/oxygen
mixture, combined with the use of a proper compression rate, ameliorates

HPNS

many

of the serious

symptoms of

(Bennett 1982).

char-

dizziness, nausea, vomiting,

and intention tremors, fatigue and somnolence,

3.3

OXYGEN POISONING

in intel-

Prolonged exposure to higher than normal oxygen

and psychomotor performance, poor sleep with
nightmares, and increased slow wave and decreased
fast wave activity of the brain as measured by an

manifestations are referred to collectively as oxygen

myoclonic jerking, stomach cramps, decrements
lectual

electroencephalogram (Bennett et
First noted in the
initially as

1960's,

al.

was referred

to

helium tremors. Since that time, numerous

studies have been conducted that were designed to

determine the causes of
of preventing

ameliorating

3-22

it

HPNS

and

to develop

means

(Bennett 1982). Methods of preventing or

HPNS

poisoning.

include using a slow and steady

It

is

now believed most

likely that

whose

oxygen

by increased rates of formation
of superoxide, peroxide, and other oxidizing free radicals that ultimately cause critical enzyme inactivation, lipid peroxidation, and impairment of cell mempoisoning

1986).

HPNS

partial pressures causes a variety of toxic effects

is

initiated

brane function, with resultant disruption of intracellular
metabolism. These adverse effects of oxidant species
are opposed by anti-oxidant protective

NOAA

Diving Manual

mechanisms

— October 1991

Diving Physiology

the defenses are

until

overwhelmed by the magnitude

continuous oxygen exposure. Other symptoms or signs

CNS

and duration of oxidant stress. Thus, the onset time,

of

nature, and severity of overt manifestations of oxygen

irregularities in breathing pattern,

determined by the inspired oxygen presduration
of exposure, as well as by unique
and
sure
characteristics of enzyme function and external mani-

spasms, muscular incoordination, fatigue, confusion,
and anxiety. Extreme bradycardia to a degree suffi-

toxicity are

festations of specific disruptions of intracellular

Since oxygen toxicity

lism.

non

in all

phenome-

a generalized

that affects all living cells,

ultimately expressed
tions

is

metabo-

its

(Lambertsen 1978).

in

the ears,

diaphragmatic

cient to cause cerebral ischemia with transient loss of

consciousness

sure at 3.0

may

occur during prolonged oxygen expo-

atmospheres (Pisarello

et al. 1987).

Oxygen effects on organs other than the lungs and

adverse effects are

organ systems and func-

oxygen poisoning include ringing

CNS

undoubtedly occur

to

some degree during expopulmonary

sures that produce overt manifestations of

Pulmonary oxygen poisoning

occur during

will

prolonged exposure to any oxygen partial pressure above
0.5 atmosphere.

At the lower end of

ble degrees of

pulmonary intoxication would occur

this range, detecta-

1983, Lambertsen

or neurologic oxygen poisoning (Clark

1978). These effects go unnoticed because they are not

associated with chest pain, convulsions, or other obvious indications of oxygen poisoning. Although the nature

weeks of saturation exposure
(Clark and Lambertsen 1971a). During continuous
administration of 100 percent oxygen, pulmonary symp-

and degree of such effects are not now known,

toms have been observed within 12 to 24 hours at
1.0 atmosphere (Comroe et al. 1945), 8 to 14 hours

in

many days

only after

at

1.5

atmosphere (Clark

2.0 atmospheres (Clark
3

to

hours

3.0

at

onset of

et al.

1987), 3 to 6 hours at

and Lambertsen 1971b), and

atmospheres (Clark

symptoms

is

et al.

then more rapidly until each inspiration

it

to

The

1987).

usually characterized by mild

substernal irritation that intensifies slowly at

Coughing

1

first

is

and

painful.

also progressively increases in severity until

cannot be suppressed after deep inspiration. Short-

and hematopoietic

tissues.

In addition, a regular increase

myopia (near-sightedness) has been noted

patients

who

in

some

receive daily hyperbaric treatments (Lyne

Farmer 1978). Individuals exposed
oxygen in saturation
diving conditions also have been found to experience
potent visual effects (Kinney 1985).
1978, Anderson and

to elevated partial pressures of

In the

absence of definitive information regarding

the subtle effects of oxygen toxicity,

it

is

important

to

remain aware that organ systems and functions external to the lungs

and

CNS may

be adversely affected by

may

either prolonged and continuous or repeated and

severe exposures, presumably because of
vital capacity, which can occur before symp-

ness of breath during exertion, or even at rest,

occur

likely

target sites include the liver, kidney, endocrine organs,

intermittent oxygen exposures.

poisoning cul-

It is likely that such
would be most evident either near the end of a
continuous oxygen exposure or within several hours
after exposure termination. During a series of inter-

generalized convulsions followed by un-

mittent oxygen exposures, the probability of detection

dominant manifestation of oxygen
intoxication during exposures to oxygen partial pressures above 2.0 atmospheres. Convulsions may also
occur while breathing oxygen at lower partial pres-

of subtle adverse effects will increase directly with the

in

decreased

toms are obvious.
Central nervous system

minating

in

consciousness

is

(CNS) oxygen

a

sures during periods of exertion, particularly

when

combined with underwater immersion, during periods
of carbon dioxide accumulation with concurrent incre-

ments

in

cerebral blood flow and brain oxygen tension,

unusually susceptible individuals. Muscular
twitching, especially of the face and lips, or hands,

and

in

may precede
does occur,

the onset of convulsions.

it

When

this sign

should serve as a warning to reduce the

effects

number and duration of exposures.
In humans, recovery from oxygen poisoning after
oxygen pressure-exposure duration combinations that
do not produce overt intoxication appears to be sufficiently complete to allow appropriately spaced,
repeated exposures without fear of cumulative or residual
effects

(Lambertsen 1978).

Full recovery

reactivation of critical

enzymes and

alterations in cellular function.
tions of

When

reversal of early

overt manifesta-

oxygen poisoning are produced, however, recov-

inspired oxygen pressure or to terminate the oxygen

ery probably requires a

exposure immediately,

reversal of tissue inflammatory reactions

In a

if

possible.

group of 18 normal resting men breathing oxy-

gen for up

to 3.5 hours at 3.0

atmospheres

in a

hyperbaric

chamber, constriction of peripheral vision always
occurred prior to convulsions (Lambertsen

et al.

1987).

Nausea and dizziness may occur intermittently during

October 1991

— NOAA

Diving Manual

from such

conditions probably requires relatively limited and rapid

more extensive and lengthy
and repair of

cellular metabolic or structural defects.

Rates of recovery from the symptomatic and functional effects of

effects

of most

oxygen

and different

toxicity are variable for different

individuals.

The complete

symptoms associated with

CNS

resolution

oxygen poisoning

3-23

Section 3

occurs within minutes after the inspired oxygen pressure

is

reduced

to

normal

levels.

Even

after an

oxygen

convulsion, recovery can occur within 30 minutes, but

may

require an hour or

more

some

low oxygen pressures. Possible causes of
carbon dioxide retention include faulty CO absorpat unusually

tion in closed-circuit breathing

equipment, inadequate

Chest pain and cough associated with oxygen-induced

pulmonary ventilation while exercising under conditions of excessive external resistance to breathing, and

tracheobronchitis usually resolve within 2 to 4 hours

intentional hypoventilation to conserve air. Cerebral

it

in

individuals.

after exposure termination, but unusual fatigue

mild dyspnea on exertion

may

and

occasionally persist for

few weeks after exposure. Although

vasodilation,

which occurs

ide retention,

is

in

response to carbon diox-

responsible for the prominent eleva-

nary diffusing capacity for carbon monoxide often
requires 1 to 2 weeks or more (Clark et al. 1987).
Hyperoxic exposures for diving and decompression

tion of brain oxygen tension during oxygen breathing
and accounts for most, if not all, of the associated
decrement in CNS oxygen tolerance.
Extending human oxygen tolerance by means of drugs
that have been shown to delay one or more manifestations of oxygen toxicity has not to date been shown to
be practical. Since such an agent ideally would have to
be distributed throughout all body tissues and oppose

applications should be planned to remain well within

toxic effects on a variety of

known oxygen tolerance limits. They should also be
appropriately spaced to ensure complete recovery

likely that

than a limited potential for practical application (Clark

between exposures. This approach will both avoid the
cumulative, residual effects of oxygen poisoning and

useful procedure for extending

several days or even a

there

is

a wide range in individual variability, oxygen-

induced deficits in vital capacity and forced expiraand inspiratory flow rates typically reverse within
1
to 3 days after exposure, while recovery of pulmo-

tory

the

enzymatic targets, it is not
any drug now available will ever have more

1983, Lambertsen 1978).

At the present time, the most
human oxygen toler-

maintain a reserve of oxygen tolerance in case hyperis required for decompression sick-

ance employs systematic alternation of hyperoxic and

complex

tolerable duration of exposure to a selected level of

oxygenation therapy

ness or gas embolism. If (as might occur in a

treatment) oxygen therapy makes
a significant degree of

it

necessary to cause

pulmonary intoxication

in a

normoxic exposure intervals

to increase greatly the

hyperoxia. This procedure takes practical advantage
of the empirical observation that

many

early, subclini-

effects of oxygen toxicity are reversed more rapidly

patient, subsequent operational exposures to hyperoxia

cal

should be delayed for at least several weeks to allow

than they develop. Interrupted exposure as a means of

complete recovery.

oxygen tolerance extension was initially studied in animals (Clark 1983, Lambertsen 1978), and its effectiveness was later demonstrated directly in man (Hendricks

A

variety of conditions, procedures, and drugs can

be used to modify the oxygen tolerance of humans
(Clark and Lambertsen 1971a). These factors may

et al.

affect the time of onset, rate of progression, or severity

exposure has been a component of the U.S.

of one or more of the diverse manifestations of oxygen
poisoning. Of all the factors known to hasten the development of oxygen poisoning, the effects of exercise and

1977). Although periodic interruption of oxygen

gen treatment tables
its

potential for

(US Navy

1985) for

Navy oxymany years,

oxygen tolerance extension has been

only minimally exploited to date.

carbon dioxide accumulation are most relevant to diving operations.

By mechanisms

that are not well understood (apart

3.4

EFFECTS OF COLD (HYPOTHERMIA)
a condition in which the deep tissue or

from the possible influence of concurrent carbon diox-

Hypothermia

ide retention), physical exertion itself exacerbates the

core temperature of the body

development of
in

CNS

CNS

oxygen poisoning. This reduction
oxygen tolerance is expressed both by the

earlier onset of convulsions at

oxygen pressures above

which

is

is

falls

below 95 °F (35 °C),

the temperature at which malfunctions in

normal physiology begin to occur.

If the core

tempera-

ture drops below 96.8 °F (36 °C), diving operations

and by the occurrence of convulsions

should be terminated because the consequences of con-

during exposure to oxygen pressures at which oxygen-

tinuing are serious. If the core temperature falls to

in

induced seizures would otherwise almost never occur
normal, resting individuals. The adverse effects of

emergency rewarming and medical treatment are

exercise on pulmonary or other non-neurologic mani-

Between 86° and 89.6 °F (30° and 32 °C),
cardiac irregularities commence and unconsciousness

2.0 atmospheres

festations of

oxygen intoxication have not been de-

Elevated arterial carbon dioxide pressure will also

3-24

required.

may

monstrated.
hasten the onset of convulsions or cause

93.2°F (34°C), temporary amnesia may occur and

them

to

occur

result.

Because water has a specific heat approximately
1000 times greater than that of air and a thermal

NOAA

Diving Manual

— October 1991

Diving Physiology

conductivity 24 times greater than that of air, the
body loses heat much faster in water than in air of the

During swimming, the increase
resulting from exercise

is

energy production

in

counterbalanced by the increase

same temperature. Fortunately, the thermoregulatory
system of the body is highly sensitive to stimulation

in

from the hands and feet, so that the body's heat generating systems are activated before the core temperature is affected seriously. The fact that the hands and

the core to the periphery, and this heat

feet get cold first

is

thus, in this sense, an advantage.

muscle blood flow resulting in greater heat transfer.
Thus swimming promotes faster transfer of heat from
the water (Nadel 1984). This

immersed

in

why

is

in

is

turn lost to

persons suddenly

cold water or divers becoming cold are

better off remaining

than trying to swim. Rapid

still

and with core temperatures below
96.8° F (36°C), the defense mechanisms of the body
are activated. These mechanisms consist of shivering,
which can increase basal body heat production by up to
five times, and vasoconstriction, which reduces blood
flow to the periphery and thus reduces heat loss.
Unfortunately, these mechanisms rarely achieve heat

heat loss provokes strong shivering, so that the diver

balance, so that the diver continues to lose heat.

long slow cooling and undetected hypothermia even in

body heat by conductive loss
from the skin, a significant loss (10 to 20 percent of
total body heat loss) occurs by evaporation from the
lungs. The percentage is dependent on the humidity of

tropical water. This affects

With cold

skin

In addition to losing

the inspired

since the drier the air the greater the

air,

evaporative heat

Further, as divers go deeper and

loss.

heat loss increases.

becomes more dense, convective
Breathing gas heating is needed

beyond depths of 400

feet

their breathing gas

warned. Gradual heat

not cause shivering, yet the accumulated cooling and

apparently adequate thermal protection

in

dives, or repeated dives over several days,

may produce

memory and

a diver's effectiveness

and possibly endangering him

may

thermal protection

lead to an unwillingness to

dive again or to disabling fatigue

known

Symptoms

of

and diminished usefulness.

On

Because of large individual difmust determine
the most suitable protection on an individual basis. A

uals are poor judges of their

ferences in cold tolerance, every diver

body heat

available, ranging

suits

and dry

from standard

suits to specially

heated suits (for detailed descriptions of these

suits,

of protective equipment, however, creates a

complication because the body's defense mechanism

is

modified by the thermal barrier of the clothing. This
complication is only just being recognized as impor-

and divers should be aware that the faster the rate
of heat loss, the smaller the drop in core temperature
tant,

for a given quantity of heat loss.

rate of

body heat

(3) the

body

size.

loss; (2)

fer

is

the

amount

of

body

fat;

and

Larger, fatter people are less affected by

a given cold exposure

amount

Furthermore, whether

strongly influenced by: (l) the

is

is

1985).

is

lost,

tal

in

and

less

affected by a given

of heat loss. For example, because heat trans-

about 100 to 200 times faster

water than

in

the heat that reaches the skin surface

is

in air,

rapidly trans-

own thermal

state.

As

the body approaches hypothermia;

recognizing hypothermia in

problem

the other hand, loss of

extremely difficult to recognize. Individ-

diving.

its

early stages

at this stage, a diver

is

a serious

Deep hypothermia, meaning

temperature of 95 °F (35 °C) or lower,

may become

is

a rec-

dangerous;

helpless.

enough to threaten life,
will produce loss of dexterity and sense of touch in the
hands, making it difficult for a diver to do useful work
or even to control diving equipment such as weight
Chilling, even

10.8).

or not a person shivers

(Webb

easy to recognize that hands and feet are cold by

protective clothing.

The use

now

states that are

Hypothermia

body heat

and

—

be associated with being cold

to

the familiar sensations of discomfort, numbness, pain,

Obviously, a diver exposed to cold water or even
warm water for long periods must wear

see Sections 5.4

the speed of

or her. In addition, repeated diving with inadequate

moderately

foamed neoprene wet

prolonged

reasoning and other cognitive functions, thus reducing

It is

is

greater,

with the likely result of impaired performance. Use of

(122 meters).

Thermal Protection

variety of diving suits

may be even

the likelihood of hypothermia

3.4.2
3.4.1

is

over a long time often will

loss

belts

if

not severe

and buoyancy compensators. Shivering causes a

lack of coordination and

may make

it

difficult

diver to hold the mouthpiece in place.

By

for a

the time

shivering becomes uncontrollable, oxygen consumption

has increased significantly. Before

this,

however, the

dive should have been terminated and rewarming started.

The

ability to think clearly

also

may

and short-term memory

be affected seriously by cold. Figure

3-1

1

shows the effect of cold water on psychomotor
performance when a diver is wearing a 1/4-inch
(0.63 centimeter) wet suit, with hood, gloves, and

ferred to the water. Generally, the thicker the layer of

booties.

subcutaneous

and the execution of a simple assembly task are affected

fat,

October 1991

the greater the insulation.

— NOAA

Diving Manual

For example, both fine digital manipulation

3-25

Section 3
Figure 3-11

Exposure Duration on
Psychomotor Task Performance
in Cold Water
Effect of

(

Or-

20

-

o
E
o
.c
o
>.
CO

Q-

c
o

li
E
CD
O

40

-

I

CD

Q
CD

O
c
E
o

Proper Decrement Curve

CO

Type Task

Water Temperature
60

50

40

1

3

6

7

1

2

4

6

1

2

2

3

70

60

"[

Fine Digital

Manipulation

Simple

Assembly
Gross Body &
Power Move.

<
80

,OStang& Wiener (1970)
* Bowen (1968)
O Weltman & Egstrom Et Al (1970)
'

D Weltman & Egstrom Et Al (1971)
30

20

10

50

40

Time(Min)

Source: Egstrom (1974)

seriously at 50 °F

(10°C) and 40 °F

tures, respectively, as

have shown that

also

air

much as 29 percent when
andHayford 1981).

When
diver
•

(4.5 °C) temperaFigure 3-11. Studies

•

consumption can go up by as

•

shown

in

•
it

is

essential for the

•

Wear thermal
Note the

first

Be aware that even when properly dressed, hypothermia

may

Watch

the

behavioral

develop without shivering

buddy diver and take heed of any
changes that may indicate existing or

protection appropriate for the water

signs of cold hands

3.4.3 Survival in

and

feet

and

loss

If ship

Cold Water

abandonment

is

necessary, there are proce-

of dexterity and grip strength

dures that can significantly increase the chances of

Note

survival, even in extremely cold water.

difficulty in performing routine tasks, con-

fusion, or a
•

any of the above symptoms are

approaching hypothermia.

to:

temperature (see Figure 5-17)
•

if

present

diving in cold water (Dunford

diving in cold water,

Terminate a dive

Note

tendency to repeat tasks or procedures

Records show

that ship sinkings, even in the worst cases, usually

feelings of being chilled followed by inter-

require at least 15 to 30 minutes. This affords valuable

mittent shivering, even though routine tasks can

time for preparation. The following procedures should

still

3-26

be performed

be carried out (U.S. Coast Guard 1975):

NOAA

Diving Manual

— October 1991

(

Diving Physiology

Locate and don a personal flotation device as quickly

tion.

as possible.

body heat

Try

to enter the

water

avoid

in a lifeboat or raft to

it

Several hours

the loss of

Wear

is

Even

air provides insulation.

in

the water, the extra

layers of clothing will reduce the rate of

body heat

be required to restore
is

all

the

not beneficial, because

increases circulation of blood to the skin and speeds

wetting insulating clothing and losing body heat.
several layers of clothing because the trapped

may

Drinking alcohol

lost.

body heat

or lethargic should be

is

diver

who

helpless, irrational,

rewarmed more

a hot bath should be used, but

ally,

A

cold surroundings.

in

so hypothermic that he or she

if

vigorously. Ide-

none

is

available,

loss.

a hot water suit, electric blanket, or inhalation rewarming

Especially protect the head, neck, groin, and the

are suitable methods.

sides of the chest, because these are areas of rapid

less,

heat

loss.

cal attention

If

is

it

necessary to enter the water, do so slowly to

minimize the likelihood of increasing breathing
swallowing water, shock, and death. If jumping
is necessary, pinch the nose and hold the breath.

A

hypothermic diver who

irrational, lethargic, or

help-

is

unconscious needs medi-

and immediate and vigorous rewarming,

by any of the prescribed techniques (see Section 18.8.3
for further discussion of

rewarming).

rate,

Once

in

the water, orient yourself with respect to

lifeboats, floating objects, etc.

WARNING

Also button up and

Who Have Been

turn on signal lights as quickly as possible before

Divers

manual dexterity

sion Dives (or Dives Near the Decompression Limit) Should Not Take Very Hot Baths
or Showers Because These May Stimulate

Do

is lost.

not attempt to

swim except

to a

pump

out the

nearby

warmed water between

will

the body and

Unlike hypothermia, hyperthermia rarely
is

to hold

the knees against the chest in a doubled-up fash-

arms

around the side of the
chest. If others are nearby, huddle together and
maintain maximum body contact.

Keep
make

EFFECTS OF HEAT (HYPERTHERMIA)

3.5

Keep the head and neck out of the water.
The best position to conserve body heat

Board a

Bubble Formation

to the extremities, thus increasing

the

ion with the

life raft

tight

or floating object as soon as possible.

a positive attitude, because a will to live does
a difference.

by immersion

in water.

and bathe
rewarming

dive, a cold diver should be

soup or coffee, dry off

rewarmed.

in a

warm

place,

in

warm

in

104° F (40°C) water reestablishes nor-

water. Studies have

mal body temperature 67 percent

shown

faster than

that

rewarming

100°F (38°C) air (Strauss and Vaughan 1981).
Cold divers should not make a second dive on the same
day, because it is difficult to know when body heat has
in

been restored. However,
it

is

if

a second dive

is

necessary,

advisable to overdo the rewarming until sweating

occurs, which indicates that

body heat has been

Exercising to generate internal heat

little

cannot be transferred to the water.

produced

or no difference

If

heavy exercise

is

performed under such conditions, there can be serious
overheating problems (Bove 1984).

Hyperthermia

is

encountered more commonly durwhere a

wet

one encased

diver, especially

suit in the hot sun,

can overheat.

is

restored.

also helpful to

of dizziness, disorientation, rapid pulse, hyperventilation,

and potential

loss of consciousness.

ous result of hyperthermia

more

seri-

An

important factor
is

dehydration,

which can develop quickly as a result of excessive
sweating and lack of fluid replacement. Because it
reduces the volume of blood available for circulation
to the skin,

dehydration increases the chances of divers

becoming hyperthermic. Dehydration

also increases

the likelihood of decompression sickness as a result of

inadequate blood flow to the muscles and

and juices are recommended
hol

make matters

worse. Divers

should be put

in a

Diving Manual

A

heat stroke, which can

that increases the risk of hyperthermia

change into warm, dry clothing and continue some
mild exercise to improve heat production and circula-

— NOAA

is

cause death (see Section 18.1.8).

speed up the rewarming process. The diver should then

October 1991

is

is

the water temperature

The symptoms of hyperthermia include heat exhaustion (see Section 18.8.1), with accompanying feelings

This can be accomplished by having the diver drink hot
liquids such as

if

temperature between the skin and water and heat

in

ing dive preparation

Rewarming

At the end of a

However,

reaches 85 °F (29.4 °C), there

for a long time in a

3.4.4

Decompres-

move from

clothing layers and cause the blood to

body core
body heat loss.

craft,

Swimming

fellow survivor, or floating object.

Chilled on

and other

for ingestion

fluids act as diuretics,

tissues.

Water

because alco-

which

will only

who develop hyperthermia

cool place, given fluids, and cooled

3-27

Section 3

While taking medication, therefore, careful consid-

with water poured over the skin until the body temperature returns to normal.

eration should be given to the following elements before

diving:

DRUGS AND DIVING

3.6

•

Why

are the drugs being used, and are there underly-

ing medical conditions that

The use

of prescribed or over-the-counter medications

is a complex issue. There are no simple
answers to questions about which drugs are best for
which conditions in a hyperbaric environment. Indi-

while diving

use should the

associated risks of diving to an unacceptable level?

Prescription Drugs
re-

its

Will the side effects of the drug increase the

•

all

Drug-induced physiological and psychological

the half-life of the drug, and for what

diver not be exposed to a high-pressure environment?

macologically active agents are used.

3.6.1

is

period of time before or after

and the mental and physical requirements of
must be taken into account before phar-

ditions,

be relatively or

1976)?

What

•

vidual variability, existing medical and physical con-

diving

may

absolutely contraindicated for divers (Kindwall

A

•

Will the drug interfere with physical performance?

•

Will the drug impair exercise tolerance?

•

Does the drug produce rebound phenomena?
conscientious diver will discuss these questions with

sponses often are altered in a hyperbaric environment.

his/her physician before diving while taking prescribed

The normal metabolic and excretion patterns of drugs
taken at one atmosphere may be significantly and
pathologically altered once the diver becomes pressur-

or over-the-counter medications.

An

ized.

understanding of the types of changes that

occur, the implications of these changes, and the relationships between

and among drugs, the environment,

and the diver are

critical

to

if

therapeutic accidents are

The manner
olized,

in which the drug is absorbed, metaband excreted by the body in a hyperbaric

environment;
•

The

physical impact of the type of breathing gas,

increased density of the gases, water temperature,

and other environmental
diver exertion

all

factors,

It

obvious that cognitive and motor performance

is

can be impaired by the abuse of psychoactive agents.
Alcohol and marijuana (and other cannabis products)

and the degree of

contribute to the total effect of a

drowsiness from
antihistamines, may be tolerated on the surface.

Acceptable side effects,

like

In the hyperbaric environment, however, such side
effects

may become

unacceptable, leading

in

cates that their use

some

cases to serious morbidity or even death. Impairment

of cognitive function, neuromuscular strength and

coordination, or integration of thought and action

can have catastrophic results while diving.
In addition to the antihistamines, drugs

may

central nervous system

is

addictive and in

some cases

potentiate other central nervous system depressants.

For example,

in

addition to being a depressant and

having other subjective effects, alcohol can cause reduced

blood glucose levels, which can lead in turn to weakness and confusion. Alcohol also causes blood vessel
dilation,

which can interfere with proper maintenance

of body temperature while diving (see Section 3.4).

Because of

its

diuretic action, alcohol can contribute

body dehydration, especially in the
where divers may combine alcohol with the

significantly to

consumption of caffeine-containing drinks such as
coffee,

and

There are reports that the use of marijuana preceding cold water dives can reduce a diver's cold tolerance

commonly

adversely affect diver safety and per-

and breath-holding capability, cause general discomfort, unexplainable apprehension, and a desire to ter-

formance include: motion sickness remedies, amphet-

minate a dive prematurely (Tzimoulis 1982).
tant to note that the effects of

and decongestants, some of which have been found

last for

to

induce impaired coordination, cardiovascular effects,

up

Cocaine

to
is

It is

nervous system stimulant.

noteworthy that the effects of some of these drugs

may

belies the hazard

to

have worn off on the surface, only to return

the diver

3-28

becomes pressurized (Anonymous 1986).

It

is

impor-

smoking marijuana can

24 hours (Anonymous 1986).

commonly abused

central

Its relatively short

action

currently the most

addiction, and inflammation of the lower airways.

when

tea,

colas.

amines, tranquilizers, sedatives, hypertensive drugs,

appear

(e.g.,

with concurrent administration of barbiturates) can

tropics,

used that

commonly abused

depressants in the world today. Research clearly indi-

medication;
•

Drugs

Illicit

are the most

be avoided. Specific concerns include the following:
•

3.6.2

it

poses to the diver. The hyper-

metabolic state that occurs during the use of cocaine
(it is

rarely used alone

NOAA

and

is

often used with alcohol or

Diving Manual

— October 1991

Diving Physiology

marijuana)

may

place the diver at risk of subsequent

discouraged from using medications before diving. The

sharing of medications

among

and the inability
to respond promptly to life-threatening emergencies.
It also increases the likelihood of an oxygen seizure
and can disturb the normal rhythm of the heart (Anon-

drug

ymous

Conservative and safe practices are required for the

fatigue, mental depression, acidosis,

1986).

Divers and their physicians have an obligation to

communicate with one another. The

clinician has the

responsibility to explain the nature of his or her treat-

ment

to the diver,

and the diver has the responsibility

discouraged.

A

diving exposure

divers also should be
is

nity for either a clinician or a diver to
will

not a good opportu-

determine whether a

be safe and efficacious for a given individual.

well-being and survival of the diver. Abstinence from
diving

may

be the most conservative approach for an

individual requiring systemic medication (Walsh and

Ginzburg 1984). (For

a

comprehensive review of the

of indicating to the treating clinician that a diving

effects of drugs in a hyperbaric environment, the reader

exposure

referred to

is

anticipated. In general, divers should be

October 1991

— NOAA

Diving Manual

is

Walsh 1980.)

3-29

t

<

Page

SECTION

4

COMPRESSED
AIR AND
SUPPORT

4.0

General

4-1

4.1

Compressed Air

4-1

4.1.1

4.2

EQUIPMENT
4.3

General Safety Precautions for Compressed Air

Air Compressors and Filtering Systems

4-1

4-2

4.2.1

Maintenance

4-5

4.2.2

Lubricants

4-5

Compressed Gas Cylinders
4.3.1
Cylinder Markings

4-5
4-5

4.3.2

Cylinder Inspection and Maintenance

4-7

4.3.3

Cylinder Valve and Manifold Assembly

4-10

4.3.4

Low-Pressure Air Warning/Reserve Air Mechanism

4-1

4.3.5

Submersible Cylinder Pressure Gauge

4-1

c

«

<

COMPRESSED AIR
AND SUPPORT
EQUIPMENT
4.0

GENERAL

This section describes the composition and characterof compressed

istics

air,

the most

commonly used

Table 4-1
Composition of Air

in its

Natural State

breathPercent

and the precautions that must
be taken when compressed air is used as a breathing
ing mixture for diving,

medium
used

for divers.
air diving,

in

and

ders,

It

also discusses the

COMPRESSED

4.1

by volume

equipment

including compressors and cylin-

maintenance and inspection.

its

Gas

Nitrogen

78.084

Oxygen
Argon
Carbon dioxide

20.946
.934
.033
.033

Rare gases

AIR

Compressed air is the most frequently used diver's
breathing medium. In its natural state at sea level

Source:

NOAA

(1979)

pressure, compressed air consists of nitrogen, oxygen,

argon, carbon dioxide, and trace amounts of other

shows the natural composition of

gases. Table 4-1

All

ambient

air

air.

coolers,

does not meet the standards of purity

necessary for use as a diver's breathing medium. For

example,

urban areas the carbon monoxide concen-

in

tration in the air

may

be high, and

in

some cases

it

may

reach a concentration of 50-100 parts per million (ppm).

Ambient

air

may

also contain dust, sulfur, oxides,

cooling water circulation, or, in the case of air radiator

and

sources and automotive exhausts and must be

avoided

breathing air supplied to a diver.

in the

Scuba cylinders should
air source

when an

is

in effect.

The

Environmental Protection Agency (EPA) monitors ozone

and other oxidants

EPA
is

in

flow caused by trash, dirt,

Potential contaminants include engine or venti-

nants.

lation exhaust;
fuel, or paint;

No

fumes or vapors from stored chemicals,

and excess moisture.

compressor should be allowed to operate with

its

intake or first-stage suction blocked, because this will

produce a vacuum within the cylinders that can rap-

not be filled from an ambient

air pollution alert

loss of cooling air

The free air intake of the compressor must be located to
draw air from an area where there are no contami-

other impurities. These contaminants derive from industrial

by

or lint getting into the radiator fins.

metropolitan areas, and the local

idly

draw lubricating

oil

or

oil

vapor from the compressor

crankcase into the air system.

Some

effective

methods

of preventing the intake of contaminated air are discussed

below.

office should be consulted before a diving operation

undertaken

in

pollutant levels.

an area suspected of having high
potential hazard presented by

The

breathing air obtained from ambient sources

is

4.1.1

General Safety Precautions for

Compressed

under-

Air

in

There are three primary safety concerns associated

the United States were unable to achieve compliance with

with the use of compressed air or any compressed gas.

Federal limits for carbon monoxide by the end of 1987.

These

lined by the fact that at least

In addition

to airborne

70 metropolitan areas

pollutants, the air

compressor
•

machinery and storage system themselves may introduce contaminants, including lubricating oil and its

medium. Additionally, the

temperature of the gas being compressed can be high
•

enough

each successive stage to cause pyrolytic
decomposition of any hydrocarbon compounds pres-

ent.

This

That the gas be sufficiently pure and appropriate
for

•

vapor, into the breathing

are:

its

intended use;

That compressed gas cylinders or storage cylinders be properly labeled and handled;
That cylinders be protected from fire and other

at

is

particularly true

if

hazards.

Compressed

the compressor's interstage

air

is

available from

produced

many

sources.

Most
and

coolers are not functioning properly. Intercooler mal-

of

it,

function can be caused by excessive condensate, impaired

is

therefore not of the purity necessary for use as a

October 1991

— NOAA

Diving Manual

however,

is

for industrial purposes

4-1

Section 4

medium. When compressed

essential that the

any attempt is made to repair the leak. Leaks can
sometimes be detected by painting a 20 percent deter-

gas be certified by the manufacturer to be of high

gent soap solution (called a snoop) over the external

and suitable for breathing. Compressed air suspected of being contaminated
should not be used for diving until tested and found

obvious because they will cause a froth of bubbles to

diver's breathing

purchased from a manufacturer,

is

it

air

is

purity, free of oil contaminants,

parts of the valve with a brush.

Proper identification and careful handling of com-

Compressed

pressed gas cylinders are essential to safety.

leaks will be

form. After the leak has been repaired, the soap solution used for leak detection

safe.

Even small

must be removed completely

with fresh water and the valve dried carefully before
reassembly.

gas cylinders used to transport gas under pressure are

Scuba cylinders generally are not color-coded or

Department of Transportation (DOT) regulations. These regulations include design, material,
inspection, and marking requirements (see Section 4.3).
Compressed gas cylinders can be extremely hazardous
if mishandled and should be stored securely in a rack,

labeled as to type of gas contained; however, large gas

subject to

preferably in the upright position.

When

in transit, cylinders

allowing

it

to roll

may be

color-coded and labeled.

The

label

should be used to identify the contents of a gas cylinder, because color-coding

is

not standardized.

WARNING

should be secured against

Standing an unsecured cylinder on end or

rolling.

cylinders

unsecured could result

in the explo-

sive rupture of the cylinder. Cylinders can

become

deadly projectiles capable of penetrating a wall, and

Because Colors Vary Among Manufacturers,
the Content of Large Cylinders Should Always
Identified By Label— Do Not Rely on Cylinder Color

Be

they can propel themselves at great speeds over long
distances.

Scuba cylinders are often

fitted with a

plastic boot that has holes in

it

to

rubber or

permit draining.

Several special safety precautions to be observed

when using compressed gas

are noted on the label of

These boots fit over the base of the cylinder and help to
keep the cylinder in an upright position. However,
cylinders equipped with such boots should not be left
unsecured in an upright position, because the boot

gas cylinders. In general, these precautions concern

alone does not provide sufficient protection against

fore not be used or stored in an area

falling.

hot work, or flammable gases are present.

NOTE

4.2

Cylinder boots should be removed periodically and the cylinder checked for evidence

Air compressors are the most

the flammability of the gas and

combustion. Although not

ing

Compressed gas cylinders are protected against excesby a rupture disk on the valve. Because

sive overpressure

regulators or gauges

opened

to

may

fail

when

a cylinder valve

check the cylinder pressure,

it

is

is

important

to stand to the side rather than in the line of discharge
to avoid the blast effect in case of failure.

the Line of Discharge
Opening a High-Pressure Cylinder
in

If a cylinder valve

seal leak,

4-2

it

is

flammable, com-

where open flames,

COMPRESSORS AND
FILTERING SYSTEMS
AIR

is

air.

common

The compressor used

source of diver's

for umbilical div-

generally backed up by a bank of high-pressure

gas storage cylinders to reduce the possibility of
interrupting the diver's breathing gas supply because
of loss of power or compressor malfunction.

There are two main types of compressors: highpressure, low-volume, for use in filling scuba cylin-

and low-pressure, high-volume, used for umbiliA compressor is rated at the pressure at
which it will unload or at which the unloading switches
will activate. A compressor must have the output volume to provide sufficient breathing medium and to
provide pressure above the range equivalent to the
ambient pressure the diver will experience at depth.
When evaluating compressor capacity, the different
overbottom pressure and volume requirements of different types of underwater breathing apparatus and/or
ders;

cal diving.

WARNING
Do Not Stand

ability to support

pressed air does support combustion and should there-

breathing

of corrosion.

its

in itself

When

suspected of having a thread or

should be completely discharged before

NOAA

Diving Manual

— October 1991

Compressed

Air

and Support Equipment

helmets must be taken into consideration, as well as
umbilical length and diameter.

Any

air

compressor used for a diver's surface-supplied

system must have an accumulator (volume cylinder) as
an integral part of the system. The accumulator will
provide a limited emergency supply of air
pressor

As

if

the

com-

fails.

number

the

of scientific, educational, and sport

divers increases, there

is

a concomitant rise in the

num-

ber and variety of air compressors being used to supply

breathing

air.

Operators should become thoroughly

familiar with the requirements associated with the
production of breathing

air.

To ensure proper mainte-

nance and care, organizations using compressors should
assign the responsibility for the operation of compres-

Air compressors are generally rated by two paramethe

maximum

ient access to a

pressure (measured in pounds per

when

there

is

conven-

high-pressure compressor for recharging.

Using cylinders as the gas source reduces the chance of

volume of
compressed and stored before
the dive. Most lockout submersibles carry the diver's
losing the primary supply, since the entire

gas needed for a dive
gas supply

in

is

high-pressure cylinders incorporated into

Compressed gas cylinders are also generally mounted on the exteriors of underwater habitats,
submersibles, and diving bells to provide a backup gas

the system.

supply

case of emergency, and divers using the habitat

in

as a base can refill their

mounted

scuba cylinders from these

cylinders.

Many

types of compressors are available: centrifu-

gal, rotary screw, axial flow,

sors to a specific individual.

ters:

Large, high-pressure cylinders are advantageous to
use as a source of breathing gas

most commonly used type

and reciprocating. The

in the

diving industry

is

the

reciprocating, or piston-in-cylinder, type. These

square inch gauge, or psig) they can deliver and the

compressors are further classified as "oil-lubricated"

output volume (measured jn standard cubic feet per

or "non-oil-lubricated," depending on whether or not

minute, or scfm) that can be delivered at that pressure.

they require lubrication of their compression cylinders.

To be

volume and pressure
or exceed the requirements of the

effective, both the output

must be equal

to

system they supply.
Air compressors
breathing air

may

In an oil-lubricated compressor, the oil in the crank-

case assembly also lubricates the pistons and cylinder
walls.

commonly used

be classified

in

to provide divers'

the following groups:

As

a result,

some of

the

oil

may come

contact with the air being compressed.

used

in

machines that provide breathing

into direct

The
air

lubricants

must be of

the quality specified for breathing air and be so desig-

• High-Volume, Low-Pressure Air Compressors.
These compressors are most often used to support

should not be substituted for another unless the manu-

surface-supplied operations or to supply hyperbaric

facturer's directions so specify. Chlorinated lubricants,

chambers. They are generally found

where
large-scale diving operations are being conducted
or aboard surface platforms fitted out for diving.
Units commonly used have output volumes of
between 50 and 200 scfm at maximum discharge
pressures of between 150 and 300 psig. These units
may be either permanently installed or portable.

synthetics, or phosphate esters (either pure or in a

Portable units are generally built into a skid assem-

facturers describe their machines as oil-free, even

bly along with a

power source

line engine, or electric
filter

air,

at sites

(diesel engine, gaso-

motor), volume cylinder,

assembly, distribution manifold for divers'

and a rack

for storing divers' umbilical as-

semblies.

One

lubricant

mixture) should never be used. Oil-free compressors
usually

employ

a standard oil-lubricated crankcase

assembly similar

to that of oil-lubricated

however, the pumping chambers

in

oil-free

machines;

machines

are designed to run either with water lubrication or
with no lubrication at

all.

For this reason, some manu-

though the breakdown of such compressors could still
result in oily breathing air. The mechanical connections

between the pumping chambers and the crank-

case on oil-free machines are carefully designed to
oil into the pumpThe all-purpose crankcase lubricant

prevent the migration of crankcase

• Low-Volume, High-Pressure Air Compressors.
These compressors are used for filling scuba cylinders and high-pressure air storage systems that
provide support for surface-supplied diving and
hyperbaric chambers. Portable units used for filling scuba cylinders are

commonly

available with a

volumetric capacity of 2 to 5 scfm at a discharge
pressure adequate to fully charge the cylinders

(2250 or 3000

psig,

depending on the type of

cylinder).

October 1991

nated by the equipment manufacturer.

ing chambers.

recommended by

the manufacturer can usually be used

for oil-free compressors.

The compressors used

but these machines are

still

not widely used in opera-

tional diving.

The production of compressed air is a complex procThe process begins as the piston in the first/second
stage head strokes upward in its cylinder. At that
ess.

point, the intake valve to the first stage closes

— NOAA

Diving Manual

to pro-

vide breathing air in hospitals are of the oil-free type,

and the

4-3

Section 4

intake valve to the second stage opens.

maximum

stage opens and compressed air
first-stage

At the

is

admitted

condense and collect as the

air passes

air/liquid separator at the discharge

The separator

cooler.

first

to the

Intercoolers cool the air before

intercooler.

further recompression and cause water and
to

point of

compression, the exit valve from the

oil

vapors

through the

end of the

inter-

fitted with a drain valve that

is

them

to

inert

and virtually unchanged physically during the

adhere to

its

purification process.

surface, the sieve itself remains

With appropriate periodic

re-

generation processes, most molecular sieves are capa-

removing a wide range of contaminants, includ-

ble of

ing nitrogen dioxide and most odors.

However, the
remove hydrocarbons and odors
with the use of activated carbon, which acts

most effective way
still

is

much

to

must be opened periodically to drain off accumulated
liquids. Each intercooler assembly is also fitted with a
relief valve that opens if the pressure rises above a safe

Another popular filtration system involves the following components, which are used in the sequence

level.

shown:

The second stage
downstroke of the

which the secondvalve closes and the air is further com-

stage inlet

At

pressed.

of compression takes place on the

exit valve to the

of

maximum

coalescing section to remove

•

dessicant section to remove water vapor, nitrogen

second stage opens and compressed

activated charcoal section for removal of resid-

taken

and

from ambient pressure

to approximately

2250

psi.

Commay

tastes;

The Hopcalite®

bon dioxide. Hopcalite®

Each succeeding cylinder

tion

is

proportionately smaller in

is lost because of the volume of the
and residual cylinder volumes; this factor

and

process.

the catalytic action

intercoolers

insignificant.

Air leaving a compressor must be cooled and passed
through an air/liquid separator to remove any condensed water and oil vapors before storage or immedi-

from an oil-free compressor does not genany further treatment unless the applica-

erally require

tion requires that

it

be further dried or there

is

concern

about possible contamination of the intake air. Air
from an oil-lubricated compressor must be carefully
filtered to

remove any possible

mist, oil vapors,

oil

from oil oxidation in the compressor (predominantly carbon monoxide), or odors. Sevpossible byproducts

eral types of filtration

most

filtration

them

in

this,

is

so small as to be physiologically

The amount

of oxygen used up

is

approxi-

mately 0.5 part of oxygen per million parts of carbon

called volumetric efficiency.

ate use. Air

to car-

a true catalyst in this reac-

is

is neither consumed nor exhausted in the
The amount of carbon dioxide produced by

mately 10 percent)

is

monoxide

oxidizes the carbon

vary with different makes and models of compressors.

volume than the previous one. Some efficiency (approxi-

and

Hopcalite® section for carbon monoxide removal.

•

pressors typically use a ratio of 6:1, although this

re-

air

ual odors
is

mist;

movable by adsorption;

admitted to the second-stage intercooler.
In a typical three-stage compressor, the air

oil

and other contaminants

dioxide, hydrocarbons,

compression, the
•

is

molecular sieve.

•

piston, during

moment

the

like a

systems are available. To use

agents properly,

it

is

necessary to place

the filtration system in a specific order.

To do

the direction of the air flow through the filter

monoxide, which has no appreciable effect on the

air

produced. The lifetime of this system is usually
determined by the lifetime of the dessicant, since
Hopcalite®

is

quickly "poisoned" and rendered ineffective

An

by excessive water vapor.
that

is

not widely understood

is

aspect of this process

that the carbon

monoxide

oxidation process releases substantial quantities of heat.

Hopcalite®

If a

becomes extremely hot or shows

filter

signs of discoloration, the compressor output air should be

checked for elevated carbon monoxide

levels.

In addition to Hopcalite®, the use of activated alu-

mina

No

in

combination with Multi-sorb®

matter what technique

is

is

also widespread.

employed, the location of

the compressor intake with respect to possible sources

of contamination

is

an important factor

in

ensuring

it

satisfactory air quality. Compressors should not be

should be checked. Like other high-pressure compo-

operated near the exhausts of internal combustion

system must be known, and,

if

there

is

any doubt,

nents, filter canisters should be inspected visually for

engines, sewer manholes, sandblasting or painting opera-

damage (High 1987). An
can be helpful when performing

inspection protocol

tions, electric arcs, or

filter canister

tainers of volatile liquids

corrosion

in-

For purposes of dehydration and adsorption, sub-

known

molecular sieve

as molecular sieves are often used.
is

4-4

it

A

a material having an extremely large

surface area to enhance

Since

can give off fumes even when

they are tightly closed. Intakes must be provided with

spections.

stances

sources of smoke. Plastic con-

its

capacity for adsorption.

removes harmful contaminants by causing

filters for

removing dust and other

orientation to wind direction

up

air

The

is

particles.

Proper

also critical in setting

compressor systems.
final step in the

filling station,

production of pure air

is

the

usually located in a dive shop, on board

NOAA

Diving Manual

— October 1991

Compressed

Air

and Support Equipment

ship, or near a diving installation.

It

is

important for

the diver to inspect the filling station to ensure that

proper safety precautions are being observed and that
Federal, state, and local regulations are being followed.

Figure 4-1

a schematic of the processing of air from

is

the intake to the scuba cylinder. (Note that the system

depicted

Figure 4-1 includes a high-pressure booster

in

pump, which can increase the efficiency of cylinder
filling

operations by providing air at the filling station

at a pressure

above that of the

air storage cylinder.)

For some diving operations,
manufacturer

in

air

is

supplied by the

banks of high-pressure cylinders. These

some
This

of this

oil

mixes with the

air

being compressed.

by the compressor's filtering
system. Because an improperly functioning filter can
oil

temperatures sufficiently to decompose or ignite

raise

the

filtered out

is

oil,

it

is

important to select

oil

to be

used as a

lubricant carefully.

The

oil's flashpoint (the temperature of the liquid oil
which sufficient vapors are given off to produce a
flash when a flame is applied) and auto-ignition point
(the temperature at which the oil, when mixed with air,

at

burn without an ignition source) are both impor-

will

tant considerations.

The most desirable compressor

cylinder banks are fitted with valves and manifolds

lubricants have higher-than-average flashpoints and

and may be used

low

provide breathing air in surface-

to

supplied diving operations and for

filling

The

volatility.

recommended by

oils

most efficient lubricants
4.2.1

for this

and

equipment.

Maintenance

Both the compressor and filter system must be
maintained properly. When running, the compressor
must be cooled adequately, because the primary factor
causing the breakdown of lubricants and contamination of the compressed air is high temperature in the

may be cooled by
blowers or water spray systems or by cooling sys-

compressor cylinder. Cylinder heads
air

the manufac-

turer of the compressor are generally the safest

scuba cylinders.

tems integral

to the

compressor machinery.

head temperature controller

is

valuable

in

A

cylinder

eliminating

the possibility of excessive cylinder temperatures.

Partic-

4.3

COMPRESSED GAS CYLINDERS

The scuba cylinder

or cylinders are secured to the
back by an adjustable harness or form-fitting
backpack assembly equipped with a clamping mechanism. Regardless of which model is employed, all straps
diver's

securing the apparatus should be equipped with corrosion-resistant, quick-release buckles to permit rapid
opening under emergency conditions.

Scuba cylinders contain the compressed breathing
gas (usually air) to be used by a diver. Most cylinders

ular attention should be paid to draining the interstage

for diving are of steel or

and final-stage separators. Compressors and

specially designed

filters

aluminum

alloy construction,

and manufactured

to contain

com-

are usually given routine maintenance on an hours-of-

pressed air safely at service pressures from 2250 to

operation basis. Filters should be examined and replaced

3000 psig (158

accordance with the manufacturer's specifications.
The compressor lubricant and mechanical parts should be
replaced on a rigorous schedule, based on the manu-

to 21

1

kg/cm

2

)

or greater.

in

facturer's
analysis.

recommendations or the

results of

an

air

Analysis of the output air from oil-lubricated

compressor systems should be performed on a periodic
basis. Oil mist analyses are difficult to

perform and

4.3.1

Cylinder Markings

Regardless of cylinder type, data describing the cylinder must be clearly stamped into the shoulder of the
cylinder,

which must be manufactured

require careful collection techniques as well as quali-

state

Commerce Commission (ICC)

fied laboratory analysis of the samples.

However, carthe most important, can

after

by the

bon monoxide analyses, by far
easily be performed in the field using colorimetric

inders as

tubes. (See Section

15.4 for information on contami-

nant analysis.)

A

log should be kept for

should record

all

time

each compressor. The log

in service,

maintenance, and

air

analysis information.

CTC/DOT,

on the interior of the cylinder's walls, and

October 1991

— NOAA

recently reflected on cylwhich indicates equivalency with

DOT (or ICC). 3AA
pressure of 2250 psig

cylinders carry the code

kg/cm

2

)

and

a service

or higher on the

first line.

These marks are

followed by the serial number, cylinder manufactur-

Oil-lubricated compressors always have a small
oil

1970), there-

(High 1986a).
Regulatory changes in the more than 35 years since
scuba cylinders entered service in the United States
have produced a variety of code markings. Typically,

(158

amount of

(until

requirements of the Canadian Transport Commission

steel

Lubricants

accordance

DOT, and most

(steel type),

4.2.2

in

with the precise specifications provided by the Inter-

Diving Manual

symbol (before 1982, the symbol of the user or
equipment distributor), the original hydrostatic test
er's

4-5

Section 4

Figure 4-1

Production of Diver's Breathing Air

<
Priority

Back Pressure
Valve

Pressure

Gauge

%-M

Auto Air Distribution Panel

Isolation

Relief Valve

Valve

%
Magnetic Starter

High Pressure Air Booster

Check Valve

Final Moisture Separator

& Hour Meter

a
Pressure Switch

FT-i

i

.

.

!

i

Bleed
Valve
i

:

Chemical

Filters

X

!_

Check Valve
Auto Air

— Moisture Separator

Fill

Panel

fS>-Auto Condensate Dump
*

'

i

i

i

i

Low Oil

"Compressor

i_

Level Switch
Fill

»

Hoses

High Pressure Lines
Electrical Lines

Air Storage Cylinders

Courtesy Skin Diver Magazine

date with testor's symbol, and a plus
indicates that a 10 percent
is

fill

(

+

)

mark, which

over-service-pressure

allowed for the 5-year period of the original hydro-

indicated in

Additional hydrostatic test dates, with the testors'

some code markings

(

+

)

to

3000

psi

cylinders. Currently,

5-year or shorter intervals. However, since hydrostatic

and

scuba cylinders appropri-

ately to permit inclusion of the plus

mark

(

+

)

for

few steel cylinders are
filled in excess of the designated service pressure
after the initial period. (Figure 4-2 shows steel scuba
cylinder markings.) Current practice allows a cylinder
submitted for the plus ( + ), that is the 10 percent
overfill, to fail the elastic expansion test and to be
reevaluated at the lower service pressure on the basis
of the permanent expansion test (High 1986b).
Aluminum alloy scuba cylinders entered U.S. commercial service in 1971 and are code-marked in a
somewhat different manner than steel cylinders. Initially, DOT issued special permits or exemptions for
continued 10 percent

4-6

overfill,

as

(174 to 211

or overfill allowance

codes, will be added on successful retest at required

test facilities rarely retest

cylinders. These are

SP6498

or E6498,

followed by the service pressure, which typically ranges

from 2475

static test.

aluminum

the manufacture of

CTC

that the cylinder
in

2

).

No

plus

used with aluminum alloy

aluminum cylinders reflect DOT
new material designation (3AL),
and a mark indicating volume and

equivalency, a

the service pressure,

shown

is

kg/cm

is

intended for scuba service (S80), as

Figure 4-3.

NOTE
Aluminum
filled in

alloy cylinders should never be
excess of marked service pressure,

steel cylinders without a plus ( + ) after
the current hydrostatic test date should also
not be filled over their marked service pres-

and

sures.

NOAA

Diving Manual

— October 1991

i

Compressed

Air

and Support Equipment

Figure 4-2
Steel Cylinder Markings

Steel Alloy Specification

Manufacturer
Initial

Test

Hydrostatic

£ 073440

Company

PST
(DACOR)

Distributor

4-83 +
Number

Serial

NOTE

There are four major manufacturers

of

scuba cylinders

in

(he United States

names and symbols are shown below

Their

Manufacturer's

Symbol

Manufacturer

Name

Inspector's
Official

Mark

A

Luxfer

Pressed Steel

or

Authorized Testing

G

PST
(k)

Walter Kidde

WK
WK&Co
of

Norns Industries



of

Inspection Service

Cochrane Laboratory

T. H.

& ®

Arrowhead Industrial Service
or Hunt Inspection

C

T H Cochrane Laboratory

Derived from

The

volume of

internal

physical dimensions and

a cylinder

may

inches or cubic feet.

Of more

the cylinder, which

is

a function of

is

be expressed

interest

in

the capacity of

is

the quantity of gas at surface

The capacity usually

standard cubic feet or standard

liters

is

expressed

:
,

or 153 atm) and contain

64.7 standard cubic feet (1848 standard liters) of gas.

Cylinders with capacities from 26 standard cubic feet

(742 standard

liters)

(2857 standard

liters)

October 1991

— NOAA

to over

100 standard cubic feet

are used for scuba diving.

Diving Manual

Do Not

Fill

Cylinders Beyond Their Service

Pressure

in

of gas. Cylinders

scuba cylinders generally have a rated working pres-

kg/cm

WARNING

its

of various capacities are commercially available. Steel

sure of 2250 psig (158

(1979)

cubic

pressure that can be compressed into the cylinder at

rated pressure.

its

NOAA

4.3.2

The

Cylinder Inspection and Maintenance
exteriors of most steel cylinders are protected

against corrosion by galvanized metal (zinc), epoxy

The zinc bonds to the
from air and water. Galvanized exteriors are recommended for protection against
corrosion; however, epoxy paint or plastic is unsatispaint, or vinyl-plastic coating.

cylinder and protects

it

factory for use over bare steel cylinders, because even

4-7

Section 4

Figure 4-3

Aluminum Cylinder Markings

Aluminum

Alloy

Specification

Service Pressure

Scuba Service

Agency Responsible
for

Standard

3000 S8oAr(OmittedA

CTC/DOT 3AL
/

(DOT)
Serial

Number

\

SP6498
E6498
,

\

)

Cylinder

\

Hydrostatic

First

^prest
2 A85 "*\Test
2/^v85

P71841^Luxfer

Volume

and Company

ark

(A5081)<^

(Distributor)

Test

Initial

Manufacturer-

NOTE

There are four major manufacturers of scuba cylinders
Their names and symbols are shown below
Manufacturer's

Symbol

Manufacturer

Luxfer

Pressed Steel

PST

G

WK

WK&Co.

or

Norns Industries

or

<8>

Name

&

Mark, With
Manufacturer's
Mark Separating

of

Inspection Service

Mark

Official

A

(k)

the United States

Inspector's

o

Walter Kidde

in

Showing Testor's

Test Month
and Year.

Authorized Testing

T. H.

Cochrane Laboratory

Arrowhead

£>

Industrial Service

or Hunt Inspection

C

T. H.

Cochrane Laboratory

Courtesy William

minor abrasions

may

penetrate these two coatings and

expose the underlying metal, allowing oxidation (rusting)
to begin

immediately. Epoxy paint or plastic

able, however, over zinc-galvanized surfaces
it

accept-

is

because

reduces electrolytic corrosion of the zinc by

salt

L.

High

or assessed. Also, the lining tended to loosen and, in

some

cases, the resulting flakes clogged the valve or

the regulator.

A
ally

Damaged

linings

must be removed.

corrosion-inhibiting epoxy-polyester finish usuis

aluminum

applied to the exterior of

cylinders

water and imparts an attractive appearance. With proper

both to protect them and to give them an attractive

preventive maintenance, electrolytic corrosion

color. If this coating scrapes off,

tively insignificant

is

rela-

on bare zinc coating.

Since internal rusting

is

a problem,

manufacturers

formerly applied protective linings on the interiors of
cylinders.

The use

an oxide layer forms

that tends to protect the cylinder

of internal coatings has only been

sion.

Often the

interiors of

from further corrocylinders have a

aluminum

protective layer over the base metal, such as Alrock® or
Irridite®,

which

is

applied during the fabrication process.

lining allows moisture in the cylinder to penetrate to

Air cylinders and high-pressure manifolds should
be rinsed thoroughly with fresh water after each use to

bare metal. Corrosion under the lining cannot be seen

remove traces of

relatively successful,

4-8

because even a small flaw

in the

salt

NOAA

and other deposits. The exterior
Diving Manual

— October 1991

Compressed

and Support Equipment

Air

The

of the cylinder should be visually inspected for abra-

and corrosion.

sion, dents,

abrasions or dents,

If

the cylinder has deep

should be tested hydrostatically

it

before refilling; external corrosion should be removed
a protective coating applied to prevent further

and

Care

deterioration of the cylinder wall.

When

a cylinder

is

may

pared to standards

is

(1) cuts, gouges, corrosion (general, pitting, line),

completely drained

and

stress lines;

(2) dents or bulges;

damage;

(3) signs of heat

if

depressed, allowing the second-

(4) general abuse;

stage valve to open. Cylinders used under water as a

(5) condition of plating;

source of air for power tools or for

(6) current hydrostatic test date.

bags often
become contaminated by moisture returning through
the valve. Cylinders should be stored with about
100

psi of air

remaining

in

lift

Interior cylinder evaluations to standards should assess:

assembly

is

(2)

(3) thread integrity;

attached, because small

amounts of water may be trapped in the valve orifice
and injected into the cylinder. Moisture in a cylinder
often can be detected by (1) the presence of a whitish
mist when the valve is opened; (2) the sound of sloshing
water when the cylinder is tipped back and forth; or
(3) a

damp

Water

in

in

if

the

first

steel

stage or in the hose prior to the second-

sion,

and the water jacket method. The most common
is the water jacket method, which involves

method
filling

and aluminum cylinders should be inspected

frequently,

they are used

filled

the cylinder with water, placing

cylinder with a hydraulic

amount

and perhaps as often as every

displacement. The pressure

in

3 months,

a tropical climate or aboard ship, or

A

special rod-

regulations, a

more of the
is

is

total

expansion indicates that the cylinder

unsafe for use and should be condemned.

short periods of time.

High (1987).

to store cylinders over longer periods with
to

forms of inspection are used, depending on the

interval since the previous inspection or the nature of

An

the suspected problem.

informal inspection

is

a

cursory look at a scuba cylinder's exterior and interior
to

determine

A

formal inspection
in which

if

there

is

standards,

a

dence of the inspection

form of a sticker that
ity

for continued use.

a reason to

is

a

it

further.

complete evaluation against

judgment
is

examine

is

reached and

evi-

affixed to the cylinder in the

ensure that the valve

There

is

is

low pressure

not inadvertently opened.

a potential for moist ambient air to pass through

the open valve into the cylinder as air temperatures

change.

If there is

moisture

in the cylinder, air at the

higher pressure (higher partial pressure of oxygen)
accelerates corrosion.

However, a greater danger

aluminum

exists

when

partially filled

cylinders are exposed to heat, as might occur

The metal can

attests to the cylinder's suitabil-

during a building

The

temperature-raised pressure reaches that necessary to

sticker should indicate the

fire.

An

soften before the

standard used, the date of inspection, and the facility

burst the frangible safety disk.

conducting the inspection.

well below the cylinder service pressure.

October 1991

DOT

permanent expansion of 10 percent or

Two

in

column

increased to five-thirds

Scuba cylinders may be stored at full pressure for
However, it has been traditional

Standards and procedures for the visual inspecin detail

pump, and measuring the

the rated pressure of the cylinder. According to

type low-voltage light that illuminates the entire inside of

compressed gas cylinders are discussed

a water-

of cylinder expansion in terms of water

the cylinder should be used for internal visual inspec-

tion of

in

it

pressure chamber, raising the pressure inside the

corrosion. Cylinders should be inspected

they receive especially hard service.

tion.

and
neck cracks.

There are several methods of hydrostatic testing of

damage and

if

any);

(if

(7) internal

cylinders, including direct expansion, pressure reces-

internally by a trained technician at least once a year

more

presence of manufacturer's re-call items

(6)

cold water diving, because ice can

in

interrupted.

for

(5) sign(s) of substantial material removal;

or metallic odor to the air in the cylinder.

stage valve, causing the flow of air to the diver to be

Both

(4) defects in interior coating (if any);

a cylinder can create a particularly danger-

ous condition
form

and amount of cylinder contents (if any);
magnitude of general, pit, or line corrosion;

(1) type

Cylinders should never be submerged completely
filler

and

the cylinder to keep water from

entering the cylinder.

before the

should be com-

for:

must be

also

enter the cylinder through the regulator

the purge button

neither

is

should be performed

In general, the cylinder exterior

tools.

of air while being used with a single-hose regulator,

water

it

only by persons properly trained and using appropriate

taken to prevent moisture accumulation inside highpressure cylinders.

visual cylinder inspection procedure

complex nor time consuming, but

— NOAA

Diving Manual

explosion

may

occur

4-9

Section 4

Rules for the use of scuba cylinders are:
(1)

Do

not

fill

high-pressure cylinders

if

the date of

the last hydrostatic test has expired (5 years for

and aluminum cylinders) or

steel

year has passed since the

1

last

if

more than

formal visual

Charge cylinder

at a slow rate to prevent exces-

sive heat buildup.
(3)

valve of the double-

hose regulator rides at the back of the diver's neck. The

demand

valve of the single-hose regulator

positioned at

is

the diver's mouth, regardless of cylinder orientation.

The demand

valves of both types

must be kept

Never exceed the maximum allowable pressure
any particular cylinder.
Never perform maintenance or repairs on a

in close

minimum

proximity to the diver's lungs to ensure a

inspection.
(2)

demand

this configuration, the

hydrostatic pressure differential between demand valve
and respiratory organs, regardless of diver orientation.
If this is not achieved, the diver's respiratory system

must work harder than necessary

to

overcome

this

for

(4)

cylinder valve while the cylinder
(5)

is

charged.

Handle charged cylinders carefully. Handling
by the valve or body is preferred. Handling by
straps or backpack may allow the cylinder to

on orientation). Thus, the position of the cylinders on
the diver's back

hose regulator

If diver's air

especially important

is

charged cylinders

an upright position

in

shady place to prevent overheating.
Secure cylinders properly to prevent falling or

in a cool,

(7)

when

a double-

employed.

is

to

is

be supplied by two or more cylin-

ders simultaneously, a manifold assembly

slip or drop.

(6) Store

depending

differential during inhalation (or exhalation,

to join the cylinders

and provide a

employed

is

common

outlet.

The

manifold consists of sections of high-pressure piping

and appropriate

fittings specially configured

and

threaded to incorporate two or more cylinders, a valve,

rolling.

(8) Internal inspections, hydrostatic tests,

and repair

work should be performed only by those formally

and frangible burst disks into a single functional
In addition,

Have

cylinders visually inspected for interior

deterioration annually (or

depending on

more frequently,

use).

(10) Inspect cylinders externally before and after

each dive for signs of general pitting or
rosion, dents, cracks, or other

line cor-

damage. Never use

a welded, fire-damaged, uninspected, gouged,
or scarred cylinder.

(11)

Remove

cylinder boot periodically to inspect

for corrosion

and

rusting. Boots that inhibit rapid

draining and drying should not be used because

they allow water to remain in contact with the
cylinder, forming corrosion.

(12)

Do

not completely drain the cylinder of air

during dives. This prevents moisture from enter-

may

unit.

also contain a reserve valve.

The cylinder valve assembly

trained to do so.
(9)

it

is

a simple, manually

operated, multiple-turn valve that controls the flow of

high-pressure gas from the scuba cylinder.

the point of attachment for the

demand

It also is

regulator.

After the regulator has been clamped to the cylinder
valve and just before using the apparatus, the valve is
opened fully and then backed off one-fourth of a turn.
It remains open throughout the dive. On completion of
the dive, the cylinder valve is closed and should be bled

atmospheric pressure, which prevents the O-ring
from blowing out while the regulator is removed.

to

When

a single cylinder supplies diver's air, the cyl-

inder valve unit

is

generally sealed directly into the

neck of the cylinder by a straight-threaded male connection containing a neoprene O-ring on the valve body.

Most cylinders placed
fitted with a valve

ing the cylinder.

without O-rings.

in service

before 1960 were

having a 0.5-inch tapered thread

When

a single cylinder

is

utilized, the

cylinder valve assembly houses a high-pressure burst

WARNING

disk as a safety feature to prevent cylinder pressure

Aluminum Cylinders Should Not Be Heated
Above 350° F (177° C) Because This Reduces

conditions of elevated temperature. Old-style lead-filled

from reaching a

the Strength of the Cylinder

and Could Cause

Rupture

critical level

during charging or under

blowout plugs must be replaced with modern frangible
disk assemblies. When a pair of cylinders is employed,

two burst disks are installed in the manifold assembly.
Valve manufacturers use burst disks designed to rupture at between 125 and 166 percent of the cylinder
service pressure. The rating may be stamped on the

Cylinder Valve and Manifold Assembly

face of the burst disk assembly to prevent confusion,

Open-circuit scuba cylinders are normally worn on

and disks of different pressure ratings must not be used
interchangeably. Valves are not interchangeable between

4.3.3

a diver's

4-10

back with the manifold/valve assembly up. In

NOAA

Diving Manual

— October 1991

Compressed

and Support Equipment

Air

Figure 4-4
Valve Assemblies
cylinders having different service pressures unless their

respective burst disk assemblies are also interchanged.

NOTE
The standard cylinder valve assembly described above is known as a K-valve. A
cylinder valve that incorporates a low-air
warning/reserve air mechanism is known as a
J-valve.

4.3.4

Low-Pressure Air Warning/Reserve

A. Cylinder Valve

B.

Reserve Valve

Mechanism

Air

Source:

NOAA

(1979)

then

made

Several mechanisms are used in open-circuit scuba

perform the important function of warning divers
that the air supply is approaching a critically low level.
to

Some

300 or 500

psi (23 or

30 kg/cm

2

of air

)

is

available to the diver.

of these devices also provide a reserve air supply

Divers should be aware that the availability and

that allows the diver to proceed safely to the surface.

duration of the reserve air supplied through a reserve

Such

valve are dependent on the

a device

generally one of the following: J-valve,

is

submersible cylinder pressure gauge, or auditory warning

mechanisms may be incorporated into
valve/manifold
assembly or into the demand
the cylinder
devices
regulator. These
and their limitations are

device. These

discussed

in

the following paragraphs.

number of cylinders carried
The 300 psi (23 kg/cm )
2

as well as the depth

of the dive.

reserve available

at actual cylinder pressure;

is

it

is

not

above ambient pressure. Thus, at a depth of
100 feet (ambient pressure of approximately 50 psi),

300

psi

only 250 psi (17

kg/cm

starts to ascend.

Also, the reserve valve

2

is

)

available until the diver

mechanism

retains a reserve air supply only in one cylinder of a

Reserve Valve

twin set of cylinders; the other cylinder or cylinders

The
in

reserve valve (also called a J-valve), illustrated

Figure 4-4,

is

a

spring-loaded check valve that

begins to close as the cylinder pressure approaches a

300 or 500 psi (23 or
30 kg/cm ). Until this pressure is approached, the
reserve valve permits an unrestricted flow of air to the
regulator throughout the dive. At the predetermined
pressure, a spring forces a flow check against the port
orifice and restricts the air flow, causing increased
predetermined

level, generally

when the reserve valve trips.
mechanism is activated, the reserve

are at a lower pressure

When

the reserve

air distributes itself proportionately

For

this reason, the reserve valve

in

cylinders.

all

mechanism employed

:

breathing resistance. This
tion of air flow

The remaining

if

is

followed by total obstruc-

the reserve air

is

not manually released.

with twin cylinders must be set to provide a 500-psi
reserve. Unfortunately,

reserve valve

though generally

mechanism

is

or mechanical failure and,

1/4",

may

reliable, the

subject to physical
if

moved

as

little

be tripped inadvertently early

which allows the reserve

air to

damage

as 1/8" to

in

the dive,

be exhausted without

the diver's knowledge.

or reserve air can be released by manually

overriding the spring-loaded check valve.

NOTE
NOTE

Reserve valves should be inspected annually
defects or whenever a malfunction is
suspected.

for

The reserve valve
position

when

lever

must be

in

the

down

charging cylinders.
4.3.5

When

a diver depresses the cylinder valve/manifold-

mounted reserve

lever, a

plunger pin within the reserve

valve advances, forcing the flow check to back off the
orifice against the action of the spring.

October 1991

— NOAA

Diving Manual

The remaining

Submersible Cylinder Pressure Gauge

Use of
ure 4-5)

is

a submersible cylinder pressure

a requirement in nearly

scientific diving.

all

gauge (Fig-

recreational and

These gauges have largely replaced

constant reserve valves and audio systems.

When

reading

4-11

Section 4

Figure 4-5

Gauges
be positioned carefully as a result; the high-pressure
hose can be run inside the waist strap on the back pack
so that the gauges are located on the thigh in a read-

When worn

able position.

improperly, a submersible

pressure gauge positioned at the end of a 2- to 3-foot
(0.7 to

1

m)

length of high-pressure hose can increase

the chance that a diver will foul on bottom debris

.or

become entangled with equipment. The gauge supply
hose muSt be connected to a high-pressure port with
compatible threads or be used with an adapter.

The high-pressure hose normally has brass

fittings

with a restricting orifice. Should the high-pressure
hose rupture, this orifice prevents rapid loss of cylinder air and allows the diver time to abort the dive and
surface.

Care must be taken

to

keep water from getting

into the first stage of the regulator before the cylinder

valve

opened, because otherwise water could be blown

is

into the submersible pressure

gauge and other regula-

tor parts. Divers also should never

scuba cylinders when the valve

is

off

submerge
and there

their
is

no

pressure in the attached regulator.

Gauge readings

much

that err by as

as 300 psi

more may occur because gauge accuracy
declines with use, especially if small amounts of water
have entered the mechanism. Divers should therefore

kg/cm

(23

compare
Courtesy William

L.

High

ularly;

2

)

or

their

gauges to known cylinder pressures reg-

gauges should be checked at various pressures.

Professional dive facilities often use gauges in their

high-pressure air systems that are accurate to
a

gauge

is

difficult, as is the case in low-visibility

conditions, a constant reserve valve can be carried as
well.

In addition, dial faces that glow in the dark

increase gauge readability under marginal light conditions.

the

Some newer gauges

amount

are able to provide data on

make

cylinders with

known

1

sures available to their customers for comparison.

NOAA

all

or

pres-

At

diving units, pressure gauge testing devices

are available that can be used for gauge calibration

and

to assess erratic needle

movement.

of time remaining for the dive at the cur-

rent breathing gas

consumption

rate.

This feature cal-

culates the pressure drop in the cylinder over time and

predicts the

2 percent so they can

amount of

air

time remaining, assuming a

continued constant rate of use. However, divers should

be aware that changing their respiration rates can
dramatically alter the amount of time remaining at

WARNING
Do Not Look Directly At the Face of Any Pressure Gauge When Turning on the Cylinder
Because of the Possibility of Blowout

low cylinder pressures.

to

The use of
be added

increased the

when

Because the accuracy of the slow indicator needle

submersible pressure gauge has

declines during normal use, the needle on a defective

amount of information

that can be obtained

a diver monitors the submersible cylinder pres-

sure gauge.
ers,

consoles that allow other types of gauges
to the

Maximum

depth indicators, bottom tim-

and compasses are now commonly associated with

pressure gauges. However, this use of console gauge

holders has added considerably to the mass of the
high-pressure hose end, and the hose and gauge must

4-12

unit

might

stick,

which could cause the pressure read-

ing to be higher than

it

actually

is.

Divers

in the field

can assess the adequacy of submersible gauge needle
function by releasing pressure from the gauge over a

3-minute period while they observe the needle for
movement. Defective gauges must be returned
to the manufacturer for replacement of parts.
erratic

NOAA

Diving Manual

— October 1991

Page

SECTION

5

DIVER AND
DIVING

5.0

General

5.1

Open-Circuit Scuba
5.1.1

EQUIPMENT

5-1

Demand

5-1

Regulators

5-1

Two-Stage Demand Regulators
5.1.1.2
Breathing Hoses
5.1.1.3
Mouthpieces
5.1.1.4
Check Valves and Exhaust Valves
Preventive Maintenance for Regulators
5.1.1.5
Surface-Supplied Diving Equipment
5.1.1.1

5.2

5-6
5-6

Lightweight Free Flow Helmets

5-8

5.2.3

Lightweight Free

5.2.4

Umbilical Assembly

Flow/Demand Helmets

5.2.4.3

Gas Supply Hoses
Communication Cables
Pneumofathometer Hoses

5.2.4.4

Strength

5.2.4.5

Hot-Water Hoses
Assembly of Umbilical Members
Coiling and Storage of Umbilical Hose
Umbilical Maintenance
Harness
Weighting Surface-Supplied Divers

5.2.4.8
5.2.4.9

5.2.4.10

Members

Diver Equipment.

5-8
5-8
5-9
5-9
5-9

5-9

5-10
5-10
5-10

5-10
5-1
5-1

5-1

5.3.1

Face Masks

5-1

5.3.2

Flotation Devices

5-1

5.3.3

Weight

Belts

5-13

5.3.4

Diver's Knife

5-14

5.3.5

Swim

5-14

Fins

Protective Clothing

5-14

5.4.1

Wet

5-15

5.4.2

Dry Suits
5.4.2.1
Dry Suit Insulation
5.4.2.2
Variable-Volume Neoprene or Rubber Dry Suits
Hot-Water Suit Systems
5.4.3.1
Open-Circuit Hot-Water Suits
5.4.3.2
Hot-Water Heater and Hoses
5.4.3.3
Closed-Circuit Hot-Water Suits
Accessory Equipment

5.4.3

5.7

5-5

5.2.2

5.2.4.7

5.6

5-5

Flow/Demand Masks

5.2.4.6

5.5

5-4

Free

5.2.4.2

5.4

5-4

5.2.1

5.2.4.1

5.3

5-2

Diver's

Suits

5-16
5-17
5-17

5-18
5-18
5-18

5-19
5-19

5.5.1

Snorkels

5-19

5.5.2

5-20

5.5.3

Timing Devices
Depth Gauges

5.5.4

Wrist Compass

5-21

5.5.5

Pressure Gauges

5-21

5.5.6

Underwater Slates

5-22

5.5.7

Diving Lights

5-22

5.5.8

Signal Devices

5-22

5 5.9

Safety Lines

5-24

5.5.10

Floats

5-24

5.5.1
Accessories That Are Not Recommended
Shark Defense Devices
Underwater Communication Systems
5.7.1
Hardwire Systems
5.7.2
Acoustic Systems
5.7.3
Modulated Acoustic Systems

5.7.4

Non-acoustic Wireless Systems

5-20

5-24
5-24
5-25
5-25

5-26
5-26
5-27

4

<

DIVER AND
DIVING

EQUIPMENT
GENERAL

5.0

This section describes diving equipment that has proven

be reliable

to

in a

Figure 5-1
Open-Circuit Scuba Equipment

wide variety of underwater environ-

New

models and new types of diving equipment
come on the market regularly, and divers should be
ments.

when selecting equipment to ensure that the
equipment they have chosen is both safe and efficient.
Diving equipment must be maintained properly to percareful

form

at its best; selection

mental

5.1

and maintenance are funda-

to safe, effective diving.

OPEN-CIRCUIT SCUBA

Self-contained underwater breathing apparatus (scuba)
was developed to allow the diver freedom of movement
under water. In this diving mode, divers carry their
breathing medium on their backs, which allows dives
to be conducted without surface support.
A typical open-circuit scuba system consists of a
compressed air cylinder (tank) that contains high-

pressure

air,

a regulator that reduces the pressure of

the air in the tank to a pressure equal to that of the

environment (ambient pressure), and a means

diver's

of attaching the tank and regulator to the diver.

A

standard open-circuit scuba system

is

shown

in

Figure 5-1.

Three major categories of scuba are currently

in use:
Courtesy U.S. Divers

•

Open-circuit demand;

•

Semi-closed-circuit (for mixed gas applications);

•

Closed-circuit.

and

To

•

equipment that is appropriate for a particular dive, divers must know and understand the difference between self-contained diving (open-circuit air)
and surface-supplied diving.
The advantages of open-circuit scuba are:
It

•

The equipment needed can be carried

for dives of long

•

Does not permit communication between the diver
and the surface;

•

Cannot be used under conditions of poor visibility;
Cannot be used for cold-water diving; and
Requires a minimum of two divers (i.e., use of the
buddy system) for safety.

•
•

permits diver mobility;

•

Cannot supply breathing gas
durations;

select

or trans-

ported easily;
•

can be conducted from small boats (i.e.,
mode requires little support equipment); and

•

Training for this

It

The disadvantages
•

Cannot be used

October 1991

mode

is

at great depths:

Diving Manual

5.1.1

Demand

Demand

widely available.

of open-circuit scuba are that

— NOAA

this

Regulators

regulators are used to reduce the pressure

of the breathing gas

coming from high-pressure

cylin-

ders to ambient pressure and to provide gas to a diver
it:

on demand; the pressure differential created by the
respiratory action of the diver's lungs

is

the signal to

5-1

Section 5

Most

depth or respiration rate and conserve the gas supply

exhausted at the regulator through the hose leading
over the left shoulder. The two-hose regulator is no
longer widely used, and it is not currently in commer-

by delivering only the quantity of breathing gas required.

cial production.

the regulator to provide gas to the diver.
tors automatically adjust to

changes

regula-

in the diver's

The function of "upstream" and "downstream" valves
is

critical to the

operation of regulators.

An upstream

is one that opens against the air flow coming
from the high-pressure gas in the cylinder. Because
this valve is forced closed by gas of higher pressure, it
increases breathing resistance. If a major regulator
malfunction occurs, the upstream valve is closed by

valve

the higher pressure gas, which, in turn, shuts off the
diver's supply.

As

a consequence of this feature, these

valves are only rarely manufactured today.

stream valve, on the other hand, opens

A

down-

same

in the

direction as the airflow, which causes such valves to be

forced open by the higher pressure

This method of

air.

operation results in smoother operation and reduced
inhalation effort. Almost
regulators are

Many

stage valves.

all

commercially available

now equipped with downstream seconddifferent

demand

regulators are

available that deliver breathing gas at remarkably
consistent, low-differential pressures.

The single-hose regulator
first

pressure reduction

is

designed so that the

stage mounts directly on the

tank manifold or valve, and the second pressure reduction stage

is

contained in an assembly that also includes a

mouthpiece and exhaust ports. The first and second
stages are connected by an intermediate pressure hose.
Air is delivered from the first stage at intermediate
pressure (110-160 psi over ambient) and from the
second stage at ambient pressure. The exhaust gas is
released into the water from the mouthpiece through
the exhaust port (non-return valve).

two-stage regulator

is

the most

The

common

single-hose,

regulator in

use because of

its reliability, simplicity, and ease of
maintenance (Cozens 1980). Lighter weight plastics
are being used in second-stage housings, and silicone
rubber components have largely replaced less durable
materials. The performance characteristics of secondstage components have also been improved by elimi-

nating metal-to-metal interfaces.

First-stage regulators are available in two types,
5.1.1.1

diaphragm and

Two-Stage Demand Regulators

Two-stage regulators are designed to reduce the
breathing gas in a cylinder to ambient pressure in two
stages.

The

first

stage reduces the pressure to approx-

imately 110 to 160 psi above ambient pressure, and the

second or demand stage reduces the pressure from this
level to

ambient pressure. The major advantage of the

second stage

is

that air

is

supplied to the

demand

stage

which allows both a
reduction in breathing resistance and fewer fluctuations caused by changes in depth and decreasing cylinat a nearly constant pressure,

der pressure. Breathing resistance
the
(1

demand

is

reduced because

valve works against a controlled pressure

10 to 160 psi above ambient from the

produced in two
and balanced (Figure 5-2).
The diaphragm first-stage regulator (Figure 5-2a)
contains an unbalanced upstream valve (i.e., high-

acts against a flexible diaphragm.

by the
air

still

in

combine

is

the double-hose

lung developed by

original two-stage regulator

model similar to the original AquaGagnon and Cousteau in 1943, in

which both pressure reduction stages are combined
into one mechanical assembly that mounts on the tank
manifold. Two flexible low-pressure hoses lead from
either side of the regulator to a mouthpiece that contains both the inhalation

The hose

until equilibrium

forces exerted

During descent, the

is

restored.

When

the diver inhales,

the reduced pressure in the intermediate

is

chamber

dis-

achieved.

The balanced diaphragm

and exhaust non-return

valves.

that leads over the right shoulder supplies the

ure 5-2b)

first-stage regulator (Fig-

designed so that the valve stem extends

anced configurations of the diaphragm first-stage
regulator, failure of the diaphragm causes the valve to
close.

The unbalanced

piston first-stage regulator (Fig-

ure 5-2c) contains a downstream valve
pressure air acts to open the valve).
in

the exhaled gas exits through the mouthpiece and

pressure,

is

is

completely through the high-pressure chamber; the
operation of the balanced valve is thus independent of
the tank (supply) pressure. In both balanced and unbal-

breathing (inhalation) gas at ambient pressure, and

5-2

to activate the valve.

The

and the high-pressure

demand

few two-stage, two-hose regulators are
use, and single-stage, two-hose regulators can

The

spring, the water (ambient),

chamber displaces the diaphragm and opens the valve

A

be seen occasionally.

spring applies a

increasing hydrostatic pressure in the free-flooding

librium
regulators.

A

pressure air acts to close the valve).

force that opposes that of the high-pressure air and

places the diaphragm and opens the valve until equi-

first stage).

All single-hose regulators are two-stage

piston; both types are

configurations, unbalanced

the free-flooding

and

chamber

A

(i.e.,

higher

bias spring

controls the intermediate

a hole in the shaft of the piston allows

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-2
First-Stage Regulators
of the valve
a.

therefore independent of tank (supply)

is

Unbalanced Diaphragm

uration, failure of the piston seal tends to cause the
•

Diaphragm

Valve Seat

valve to

fail in

the open or free-flow mode.

The second-stage
HP

[BM

Air-

Valve

b.

piece,

—Water

medium

To 2nd

Tension

Stage

Spring

Seal\

HP

a»
To 2nd

Ambient
Water

*

Pressure

Spring

to

Stage

the

improve the dynamic breathing characteristics of

phragm inward, which reduces inhalation effort. On
diaphragm returns to a neutral posi-

Hollow

exhalation, the

Air

Piston

tion, releasing

pressure on the stem or linkage, which

returns to

normal position, closing the medium-

its

pressure valve.

To 2nd
Stage

As exhalation
chamber to

one-way mushroom valve

\

Ambient
x Water

increases the pressure in

Stem

above ambient,

levels

A

Adjustable

imum

of dead space, which limits the

/Tension

that will be rebreathed.

/

Spring

Valve
Seat

properly constructed second stage has a min-

The pilot
number of

To 2nd

valve that

Stage

valve second stage also has

regulators;
is

it

amount

of air

been used with a

incorporates an air supply

opened and closed by

air pressure rather

than by mechanical leverage. The opening pressure

Air

downstream pilot valve. A simple mechanical linkage
is used between the diaphragm mechanism and the

Ambient
Water

Seals

is

generated by air flow through a diaphragm-activated

Piston
'O" Ring

a

unseated, which allows

water.

Balanced Piston
Hollow

is

the exhaled gas to be exhausted into the surrounding

Pressure

HP

in

the regulator; the venturi effect tends to pull the dia-

the low-pressure

d.

chamber

mouthpiece. In addition, most regulator manufactur-

Valve
Seat

Seals

The

pressure to a valve in the mouthpiece.

ers incorporate aspirators (venturi's) into their designs

Stem

"O" Ring

by a medium-

long as a diver inhales, air will continue to flow into the

Diaphragm

Unbalanced Piston

HP

to the first stage

mouthpiece caused by inhalation results in distortion
of a diaphragm. This distortion applies pressure to a
stem or linkage that is connected directly to the mediumpressure air inlet valve, opening the valve and admitting air into the mouthpiece at ambient pressure. As

Tension

Valve
Seat

mouth-

regulator, located in the

reduction in pressure in a low-pressure

Adjustable

Air-

connected

is

pressure hose; this hose, in turn, supplies a constant

Pressure

Balanced Diaphragm
"O" Ring

c.

Ambient

Adjustable

Upstream

and unbalanced config-

pressure. In both the balanced

Pressure

pilot valve.
Source:

NOAA

Because the

pilot valve

amount of spring tension needed

to

is

very small, the

counterbalance the

(1979)

pressure

is

small and less force

close the valve.
to

The

is

pilot valve

necessary to open and

opens only a

little

way

permit the air supply valve to pass a small amount of

air into a control

chamber. With

this

system, air supply

the dry side of the piston to be equalized at the inter-

valve openings larger than those used in conventional

mediate pressure. During descent, the increasing hydro-

leverage systems can be used in the second stage.

static pressure in the free-flooding

chamber

displaces

the piston, opening the valve until equilibrium
restored.
in

When

the diver inhales, the reduced pressure

the intermediate

chamber displaces

opening the valve until equilibrium

The balanced
the high-pressure

is

the piston,

achieved.

movement

chamber by an

— NOAA

is

isolated

is

from

0-ring: the operation

Diving Manual

Because there

is

a piston opposite the valve opening

that exactly counteracts the opening force of the air
pressure, the supply valve

is

balanced and therefore

not affected by intermediate pressure variations.

is

The

system can be described as a pneumatically amplified

piston regulator (Figure 5-2d)

designed so that the piston

October 1991

is

second stage; this means that a small force, the
valve,

is

pneumatically amplified to move

pilot

a larger

force, the air supply valve.

5-3

Section 5

Figure 5-3
Breathing Hoses

The

aspirator port, mentioned previously,

directed

is

A.

Corrugated Hose

B.

Low-Pressure Hose

Fitting

toward the mouthpiece inside the regulator and gener-

vacuum within
As a result, less

ates a slight
is

flowing.

the regulator case
effort

tain air flow during inhalation.

for

demand

is

when

air

required to main-

Although normally

set

breathing, the aspirator can be set for

positive-pressure breathing.

The

regulator

tive to pressure variations that, in

dive/predive switch

is

is

so sensi-

some

cases, a

incorporated to decrease the
Source:

response of the regulator. Normally, a regulator requires

NOAA

(1979)

a pressure or suction equivalent to that of a 2-inch

cm) water column

(5.1

to activate air flow; the pilot

system requires a pressure equal to that of a 0.5-inch

cm) water column.
The operation of the regulator

connections that are covered by hose protectors espe-

(1.3

initiated

is

by a

slight

diaphragm
to be drawn downward. The resulting linkage movement opens the pilot valve, and air flows to pressurize
inhalation effort that causes the regulator

the control chamber; this, in turn, opens the air supply
valve.

and

The

air

between the

structural arrangement

pilot

supply valves provides a controlling feedback

move

that allows the air supply valve to

response to the pilot valve.

The

only in exact

pilot valve acts as a

safety relief valve in the event of first-stage malfunc-

A

tion.

mechanical override also

is

incorporated into

cially carefully before diving,

because the protectors

sometimes conceal damage.

Mouthpieces
The mouthpiece (Figure

5.1.1.3

5-4) provides a channel for

the flow of breathing gas between the diver and the
life-support system.

piece differ

The

among

size

and design of the mouth-

various manufacturers, but the

mouthpiece generally

is

molded of neoprene,

silicone

rubber, or other materials that have a low deterioration rate. (Silicone rubber has the

added advantage of

the system to ensure operation in case the pilot valve

being hypoallergenic.) Typically, the mouthpiece con-

malfunctions.

sists

of a flange that

teeth. Bits,

Breathing Hoses

5.1.1.2

ure 5-3A) are flexible, large-diameter rubber ducts that

provide passageways for air from the cylinder to the

may

Corrugated rubber hoses are common, but hoses

also be

made

of rubberized fabric with metallic

rings or spiral stiffening.

To provide minimum

resist-

ance to breathing, the hose should have an inside diameter
of at least

1

inch (2.5

cm) and should be long enough

in

the "relaxed" state to allow full freedom of body move-

ment. The hose must be capable of stretching to twice
its

relaxed length without collapsing or buckling.

Single-hose scuba, with the second stage of the
regulator mask mounted or mouthpiece mount-

demand

ed, does not require the large-bore,

ambient pressure

breathing hose described above because the gas in the

hose

is

at

medium

pressure (110 to 160 psi above

ambient) rather than at ambient pressure (Figure 5-3B).
or demand valve is connected to a
cylinder-mounted first-stage regulator by a single,
medium-pressure hose of relatively small diameter.
Exhaled gases are discharged directly into the water

The second-stage

through an exhaust valve

in the

mask

or mouthpiece.

Breathing hoses should be checked for cracks or
chafing before every dive. Divers should check the

5-4

between the

space the jaws. The mouthpiece should

In double-hose scuba, the breathing hoses (Fig-

diver.

fits

diver's lips

and

one on either side of the opening, serve to

comfortably

fit

and be held in place when a slight pressure is exerted
by the lips and teeth. The novice diver often forgets
that the bits are spacers and should not, under normal
conditions, be used as grips. In an emergency, the bits
will

provide a reliable grip, but continuous force exerted

through the teeth

weaken the

will

bits

and cause con-

siderable fatigue of the muscles around the jaws.

Many

individuals have difficulty with temporal

dibular joint

(TMJ) pain when gripping

man-

the mouth-

piece tabs too firmly during a dive. Mouthpieces that

spread the load to the rear teeth are more comfortable.

Learning to relax the jaw
tive deterrent to

On

TMJ

is

probably the most effec-

pain.

a two-hose regulator, the mouthpiece assembly

incorporates a system of one-way check valves, and

clamps are provided for the breathing hoses. In a
hose scuba regulator, the mouthpiece
into the second-stage
cases, the

by a

full

demand

is

single-

incorporated

valve housing. In

some

mouthpiece assembly can be replaced entirely
face mask.

The use

of a full face

mask

in lieu

of a mouthpiece facilitates voice communication by
freeing the diver's mouth; however, with this configuration, an oral nasal

mask must be used

to prevent

carbon dioxide buildup.

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-4

Mouthpieces
Double Hose

A.

B. Single

Hose

5.1.1.5

Preventive Maintenance for Regulators

Because regulators are one of the primary components of a life-support system, they require careful

maintenance.

An

to ensure that

no foreign matter has entered any of the

essential element of

maintenance

is

regulator's components; introducing foreign matter into

an area of close tolerance or into a perfect seal could
cause a malfunction. The primary entry point for foreign matter
Courtesy U.S. Divers

For

the high-pressure inlet in the first stage.

is

this reason, the dust

cap should be kept

in position

over the high-pressure inlet whenever the regulator

is

not in use. Salt water entering the high-pressure inlet
will leave deposits of salt that

5.1.1.4

ation or pit valve surfaces.

Check Valves and Exhaust Valves

Check

valves and exhaust valves (Figure 5-5) are

designed to permit gas flow

in

one direction only. Check

valves direct the flow of inhaled and exhaled gases

through the breathing system. During inhalation, pres-

chamber (now lower

sure decreases in the mouthpiece

successive days can substantially degrade the perform-

ance of most regulators.
Divers should be alert for early

resistance

moving

is

directed out through the mouthpiece
to the exhaust valve. This pair of

valves within the mouthpiece assembly minimizes dead

symptoms of equip-

ment malfunction. For example, increased breathing

but opens the inhalation check valve. During exhala-

and exhalation tube

of a few drops

of salt water into the high-pressure filter on several

than ambient), which seats the exhalation check valve
tion, the air

can prevent proper oper-

The addition

may

parts,

be caused by the corrosion of internal
and water leakage in the mouthpiece can

occur as the result of deterioration of the second-stage
exhalation valve. Other signs that indicate problems
are rusting or clogging of the first-stage

filter,

free

mini-

flowing, and 0-ring leaks. These and other signs of

mizes the rebreathing of exhaled gases. The inhalation

trouble should be thoroughly evaluated before any

air

space within the system, and

this,

in turn,

demand

check valve also prevents water from entering the
regulator

An

when

the mouthpiece floods.

exhaust valve

is

The most important maintenance

a special check valve that per-

mits the discharge of exhaled gas from the breathing

system and prevents the entrance of water.
valve (also called a flutter valve)

exhaust valve

mushroom

in

is

A

flapper

typically used as an

the double-hose regulator, while a

valve generally

single-hose model.

A

fulfills

this function in

flapper valve

is

simply

the

a soft

rubber tube collapsed at one end; when ambient water
pressure

is

further dives are made.

greater than the air pressure within the

a regulator

is

to be

performed on

a fresh water rinse after each use; this

salt and other debris (sand, dirt,
from the regulator and prevents deterioration.
Rinsing should be done within a few hours of the completion of a dive, regardless of whether the dive was

procedure removes
etc.)

conducted
single-

in fresh or salt water.

Procedures for washing

and double-hose regulators vary significantly

and are discussed below.

With

a single-hose regulator, the first stage should

valve, the valve remains in the collapsed condition.

be held under a stream of warm, fresh water for at least

During exhalation, however, the increase

2 minutes while the dust cap remains sealed in place,
and water should be allowed to flow freely through any
open ports. This is especially important with pistontype regulators, because it prevents the buildup of
salt on the piston tracks. Because the dust caps pro-

in

pressure

above ambient pressure forces the flapper open, allowing
the gas to escape.

Water cannot enter the valve while
and when the pressure

the higher pressure gas escapes,

equalizes, the flapper returns to the relaxed or closed
position.

The mushroom valve on

single-hose models

is

made

of extremely soft, flexible rubber, which renders
very sensitive to changes
valve.

A

in

pressure across the check

wheel-shaped valve seat

the rubber

mushroom

valve seat support the

is

fashioned to hold

rinsing the regulator.

When
tor, the

rinsing the second stage of a single-hose regula-

diver should permit water to enter through the

in place.

Rigid spokes of the

mouthpiece and

mushroom

valve against a clos-

flow

ing pressure but permit the flow of air

when pressure

within the mouthpiece exceeds ambient pressure.

October 1991

it

vided with some regulators are not watertight, the
diver must make sure the cap is watertight before

— NOAA

Diving Manual

in

exit via the exhaust.

Allowing water

to

the direction of the non-return exhaust valve

washes sand,

dirt, etc.,

out of the mouthpiece.

The

purge button should not be pushed unless the system

is

5-5

Section 5

Figure 5-5

Check and Exhaust Valves
5.2

SURFACE-SUPPLIED DIVING
EQUIPMENT

One

of the major constraints of scuba diving

is

the

limited quantity of breathing gas the diver can carry;

with umbilical (surface-supplied) diving, divers have

them to spend
more time on the bottom. The increased safety pro-

a continuous air supply, which allows

vided by umbilical equipment

Source:

NOAA

(1979)

is

also important. In this

mode, the diver is tethered and has direct voice communication, which permits safe operation under conditions considered too hazardous for the self-contained

becomes fouled

diver. If a surface-supplied diver

pressurized, since doing so opens the air inlet valve

and

or

disabled, a continuous air supply can be maintained

through the middle-

from the surface and a standby diver can locate the

pressure hose to the high-pressure stage. If the regulator

diver by following the entrapped diver's tether. In

might allow dirty water
is

to pass

to be stored for a long period of time,

it

may

be

remove the band holding the two sections
of the second stage and the diaphragm in place and to
desirable to

rinse

each separately. Rinsing procedures for the double-

hose regulator are more complicated than for the single-

hose model.

As with

the single-hose regulator, rinsing

should be conducted with the watertight dust cap in

The exhaust

place.
holes,

side of the regulator has a series of

and water should be allowed

to flow freely

through

addition,

if

strong currents are a problem, the tethered

diver can use additional weights to increase his or her
stability.

Surface-supplied diving can be conducted from
locations:

many

from the surface, a habitat, a personnel transfer

An

capsule, or a lockout submersible.

umbilical to the

diver that runs from the gas storage cylinders of the
habitat, capsule, or submersible provides the diver's
(if required), and a communiThe major disadvantage associated with
surface-supplied diving is that this mode requires more

breathing gas, hot water
cations link.

this section.

Care must be taken when

rinsing the hose

piece assembly because any water that

high pressure into the mouthpiece

may

is

and mouth-

forced under

bypass the soft

rubber non-return valve and enter the intake side,
which may cause corrosion. During rinsing, the mouthpiece should be held with the air inlet valve up, and
water should be allowed to enter the mouthpiece, flow
through the exhaust valve and hose, and exit at the

main body of the

regulator.

To remove water from

the

corrugations in the hose, the hose should be stretched

support equipment and personnel than

is

the case for

the scuba mode.

Many

safe

and

efficient diving

are available commercially. All

masks and helmets
masks and helmets

provide the diver with a continuous supply of breath-

and some models allow the diver to elect either
demand operating mode. A communisystem is standard equipment on modern surface-

ing gas,

the free flow or
cation

supplied helmets.

and the diver should blow through the mouth-

lightly

piece, allowing excess water to pass out through the
exhaust.

The

To avoid

hung by the mouthand weaken the hose.

regulator should not be

because

piece,

this will stretch

cultivating bacteria in the corrugations, the

interior of the hoses should

be dried periodically. Scuba

regulators should be tested functionally on a regular
basis

and

at least as often as

every 6 months. Perform-

ing this test usually requires nothing

more than

Free Flow/Demand Masks
The free flow/demand mask is designed

5.2.1

to

be used

with an umbilical hose that supplies breathing gas

from the surface, an underwater habitat, or a personnel transfer capsule (submersible decompression chamFree flow systems supply sufficient ventilation
for heavy work and also provide divers with an adjustable-flow, off-on supply to the interior of the mask

ber).

a

manometer.

through the muffler deflector. In addition to supplying
the diver with a steady flow of breathing gas, the

NOTE

deflector directs gas across the viewing lens to prevent

Hoses (especially exhaust hoses) should be
removed periodically and should then be
washed with surgical soap to prevent bacterial

5-6

buildup.

fogging.

When

the umbilical hose

breathing gas, the
at all times.

The

demand

pressurized with

is

regulator

is

regulator provides a

pressure-loaded

demand

breath-

ing system, similar to that of standard open-circuit

NOAA

Diving Manual

—October 1991

Diver and Diving Equipment

scuba, which

Low volume
Easy strap adjustment
Secure strap fasteners

adjustable for gas supplied at pressures

•

ranging from 60 to 180 psi over ambient pressure.
Demand systems are preferred for light to moderate

•

work because they economize on gas requirements and
enhance communication. A nose-blocking device is
incorporated into demand systems to facilitate sinus
and middle-ear equalization, and an oral-nasal mask
assembly is used to reduce dead air space and eliminate the possibility of a dead air space carbon dioxide

•

Hypo-allergenic material

•

Tempered

is

buildup.

Some lightweight masks and helmets conventionally
used for surface-supplied diving are equipped with
demand

regular scuba

regulators and can be adapted

•

Divers who must wear eyeglasses on land generally
need some form of optical correction under water.
Several methods for accommodating corrective lenses
in divers' face masks have been developed:
•

masks consume more

air

•

consumption rate should be determined at
work loads before actual diving oper-

•

To permit buddy

ations begin.

breathing, an octopus

•

ability to utilize a tape recorder or diver-to-diver

Lenses can be mounted

•

Standard glasses can be mounted inside the faceplate with stainless steel spring wire;

•

Face masks may be equipped with nose-blocking

Each

methods has advantages and disadvanworn inside a mask
because the temples cause the mask to leak. Wearing
of these

lens inserts inside the face

descent. Blocking off the nose to aid in equalizing

sive but provides

the ears

is

accomplished easily either by

pushing upward on the bottom of the mask to create a

when using masks with nose

seal or gripping the nose

pockets.

Masks

valve to aid
high-quality

also

may be equipped

with a purge

in clearing water from the mask. Only
masks with large purge valves are recom-

mended, because purge valves are subject

to failure or

Face mask selection
fit,

is

a matter of individual prefer-

comfort, and other diver requirements.

Masks

are available in a variety of sizes and shapes that will

accommodate
the lens

is

different lens configurations.

The

closer

located to the eye, the wider the peripheral

(Egstrom 1982). Selection of a mask that
well can provide easy clearing and an optimal

visual field
fits

the-shelf

mask

simple and inexpen-

is

an extra surface to

masks are available with

Some

fog.

off-

built-in correction;

whether or not these are useful to a given individual
depends on several factors, including the type and

amount

of refractive error, the similarity of error in

the two eyes, and the interpupillary distance.

The use of contact

lenses

under the face mask pro-

vides good vision under water, offers a wide field of
view, and eliminates problems with fogging. However,

leakage.

ence,

and

Soft or fenestrated contact lenses can be worn.

devices to facilitate equalization of pressure during

in

frame and be

tages. Glasses generally cannot be

communication.

pressure

in a special

secured to the inside of the faceplate;

first stage.

The advantages of this setup are greater comfort around
the mouth and jaws during long exposures and the

Large-size prescription lenses can be bonded perma-

nently to the inner faceplate surface;

several different

second-stage regulator can be added to the

Prescription lenses can be incorporated into the
faceplate;

than they do with regular scuba mouthpieces, and each
diver's air

Individual prescription lenses can be inserted into

goggle-type masks;

easily for use with self-contained air supply (scuba

tanks). Divers using these

safety glass.

visual field.

A

plastic or clear

problem with some of the new clear
rubber masks is that they allow light to

enter from the side, which

may

cause a mirror effect on

some people do not tolerate contact
some lenses cause corneal edema. The

signs

toms of corneal edema, which include discomfort, haloes

around
found

lights,

to

and

loss of visual acuity,

The following features should be looked

for

when

are used; soft lenses or fenestrated hard lenses do not

cause this condition, which has been attributed to the
inability of

1978,

hard lenses to "breathe" (Simon and Bradley

1980). Because a dislodged lens can be very

painful and debilitating, Cotter (1981) has suggested

eye trouble"

if

means

"lens or

either diver wears contact lenses.

options available to individuals

selecting a face mask:

have been

occur when unfenestrated hard contact lenses

that dive buddies establish a signal that

the lens.

and
and symp-

lenses well,

who have

(The

different

types of refractive error but wish to dive, and the
•

Light weight

•

Comfortable

•

Wide-angle vision

•

Easy closure of

October 1991

advantages and disadvantages of the various methods,
are discussed fully in Kinney (1985).)

fit

Ventilation across the faceplate generally

nostrils for equalization

— NOAA

Diving Manual

and the glass tends

to fog easily.

To minimize

is

poor,

fogging.

5-7

Section 5

Figure 5-6
Lightweight Helmet
the inside of the faceplace should be smeared with

and then be rinsed before wearing. Anti-fogging
commercial preparation) may be applied to the inside of
the faceplate. The faceplate should be washed frequently
saliva

solutions (such as a mild liquid soap or a special

in

detergent to remove

oils or

which enhance fogging.

If the

drops of water should be

surface film, both of

mask

fogs during use,

the

mask and should

let into

then be rolled across the fogged areas to clear them.
If the

mask has

a purge valve, the valve should be

thoroughly washed out to remove any sand that might
prevent it from sealing properly. The mask should not

be

left in

the sun for any extended period because

make the headstrap and sealing edge
Although the headstrap can be replaced easily
and economically, cracking of the sealing edge will
sunlight will

brittle.

make

the

mask

useless.

Self-contained emergency gas supply systems (or
bailout units) are used in conjunction with surfacesupplied diving equipment to perform work at depths
in excess of

60

pipes, etc., or

feet (18.3 m),

where there

is

when working

®Diving Systems International
1990 All Rights Reserved.

in tunnels,

the danger of entangle-

ment. These units consist of a scuba cylinder assembly,
a reduction regulator

(i.e.,

first

stage of a standard

and a backpack-harness assembly. The capacity of the scuba cylinder assembly varies
from 10 ft 3 to 140 ft 3 depending on the diver and the
situation. Emergency gas may be fed directly into the
diver's mask through a special attachment on the side
single-hose regulator),

,

valve or be introduced directly into the diver's air hose

assembly. In the latter case, a check valve must be
located between the intersection of the emergency gas

supply hose and the primary surface supply hose. A
completely separate bailout system, which includes a
scuba tank and regulator, may be used. If the umbilical air supply

is lost,

the full face

mask must be removed

before the diver ascends to the surface using the scuba

tank and mouthpiece. If an emergency gas supply sys-

tem

is

carried.

selected, a second face

The advantage

mask should

also be

comcomputting on the face mask

of this configuration

is

plete redundancy; the disadvantages are loss of

munication and difficulty

in

and locating the regulator.

standardized interchangeable fittings, improved valves,

unbreakable faceplates, better ventilation (low C0 2
buildup), improved visibility, better communication,
versatility because they can be used with any type of
dress, bailout capability, and simplicity of use and
maintenance. Modern helmets can be used with a
neoprene wet suit, a hot-water suit, or a variablevolume suit. Some helmets attach to the neck bands of
specially adapted dry suits for use in cold or contaminated water.

5.2.3

Lightweight Free

Flow/Demand Helmets

Free flow/demand system dry helmets combine the
full head protection, communications,
and the breathing characteristics of a standard dry
helmet with the gas economy and comfort of a demand
mask. Weight is distributed throughout the helmet
to achieve balance and optimum performance without
neck strain or effort. The helmet is designed to be

advantages of

neutrally buoyant in seawater. It
auxiliary (or

5.2.2

Lightweight Free Flow Helmets

Many

equipped with an

valve and with communication earphones and microphone.

lightweight free flow diving helmets have been

designed and manufactured in recent years.

is

emergency) system valve and a non-return

An oral-nasal mask reduces

the potential for

C0 2 buildup.

Some manu-

facturers have constructed helmets of the traditional

Assembly

spun copper, which emphasizes indestructibility, while
others use fiberglass and emphasize comfort, light

5.2.4 Umbilical

weight, and maneuverability. In general,

weight helmets and free flow/demand masks generally

modern

light-

weight helmets (Figure 5-6) feature streamlined design,

5-8

The umbilical assembly

for surface-supplied light-

consists of a gas supply hose, a

NOAA

pneumofathometer

Diving Manual

— October 1991

Diver and Diving Equipment

communications wire, and a strength member.
Depending on dive requirements, a hot-water supply
hose, a

may

hose

assembled

also be included. Umbilical
in

members

continuous lengths; for example,

low water diving operations

to

(i.e.,

depths

are

in shal-

less

than

90 fsw (27 m)), a 150-foot (45 m) assembly may prove
satisfactory. Regardless of length, all members should

The wire

is

fitted with

ble with those on the

connectors that are compati-

helmet or mask.

A

waterproof, "quick-connect" connector

four-conductor,

often used;

is

these connectors have a socket-type configuration.

When

joined together, the four electrical pin connec-

be in continuous lengths because umbilical assemblies
designed with fittings and connectors have a greater

and a watertight seal is formed,
which insulates the wire from the surrounding seawater. To be secure and waterproof, these connectors
should be molded to the communication cable. Profes-

likelihood of failing or separating.

sional installation

tions are established

is

desirable. For field installation,

rubber electrical tape overlaid with plastic electrical
tape has been successful, although

Gas Supply Hoses
3/8-inch (1.2 cm) or

A

larger synthetic rubber,

braid-reinforced, heavy-duty hose

carry the diver's air supply.

is

generally used to

The hose must have

a

working pressure of at least 200 psig (this pressure
must exceed the diver's required supply pressure). The
outer cover of the hose must be durable and resistant to
abrasion, weathering, oil, and snag damage. The inside
tube of the hose must be non-toxic and impervious to
any breathing gas to be used. Hoses must be flexible,
kink resistant, and easy to handle. Although a hose
may have a sufficient pressure rating, it may shrink
considerably in length because

it

increases in diameter

when pressurized, which causes looping of the other
members of the umbilical assembly. To avoid problems, the percentage of shrinkage should be determined

before purchasing the hose, and the assembly should

be taped while the hose
less

is

pressurized.

than 150 psig, the change

in

At pressures

nector, generally of the standard terminal post type,
that

is

should be tagged with a serial number.
is

during use

resistant to

is

compatible with the communications

unit.

Many

divers use simple terminal or binder post connections

on masks and helmets. The ends of the wire are prepared with solder, inserted into the binder post termi-

and secured. Although less satisfactory than the
mentioned above, the use of terminal or binder post connections is satisfactory and

nal,

special connectors

economical.

Standard two-wire "push-to-talk" communicators
commonly used in diving. By using all four wires in
the communication wire, the system can be set up so
are

that the diver's voice

is

"live" at

all

times. All

commu-

nication wires should be tagged or coded for record-

keeping purposes, and lines should be checked before
being issued for use on any dive.

5.2.4.3

lost

less satisfac-

length should not

facilitate recordkeeping, all air supply hoses

ging band that

is

The surface end

of the wire should be fitted with an appropriate con-

exceed 2 percent.

To

it

tory than special molding processes.

5.2.4.1

damage and

A

metal tag-

unlikely to be

desirable. Purchase, test,

and usage

records should be maintained for each hose assembly.

Pneumofathometer Hoses

The pneumofathometer hose

is

a small hose that

is

end and connected to an air source
and pneumofathometer at the surface. Pneumofathom-

open

at the diver's

eters are precision pressure
in feet

gauges that are calibrated

of seawater and are used to determine the pre-

depth of the diver under water. Pneumofathometers
must be protected from abuse and should be calibrated
regularly. Lightweight air or oxygen hose (0.24-in.
(0.6 cm) i.d., 200 psig working pressure) is generally
used. Standard oxygen fittings are used for surface
cise

5.2.4.2

Communication Cables

Communication cables must be durable enough to
when a strain is placed on the umbili-

prevent parting

cal assembly; they

waterproof and

must

also have an outer packet that

and abrasion-resistant. Multiconductor shielded wire (size 14 to 18) that has a
is

neoprene outer jacket
diving. In
at

is

satisfactory for shallow water

normal service, only two conductors are used

any one time. The wire-braid shielding adds consid-

erable strength to the umbilical assembly.

should be

in

a

The cable

continuous length, with an additional

end and the surface end to allow
room to install connectors, make repairs, and connect
the communication equipment.
few

feet at the diver's

October 1991

connections.

oil-

— NOAA

Diving Manual

5.2.4.4

Strength

Members

The U.S. Navy recommends the use
member in the umbilical assembly. The
strength members include:

of a strength
lines

used as

cm) nylon braided line
cm) synthetic polyolefin braided or

•

3/8-in. (1.2

•

3/8-in. (1.2

3-strand twisted line

5-9

Section 5

cm) manila

•

3/8-in. (1.2

•

thin stainless aircraft-type cable.

surface

line

•

Each type of
Braided nylon

line has

line

is

it

advantages and disadvantages.

and handling

qualities,

stretches under high load conditions;

and expensive. Some divers use hollow-

flexible

"whip" (short length

accordingly.

zations, including the U.S.

pact, lightweight,

more

used between the helmet and the main

and the supply hose should also be adjusted

organi-

Navy, use this type of line.
Polyolefin line floats and thus reduces the in-water
weight of the umbilical assembly somewhat, but this
type of line can be abrasive to the hands. Manila line is
readily available and is the least expensive, but it
deteriorates rapidly. Aircraft-type cable is strong, com-

is

umbilical air supply hose, the communication line

although

many

If a lightweight,

of hose)

commonly used and has accepta-

ble strength, durability,

placed on the harness and not on the diver's

is

helmet, mask, or fittings.

•

If a

whip and special auxiliary

air

supply line valve

are used for helmet diving, their length should be
adjusted.

The diver should have sufficient hose and cable length
between the safety harness attachment point and the
mask (or helmet) to allow unrestricted head and body

core polyolefin line, with the communications line run-

movement without placing

ning through the hollow core, to combine the strength

connections. Excessive hose should not, however, form

and communication members.
strength

A

few combination
lines are com-

member/communicator wire

between the harness connection and the

a large loop

mask.

The communication

mercially available.

excessive stress on the hose

should be slightly longer

line

than the rest of the assembly to permit repairs at the
diver's end.
5.2.4.5

Hot-Water Hoses

When

hot-water wet suits are worn on a dive, a
specially insulated hose is required. This hose can be
obtained in either 1/2- or 3/4-inch (1.2 or 1.8 cm)
inside diameter size,

ume

The

snap hook that

depending on the depth and

of water to be supplied to the diver.

The

vol-

insulation

is

diver's

end should be

fitted with a

secured to the strength

member and

the rest of the assembly to facilitate attachment to the
safety harness.

The surface end

of the strength

mem-

ber and other components also are secured to a large
D-ring, which allows the assembly to be secured at the

diving station.

reduces the loss of heat to the open sea, which allows a

The hose should
be equipped with a quick-disconnect female fitting
that is compatible with the manifold attached to the
lower boiler operating temperature.

suit.

To prevent handling problems,

the hot-water hose

5.2.4.7 Coiling

and Storage

After the umbilical hose

of Umbilical

is

assembled,

Hose
it

should be

stored and transported; protection should be provided

should be joined to the diver's gas and communications

for hose

umbilical.

dures.

and communications

fittings

during these proce-

The hose ends should be capped with

plastic

protectors or be taped closed to keep out foreign mat-

and to protect threaded fittings. The umbilical hose
may be coiled on take-up reel assemblies, "figureeighted," or coiled on deck with one loop over and one

ter

Assembly

5.2.4.6

of Umbilical

Members

The various members of the umbilical assembly should
be bound together with pressure-sensitive tape. Twoinch (5 cm) wide polyethylene cloth-laminated tape or
is commonly used. Prior to assembly, the
members should be (1) laid out adjacent to
each other, and (2) inspected for damage or abnormal-

duct tape
various

and connections should be installed in
advance. The gas supply hose and pneumofathometer
hoses should be connected to the air supply and should
ities; all fittings

loop under. Incorrect coiling,

all in

the

same

direction,

will cause twist and subsequent handling problems.
The tender should check the umbilical assembly at the
end of each dive to ensure that there are no twists, and

the coil should be secured with a

number

of ties to

prevent uncoiling during handling. Placing the umbilical

assembly

in a large

tarpaulin will prevent

canvas bag or wrapping

damage during

it

in a

transport.

be pressurized to about 150 psig to ensure that shrink-

age does not cause looping.

The following

5.2.4.8

guidelines should be observed

when

assembling umbilical members:
•

The strength member should terminate
to

hook

After a day's diving, the umbilical should be washed

with fresh water, be visually inspected for damage,
in a position

to the diver's safety harness, generally

on the

left-hand side, so that the strain of a pull from the

5-10

Umbilical Maintenance

and be carefully stored

to prevent kinks. If the umbili-

be stored for a long period of time, the hoses
should be blown dry and the connectors should be
cal

is

to

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

capped

foreign matter from entering. Con-

to prevent

required for weight belts

fresh-water washing after

is

nectors should be lubricated with silicone spray after

use and predive checks of the quick-release

capping.

to ensure that

5.2.4.9

The
tate

Harness

wear a harness assembly to faciliattachment of the umbilical assembly. The hardiver should

ness should be designed to withstand a

1000-pound (454 kg)

pull in

minimum

any direction, and

it

of a

must

mask or
helmet when a pull is taken on the hose assembly. The
location of the attachment depends on the type of
harness assembly worn by the diver, but the harness
prevent strain from being placed on the diver's

should not be attached to the weight belt
latter

mechanism

operating properly.

is

it

in

case the

needs to be dropped.

5.3

DIVER EQUIPMENT

The on-scene dive master determines which items of
equipment are required to accomplish the particular
underwater task. Unnecessary equipment should be
left on the surface because excessive equipment can
become a hazard rather than an asset. This is particularly true when diving in a strong current, under conditions of limited visibility, or in

heavy surge, because

each additional item of diving equipment (especially
additional lines) increases the probability of fouling
the diver.

WARNING

Diver equipment considered

in

this section includes

face masks, flotation devices, weight belts, knives, and

Never Attach the Diver's Umbilical Directly
Weight Belt. A Separate Belt or Harness is Required To Permit the Weight Belt
To Be Dropped If Necessary
to the

swim

5.3.1
5.2.4.10

Weighting Surface-Supplied Divers

To weight

the diver properly, lead weights (3, 5, or

8 lbs (1.4, 2.3, or 3.7 kg)

The

with bolts.

wide and

is

belt

is

each) are secured to the belt

approximately 4 inches (10.2 cm)

fitted with a quick-release fastener.

The

weight belts used for arctic diving are heavier than
most belts because of the bulk and positive buoyancy
of cold-water exposure suits.

A

shoulder harness that

is

similar in configuration to a fireman's suspenders

is

the best

belts

method of preventing the heavy, unwieldy

from slipping

off.

If a leather belt

should be coated regularly with neat's-foot

Weighted shoes

or leg weights

may

is

used,

overcome

bility to the diver.

positive

the diver's eyes and the water. There are two general

classes of face masks: separate face

be used

buoyancy and

in

mask, which covers only the eyes and nose,

is

generally

used for scuba diving (when equipped with a mouthpiece)
or for skin diving. Full face

masks are used with

special

scuba and surface-supplied diving apparatus. Full face

masks consist of

The faceplates

con-

to give sta-

and a protective brass toe piece.
Leg weights consist of one large or several small

weights attached to leather or nylon straps. The straps
are fitted with buckles for securing the weights to the

The weights vary from

pounds (0.9 to 4.5 kg) each, depending on the
Leg weights provide improved stability and protection against blowup, because divers
wearing variable-volume suits can swim with relative
2 to 10

diver's preference.

ease while wearing fins and leg weights. For safety,
the weight belt should be worn outermost so that

it

can be freed easily when released. The only maintenance

Diving Manual

masks and full
The separate

face masks (Figure 5-7) (Hall 1980a).

tic,

place,

— NOAA

Face Masks

Face masks are used to provide increased clarity and
visibility under water by placing an air space between

a faceplate, a frame,

made

are

tempered safety

a lead or brass sole, leather straps to hold the shoe in

October 1991

sections below discuss each of these

and a headstrap.

of highly impact-resistant,

it

Standard weighted shoes consist of

diver's legs near the ankle.

The

(Glass

glass.

is

still

better than plas-

oil.

junction with the weight belt (primarily by tethered
divers) to

fins.

items in turn.

because plastic faceplates are subject

tion, abrasive

to discolora-

damage, and fogging.) The frame

is

designed to hold the faceplate and to provide a watertight seal;

it

is

usually

made

of plastic. Silicone rubber

has largely replaced less durable materials as face seal

components; the widespread use of silicone materials
in diving has significantly extended the useful life of
most rubber components. The mask should be sufficiently
rigid to hold the

rubber plate away from the diver's

nose and should be pliable enough to ensure perfect

and

still

retain

its

approximately
rear holds the

l

An

inch (2.5

mask

5.3.2 Flotation

A

shape.

fit

adjustable rubber headstrap

cm) wide and

split at the

to the diver's head.

Devices

is an essential part of a diver's
and buoyancy control system; it is also an

flotation device

life-support

5-11

Section 5

Figure 5-7

Face Masks
A.

Separate Masks

item of rescue and safety equipment. Many different
buoyancy compensators have been developed during
the past few years, including those with the popular
stabilizing jacket and compensators using the horse
collar designs (Figure 5-8).

and

These devices are available

backpack-mounted

as vest units,

units, stabilizer jackets,

wide range of variable-volume dry suits.
Although almost all divers would agree that some type
of buoyancy compensation is necessary, they would not
agree about which configuration or design is best.
When selecting a buoyancy compensator (BC), a
number of factors must be considered, including: type
in a

of exposure suit, type of scuba cylinder, diving depth,
characteristics of the breathing equipment, nature of

diving activity, and type of accessory equipment and

BC

weight belt (Snyderman 1980a, 1980b). The
be compatible with the exposure suit.

must

NOTE
Buoyancy compensators should not be used
ability and physi-

as a substitute for swimming
cal fitness.

Flotation devices should be designed so that a diver,

even when unconscious,

will float

with face up. The

mechanism of the device should be constructed
of corrosion-resistant metal, and a relief valve should
be part of the device when it is used for buoyancy
compensation. Most devices are designed to inflate
inflating

Courtesy Glen Egstrom

B. Full

Face Mask

automatically either
tured or

when

filled

when

a

C0 2

cartridge

is

punc-

with air supplied by a low-pressure

hose from the scuba cylinder. Regardless of their method

of inflation,

all

flotation devices should be

with an oral inflation tube.

The

equipped

oral inflation tube

should have a large diameter and be able to be operated with either hand.

Recent studies have determined that a minimum of
25 pounds (11 kg) of positive buoyancy is required to
support a fully outfitted diver operating in Sea State 1
conditions.

To achieve

this, a 19-25

gram

C0 2

car-

must be used with a properly designed buoyancy
compensator. U.S. Coast Guard regulations require
life vests to have a positive buoyancy of 24.5 pounds
(11 kg) to support a fully clothed adult. Divers and
boat operators should keep themselves informed about
tridge

the status of

life

vests (personal flotation devices),

because, for example, the Coast

Guard

recently issued

a warning cautioning against the use of
vests in
'

B Diving

1990

5-12

Systems

All

rough water because they

will not

Type

III life

keep a diver's

International

Rights Reserved

head clear

in

choppy water. Flotation devices that use

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-8
Flotation Devices

with a silicone lubricant.

The threads on

CO,

the

car-

tridge should also be lubricated.

The most frequent cause

of flotation device mal-

corrosion caused by salt water entering the

function

is

inflation

compartments; the resulting residue can block

C0 2

and cause significant deterioration
mechanism. If this occurs, the
device should be filled approximately one-third full of
warm fresh water, the water should be circulated rapidly through the vest, and the water should then be

the passage of

of the inflation-release

drained out through the oral inflation tube. Fresh water
also should be flushed through the passage

the vest and the

between

C0 2 cartridge.

Courtesy Glen Egstrom

NOTE
larger cartridges than those required, multiple cartridges,

and one or two

available; these

pensators

if

the oral or

inflation

compartments are

also

models can be used as buoyancy com-

Buoyancy compensators should not be worn
with a variable-volume dry suit if the BC hinders easy access to the suit's valves.

the diver partially inflates the device through

power

inflation tube while he or she

is

still

Periodic checks of the inflation device are also

The device should be

required.

submerged.
Specially designed buoyancy compensators that have

and separate inflatable cham-

large oral inflation tubes

bers are commercially available.

A

large cylinder of

inflated

and hung up

over night and/or be submerged periodically to check
for leaks. If leaks are observed, they should

before the device

is

used again. The

C0 2

be repaired
cartridges

chargeable from a standard
scuba air cylinder is an integral part of some buoyancy
compensators; this arrangement allows for partial or
complete inflation while the diver is submerged. Pressure relief valves are provided for each compartment

should be weighed frequently to ensure that they have

to prevent overinflation.

with that device. Cartridges should also be inspected

compressed

air that

Training divers

is

use of specific

in the

BC

devices

essential because these devices vary widely in

control locations, control operation,

is

terms of

and potential buoy-

not lost their charge;

grams

less

if

their weight

is

more than

3

than the weight printed on the cylinder, the

cartridge should be discarded.
flotation device should

The

cartridge used in a

be the one designed to be used

to ensure that the detonating

mechanism has not punched

a pinhole into the top of the cartridge that has allowed

the

C0 2

to escape.

ancy. Regardless of the diver's choice, training and
practice under controlled conditions are required to

master buoyancy compensation procedures. Divers must

WARNING

be trained not to use excessive weights or to be overly

BC to compensate for diving weights.
Because rapid, excessive inflation can cause an uncontrolled ascent, divers must learn to vent air from
dependent on a

Buoyancy Compensators Should Not Be Used
As Lift Bags Unless They Are Not Attached

To the Diver

the compensator systematically during ascent to maintain

proper control.

After each use, the exterior of the device should be
rinsed thoroughly with fresh water. Special attention

C0

5.3.3

Weight Belts

Divers use weight belts to achieve neutral buoyancy;

mechanism, oral
and power inflators, and other movable mechanical
parts to ensure that they operate freely and easily. The

they should carry enough weight so that their buoy-

C0 2

positive

should be given to the

2

release

actuating lever, with cartridge removed, should

ancy

at the surface

and becomes

is

slightly negative with a full tank

slightly positive as air

buoyancy provided by the

is

consumed. The

diver's suit

is

prob-

be worked up and down while fresh water is being
flushed through the mechanism. The mechanical parts

ably the largest contributing factor in determining

should be allowed to dry and should then be lubricated

suit,

October 1991

— NOAA

Diving Manual

appropriate weight requirements. Without an exposure

most divers can achieve neutral buoyancy with

5-13

Section 5

Figure 5-9
Fins

Swim
than 5 pounds (2.3 kg) of weight, whereas 10 to
30 pounds (4.5 to 13.5 kg) may be required, depending on
depth, if a full suit is worn. Dry suits may require even
less

more weight. Divers must accurately determine
weight requirements

their

water before undertaking

in shallow

a working dive. Failure to establish the proper buoy-

ancy can consume
following test

air

and energy unnecessarily. The

can be performed to determine the proper

amount of weight

to be carried: a full lung of air at the
maintain
a properly weighted diver at
surface should
water;
exhalation should cause the
eye-level with the

diver to sink slowly, while inhalation should cause a

slow rising back to eye-level with the water. (This test

should only be performed on the
it

As

a general rule, the deeper the dive, the less

because
status.)

weight will be required to achieve the desired buoy-

ancy because of the exposure

When

suit's compressibility.

using exposure suits with increased thickness or

should be taken to ensure that the diver

air spaces, care

has adequate weight to permit a slow, easy ascent,
especially during the last 10 feet (3

m)

of ascent.

5.3.4 Diver's Knife

A

diver's knife serves a variety of purposes, the

common

most

being to pry and probe at underwater rocks,

organisms,

etc.,

and

to free the diver in the event of

entanglement (Boyd 1980).

A

diver's knife should

be

constructed of a corrosion-resistant metal, preferably

Handles must provide a good, firm grip
The knife should be
worn where it is easily accessible in an emergency;
knives are worn on the inside of the calf or on the upper
stainless steel.

and be

resistant to deterioration.

arm. Carrying the knife on the inside of the calf
popular because this position makes
ble with either

hand and

Courtesy

dive of the day

last

will influence the diver's repetitive dive

it

is

readily accessi-

lessens the likelihood that the

and are slightly more flexible than the
and they use approximately as much force
on the up-kick as on the down-kick. The swimmingstyle fin is less fatiguing for extensive surface swimming, less demanding of the leg muscles, and more
comfortable. Power-style fins are longer, heavier, and
more rigid than swimming fins. They are used with a
slower, shorter kicking stroke, with emphasis on the
power

style,

down-kick. This style of fin

cal condition

Swim

fins

blade

is

sharp;

if

The

properly maintained, the material

to

be performed.

inside, or

diving in

kelp beds, surf grass, or pond weeds. If this

may

knife should be rinsed with fresh water, dried, and
to ensure that the

and the nature of the task

down before

larity

prior to storage.

maximum

with adjustable heel straps either should

the ends of their straps taped

progress.

oil

designed for

have the straps reversed, with the bitter ends

plants

must be checked frequently

is

power thrusts of short duration, and these fins sacrifice some comfort; power fins are the preferred style
for working divers. A narrow, more rigid fin provides
the best thrust-to-energy cost ratio. The fin must fit
comfortably, be sized properly to prevent cramping or
chafing, and be selected to match the individual's physi-

knife itself will foul. This placement also maintains a

knife

Divers, Inc.

lighter weight,

clear drop-path for the weight belt. After each use, the

coated with a layer of light

New England

A

catch

in the straps

number

is

not done,

and impede further

of plastic fins have gained popu-

because of their good propulsion characteristics
and light weight; these fins couple a plastic blade with
a neoprene rubber foot pocket and an adjustable heel
strap.

used in most diving knives will retain a good cutting

edge for a long time.

5.4

PROTECTIVE CLOTHING

Divers usually require some form of protective cloth-

5.3.5

Swim

Fins

ing.

This clothing, known as a suit or insulation, mini-

available in a variety of sizes and designs.

mizes thermal exposure effects. In addition, it protects the diver from abrasions and minor bites.
Suits must be selected with certain diving conditions in mind; elements to consider include water tem-

In general, there are two styles of fins: swimming
and power (Hall 1980b). Swimming fins are smaller, of

should be considered

Swim

fins

(Figure 5-9) increase the propulsive force

of the legs and,

when used

properly, conserve the diver's

energy and facilitate underwater movement. They are

5-14

perature, depth,

and

activity level. The following points
when evaluating thermal needs:

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-10

Neoprene Wet
trapped air or gas.

•

All insulation

•

Cold water absorbs heat 25 times faster than
Fifty percent of the average diver's energy

•

Suit

is

air.
is

con-

sumed just trying to keep the body warm.
The greater the temperature difference between
the body and the surrounding water, the faster

•

heat leaves the body.

The

•

larger the

body mass, the better the heat

retention.
•

takes time, rest, and food to replace lost heat

It

energy.

5.4.1

Wet

Suits

The neoprene wet

suit

the most

is

common form

protective clothing in use (Figure 5-10).

It

of

provides

thermal protection, as well as protection against coral,
stinging coelenterates, and other marine hazards.
suits are

Wet

constructed of closed-cell foamed neoprene

and generally are 3/ 16- or 1/4-inch (approximately
cm) thick, although suits as thin as 1/8 (0.3 cm)
and as thick as 3/8 of an inch (1.2 cm) are available.
Wet suits rely on air bubbles in the closed foam to act
as insulation. Because the foam is compressible, how0.6

ever, the suit rapidly loses

insulative capability as

its

depth increases. For example, one-half of a wet
insulating capacity

is

suit's

33 feet (10 m), two-thirds

lost at

66 feet (20 m), and three-fourths at 99 feet (30 m).
Consequently, wet suits are recommended only for
at

shallow water diving or snorkeling and generally are

recommended

not

for diving in

below 60°F (15. 6°C).
The wet suit used in

warm

water

at

temperatures
Courtesy Diving Unlimited International

water consists of neoprene

pants and jacket, with optional boots, gloves, hood,

and

vest.

For warm-water (80°F; 26.7°C) diving, a

brief vest that covers only the body's trunk

Full-length styles that cover the entire

ing the hands, feet,

is

available.

body (includ-

the effectiveness of a wet suit;

some

Fit

is

divers

important to

may need

a

custom suit to achieve proper fit. Thinner suits provide
more freedom of movement, while suits of thicker mateprovide better thermal protection. Most suits use a

nylon liner on the inside surface of the neoprene to
limit tearing

and

is

to facilitate

easy entry. Models are

available with nylon on both the inner
faces to minimize tears and

damage

to

and outer surthe suit; howev-

prevent separation. Neoprene glue

surface nylon does not repair well with ordinary cement,

have as many as

in, which may be a probNylon on the outside cuts down on
abrasions but tends to hold water, which acts as an

they also allow water to seep

lem
suit

in

cold water.

October 1991

— NOAA

Diving Manual

five zippers,

one

in

A

wet

suit

may

each ankle and

sleeve and one in the front of the jacket. In colder
waters, zippers can
loss,

if

become

a significant source of heat

and care should be taken either

number

suits are flexible

suit,

available in small

so tears in this material should be sewn.

suits with

nylon inside offer easier entry into the

is

cans for quick and easy wet suit repair. However, double-

length and

the

the diver

glue.

added layer of nylon further restricts the diver's
movements, as do elbow and knee pads. Although wet

er,

when

on the surface.

The sections of a wet suit are joined by neoprene
The seams on better models are sewn together to

and head) except the face are

available for use in colder waters.

rial

evaporative surface and causes chilling

to

minimize zipper

or to provide waterproof zippers

extended cold-water work is anticipated. Some
and strong enough to be constructed

without ankle and sleeve zippers.

When

water temperatures approach 60 °F (15.6°C),

the hands, feet,

and head

lose heat at a rate that

makes

5-15

Section 5

Figure 5-11
Effects of

Water Temperature

diving without protective gloves, boots, and a hood
°C

impractical. Even in tropical climates, divers often
elect to

Normal Body
Temperature

wear some form of boot and glove for abrasion
In colder waters, loss of body heat from

35

—

4 Resting

protection.

these body areas

may

Diver
30-

formance unless some form of thermal protection is
worn (Figure 5-1 1).
Thermal protection of the hands is necessary because
tiveness.

Most divers

in

movement and

-80

During

Resting Diver Chills

25H

Moderate

In

Work

temperate climates prefer cot-

touch. Five-fingered

prene gloves are available

in

foamed neo-

1

-2

Hours

-70
20-

ton gloves because these gloves do not severely restrict
finger

Overheat

4 Working

Comfortable

reduces a diver's effec-

loss of dexterity significantly

Will

-90

significantly affect diver per-

Diver

s

Underwear

0)

May

1/8- or 3/16-inch (0.3 to

Suffice

60

15-

'Approximate
Tolerance Time

cm) thicknesses that permit a satisfactory degree
of finger movement. Three-fingered "mitts" are used
0.4

in

cold water (Figure 5-12). Proper

because too tight a

will restrict

fit

and increase the rate of heat

fit

is

Of Working
Suits etc.

important

Diver Without
Protection

-50

10-

I

Required

2

1

blood circulation

Hours

loss.

-40

Failure to wear a hood in cold water can result in
Fresh

numbing of

the facial areas

and a feeling of extreme

pain in the forehead immediately on entering the water,

-30

Water

Freezing

Sea

Point

Water

phenomena that persist until the head becomes acclimated to the cold. Fifty percent of body heat can be

-5-

from the head and neck during submersion in cold
water. Hoods that are attached to jackets generally
lost

provide better thermal protection than separate hoods.

The hood should have an adequate
at least

midway onto

skirt,

Source:

one that extends

NOAA

(1979)

the shoulders, to prevent cold

water from running down the spine. In extremely cold
water, a one-piece hooded vest

is

recommended.

Fit

important when selecting a hood because too tight a

is

fit

to rot,

become

brittle,

and crack. Storing

suits in hot,

dry environments also can lead to deterioration.

can cause jaw fatigue, choking, headache, dizziness,

and inadequate thermal protection.
Wet suits must be properly cared

for

and maintained

5.4.2

Dry Suits

should be washed thoroughly with

Dry suits that are made of waterproof materials are
becoming more widely used than wet suits. Commonly

should then be allowed to dry before

called shell suits, these fabric suits are designed to be

being stored. The suit should be inspected carefully for

worn with undergarments; they are usually used with

if

they are to

last for a

each use, the
fresh water;

rips;

if

suit

it

reasonable length of time. After

any are found, the

before being used again.

mately 10 minutes after
best results

it

A
it

should be repaired

suit
suit

can be used approxi-

has been repaired, but for

should not be used for several hours. Suit

zippers and metal snaps should be inspected frequently

and be kept corrosion

lubricants; petroleum-based products will cause

neoprene materials

Dry

suits

can be inflated via the

to deteriorate.

regulator,

and

air inside the suit

an exhaust valve.

Some

Suits should be

hung

for

can be expelled through

automatic buoyancy control. By manipulating the

valves, a properly

weighted diver can maintain buoyA power exhaust valve can

ancy control at any depth.

evacuate excess air from the

They may

easier to deflate.

up or laid flat, but they should
not be folded because prolonged folding may cause
creasing and deterioration of the rubber at the folds.
also be rolled

Suits should be stored out of direct sunlight because

5-16

on the

valves are equipped with an

on wide, specially padded hangers to prevent tearing.

prolonged exposure to the sun

inlet valve

diver's air supply at the low-pressure fitting on the

adjustable over-pressure relief mechanism, which allows

free.

Special silicone greases are available for use as equip-

ment

hoods and gloves and are relatively easy to doff and don.

will

cause the neoprene

Because

flotation capability, a

suit,

which makes the suit
have no inherent

shell suits

buoyancy compensator that does

not cover the suit's valves should be worn.

Dry

suits

must be maintained properly. They should

be washed with fresh water after each use, and water

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-12

Cold-Water

Mitt, Liner

Included

Underwear made of such material provides primary
thermal protection when divers wear a dry
the shell of the suit loses

garments have

diver's other outer
lation.

suit

because

insulation with depth

its

little

and a

inherent insu-

Leaks can always be a problem with

shell suits;

however, divers equipped with dry suits and nylon

pile

or Thinsulite® undergarments have been able to work

2°C

intermittently for 6 hours in

(35 °F) water (Zumrick

1985).

Variable-Volume Neoprene or Rubber Dry

5.4.2.2

Suits

Variable-volume dry suits differ from dry fabric-

They are one-piece suits that are made of
foamed neoprene or rubber compounds.
These suits are designed to conserve body heat in
shell suits.

closed-cell

extremely cold water for an extended period of time
(Hall 1980c). Variable-volume rubber suits are light

and require no surface support, which makes them
ideal for use at remote locations. These suits also are
simple and reliable, which greatly reduces their maintenance and repair requirements. Operations have been

conducted

using suits of this type for

in arctic regions

long-duration dives (2 hours) under ice in 28.5 °F to

30°F(-1.9°C

Most

(0.4 or 0.6
Courtesy Trelleborg/Viking

to

-l.rC) water.

suits are constructed of 3/ 16- or

cm)

closed-cell

1/4-inch

foamed neoprene and have a

Inc.

One style is availacompound over a tricot

nylon interior and exterior lining.
ble that

is

made from

a rubber

should be sprayed directly into the suit's valves to

material. All suits of this type are designed to be

wash out sand. If the suit develops mildew spots, it
should be washed with soap and water. Finally, the suit

with thermal underwear, are of one-piece construc-

should be allowed to dry while hanging so that

proof zipper.

it

will

tion,

worn

and are entered through a water- and pressureThe hood and boots usually are an inte-

dry thoroughly inside and out.

gral part of the suit, but the gloves are separate.

Dry suits should be stored away from sunlight and
from ozone-producing sources, such as cars or gas-

prevent separation,

fired

household water heaters. The
can be extended by storing the

life

of the suit's

abuse, knee pads often are attached permanently to the
suit to

bag with talcum powder during long periods of non-

The

suit in a

use.

To

seams are glued and sewn. Because

the knees of the suit are the point of most frequent

dry plastic

seals

all

reduce the likelihood of leaks.
suit

may

be inflated via an

to the diver's air

inlet valve

connected

supply at the low-pressure fitting on

the regulator. Air inside the suit can be exhausted
5.4.2.1

Dry Suit Insulation

determined by water temperature, duration of the dive,

and the age, body size, sex, and exercise rate of the
diver. However, many suits are insulated with materials that trap air and stabilize it. The most common
insulation materials in use are synthetic fibers
polyester, nylon,
in piles,

and polypropylene. These

made

fibers,

of

used

buntings, and batting, are selected because of

their low water absorption.

October 1991

— NOAA

the inlet valve or one on the suit's arm.

By manipulat-

two valves, a properly weighted diver can
maintain buoyancy control at any depth.
When diving in cold weather, care must be taken to
avoid icing of the suit's inlet and exhaust valves. The
inlet valve may be frozen in the open position if the suit
is inflated with long bursts of expanding air instead of
ing these

several short bursts.

open position, the

When

suit

uncontrolled ascent.

Diving Manual

from

either by a valve on the opposite side of the chest

The amount of suit insulation needed for a particular diver to remain comfortable on a given dive is

If

the inlet valve freezes in the

may overexpand and
there

is

more

cause an

air in the suit

than

5-17

Section 5

Figure 5-13
Open-Circuit Hot-Water Suit
the exhaust valve can exhaust, the diver should hold up
one arm, remove his or her tight-fitting glove, and
allow the excess air to escape under the suit's wrist
seal.

The disadvantages

of variable-volume dry suits are:

•

Long

•

Air can migrate into the foot area

suits are fatiguing

because of the

suit's bulk;

if

the diver

is

horizontal or head down, causing local overinflation

and
•
•

loss of fins;

and exhaust valves can malfunction; and
seam or zipper could result in sudden
and drastic loss of buoyancy, as well as significant
Inlet

A

parting

thermal

stress.

Divers planning to use any type of variable-volume
dry suit should be thoroughly familiar with the manufacturer's operational literature

and should perform

under controlled conditions before wearing

training dives

the suit on a working dive.

Maintaining variable-volume dry suits

is

relatively

simple. After every use, the exterior of the suit should

be washed thoroughly with fresh water, and the

suit

should then be inspected for punctures, tears, and seam
separation,

all

of which

must be repaired before

reuse.

The zipper should be closed, cleaned of any grit, and
lubricated. The zipper should be coated with waterproof grease after every few uses. The inlet and outlet
valves should be washed thoroughly and lubricated
before and after each dive. Cuffs, collar, and face seals
also require lubrication with pure silicone spray before

courtesy Diving Unlimited International

and after each dive. The inflation hose should be
inspected before each dive.

warm water

tribute
feet,

5.4.3

Hot-Water Suit Systems

Hot-water

warm by

suit

warm

water.

A

hot-

water system heats and closely controls the temperature of the water that

is

pumped through

the heated water evenly over the diver's

body inside

the passive insulation of the specially constructed suit

An

seals.

open-circuit hot-water suit allows the

heated water to flow back to the open sea after use,
while a closed-circuit hot-water suit returns the

warm

water to the heater for rewarming. Hot-water systems

The

control manifold

The

suit's

used
and neck

suit allows

arm,

must have a

leg,

single valve to

allow water to bypass the diver and to return directly to
the surrounding water.

a specially

insulated hose to the diver; the system then distributes

(Figure 5-13).

torso.

water to leak out through the

systems are designed to keep divers

encapsulating them in

to the diver's arms, hands, legs,

and front and back

The hot water

that supplies suits of this type

does not recirculate the

dumped

warm

water; instead, water

can be used to protect more than one diver at a time

water supply

the hot water in the suit, which allows the diver
1

5.4.3.1

made

of passive insulation material; they are

equipped with a control manifold and tubing to

5-18

is

interrupted, the non-return valve retains

up

to

8 minutes to return to the bell or surface.

Open-Circuit Hot-Water Suits

Open-circuit hot-water suits are loose fitting and
are

is

into the sea through the suit's vents. If the

and

to heat a diving bell.

may

and be pumped directly to the
diver or be passed to the diver from a diving bell,
submersible, or habitat. To maintain body heat, a continuous flow of 2.5 to 3.5 gallons per minute of 95 °F to
110°F (35 °C to 43 °C) water is required. This system
originate on the surface

dis-

5.4.3.2

Hot-Water Heater and Hoses

The heater

unit of these systems contains water

pumps,

a heat source, and controls that deliver hot water at a

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-14
Snorkels

The heat source may use

prescribed temperature.

a

diesel fuel flame, electric cal-rod heaters, live steam,

The heat exchanger generfrom the heat source through an
intermediate fresh water system to the diving water
system. The intermediate system isolates the diving
water system from temperature surges and reduces
heater maintenance by controlling scaling and corroor a combination of these.
ally transfers heat

For operational convenience, the controls that

sion.

operate the heat source can be located remotely.

Hot-water

The

hose.

both a

suits require

bell

bell

hose and a diver's

hose carries hot water from the heater to

the bell, and the diver's hose carries hot water either

from the heater or the

5.4.3.3

bell.

Closed-Circuit Hot-Water Suits

Closed-circuit hot-water suits consist of a dry suit

and a special set of underwear; heated water is circulated through the underwear. Water is pumped from a
heater, through a series of loops in the underwear, and
back

to the heat source.

Hot water may

Courtesy

from a heater carried by the diver or from a surface
heater. The primary advantages of closed-circuit hot-

excessive biting force. Soft rubber models are availa-

water systems are that they keep the diver dry and
ble,

retain their insulating ability for

the hot-water source

The major disadvantages

movement and

restricts the diver's

more

fails.

some period of time

if

of

type are that the special underwear severely

suits of this

TEKNA SCUBA

originate either

that these suits are

fragile than the open-circuit system.

and some have a swivel feature. Other models are

bent to conform to the configuration of the diver's

head or to have a flexible length of hose at the breathing end that allows the mouthpiece to drop away when
not in use. Although widely distributed, snorkels with
a sharp bend should not be used because they increase

airway resistance. Those with shallow bends, such as

5.5

DIVER'S

ACCESSORY EQUIPMENT

the wraparound models, reduce this resistance to a

minimum. Snorkels with corrugated

flexible tubes,

however, are difficult to clear of water and additionally cause air to move in turbulent flow, which increases

There are numerous items of accessory equipment that
have special uses and are valuable to a diver to accomplish underwater tasks. The following sections describe

breathing resistance. Snorkels should have an opening

several of these items.

of the

same

size at the intake as at the

mouthpiece;

they should not have a divider in the mouthpiece, because
the divider also will cause turbulent flow.

5.5.1

A

Snorkels
snorkel

is

Ideally, the inside

a rubber or plastic breathing tube that

allows a diver to

swim comfortably on the surface

diameter of the snorkel should be

5/8 to 3/4 inch (1.3 to 1.8 cm), and it should not be
more than 15 inches (38.1 cm) in length. Longer snor-

more

without having to turn his or her head to the side to

kels increase breathing resistance, are

breathe. Snorkels allow scuba divers to survey the

and cause additional
drag when the diver is swimming under water. Snorkels flood when the diver submerges, but these devices
can be cleared easily by exhaling forcefully through

bottom

in

shallow water without having to carry a

scuba tank.
Snorkels are available in a wide variety of designs
(Figure 5-14), and selection
preference

(Murphy

1980).

is

a

matter of individual

The most commonly used

to clear, increase

the tube.

dead

With some

difficult

air space,

snorkels, especially those with

flexible tubing near the

mouthpiece,

it

is

difficult to

amounts of

snorkel has three segments: a barrel that protrudes

clear the snorkel completely, and small

above the water, a mouthpiece tube, and a mouthpiece.

water

The mouthpiece should be

tube. Snorkels of this type can be cleared easily

selected to

fit

easily

under

the lips and should be capable of being held without

October 1991

— NOAA

Diving Manual

may remain

in the

curve or corrugations of the

when

the diver surfaces.

5-19

Section 5

Figure 5-15
Dive Timer

A

(

Timing Devices

5.5.2

watch

is

bottom time,
and assisting in underwater
imperative for dives deeper than
diver's watch must be self-winding,

essential for determining

controlling rate of ascent,

navigation;

is

it

30 feet (9 m). A
pressure- and water-proof

(a screw-type sealing crown is
recommended), and should have a heavily constructed
case that is shock-resistant and non-magnetic. An

external, counter-clockwise-rotating, self-locking bezel
required for registering elapsed time. The band should
be of one-piece construction and should be flexible
enough to fit easily over the diver's arm. A flat, scratchis

proof crystal and screw-down and lock stem also are

recommended. Electronic (battery-powered) diving
watches are now common, but divers should remember
that batteries run

down and

that

some of these watches

are sensitive to external temperatures, which could
affect their reliability during cold-water diving.

Dive timers are miniature computers that use microprocessor chips to count the

number

of dives in a day,

the current bottom time, and the current surface interval

(Figure 5-15).
after the last

Some

dive to

timers also can count the hours
let

the user

know when

it is

safe to

fly. Models are available that can operate for as long as
5 years without battery replacement. Dive timers are

activated automatically

when

«

the diver descends to a

depth below a certain depth (approximately 5 to 9 feet
(1.5 to 2.7 m)).
cally at a

During ascent, timers stop automati-

depth of about 3 to

5 feet (0.9 to 1.5

m).
Courtesy

TEKNA SCUBA

As with other diving equipment, watches and timers
must be handled with care and be washed in fresh
water after they have been used

An

water.
that

it

in salt or chlorinated

important requirement for any dive timer

have a high-contrast face

to facilitate

is

reading

Figure 5-16
Depth Gauges

under poor-visibility conditions.

5.5.3

Depth Gauges

Depth gauges (Figure 5-16) are small, portable,
pressure-sensitive meters that are calibrated in feet

and allow divers to determine their depth while submerged. Depth gauges are delicate instruments and
must be treated carefully to avoid decalibration. Accuracy is extremely important and should be checked at
regular intervals. Only a few models of depth gauges
can be calibrated in the field; most models can be
returned to the manufacturer if they need replacement
parts. During evaluation and regular use, gauges should
be checked to ensure that rough gears or internal corrosion does not cause the indicator hand to stick at par-

4

ticular depths.

5-20

Courtesy

NOAA

Diving Manual

New England

Divers, Inc.

—October 1991

Diver and Diving Equipment

Most commercially available depth gauges operate
diaphragm, or bourdon tube

either on the capillary,

gauges consist of a plastic
the water at one end and is attached

principle. Capillary depth

tube that

is

open

to a display that

to
is

calibrated in feet.

As depth

increases,

and the

the pocket of air trapped in the tube decreases

depth

read from the water level

is

in the tube.

The

diaphragm model has a sealed case, one side of which is
a flexible diaphragm. As pressure increases, the diaphragm is distorted, which causes the needle to which
it is

linked to move. Bourdon tube depth gauges are the

most fragile of these types of gauges; they require more
frequent calibration than the other types. With bour-

don tubes, water pressure causes a distortion of the
tube, which in turn moves a needle that indicates depth.
Both bourdon tube and diaphragm depth gauges are
available in models that are sealed and oil-filled for

5.5.4 Wrist

Compass

Cylinders

An underwater compass consists of a small magnetic
compass that is housed in a waterproof and pressureproof case and is worn attached to a diver's wrist by a
band. Compasses are useful for underwater navigation, especially in conditions of reduced visibility, and
they are also helpful when divers are swimming back to
a boat while submerged. Compasses do not provide
precise bearings, but they do provide a convenient,
reliable directional reference point. To limit magnetic
interference, compasses should be worn on the opposite wrist from the diver's watch and depth gauge.
Compass models are available that allow a diver to
read them while holding them horizontally in front of
them when swimming. Compasses do not have to be
recalibrated, and the only maintenance they need is a
fresh-water rinse after use.

smooth, reliable operation.

Combination depth gauges are also available; these
generally consist of combinations of a conventional

bourdon tube with a capillary gauge around the perimeter of the face. Capillary gauges generally give

more

accurate readings at shallower depths, and these gauges

can also
accuracy
has been
gauges at

Pressure Gauges
Two styles of pressure gauges can be used to determine the amount of air in a scuba tank. A surface

5.5.5

cylinder pressure gauge (Figure 5-1 7 A)

is

used to check

damaged, the readings provided by the two

amount of air in a tank on the surface. This type of
gauge fits over the cylinder manifold outlet, attaches
in the same manner as a regulator, and provides a

shallow depths will differ significantly.

one-time check of the pressure

be used as a reference for measuring the
of a bourdon tube gauge. If the bourdon tube

Bourdon tube gauges tend to retain salt water in the
tube, which may cause salt deposition or corrosion. To
prevent this, the tube should be sucked free of water
and the gauge should be stored in a jar of distilled
water. Helium-filled depth gauges leak and lose accuracy if they are not kept completely submerged in
water whenever they are exposed to high-pressure

the

release valve

is

installed

in a tank.

on the gauge so that

A

pressure-

air

trapped

gauge after the valve on a tank has been secured
can be released and the gauge removed. These small
dial gauge movements are designed with an accuracy

in the

±

of

100

psi,

but they

may become

less

accurate with

use.

The submersible cylinder pressure gauge attaches
directly to the first stage of a regulator by a length

conditions.

of high-pressure rubber hose; these gauges provide

Depth gauges are delicate, finely tuned instruments
and must be used, stored, and maintained with great
care. They are an essential part of a diver's life-support
equipment, and careless handling on the part of the
diver could prove fatal.

divers with a continual readout of their remaining

Many

air.

units have a console that holds the compass,

depth gauge, and tank pressure gauge (Figure

5-1 7B);

these consoles free the diver's arms for other dive
activities.

Submersible pressure gauges are essential

usually meas-

pieces of diving equipment; most of these devices

ured with a pneumofathometer, which is a pressure
gauge located on the surface. To determine a diver's

operate on the same principle as the bourdon tube.

For surface-supplied divers, depth

depth, air
surface.

is

introduced into the

The pneumo hose

diver's umbilical

the diver's end.

is

air

pneumo hose

is

open

end.

When

the hose

is

to the

water at

introduced at the surface dis-

places the water in the hose and forces

The gauge connected

at the

one of the members of a

assembly and

The

is

One end
and
and

is
is

gauge is sealed
move; the other end is held fixed

of the submersible pressure

allowed to
connected

air pressure

to a high-pressure air supply.

As

the

increases, the bourdon tube tends to

straighten out or to uncurl slightly.

The gauge's

dial

out the diver's

face should be easy to read and should have high-contrast

clear of water, excess air escapes.

markings. Although gauges currently in use are designed

to the

it

hose on the surface indi-

to

be accurate and reliable, they are not precision

cates the pressure (in feet or meters of seawater equiv-

laboratory instruments. Divers should not expect accu-

alent) required to clear the hose of water.

racies better than

October 1991

— NOAA

Diving Manual

± 250

psig at the upper end of

5-21

Section 5

Figure 5-17

Pressure Gauges
A. Cylinder

Underwater Slates
A slate may be a useful

Gauge

5.5.6

piece of equipment when
underwater observations are to be recorded or when
divers need a means of communication beyond hand
signals. A simple and useful slate can be constructed

from a 1/8- or 1/4-inch
acrylic plastic that has

both sides; these slates

(0.3 to 0.6

cm) thick piece of

been lightly sand-papered on
can be used with an ordinary

pencil.

Semimatte
board or
(0.01

cm)

plastic sheets can be placed on a clip

a ring binder. These sheets (about 1/32-inch

in

thick)

may

10 feet (1.8 to 3.0 m).

be purchased

up

to 6 x

as needed,

and no

in sizes

They may be cut

is required. Ordinary lead pencils can be used,
and marks can be erased or wiped off with a rubber
eraser or an abrasive cleanser. Some underwater slates
are equipped with a compass, depth gauge, and watch

sanding

Courtesy Dacor Corporation

B.

that are

Submersible Cylinder Pressure Gauge

mounted across the

When

top.

slates are used,

they should be attached to the diver with a loop or
lanyard

made

them from being

of sturdy line to keep

lost.

5.5.7 Diving Lights

A

waterproof, pressure-proof diving light

is

an impor-

equipment when divers are operating in
areas of restricted visibility. Lights are used most frequently for photography, night diving, cave diving,
wreck diving, exploring holes and crevices, or diving
under ice. Regardless of the power of an underwater
light, it will have only limited value in murky, dirty

tant item of

waters where

When

visibility is restricted

consider, such as brightness
Courtesy

TEKNA SCUBA

by suspended matter.

selecting a light, there are several factors to

and beam coverage, type

of batteries (disposable or rechargeable), size and shape,

burn time, and storage time (Figure 5-18) (Cozens 1981b).

Most
the gauge range and

between 500 and

± 100

psig at the lower end

psig (Cozens 1981a).

divers prefer the light to have a neutral or slightly

positive

buoyancy because

As with

NOTE
Submersible pressure gauges are recommended for all divers and all dives.
The only maintenance
gauge needs

is

that a submersible pressure

a fresh-water rinse after use.

To

pre-

vent internal deterioration and corrosion of a surface

gauge, care must be taken to ensure that the plastic
plug that covers the high-pressure inlet is firmly in
place.

Submersible pressure gauges should be handled

with care and should be stored securely
use.

5-22

it

is

easy to add a small

weight to keep the light on the bottom,

when

not in

all

if

necessary.

other pieces of diving equipment, lights

should be washed with fresh water after every use.

The

0-ring should be lubricated with a silicone grease

and

should be checked for debris every time the light
assembled.

When

is

not in use, the batteries should be

removed and stored separately. Before a diving light is
used, it should be checked thoroughly to ensure proper
operation. The batteries should be replaced any time
they show any signs of running low, and spare light
bulbs and batteries should be available at the dive site:
5.5.8 Signal

Devices

Signal devices are an important but frequently ignored

item of diving safety equipment for divers. They are

NOAA

Diving Manual

—October 1991

Diver and Diving Equipment

Figure 5-19
Signal Devices

Figure 5-18
Diving Lights

A. Diver's Pinger

Courtesy Battelle-Columbus Laboratories

particularly valuable

when

a diver surfaces at a great

B. Diver's Flasher

distance from the support platform or surfaces prematurely because of an

emergency. Several types of

sig-

naling devices are available (Figure 5-19).

Whistles are valuable for signaling other swimmers

on the surface. For easy accessibility, they

may

be

attached to the oral inflation tube of the buoyancy

by a short length of rubber strap.

vest

(MK-13, Mod 0, Signal Disand
Day
Night) can be carried taped to the
diver's belt or knife scabbard. One end of the flare
contains a day signal, a heavy red smoke, while the

The

military-type flare

tress,

opposite end holds a night signal, a red flare. Both ends

are activated via a pull ring. After either end of the
signal has been pulled, the flare should be held at arm's

away from the
The diver's body

length, with the activated end pointed

diver at an angle of about 45 degrees.

should be positioned upwind of the signal.

does not ignite immediately, waving

may

onds
will
if

work

assist ignition.

after

If the flare

for a

it

few sec-

After activation, the flare

submergence, although

it

will not ignite

activated under water. After every dive, the flare

should be flushed with fresh water and should then be

checked

for

damage

Courtesy Dacor Corporation

of 1500 feet (457.2 m). These lights are waterproof and

can operate submerged

at depths up to 200 fsw (61 m),
depending on the make and model. Some rescue lights
have an operational life of as much as 9 hours; the

operational
or deterioration.

by using the

Some

NOTE

of these units can be extended greatly

light only intermittently.

divers use chemical light tubes; these small

tubes contain two separated chemicals.
is

Red

life

flares

and smoke signals should be used

only as distress signals or to signal the termination of a dive.

bent, the chemicals discharge

soft

When

the tube

and mix, causing

green light that glows for several hours.

divers attach these tubes to their scuba cylinders,
straps, or snorkels as

a

Some
mask

an aid to tracking their buddies,

while others carry them as an emergency light source.

Signal devices should be carried so that they are

At

night, divers can carry a flashing rescue light that

attached to their belt, harness, or arm. Rescue lights
of this type are compact, high-intensity, flashing strobe
is

lights that are generally visible for

(16 to 24

km) from

October 1991

1

to

15 miles

a search aircraft flying at an altitude

— NOAA

Diving Manual

and will not be lost when equipment is
Buoyancy compensators frequently have a
ring that will accommodate a whistle or strobe

easily accessible

discarded.
built-in
light,

and

flares are often

taped to the scabbard of the

diver's knife with friction tape.

5-23

Section 5

5.5.9 Safety

Lines

equalization of pressure.

Diver safety lines should be used whenever divers
are operating under hazardous conditions; examples of

The

increase in pressure inside

the goggles as depth increases during the dive

may

ice, or

cause the rim of the goggles to cut deeply into the face
or the eyes to be forced against the glass plates; either

diving in strong currents. Diver-to-diver lines should

of these events can cause severe and painful tissue or

be used when the working conditions of the dive could
separate the divers who are working under water. Safety

eye squeeze.

such situations are cave diving, working under

Regulator neckstraps should also not be worn because

lines provide divers

these straps are difficult or impossible to remove in an

limited)

emergency. Some single-hose regulators come equipped
with these straps as standard equipment; the straps
should be removed and discarded before diving.

with a quick and effective (although
means of communications. Under special condia surface float can be added to the line to aid

tions,

support personnel in tracking the diver.

The most commonly used types of safety
nylon, dacron, or polypropylene.

These materials are

strong, have nearly neutral or slightly positive buoy-

ancy, and are corrosion resistant.
into

A

snap can be spliced

each end of these lines to facilitate easy attach-

ment to a float or to a diver's weight belt.
Maintenance of safety lines requires only that they
be inspected and that their snaps be lubricated. Reels
and lines used in cave diving must be dependable;
these lines require additional maintenance and careful
inspection.

Any

In addition to the specific items mentioned above,

line are

safety line should be replaced

if it

shows signs of weakness or abrasion.

any equipment that

not necessary for the particular

is

dive should be considered hazardous because extra

equipment increases a
gear should be

5.6

left

diver's

chances of fouling. Excess

on the surface.

SHARK DEFENSE DEVICES

In areas where sharks are frequent, many divers carry
some form of shark defense. Several types of devices
are available and have been shown to be effective.

These devices are designed

to be used only as defense
mechanisms; they are not effective and should not be
used as offensive weapons.

5.5.10 Floats

A

float carrying the diver's flag should

time a diver
is

is

The

a wooden club that

is

counter-weighted to facilitate underwater use and

is

be used any

operating from a beach or in an area that

frequented by small boats. Floats also provide the

oldest anti-shark device

commonly

is

called a "shark billy." It

is

used to fend off

Shark

dive master with quick and accurate information about

or to strike a shark, preferably on the nose.

the diver's location and provide the diver with a point

size

made from 3/4-inch (1.8 cm) round fiberglass stock and are 4 feet (1.2 m) long. A hole is drilled
in one end to accommodate a lanyard and a loop of

flag positioned at the top of a staff; bright colors

and the other end is ground to a point
and coated with fiberglass resin. Instruments of this
length and diameter can be moved through the water
quickly because they afford little drag under water.

buoyancy in an emergency. Floats range in
and complexity from a buoy and flag to small
rafts; the type most frequently used is an automobile
innertube whose center portion is lined with net. Float
should be brightly colored and should carry a diver's

of positive

make

billies

surgical tubing,

the raft noticeable, and the flag tells boaters that a
diver

is

5.5.11

in the water.

Accessories That Are Not

Recommended
Several pieces of equipment are sold commercially

are

If a

shark

is

circling a diver, the diver should use the

prod the shark; the butt end should be kept
against the diver's body and the sharp end should be
used against the shark. This defense should discourage
billy to

the shark from coming closer than about 4 feet (1.2

m)

from the diver. Sharks that have been prodded leave
the immediate area hastily (although they return to

but should not be used because they can cause injury to

the area almost immediately). Although brief, the shark's

the diver or convert a routine situation into an emer-

retreat usually provides sufficient time for the diver to

gency. Earplugs should never be used while diving;

leave the water (Heine 1985).

they create a seal at the outer ear, which prevents
pressure equalization and can lead to serious ear squeeze,

shark, a power head can be used. These devices,

ruptured eardrum, and, possibly, total loss of hearing

monly called "bang sticks," consist of

the plug is forced deeply into the ear cavity).
Goggles also should not be used in diving because
they do not cover the nose and thus do not permit

chamber designed to accommodate a powershotgun shell. The chamber is
attached to the end of a pole and is shot or pushed

(if

5-24

If a diver

wishes to

kill

rather than discourage a

com-

a specially

constructed

ful

pistol cartridge or

NOAA

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-20

Shark Darts
against the shark, where

power heads have

it

on impact. Although

fires

a built-in positive safety, they should

be handled with extreme caution; they also should not
be carried
also

is

in

water with poor

dangerous

to carry

visibility or at

night.

It

loaded power heads when

several divers are working closely together in the water.

Devices known as "shark darts" are available commercially; these instruments are designed to disable or

sharks by injecting a burst of compressed gas.
Shark darts consist of a hollow stainless steel needle
approximately 5 inches (12.5 cm) long that is connected to a small carbon dioxide (C0 2 ) cylinder or
extra scuba tank; they are available in dagger or spear
kill

form (see Figure

5-20).

To

use these devices, the dart

is

abdominal cavity, where it
penetrates into the animal's body cavity and discharges
the contents of the C0 2 cartridge. The expanding gas
creates a nearly instantaneous embolism and forces
the shark toward the surface. The size of the C0 2

Photo William High

thrust against the shark's

Figure 5-21

Shark Screen

in

Use

cylinder varies from model to model; a 12-gm cylinder
is

effective to a depth of 25 feet (8 m), a

16-gm

cylin-

der to 40 feet (13 m), and a 26-gm cylinder to 100 feet

(30 m). Multiple-shot compressed-air models are also
available.

NOTE
some

it is illegal to carry comweapons such as shark darts in
automobiles or on the person. Divers are

In

localities,

pressed-air

check with

therefore advised to
ties

local authori-

before carrying these devices.

One

of the most effective

methods of protecting

divers in shark-infested waters

the Shark Screen, a

is

Photo Scott Johnson

lightweight synthetic bag that has three inflatable
collars (Figure 5-21). In the water, the diver

the collars, gets into the bag, and

blows up

with seawater;

fills it

intelligibility of

messages transmitted through any type

the bag then conceals the occupant from the sea below

of diver

and keeps any effusions

blood or sweat) that

a result of the effects of pressure, interference from

When

the

might attract sharks

bag

is

in

(e.g.,

the bag.

not in use, the

folded into a small package and carried in a

life

vest or kept with other survival gear.

UNDERWATER COMMUNICATION
SYSTEMS

is

less

than optimal as

support system, and the need for a diver to

life

concentrate on behaviors other than communication.

Message

intelligibility

improves significantly, howevand

listeners in

the underwater environment (Hollien and

Rothman

er, if

5.7

communication system

divers are trained to be better talkers

1976).

The

four principal types of diver

communica-

tion systems are described in the following sections.

Several underwater communication systems have been

developed and are available commercially. These sys-

Hardwire Systems

because of their inherent
deficiencies and use constraints. Studies have shown

5.7.1

that, regardless of the efficiency of these systems, the

parable to a telephone

tems vary

in effectiveness

October 1991

— NOAA

Diving Manual

Hardwire systems employ a closed loop that is comand includes a microphone, an

5-25

Section 5

Figure 5-22
Diver Communication
earphone/receiver, and a cable over which the signal

System

\

is

transmitted. These units require a physical connection,

i.e.,

umbilical, between the talker

Hardwire systems of the type used

and the

listener.

for surface-supplied or

scuba diver communication provide the greatest degree

communication of the systems discussed
shows the surface control panel of a
hardwire diver communication system.
Most hardwire systems can be configured either for
two-wire or four-wire operation. In a two-wire system, the diver usually is the priority signal path and

of intelligible

here. Figure 5-22

Photo Michael

Pelissier,

Ocean Technology Systems

the tender listens to the diver. If the tender wishes to

must be thrown. The earphone and microphone on the diver's end are wired in
parallel (Figure 5-23A). When two divers are operating
talk to the diver, a switch

on the same radio, the tender must push a cross-talk
switch to enable the divers to talk to each other.

Figure 5-23

Schematics of Diver
Communication Systems
A.

Two-Wire Mode

A

four-wire system (Figure 5-23B) allows the tender and

divers to participate in open-line (round robin)

munication, similar to that

in a

com-

conference telephone

call.

Most hardwire

units are

powered by internal

6- or

12-volt lantern-type batteries that provide continu-

ous operation on moderate volume output for 25 hours
or more.

Some

units feature connections for

an exter-

(

power supply; others incorporate redundant batteries
so that a spare is always available in an emergency.
nal

5.7.2

P^

Acoustic Systems

The acoustic system includes
fier,

power supply, and

directly into the water

a microphone, ampli-

transducer;

it

5^f

&_

transduces speech

by means of the projector (under-

B.

Four-Wire

Mode

water loudspeaker). The signal produced can be received
either by a

hydrophone placed

in the

water or by divers

without any special receiving equipment.

Some

of these

systems also incorporate alarms or signals that can be

used to recall divers.

5.7.3

Modulated Acoustic Systems

Several units of the modulated acoustic type have
been manufactured, and these have performance characteristics that

vary from poor to excellent. The most

widely used modulated acoustic systems employ ampli-

tude modulation (AM), a technique also used by commercial

AM

broadcast stations. However, since radio

signals are absorbed rapidly

by seawater, the acoustic

carrier rather than the radio frequency carrier

ulated in diving situations.

A

is

mod-

typical system of this

MICROPHONE

type consists of a microphone, power supply, amplifier,

i

modulator, and underwater transducer (Figure 5-24).

Acoustic signals produced by such systems can be

5-26

Courtesy Michael

NOAA

Pelissier,

Ocean Technology Systems

Diving Manual

— October 1991

Diver and Diving Equipment

Figure 5-24

Modulated Acoustic
Communication System
few

result,

FM

systems adapted to underwater use are

commercially available.
Single sideband has an advantage over

AM

AM,

because

puts one-half of the total output power

and

carrier,

this

power

is

ultimately

lost.

AM

nicators have greater range than

the

in

SSB commu-

systems for the

same output power and frequency. A major drawback
to SSB is that it requires more complicated electronics
and higher initial cost than other systems, and, as a
result, most presently used underwater communication

systems

Poor

utilize the

AM

intelligibility has

technique.

been a problem for many

users of wireless diver communications. In the late
1960's, researchers at the University of Florida sponsored

a series of tests designed to elucidate this problem.
Photo Michael

Pelissier.

Ocean Technology Systems

During the tests, divers read phonetically balanced
word lists using various masks, microphones, and communicators; test results showed intelligibility scores

understood only by a diver or a topside listener equipped

with an appropriate receiver and demodulator. In one

such unit, for example, a 31.5-kHz carrier signal
modulated by the speech
into the

signal
er,

is

signal, amplified,

is

and projected

water via an acoustic transducer. The acoustic

the 50 percent range at best.

now known

that

in

many

human and equipment factors contribute to an increase in
The key elements are the microphone,

intelligibility.

mask, earphone, transmitter/speech

filter

design, and

diver training.

then picked up by another acoustic transduc-

amplified, demodulated, and heard in the normal

5.7.4

communicator

1/2 watt. Generally, a range of
1/4 mile (0.4 km) can be expected in good ocean
conditions. However, range and clarity can change
dramatically because of acoustic background noise, a
shadow effect (caused by the tank, buoyancy compensator, wet suit, etc.), or thermoclines.
is

Non-acoustic Wireless Systems

Another approach

speech mode. The power output of a typical 31.5-kHz

to

underwater communication

involves a non-acoustic wireless system that uses an
electric current field.

system

made

is

Because

barriers, or reverberation.

by the amount of power applied

diver "feels" a mild shock

communication. Generally, the higher the frequency,

the greater the absorption of sound in water.

October 1991

— NOAA

Diving Manual

As

a

Range

is

man-

determined

to the field platers

and

limited to the diver's height, and power output

tems generally require a high ultrasonic frequency

to

non-acoustic, this

by the separation between them. Separation generally
is

obtain the frequency deviation necessary for intelligi-

is

it

not affected by thermoclines, natural or

Other modulated acoustic systems involve frequency
modulation (FM) or single sideband (SSB). FM sys-

ble

It is

is

limited by what the diver can tolerate because the

mode

is

when

transmitting. This

limited, at best, to a range of a few

feet or meters.

With modification,

this

hundred

system can be

used to transmit physiological data.

5-27

i

Page

SECTION 6
HYPERBARIC

6.0

General

6-1

6.1

Hyperbaric Chambers

6-1

CHAMBERS
AND SUPPORT

6.2

Design and Certification

6-3

EQUIPMENT

6.3

Operation

6-3

6.

1

.1

Transportable Chambers

6.3.1

Predive Checklist

6.3.2

Gas Supply

6.3.3

Chamber Ventilation and
Mask Breathing System
Oxygen Analyzers

6.3.4
6.3.5

6-2

6-3

6-3

Calculation of Gas Supply

6-6
6-7
6-8

6-9

6.4

System
Chamber Maintenance

6.5

Fire Prevention

6-10

6.5.1

Ignition

6-10

6.5.2

Combustion

6-14

6.5.3

Materials

6.5.4

Management

6.3.6

6.5.5

Electrical

6-9

6-14
of a Fire

6-14

6.5.4.1

Detection

6-17

6.5.4.2

Extinguishment

6-17

6.5.4.3

Breathing Masks and Escape

6-17

Summary

of Fire Protection Procedures

6-17

«

HYPERBARIC

CHAMBERS
AND SUPPORT
EQUIPMENT
6.0

GENERAL

three terms generally describe 'chambers used prima-

Hyperbaric chambers were developed

human

to

permit

beings to be subjected to an increased pressure

environment. Such chambers are vessels capable of

accommodating one

or

pressurized so that the

more occupants and of being
environment inside the chamber

rily

treatment of pressure-related

fects of pressure, in the

refer to these as

PVHO's

6.1

Early models of hyperbaric chambers were single-

compartment
does not

diving: surface decompression;

Human

HYPERBARIC CHAMBERS

example, hyperbaric chambers are used
in

(Pressure Vessels for

Occupancy).

patient

uations that occur

is

decompression of divers). Engineers

conditions, and in the decompression of divers. For
in several sit-

and decompression cham-

for the surface

simulates water depth while the pressure outside the

chamber remains at normal (l atmosphere) pressure.
Hyperbaric chambers are used in research on the ef-

to treat diving casualties),

bers (a term used to indicate that their primary use

(single-lock)

and a tender

chambers

to enter

recommend

that allowed one

and be pressurized.

NOAA

the use of single-lock chambers

because they do not allow medical and tending person-

have access

omitted decompression; treatment of diving accidents

nel to

such as gas embolism and decompression sickness; and

modern chambers are of the multilock type (see Figure 6-1). The multilock chamber has two or more com-

pressure and oxygen tolerance tests.

changeably

to

Terms used

inter-

denote these chambers include recom-

pression, compression, or hyperbaric

chambers (these

to the patient

during treatment. All

partments that are capable of being pressurized

in-

dependently; this feature allows medical personnel and

Figure 6-1A

Double-Lock Hyperbaric

Chamber— Exterior View
Oxygen

Lifting

Eye

Gas

Nitrox Regulator

Inert

(Therapy Gas)

Regulator

Inner Lock

Analyzer

Gauge
j

Communications

/

Outer Lock

y Gauge

Outer Lock
Viewport

Viewport

C0 2

Scrubber

Controls

Design and
Cert. Plate

2 Overboard
Exhaust

E.K.G.

Air

Oxygen and Therapy
Gas Cylinders

October 1991

— NOAA

Diving Manual

Exhaust

Photo Dick Rutkowski

6-1

Section 6

Figure 6- 1B

Double-Lock Hyperbaric

Chamber— Interior View

Emergency

nterior Light

Air/Therapy

Gas Mask

Photo Dick Rutkowski

tenders to enter the

chamber

to treat the patient

and

Multiplace chambers are designed to accommodate

same time. Deck decompreschambers (located on the deck of the surface
platform or support ship) and land-based chambers

then to leave, while the patient remains at the desired

several occupants at the

pressure in the inner compartment.

sion

A chamber
•
•

A

should be equipped with the following:

two-way communication system

A mask
the

breathing system for oxygen (normally of

demand

used for recompression treatment and diving research

and research are

or for clinical hyperbaric treatment

examples of multiplace chambers.

type, although ventilation hoods are

gaining acceptance for clinical treatment) (Figure 6-2)
•

Emergency air/mixed gas breathing masks

6.1.1

Transportable Chambers
and shape

•

Pressurization and exhaust systems

•

A

•

External lighting that illuminates the interior

lightweight materials (Figure 6-3) to L-shaped, two-

•

Viewports

person capsules, have been used

•

Depth control gauges and control manifolds
Heating and air conditioning systems (highly

fire

extinguishing system

Small portable chambers, varying

in size

from single-person, folding chambers made from modern
in

emergencies to

•

Stop watches (elapsed time with hour, minute, and
second hands)

recompress divers being transported to a large wellequipped chamber. Transportable chambers are most
valuable when they are of the two-person type and are
capable of being mated to a larger chamber, because
these features allow the patient to be continuously

•

Gas sampling

tended and pressurized. Small one-person transportable

•

desirable)

6-2

ports.

NOAA

Diving Manual

— October 1991

Hyperbaric Chambers and Support Equipment

Figure 6-2

Mask Breathing System

for

Use

in

Hyperbaric

Chamber
and ancillary equipment should

quality pressure gauges

C0 2

chamber. All such
equipment should be tested and calibrated before a
diving operation. Figure 6-4 is an example of a certification plate and shows various specifications and

be used

Scrubber Motor
Viewport

Sound Powered
Phone

in outfitting a hyperbaric

certifications.

NOTE
structural modifications such as those
made, the
chamber must be recertified before further
If

involving welding or drilling are

use.

Hyperbaric chambers used

diving usually are cylin-

in

drical steel pressure vessels that are designed to with-

stand an internal working pressure of at least 6 atmo-

(ATA) (165

spheres absolute

Modern chambers

fsw).

generally are 54-60 inches (137-152 centimeters) in

may have

inside diameter but

Oxygen
Exhaust

inside diameters ranging

from 30 inches (76 centimeters) to as large as 10 feet
(3 meters). Large chambers used to house and decompress divers for long saturation exposures are outfitted

with toilet
fortable

facilities,

beds, and showers, but such

chambers usually are found only

at sites

comwhere

large-scale diving operations or experimental dives
are conducted.

C0

2

Scrubber

Canister

Photo Dick Rutkowski

6.3

OPERATION

6.3.1

chambers, although better than no recompression

A

Predive Checklist
predive check of each

chamber must be conducted

have major shortcomings because an
attendant outside the chamber has no way to perform
lifesaving measures, such as maintaining an airway,

gas source must be checked to see that the intake

performing cardiopulmonary resuscitation, or
ing a pneumothorax.

The predive checklist (see Table 6-1) should be posted
on the chamber itself or on a clipboard next to the

capability at

all,

reliev-

before operation.

If

pressurized by a compressor, the
is

clean and will not pick up exhaust from toxic sources.

chamber.

6.2

DESIGN AND CERTIFICATION

Gas Supply
A chamber treatment

6.3.2
Several codes and standards apply to man-rated pres-

sure vessels, including current standards set by the

American National Standards Institute, the American
Society of Mechanical Engineers, the National Fire
Protection Association, and, under certain circumstances, the U.S. Coast Guard. These codes are comprehensive where the structural integrity of the vessel
is

concerned and include

tion,

all

aspects of material selec-

welding, penetrations into the pressure vessel

walls, flanges for entry or exit,

October 1991

— NOAA

and

testing.

Diving Manual

Only high-

and a secondary

air

facility

should have a primary

supply that

will satisfy the follow-

ing requirements:

Primary supply

—

sufficient air to pressurize the

cham-

ber twice to 165 fsw and to ventilate

Secondary supply

throughout the treatment:

— sufficient

air to pressurize the

165 fsw and to

chamber once

to

ventilate for

hour.

l

6-3

Section 6

Figure 6-3
Transportable Chambers
A.

Total system

B.

Courtesy Draegerwerk

C.

Lightweight one-person transportable

Schematic showing victim and tender

AG

chamber

Courtesy Draegerwerk

AG

Technical Data:

Max. operating pressure:
Test pressure:

5 bar

72.5 pounds/sq.

in.

7.5 bar

108.75 pounds/sq.

in.

42,714

Total volume:

700 liters
Total outside length:
2540 mm
Total outside height:
1520 mm
Total outside width:
860 mm
Outside height (without mobile base): 1200 mm
Total inside length:
2350 mm
Largest inside diameter:
640 mm
Total weight:
approx. 500 kp
Weight of the complete base:
approx. 275 kp
Weight of the complete pressure
chamber without base:
approx. 225 kp
Acceptance:
Techn. Inspect. Agency (TUV)

cu.

•100.00

in.

59.84

in.

33.86

in.

•

•

47.24

in.

•

92.52

in.

25.20

in.

•

in.

1102.5 pounds
606.4 pounds
496.1

pounds

Photo Butch Hendrick

Figure 6-4
Certification Plate for Hyperbaric

Maximum Working

Chamber
Maximum Working Temperature

Pressure.

Manufacturer's Serial

ASME Stamp

Number

(Chamber manufactured

in accordance with ASME Code) for,
Unfired Pressure Vessel

Division of Code (Manufactured
according to Section 8, Division

1).

Arc or Gas Welded Construction.

77 PSI 150°F

Uj
DIV

W

SERIAL

NO

1973

I

^.Year of Construction

.U.S.

Coast Guard Stamp:

Class
designates either Working
Pressure between 30 and 600 psi or
working temperature between 275°
and 700 °F
II

«

b USCG CLASS
MIA 73 25

DESIGNED AND BUILT BY
PERRY SUBMARINE BUILDERS
RIVIERA BEACH, FLORIDA

Coast Guard Office
Marine Inspection

U.S.

MIA

Manufacturer

73
25

in

charge of

— Miami Office
— Year of inspection
— Sequential number of
inspection

(e.g.,

25th

chamber inspected

in

I

1973)

Source:

6-4

NOAA

Diving Manual

NOAA

(1979)

— October 1991

.

Hyperbaric Chambers and Support Equipment

Table 6-1
Hyperbaric

Chamber Predive

Checkout Procedures
Before every operation of the chamber, a predive check of

ELECTRICAL SYSTEM

the facility must be conducted. This procedure should take

Lights operational

only a few minutes, provided that the personnel are experienced

Wiring approved, properly grounded

and the chamber

is

Monitoring equipment

properly maintained.

calibrated

(if

applicable)

and operational.

Predive Checklist

COMMUNICATION SYSTEM

CHAMBER

Primary system operational
Secondary system operational.

Clean
Free of

extraneous equipment

all

Free of noxious odors

FIRE

PREVENTION SYSTEM

Doors and seals undamaged, seals lubricated

Water and appropriate fire extinguisher in chamber. For
chambers with installed fire suppression system,

Pressure gauges calibrated, compared.

pressure on tank

AIR

SUPPLY SYSTEM
Primary

air

Combustible material

supply adequate

for

165 feet plus ventilation
Secondary air supply adequate

two pressurizations

to

Fire-resistant
for

MISCELLANEOUS — INSIDE CHAMBER
Slate, chalk,

Equalization valve closed
at

Bucket and

350

psig or

250

psig,

depending

and mallet
bags

plastic

Primary medical

on working pressure (200 or 100 psi) of chamber
Fittings tight, filters clean, compressors fueled.

for

body waste

kit

Ear protection sound attenuators/aural protectors

(one pair per occupant)

OXYGEN SUPPLY SYSTEM

MISCELLANEOUS— OUTSIDE CHAMBER

marked as BREATHING OXYGEN;
cylinder valves open
Replacement cylinders on hand
Inhalators installed and functioning
Regulator set between 75 and 100 psig
Fittings tight, gauges calibrated
Oxygen manifold valves closed.
Cylinders

metal enclosure

worn by all chamber occupants
mattress and blankets in chamber.

one pressurization

and 1 hour of ventilation
Supply valve closed
Supply regulator set

in

Fire-resistant clothing

Stopwatches
Recompression treatment time

full;

Decompression time-personnel leaving chamber
Cumulative time

Spare
U.S.
U.S.

Navy recompression treatment tables
Navy decompression tables

Log
List of emergency procedures
Secondary medical kit

NITROX (Therapy Gas)
marked 60% N 2 /40% 2
cylinder valves open
Replacement cylinders on hand
Inhalators installed and functioning
Regulator set between 75 and 100 psig
Fittings tight, gauges calibrated

Cylinders

NITROX

full;

;

Oxygen analyzers

CLOSED-CIRCUIT OPERATIONS (WHEN APPLICABLE)

C0 2
C0 2

Both the primary and secondary supply

may

be pro-

vided by any combination of stored and compressor
at the
If

amounts of

air

appropriate pressure in the required times.

it

is

is

important

to

power failures and, wherever possible, to keep an
emergency generator available to provide continuous
power if service is interrupted. Personnel at chamber
installations should be familiar with local fire and
rescue units that can provide emergency power and air.

— NOAA

a card in a conspicuous

place showing the date of service and type of lubricant
used. Before activating a hyperbaric chamber, the opera-

must ensure that the predive checklist shown

Table

6-1

in

has been completed.

WARNING

be aware of the possibility

of

October 1991

absorbent

may

be used. In addition to having an adequate volume of
it

C0 2

analyzer functional.

The compressor should have

tor

not feasible to have a high-pressure system

available as a backup, two low-pressure systems

stored gas,

scrubber functional

Adequate

valves closed.

capacities that will provide the required

functioning and calibrated.

Diving Manual

Compressors Should Be Lubricated With
Lubricants That Will Not Break Down Under
Heat or High Pressure, and Filters Should Be
Changed According to Required Maintenance
Procedures
6-5

Section 6

6.3.3

Chamber

and Calculation

Ventilation

minimum

Unless the chamber

equipped with a scrubber, it is
necessary to ventilate the chamber with fresh air to
maintain safe levels of carbon dioxide and oxygen inside
the chamber.

The

The chamber

of

Gas Supply
is

rate at

which

must be circulated

air

through the chamber depends on the number of personnel inside the chamber, their level of activity, the

chamber depth, and the breathing gas being used.

chamber

supply should be maintained at a

air

supply pressure of 100 psig over
pressure. Regulator settings for

maximum

oxygen depend

on the type of oxygen breathing masks installed

in the

chamber; most masks should be supplied with gas at
between 75 and 100 psig above the chamber pressure.
Knowing the amount of air that must be used does
not solve the ventilation problem unless there is some
way to determine the volume of air actually being used
for ventilation. The standard procedure is to open the
exhaust valve a given number of turns (or fractions of a

NOTE

turn),

which provides a certain number of actual cubic
minute at a specific chamber

feet of ventilation per

The abbreviation acfm

refers to actual cubic

at the chamber pressure in
use at the time; scfm refers to standard cubic

feet per

minute

and to use the air supply valve to maintain a
chamber pressure during the ventilation period.

pressure,
constant
•

feet per minute, defined as cubic feet per
minute at standard conditions at one atmo-

The exhaust valve handle should be marked
so that

sphere pressure and 0° C [acfm = (scfm)/
(chamber pressure in atmospheres absolute,
usually expressed as (D + 33)/33), where
D = chamber depth in fsw].

the
•

is

it

number

The

possible to determine accurately

of turns and fractions of turns.

rules in this

paragraph should be checked

against probable situations to determine the rates
of ventilation at various depths (chamber pressures)
that are likely to be needed. If the air supply

The following procedures reflect various scenarios
in chamber operations:

encountered
(1)

When
(b)

(2)

occupants are breathing

acfm
4 acfm

2

(a)

air in the

for

each person at

for

each person not

chamber:

vide at least that

rest

at rest.

(b)

occupants are breathing oxygen by mask
chamber without an overboard dump system:
12.5 acfm for each person at rest
25.0 acfm for each person not at rest

(c)

Additional ventilation

a

(a)

is

not necessary for

much

flow at a deeper depth.

•

The necessary valve

•

and depths should be determined with the help of
a stopwatch by using the chamber itself as a
measuring vessel.
The ventilation rate can be calculated by using

When
in

is

ample, determination of ventilation rates for a
few depths (30, 60, 100, 165 fsw) may be sufficient, because the valve opening specified for a
given rate of flow at one depth normally will prosettings for the selected flows

this formula:

occupants who are not breathing oxygen.
(3)

Interrupted ventilation:
(a)

Should not exceed

5

V X

R =

minutes during any

(P

30-minute period.
t

(b)

When

acfm
(4)

oxygen monitoring equipment

is

where

available:

Ventilation should be used as required to

(a)

maintain oxygen concentration

in the

chamber

below 23 percent.
(5)

With an
The

installed overboard

Step

1

The quantity
is

system:

R

chamber

V

volume of chamber

t

=

ventilation rates for air breathing given

(a)
in

dump

33

and

then the normal rate should be resumed.

When

33)

X

resumed, should use twice the required

for twice the period of interruption,

+

18

above should be used.
of air ventilated through the

=

in

cubic

feet;

time for chamber pressure to change 10
fsw

P

ventilation rate in acfm;

in

seconds;

chamber pressure (gauge)

in fsw.

chamber

controlled by regulating the precalibrated exhaust

valve outside the chamber.

been established, the
to maintain a constant

6-6

air

Once

the exhaust rate has

supply valve can be regulated

chamber

pressure.

Chamber

pressure in the unoccupied

be increased to 5 fsw beyond the depth

chamber should
in question.

The

exhaust valve should then be opened a certain amount

NOAA

Diving Manual

— October 1991

Hyperbaric Chambers and Support Equipment

and the length of time
below

this

maximum

it

takes to

come up

example, if checking for a depth of 165 fsw, the
chamber pressure should be taken to 170 fsw and the
time

The

it

takes to reach

The exhaust intake must be placed

10 fsw

to

depth should be determined. (For

160 fsw should be measured.)

cham-

maximum

ensure

chamber and
from being drawn from the cham-

circulation within the

to prevent fresh air

ber during ventilations.

valve should be opened different degrees until the

setting that approximates the desired time

known;

is

Times

that setting should then be written down.

tings

determined

for these in the

A

same way.

or table of the valve settings should be
ventilation chart using this information

chart

made and

and the

a

venti-

The oxygen system provides oxygen

chamber not equipped
with a mask overboard discharge system and assuming
there are two patients and one tender in the chamber)
(for a

Cp = 10V +

48,502

where

It

also provides a source of

known clean

chamber. The

Smoking

leaks.

A

in the vicinity

hyperbaric chamber

of a

chamber

is

prohibited.

may be equipped

with both

standard and overboard discharge breathing masks.

regulator for oxygen or air supply, appropriate hoses

Cp

total

V

chamber volume

10

atmospheres needed

=

(ft

to

3

);

to pressurize twice

165 fsw;

treatment using

USN

dump

4.

Table 6-2 shows ventilation rates and total air
requirements for two patients and one attendant

(US Navy

fittings to

exhaust the diver's exhaled

breath outside the recompression chamber; overboard

during

Treatment Table

undergoing recompression treatment

and

priate hoses

total air (in scf) required to ventilate

a

and fittings, and an in-board dump (or discharge)
system (see Figure 6-2). A breathing mask with an
overboard discharge system consists of the same basic
components as the standard mask, with the addition of
a mask-mounted demand exhaust regulator and appro-

capacity of primary system (scf);

from the surface

1985).

As indicated, the maximum air flow rate that the system must deliver is 70.4 scfm (with an oxygen stop at

systems are usually used for oxygen breathing.

The oxygen cylinder pressure is reduced
mately 75 psig over chamber pressure by
regulator. This pressure differential

chamber depth. The

demand

calculate secondary system capacity, the formula

=

5V

+

to

by changes

resulting low-pressure

in

oxygen or

through a lightweight, flexible hose to a demand

A

control knob on the

regulator allows adjustment of the regulator

minimize breathing resistance or

may

4,224

a

to

permit constant

is

flow,

Cs

a pressure

maintained by

tion of a standard regulator as required

regulator located on the mask.

Secondary System Capacity

is

to approxi-

suitable tracking regulator or by operator manipula-

air flows

60 fsw).

To

pure oxygen.

air in the event of fouling of the air in the

The standard mask is generally used with air but can
be used with mixed gas or treatment gas. Overboard
discharge masks are generally used for oxygen breathing during recompression or treatments. The standard
breathing mask consists of an oral-nasal mask, demand

calculated as follows:

48,502

for that part of

the decompression/recompression schedule requiring

system should be inspected carefully and checked for

lation rates should be prepared.

Primary system capacity

Mask Breathing System

6.3.4
for

other rates and depths should be calculated and set-

is

inside the

ber as far away from the supply inlet as practical to

if

this

is

desired.

The gas

delivery pressure also

be adjusted from outside the

chamber

to

enhance

flow characteristics.

where

With the overboard discharge units, the diver's exhalais removed through a regulator that is mounted on
the side of the mask. The regulator exhaust is connected by a hose to the outside of the chamber. For a

tion

Cs

=

total

V

=

chamber volume

5

=

capacity of secondary system

(scf);

3

pressure differential

(ft );

atmospheres required

to pressurize

from

chamber

the surface to 165 feet once;

= maximum
for

October 1991

1

ventilation rate of 70.5

hour.

— NOAA

scfm

mask-mounted

regulator.

The

unit should

not be pressurized to a depth greater than 60 fsw unless
it

Diving Manual

excess of 60 fsw, an auxiliary

wall to limit the differential pressure at the

outlet of the

4,224

in

regulator must be connected between the hose and the

is

fitted

with an auxiliary

vacuum

regulator or the

6-7

Section 6

Table 6-2

and Total
Requirements for Two
Patients and One Tender
Undergoing Recompression Treatment
Ventilation Rates

Air

Depth

Ventilat

on

Rate (scfm)

of

Ventilation Air Required at

Stop

Using

(scf)

'

Stop

Air

°2

(fsw)

Stop

Stop

165

47.9

140

41.9

5

37

100

32.2

80

27.3

60
50

22.5

70.4

20.1

62.9

40
30
20

17.7

55.3

15.3

47.7

12.8

40.2

10

10.4

32.6

air

2929

4561

1772
1107

1772

1772

6183

6183

1090

1090

1090

966
328
675
603
530
916
770
1250

6898

13606

15182

6038

requirements are dependent on chamber

Depth

of

4561

4

3

1437
503
444
386
328
675
603
530

139

Total for Ventilation

Total

2A

1A

1437

120

NOTE:

6A

6

2

from 60'

Treatment Table

1540
2501

1437
503
444
386
328
675
603
530
10996
1540
1250

10778

18692

1831

4

5749
1256

5749
1256

1111

1111

966

966

821

821

8104
7234
6363
10996
1540
1250

25344
22644
19908
34344
7236
5868

45390

125247

size.

Stop

A

Duration

60'

4

Hr.

4

Hr. Air

4

Hr.

60'

4

Hr. Air

to

4

Hr.

5,400
16,903

2

3,672
14,430

2

2 Hr. Air

30'

2

Hr. Air

to

4

Hr.

10'

4

Hr. Air

10'

4 Hr.

Required

16,903

2

30'

r

1,922

1,776

10,012

2

2,726
6,262

2

624

2 Hr. Air

to
4'

at 4'

2

Hr. Air

2

Hr.

4'

499
1,563

2

26
82,718 (min)

4 Min.

to Surface

Adapted from US Navy (1985)

discharge hose has been disconnected from the exter-

the manufacturer. For further information, consult the

nal port.

appropriate manufacturer's instruction manual (see

These units should be inspected by the inside tender
or supervisor before each use. Hose fittings should be
inserted into properly labeled connectors on the wall of
the chamber. After testing, the internal and external
valves should be closed until mask breathing gas is

the predive checklist in Table 6-1).

required.

therapy, surface decompression, or research.

The mask must be cleaned with an

antiseptic solu-

and warm water, alcohol, and
sterilizing agent) after each use, air-dried, and stored
in a sealed plastic bag or be reinstalled for subsequent
use. Routine inspection and preventive maintenance
tion (antibacterial soap

when malfunctioning is evident.
Generally, inspection and repair service is provided by
are required annually or

6-8

6.3.5

Oxygen Analyzers

An oxygen

analyzer

is

useful for monitoring oxygen

concentrations in chambers where oxygen

is

used for

The oxy-

gen level in a hyperbaric chamber should be maintained
between 21 and 23 percent to reduce the danger of
fire (see Section 6.5). An absolute upper limit of
25 percent should be observed, in accordance with
current National Fire Protection Association rules.

Several oxygen analyzers are available. For units
placed outside the chamber with a remote sensor located

NOAA

Diving Manual

— October 1991

Hyperbaric Chambers and Support Equipment

Table 6-3

Chamber Post-Dive Maintenance
AIR

Checklist

SUPPLY
Close

all

Check that all log
Stow log book.

valves

Recharge, gauge, and record pressure of
Fuel

entries

banks

air

compressors

OXYGEN SUPPLY

Clean compressors according to manufacturer's

Check

technical manual.

inhalators, replace as

Close

__
VIEWPORTS AND DOORS

Bleed

Close

system

2
all

necessary

cylinder valves

2

valves

Check viewports for damage; replace as necessary
Check door seals; replace as necessary

Replace cylinders with

Lubricate door seals with approved lubricant.

Clean system

BREATHING OXYGEN,

as required

Ensure spare cylinders are available

CHAMBER
Wipe

have been made

if

contamination

is

suspected.

NITROX (Therapy Gas) SUPPLY
inside clean with vegetable-base

warm fresh water
Remove all but necessary support

soap and

Check

chamber

items from

Clean and replace blankets

Encase

all

Close

flammable material

in

inhalators, replace as

NITROX cylinder
Bleed NITROX system

Close

chamber

in

valves

all

Replace cylinders with

fire-resistant containers

necessary

valves

60% N 2 /40%

2

,

as required

Ensure spare cylinders available.

Restock primary medical

as required

kit

Empty, wash, and sanitize human waste bucket

Check presence
Air out chamber

sand and water buckets

of

in

COMMUNICATIONS

chamber

Test primary and secondary systems;

Close (do not seal) outer door. Preferably leave one

on inside chamber

to

keep moisture

make

repairs as

necessary.

light

out.

ELECTRICAL

SUPPORT ITEMS
Check and

Check
reset

stopwatches and lock them

in

Ensure presence of decompression and treatment tables.

housing

for

Turn

all

of

emergency and
Manual

ventilation procedures,

and the

_ Restock secondary medical

as required and stow

kit

If

Clean and stow fire-retardant clothing

inside the
is

When

in

chamber, an appropriate chamber penetra-

required. Small, portable, galvanic cell-type

however,

may

lights

off

Check

Diving

be placed directly

in

the chamber.

choosing portable units for hyperbaric use, the

bulbs as necessary

encased

If

NOAA

units,

circuits

light

desk drawer

list

tion

all

Replace

control

in

pressure-proof housing, check

damage
power

wiring for fraying

environmental monitoring equipment is used, maintain
accordance with applicable technical manual.

must be inspected to ensure that the
system is properly grounded and that all fittings and
terminals are in good order and encased in spark-proof
lights inside, they

housings (see the predive checklist

in

Table

6-1).

manufacturer's instructions should be consulted to be
certain that the unit

is

compatible with hyperbaric

environments. Since nearly
to partial pressures of
1

all

oxygen

ATA, mathematical

WARNING

units read out in response

relative to a pressure of

conversions must be

ascertain the true reading at depth.

made

to

The manufacturer's

Lights Inside the Chamber Must Never Be
Covered With Clothing, Blankets, or Other
Articles That Might Heat Up and Ignite

instructions should be consulted for detailed information

on specific oxygen analyzers.

6.4
6.3.6 Electrical

The

electrical

System
system

in

Proper care of
a

chamber

fiber optics or

chamber,

size of the

no less than once a month, whichever comes first, the
chamber should be maintained routinely in accordance
with the Post-Dive Maintenance Checklist shown in
Table 6-3. At this time, minor repairs should be made
and supplies restocked. At least twice a year, the chamber

to

to provide lights

keep

all

through

through port windows, and to have the

When chambers

October 1991

— NOAA

have electrical systems and

Diving Manual

hyperbaric chamber requires both

routine and periodic maintenance. After every use or

actual electrical system controls located outside the

chamber.

a

com-

varies in

plexity, depending on the capability and
chamber. Whenever possible, it is best
electricity out of the

CHAMBER MAINTENANCE

should be inspected both outside and inside.

Any

deposits

6-9

Section 6

of grease, dust, or other dirt should be

removed and the

affected areas repainted (steel chambers only).

Only

mits corrosion to be recognized easily. Painting an

aluminum chamber

(and thus

will serve only to hide

encourage) corrosion. Corrosion is best removed by
hand-sanding or by using a slender pointed tool, being
careful not to gouge or otherwise damage the base

The corroded area and

a small area around

it

should be cleaned to remove any remaining paint or

Electrostatic sparks.

The most common sources of chamber fires in the
past have been lighted cigarettes, faulty electrical
powered devices.
from overheating caused by a defective component, a short
circuit, a jammed rotor in a motor, sparks produced by
making or breaking a load-carrying circuit, or from a

NOAA

hyperbaric chambers must be pressure

The procedures

to be

followed are shown in Table 6-4, and Table 6-5 presents a checklist for

chamber pressure and leak

electrically

Electrical fires, however, can start either

device with arcing brushes.

The

safe use of electrical devices in a

chamber

is

primarily a design factor, requiring proper installation

painted with a non-toxic, flame-retardant paint.

tested at prescribed intervals.

and sparks from

wiring,

corrosion products. Steel chambers should then be
All

Heat of compression

•

chambers are painted. Aluminum cham-

steel

bers normally are a dull, uneven gray color that per-

metal.

•

of the supply wiring and properly designed devices.

Wiring should be insulated with mineral materials or
in metal conduit (which can be

Teflon® and be shielded

either rigid or flexible).

tests.

The housings

of electrical de-

vices such as instruments can be purged with an

6.5

A

FIRE

oxygen-free inert gas during operation and may or
may not be pressure proof. Lights may be enclosed and

PREVENTION

hyperbaric chamber poses a special

fire

hazard because

of the increased flammability of materials in compressed
air or

an environment otherwise enriched

in

oxygen.

purged, or they

have the

may

be external to the chamber and

light directed inside with a "light

Even an enclosed

fiber optic cable.

light

pipe" or

can generate

chambers requires basically
same practices as it does in other locations. The
chamber environment, however, involves two special

tion plan should include the capability to disconnect

the atmosphere is an "artificial" one,
and people are confined with the fire in a relatively

must be

Fire safety in hyperbaric

enough heat

the

both the design and operational stages.

considerations

small space.
sary for a

—

The

fire,

chamber

anywhere

or

else,

are a

source of ignition, combustible materials, and an oxidizer.

There are four steps

in

chamber

fire safety in

addition

to preventive measures: detecting the fire, extinguishing

—

—

mask for breathing, and if possible escaping.
A safe chamber begins in the design stage. Various
codes and design handbooks deal with this complex
subject, and it can only be touched on here (Naval
it,

using a

Facilities

Engineering

Command

1972, National Fire

Protection Association 1984). After safe design, the

manner

in

which the chamber

tance. This section reviews

is

used

chamber

is

next in impor-

fire safety,

cover-

installations, control of the electrical haz-

ber at

all.

When

electricity

is

used, however,

This

may

be accomplished by employing protective

Use of low voltages

ers.

hazard, but

it

is

(e.g.,

12 or 24 volts) avoids this

a dangerous misunderstanding to think

such voltages cannot start a

fire if

(Shilling, Werts,

and

as intrinsically safe

may

ally are

be used. Low-current, low-

considered safe. There

is

Possible sources of ignition in a hyperbaric

tion of

made

chamber

safety. Ex-

to prevent the igni-

flammable gases or vapors by sparks generated

electrical
in a

equipment;

this

is

not the expected prob-

diving chamber. Junction boxes and other

equipment made

chamber

a fundamental dif-

ference between the concepts behind "explosion-proof

lem

include:

to explosion-proof standards

may

pro-

vide the kind of protection afforded by mechanical

housings (mentioned above), but this equipment

is

designed for a purpose different from the enriched-

•

Electrical wiring or apparatus

oxygen hyperbaric environment and may

•

Cigarettes or other smoking materials

inadequate. Also, most explosion-proof boxes are

6-10

is

and qualifying

voltage devices such as headsets and microphones gener-

by

6.5.1 Ignition

high-current flow

possible. Devices tolerant of pressure

plosion-proof housings are

The Underwater Handbook

requires

devices such as ground fault detectors and interrupt-

devices and those required for

in

it

protection of the occupants from electrical shocks.

additional references, consult the section on fire safety

Schandelmeier 1976, pp. 646-664).

protec-

fire

achieved by allowing no electricity in the cham-

is

and operational techniques.
For a more thorough treatment of the subject and

ing both basic principles

A

available.

At some
ard

be considered at

power instantaneously. Auxiliary lighting

electrical

all

traditional trio of conditions neces-

in a

to start a fire, a fact to

NOAA

Diving Manual

in fact

be

much

— October 1991

.

,

,

Hyperbaric Chambers and Support Equipment

Table 6-4
Pressure Test Procedures for

A

NOAA Chambers*

pressure test must be conducted on

NOAA

every

3.

recompression chamber:

Repeat Steps
until all

and 2

1

the leaks

have been eliminated.

2.

When initially installed;
When moved and reinstalled;

3.

At 2-year intervals

1,

when

in

4.

Pressurize lock to

maximum chamber

place

operating

pressure (not hydrostatic

at a given location.

pressure) and hold for 5

The
1,

test

is

to

be conducted as

minutes.

follows:

Pressurize the innermost lock to

100

(45 psig)

feet

an equivalent
penetration
seals,

5.

solution, leak test

viewports,

fittings,

shell

all

dog

165

feet

Hold

for

(73.4 psig).
1

hour.

145 feet (65 psig)

and

locate

and mark

Mark
and

with Step 2

leaks. Depressurize the lock

all

components

adjust, repair, or replace

until final

at least

is

Viewport Leaks

gasket (replace

-

Remove

the viewport

necessary)

if

,

feet

Repeat Steps

1

through

leaving inner door

contact with any lubricant.

come

Acrylic viewports should not

in

5,

open

and the outer door closed.
Leak test only those
portions of the chamber

be lubricated

Acrylic viewports should not
in

145

wipe.
6.

come

pressure

(65 psig)

CAUTION

or

in accordance
above and

repeat this procedure

as necessary to eliminate leaks.

a.

leaks.

Depressurize chamber and

weldments.

repair leaks
2.

If

pressure drops below

door dogs (where applicable)

valve connections, pipe joints,
shell

Depressurize the lock to

Using soapy water or

.

contact

not previously tested.

with any volatile detergent or leak detector

(non-ionic detergent
leak test)

up

.

When

to

is

be used

for

reinstalling viewport,

take

retaining ring bolts until the gasket

compresses the viewport. Do not

just

overcompress the gasket.

Weldment Leaks

b.

-

Contact appropriate

technical authority for guidance on
corrective action.

*AII

NOAA

standard recompression chambers are restricted to a

too large and heavy for efficient use in the

crowded

conditions of a chamber.

Although
sphere

in

a

is

lem

pressure of 100 psig, regardless of design pressure rating.

in

the piping of oxygen-rich gases,

factor in

should be avoided, the atmo-

static sparks

chamber

maximum

usually

humid enough

to sup-

chamber

A

an explosion.

vapors, gases, or dry, finely divided materials, none of

flow through a

in

a

chamber. Static sparks

it

is

also a

Because gases heat up when

compressed, the sudden opening of a valve, which allows

an oxygen mixture

press sparks. Also, static sparks are only a hazard with

which should be present

safety.

air

is

to

compress

in

the pipes, can cause

different but related hazard
filter or

muffler

is

the gas

in the air supply. If the

produced by an oil-lubricated compressor, some

may

usually can be prevented by using conductive materi-

oil

and by grounding everything possible. In some
medical hyperbaric chambers, the patient himself is
grounded with a wrist strap.
Although the heat of compression is more of a prob-

by compression or sparks generated by flowing gas.

als

October 1991

— NOAA

Diving Manual

collect

Incredible as

on the

it

filter

may seem,

or muffler and be ignited

a

ber fires has been smoking. This

major source of chamis

less of a

hazard now

than before the risks were widely known, but the pro-

6-11

Section 6

Table 6-5
Standard NOAA Recompression
Air Pressure and Leak Test

Chamber

i
Ship/Platform/Facility

Type

of

Chamber: Double Lock Aluminum
Double Lock Steel
Portable Recompression Chamber
Other*
*

(Description)

NAME PLATE DATA
Manufacturer

Date of Manufacture
Serial

Number

Maximum Working
Date

Pressure

Pressure Test

of Last

.

Test Conducted by

(Name/Rank/Title)

1.

Conduct

Chamber

visual inspection of

chamber

to determine

if

chamber

satisfactory

ready

for test.

Initials

of Test

is

Conductor

Discrepancies of inoperative chamber equipment:

2.

Close inner lock door and with outer lock door open, pressurize inner lock to 100 fsw

components do not

(Note:

Inner lock leak
A.

(45 psig)

and

verify that the following

leak:

If

chamber has medical

lock,

open

inner

door and close and secure outer door.)

checks

Shell Penetrations

and

Fittings

Satisfactory
B.

Viewports
Satisfactory

C.

Door Seals
Satisfactory

D.

Door Dog Shaft Seals
Satisfactory

E.

Valve Connections and Stems
Satisfactory

F.

Pipe Joints
Satisfactory

G. Shell Welds
Satisfactory
3.

Increase inner lock pressure to

Record Test Pressure

225 fsw (100

psig) operating pressure (not hydrostatic pressure)

for

5 minutes.
Initials of

Satisfactory

(NOTE: Disregard small leaks

6-12

and hold

Test Conductor

at this pressure)

NOAA

Diving Manual

— October 1991

Hyperbaric Chambers and Support Equipment

Table 6-5
(Continued)

Depressurize lock slowly to 165 fsw (73.4 psig)

4.

Secure

all

supply and exhaust valves and hold

for

hour.

1

Pressure

Start time

Fnd timp
Ci iterion:

If

Pressure
pressure drops below 145 fsw (65 psig)

Innpr Inrk prpssurp drop tpst

,

locate

(NOTE:

Repeat tests

6.

tested

in

If

of sections 2.

sections

2, 3,

7.

Outer Lock Checks

A.

Shpll Penptrations

B

Vipwports

and

and

chamber has medical
3,

leaks. Depressurize, repair,

and

fsw

retest inner ock.
I

passpd

Depressurize inner lock and open inner lock door. Secure

5.

and mark

165 fsw

in

open

lock, close

position. Close outer

and secure

and 4 above when setup per section

inner door
5.

Leak

door and secure.

and ope n outer door)

test only

those portions of the char nber not

4.

Fittings

Satisfactory

Satisfactory

Door Seals

C.

Satisfactory

Door Dog Shaft Spals

D.

Satisfactory

Valve Connections and Stems

E.

Satisfactory

Pipe Joints

F.

Satisfactory
Shell

G.

Welds
Satisfactory

Maximum Chamber Operating

8.

Pressure Test (5 minute hold)

Satisfactory
Initials of

TestC onductor
Inner

9.

and Outer Lock Chamber Drop Test (Hold

for

1

Hour)

Start time

Pressure

Fnd time
Inner

Pressure

and Outer Lock Pressure Drop Test Passed

165 fsw
fsw

Satisfactorily
Initials of

TestC onductor
10

.

All

above

tests

have been

satisfactorily

completed.

Date

Test Director

Signature

Diving Officer/

Director,

October 1991

— NOAA

Diving Manual

NDP

UDS

Date

Date

6-13

Section 6

smoking

hibition against

be

and around chambers must

in

no combustion, there

a broad pressure-oxygen per-

is

centage zone of incomplete or reduced combustion.

strictly enforced.

6.5.3 Materials

6.5.2

Combustion

The

The primary factor increasing the risk of fire in a
hyperbaric chamber is the increased combustibility

An

caused by the enriched oxygen atmosphere.

oxygen atmosphere

is

one that either has a partial

pressure or an oxygen percentage that

(determined

in a laboratory

and

level air,

An

chamber

in the

is

rate

when

also has an increased percent-

The relationships among
flammability, partial pressure, and oxygen fraction
are complex and non-linear, but show a consistent
trend toward faster burning with increased oxygen
percentage or with an increasing pressure at the same
oxygen percentage (Figure 6-5). The nature of the
age

(i.e.,

fraction) of oxygen.

background gas

is

minimum, and

important, too, with helium requir-

an overboard

essential to use

when
if

risk
it

dump

is

when oxygen is
now considered

system for exhaled

divers are breathing oxygen by

decompression or treatment.
able

the

regarded as non-flammable

known

is

fuel,

i.e.,

chamber be kept

to a

Some

it

is

in air will

materi-

burn

in a

best to rely on materials

to be safe or relatively safe in oxygen.

Metals are safe, as are ceramics. For wiring insula-

TFE

(Teflon®)

is

probably the best all-around

material, but there are mineral insulations and fiber-

some hard

glass, as well as

Melmac®

that are usable in

plastics like Bakelite®

and

some circumstances. Some

fluorine-based elastomers are relatively safe in high

oxygen mixtures, but their conductive properties are
poor and they are expensive. For clothing, the popular
choice is Durette®, but Nomex® is also adequate. Beta
fiberglass

is

suitably flameproof but has undesirable

wearing properties (Dorr 1971).

Although chamber design

is

important to

fire safety,

even the well-designed chamber needs to be used prop-

Because of the greatly increased
added to the chamber atmosphere,
gas

in

a fire

safety requires that

where possible, materials that are

high oxygen mixture, so

ing higher ignition temperatures but allowing faster

burning.

that,

make

fire

not flammable in enriched oxygen be used.
als

tion,

introduced when the gas

is

combustible materials

all

twice that of sea

2.5 times as fast at 165 fsw.

it is

additional hazard

mixture

greater than

with paper strips)

equivalent to 75 fsw

is

is

The burning

that of air at sea level pressure.

the pressure

enriched

third element required to

something to burn. Chamber

It

is

mask during

a

also considered accept-

a low oxygen level can be maintained by venti-

lating or purging the

chamber with

air,

but this

is

a less

desirable option because the gas used for purging
itself fairly rich in

oxygen.

It

and high flows may
be accompanied by excessive noise and compressor
wear and tear. The "zone of no combustion" concept is
the oxygen within accepted limits,

helpful in the

management

is mandatory; all
and other flammable materials
must be stowed or removed from the chamber when it
is being operated beyond the fire-safe zone. Particularly important to eliminate are fuzzy or powdered or
finely divided materials and flammable liquids and

loose clothing, papers,

gases.

One flammable gas

is

takes high flows to keep

of fire safety in chambers.

Good housekeeping

erly to be safe.

use in diving

is

that

may come

into increasing

hydrogen. The use of this gas

explored for deep diving because of
properties (primarily

its

its

is

being

physiological

low density, which results

in

low breathing resistance). Hydrogen can be used with-

out danger of explosion (once

it

properly mixed)

is

affect burning rate, changes in the percentage of oxy-

when a mixture contains less than 5 percent oxygen,
making it suitable for diving deeper than 100 fsw.
Most of the safety problems associated with the use

As

of hydrogen as a diving gas occur during handling

This concept takes into account the fact that, although

changes

in

pressure at a constant oxygen percentage

gen have a greater

effect.

a result, there

is

a "zone"

of pressure and oxygen percentage that provides ade-

and mixing.

quate oxygen for respiration but that will not support

combustion (Shilling, Werts, and Schandelmeier 1976;
Rodwell and Moulton 1985). This is illustrated in Figure 6-6.

An

combustion

6.5.4

is

that the

saturation dives

is

chamber environment

fire safe

except

in

in

most

the later stages of

Management

The preceding

important consequence of the zone of no

chamber

fires.

of a Fire

sections addressed the prevention of

Another component of

fire safety requires

that the people involved be able to deal with a fire once

decompression. The existence of this zone allows for

it

controlled combustion, such as that of welding, to be

rapidly (National Fire Protection Association 1979),

performed safely at pressure. In addition

many

6-14

to the

zone of

starts.

Although some past chamber

fires

have spread

others have been extinguished without loss of

NOAA

Diving Manual

— October 1991

Hyperbaric Chambers and Support Equipment

Figure 6-5

Burning Rates of Filter Paper Strips
45° in N 2 -0 2 Mixtures

at

an Angle

of

4.5

P0 2 =2Atm

o

99.6%

2

CO

E

o
LU

DC

CD

1.00

2.51

50

4.03
1

00

5.54

7.06

8.57

10.1

ATA

50

200

250

300

FSW

1

PRESSURE
October 1991

— NOAA

Diving Manual

6-15

Section 6

Figure 6-6

Combustion in N 2 -Oo Mixtures Showing
the Zone of No Combustion

O COMPLETE COMBUSTION
A

INCOMPLETE COMBUSTION

O

SLIGHT COMBUSTION

Q

NO COMBUSTION

COMPLETE COMBUSTION

o
LU

o
rr
LU
Q_

LU
_l

o
Z
LU
O
>
X

o

4

12

8

TOTAL PRESSURE, ATMOSPHERES ABSOLUTE
Combustion zones are defined by
by dashed lines. The area A-D-E

solid lines
is

and normal

prolonged periods, while the area represented by A-B-C

6-16

respiration

compatible with respiration
is

for

breathe

for short

periods only

(adapted from

Shilling,

Werts, and

Schandelmeier 1976)

safe to

NOAA

Diving Manual

— October 1991

i

Hyperbaric Chambers and Support Equipment

life.

It

therefore essential that

is

chamber personnel be

trained in fire safety techniques.

At present, the best

extinguishing agent for use

fire

hyperbaric chambers

in

Water extinguishes

water.

is

primarily by cooling and works best

flame or wets the
6.5.4.1

Detection

Numerous

fire

a pressure

in

mechanisms are available

Many

of these systems are

chamber, particularly ones operating

the relatively low pressures used with compressed

at
air.

The

detection

mechanisms most

suitable for

chamber

use are those involving infrared or ultraviolet sensors.
Ionization or

smoke detectors may

also be of value.

and needs of the particular
feel, for example, that a
clinical
treating patients with open
wounds should have an alarm system only, rather than
one that automatically deluges the chamber; a preferred approach is to have both a hand-held directable
fire hose inside and switches to activate a general
deluge system easily available to both chamber occupants and the topside crew. Whether a deluge or alarm
system is used, it should be thoroughly tested at the
time of installation and periodically thereafter.
the context of the uses

Most experts
hyperbaric chamber

installation.

The

best protection against fire

crew that

is

ble detection

is

in

system

compressed

air,

the only dependa-

another person standing by to

is

watch the operation. It is best if the designated "fire
watch" person stands inside the chamber rather than
outside (Hamilton, Schmidt, and Reimers 1983).

6.5.4.2

water,

is

personnel

A

on.

fire

to a

to control small localized fires.

The

Breathing Masks and Escape
caused by smoke inhalation

fire fatalities are

fire

first

thing the

should do unless

immediate escape is possible is to don a breathing
mask. The masks should be handy and should have a
breathable gas on line or be controllable by the occupants at

all

times. If

quickly to another

it

is

possible for occupants to flee

chamber

be sealed off from the

fire,

or

compartment

that can

they should do so rather

than donning masks and trying to extinguish the
6.5.5

fire.

A summary
•

of Fire Protection

of

chamber

fire

Procedures

prevention procedures

Maintain oxygen concentration and partial pressure as low as possible, preferably within the region

Use an overboard dump system whenever pure oxygen is breathed by mask in
a chamber.

of non-combustion.

•

Eliminate ignition sources.

•

Minimize combustibles, with the complete exclusion of flammable liquids and gases.
If combustible materials must be employed, the
type and quantity and their arrangement in the
chamber must be carefully controlled.
Firewalls and other containment techniques should

•

can be smothered by reducing the oxygen

or fuel concentration to a level that will not sup-

Summary

follows:

tem-

evolution of flammable vapors.

be utilized to isolate high-risk
•

fire zones.

The extinguishing system should

involve a water

port combustion.

deluge spray that can be activated either by occu-

The fuel can be separated from the oxidizer by
removing either the fuel or the oxidizer or by

pants or topside operators and a hand
that can be controlled

mechanically separating the two. Mechanical protein

•

chamber

hose will permit occu-

fire

occupants of a chamber with a

perature below that required for ignition or the

•

must of course remain

the chamber; lights

rather than burns. Accordingly, the

accomplished by physical, or

The combustible material can be cooled

fire

in

suppression system should be tested periodically

Most

•

The

chamber should be

to the

manually directable

6.5.4.3

four basic mechanisms:

•

power

under chamber operating conditions.

a combination of physical and chemical, actions involving

•

Simultaneous with the discharge of

velocities.

electrical

shut off to prevent shorting and electrical shocks to

Extinguishment

Fire extinguishment

all

an alert chamber

backed up by detectors. During certain

welding operations

strikes the

pressure to produce the desired degree of atomization

and droplet

pants of a

There are two problems with fire detection systems:
false alarms and failure to detect a fire quickly enough.
Any detection system needs to be studied thoroughly
in

it

spray nozzle must be 50 psi or more above chamber
detection

for routine fire protection.

usable

if

spray form. The pressure at the

fire in

foams operate in this fashion by blanketing the
fuel and separating it from the oxidizers.
The reactions occurring in the flame front or just
before the flame front can be inhibited or interfered with through the use of chemicals.

October 1991

— NOAA

Diving Manual

fire

hose

and directed by the cham-

ber occupants.
•

A mask

with an appropriate gas on line should be

available for each
•

Escape

to

should be the
tions plan,

chamber occupant

at all times.

another chamber or directly into the sea
first

whenever

option

in

the fire safety opera-

feasible.

6-17

<

Page

SECTION

7

AND
SUPPORT
PERSONNEL
DIVER

7.0

General

7.1

NOAA

Divers

7-1

7.1.1

Selection Standards

7-1

7.1.2

Physical Examination

7-1

7.1.3

Swimming

7-3

7.1.4

Scuba Training

TRAINING

7.2

7-1

Skills

7-3

7.1.4.1

Classroom

7.1.4.2

Pool and

Open-Water

7-4
7-4

7.1.5

Umbilical Dive Training

7-5

7.1.6

Special Equipment Training

7-6

7.1.7

Mixed-Gas Training

7-6

7.1.8

Saturation Training

7-7

7.1.9

Chamber Operator Training

7-7

Training of Diving Supervisors

7-8

7.3

Diving Medical Technicians

7-8

7.4

Hyperbaric Physicians

7-9

7.5

Research Divers

7-10

Selection

7-10

7.5.1

Curriculum
Equipment Maintenance
7.5.2

7.6

7-1

7-1

«

<

DIVER

AND

SUPPORT
PERSONNEL
TRAINING
7.0

GENERAL

screening by experienced

This section describes the general content of diver
training programs, the training involved in preparing

under specialized circumstances, and basic
approaches to diver training. It does not prescribe
to dive

specific training procedures or attempt to teach divers

how

to

perform specific underwater

Many
the

NOAA

organizations offer diver training.

Navy

are

among

agency missions.

and universities offer diver training

Many

and

diving schools offer extensive diver training for divers
in

the commercial diving industry. These training organi-

zations select students on the basis of their personal
motivation, physical fitness, and basic

swimming

NOAA

This section emphasizes the training of

all

ation interview helps to identify any misconceptions

NOAA diving work.
7.1.2 Physical

divers.

The physical examination

NOAA

Corps

universities and organizations involved in

sponsored programs that require diving

officers,

skills.

by a trained hyperbaric physician. Military, com-

tion

mercial, and scientific divers are evaluated according
to standards set forth

organizations.

NOAA

cal standards for

NOAA

from other Federal agencies. All of
the candidates who apply to NOAA's diving program

tions increase the risk of serious injury or disability in

framework

programs can vary

who

greatly:

NOAA

shallow water as well as divers

who

•

Any

Allergy to materials used

comes

terms of

in

diving equipment that

into contact with the skin

is

a relative

•

History of sensitization or severe allergy to marine
or waterborne allergens should be disqualifying.

Psychiatric
•
•

Acute psychosis should be disqualifying.
Chronic or acute depression with suicidal tendenbe disqualifying.

Chronic psychosis

in

partial

remission on medica-

tion should be disqualifying.

divers are selected from volunteers on the
fitness

The psychological evaluation

•

and

Substance use or abuse, including abuse of alcohol
or use of mood-altering drugs, should be disqualify-

for

acceptance into the program consists of a personal
interview, an assessment of motivation, and a general
Diving Manual

in

contraindication.

Selection Standards

— NOAA

rank systems

chronic or acute dermatitis adversely affected

cies should

October 1991

to

by prolonged immersion should be disqualifying.

•

and physical

made

Skin

are required to

The selection
and training of NOAA divers are monitored carefully
by the NOAA Diving Program.

basis of their psychological

is

their relative importance.

divers

dive only occasionally

dive regularly as part of their normal duties.

their water skills.

The guidelines below present

for individual dive fitness evaluations;

and no attempt

of diving involved in the dif-

include senior researchers

NOAA

divers.

conditions disqualify a person for

diving with compressed gas, and other medical condi-

•

are volunteers.

7.1.1

its

Many medical

by their respective agencies or

has developed and enforces medi-

NOAA-

also trains divers

in

if

they are not established standards. These guidelines

researchers, diving technicians, and individuals from

NOAA

of divers to determine

they are medically qualified to dive requires evalua-

are organized in accordance with a systems approach,

NOAA-certified divers include

ferent

Examination

the diving environment.

NOAA DIVERS

The amount and type

training or the require-

ments, conditions, and responsibilities of subsequent

a

7.1

may have about

the candidate

skills.

divers

and other personnel, but many of the principles described
here apply to the training of

divers to identify

and research diving. The evalu-

stresses of operational

to students

Commercial

local dive shops.

NOAA

are unlikely to be able to handle the

col-

and faculty members who use diving as a research tool.
Diver training also is available from diver certification organizations

who

and

those government agencies that

train divers in support of

leges

tasks.

individuals

ing.
•

Careful attention should be paid to the maturity of

prospective candidates, their ability to adapt to

7-1

Section 7

stressful situations, their motivation to

pursue div-

or has been surgically repaired

and their ability to understand and follow
decompression tables and directions.

ing,

is

ally cleared for diving with the

may

perforation

Neurologic
•
•

Closed head injury; following

full

recovery, any

neurologic deficit (including an abnormal

EEG

post-traumatic seizures) should be disqualifying.

Spine injury, with or without cord damage,

may
•

and attendant lower extremity paralysis. Prior cord
decompression sickness with residual symptoms

Chronic or acute

•

•

corrected) should be evalu-

Meniere's disease and other conditions that are
Extensive mastoid surgery, stapedectomy, or

disorder that causes or results in loss of con-

includes any form of seizure, previous gas

•

•

patent nasal passage and the absence of sinus and

Nasal polyps, deviated nasal septum, and other
diving

is

permitted.

•

Acute or chronic

ated individually; however,

•

A

is

not an absolute

infection should be disqualifying.

history of long-term decongestant use should

contraindication. Issues to be considered include

trigger a search for the cause of the congestion,

d

absence of seizures, presence of residual neurologic

and candidates should be warned about the dangers
of the chronic use of chemical agents while diving.

\

deficit,

and impairment of regional perfusion.

Ophthalmologic

Oral and Dental

Candidates should demonstrate adequate visual
acuity to orient themselves in the water and on a
boat. Corrective lenses, either fixed to the face

mask

•

Candidates must be able to be

fitted with

and hold

a scuba mouthpiece.
•

or soft contact lenses (which allow for gas

Where

there

is

a danger that trapped gas could get

under a tooth and rupture

transfer), are acceptable.
•

A

Diving after intracranial surgery should be evaluit

motility has returned to normal.

obstructive nasal lesions should be corrected before

dispose to decompression sickness).

•

membrane

nasal congestion are essential in diving.

regional perfusion abnormalities that would pre-

•

Barotitis should be disqualifying until all middle

Nose and Paranasal Sinuses

embo-

lism, or prior cerebrovascular accident (due to

arti-

cochlear implant should be disqualifying.

panic

neuropathy.

Any

externa should be dis-

ear inflammation and fluid have resolved and tym-

ated on an individual basis, as should peripheral

sciousness should be absolutely disqualifying. This

otitis

associated with vertigo should be disqualifying.

should be disqualifying. Herniated nucleus pulposis

•

recur.

Active ear infection should be temporarily dis-

ficial
(if

condition-

warning that the

qualifying until healed.

carry an increased risk of decompression sickness

of the lower back

may be

qualifying.

or
•

•

and the candidate

able to auto-inflate, he or she

it,

diving should not be

permitted.

Narrow-angle glaucoma, aphakia with correction,
motility disorder, cataract, and retinitis pigmentosa

•

Badly decayed or broken teeth should be

dis-

qualifying.

are relative disqualifications for diving; a skilled

Pulmonary

ophthalmologist should be consulted.
•

Because color vision

is

required for certain diving

tasks, deficiencies in color vision

may

•

Because any abnormality
tion

be dis-

rax, or

qualifying.

•

As

a prerequisite to diving, candidates

must have

tympanic membranes and be able to automiddle ear. Performing a Valsalva or
Toynbee maneuver can be used to indicate whether
the candidate can inflate his or her middle ear
(inability to do so predisposes to rupture of the
tympanic membrane or round window).
Tympanic membrane perforations should be disqualifying (an opening in the tympanic membrane
would allow water to get into the middle ear). If a
tympanic membrane rupture is completely healed
intact

7-2

be absolute disqualifications for diving:

— Bronchial asthma;
— History of traumatic or spontaneous pneumo— Previous penetrating chest trauma surgery of
the
—Chronic obstructive lung
including
—Active pneumonia or lung
and
disease with cavity formation.
— Mycotic

A

Long-term cigarette smoking increases the

^

thorax;

inflate the

•

pulmonary system func-

pneumomediastinum, the following condi-

tions should

Otolaryngologic

in

can cause arterial gas embolism, pneumotho-

or

chest;

disease;

infection,

active tuberculosis;

(fungal)

•

risk

of pulmonary complications while diving.

NOAA

Diving Manual

— October 1991

Diver and Support Personnel Training

•

All candidates should be given a screening chest x

ray to determine

if

•

Obesity increases the relative

risk of

developing

decompression sickness because of the decrease

they have a disqualifying lesion.

in

gas diffusion through adipose tissue.

Cardiovascular
•
•

Cardiovascular defects can be disqualifying because they predispose the individual to unacceptable risks. Conditions that should be disqualify-

— Cyanotic heart
coarctation of the
— Aortic
— Prosthetic heart
— Exercise-induced rhythm disorders,

Paralytic disorders should be relatively disqualifying.

disease;

stenosis or

basis.

Musculoskeletal
•

ing are:

Other endocrine abnormalities should be evaluated
on a case-by-case

•

Bone fractures that are incompletely healed and

aorta;

osteomyelitis that

is

actively draining should be

valves;

disqualifying.

including
•

disorders that manifest as paroxysmal tachycardias despite control with drugs;

— Heart block;
— Cardiac or pulmonary A-V shunts;
— Candidates with pacemakers should

ment should be
•

disqualifying.

Inadequate physical fitness

to

handle the physical

work of diving should be disqualifying.
be indi-

vidually evaluated and generally should be disqualified.
•

Deformities, either congenital or acquired, that
impair the candidate's ability to use scuba equip-

Obstetric and Gynecological
•

Coronary artery disease should be evaluated by

Pregnancy should be absolutely disqualifying because of the risk of bubble formation in the developing fetus during decompression.

an expert.
•

Peripheral vascular disease requires case-by-case
evaluation.

•

7.1.3

Candidates taking cardiovascular drugs (including

Skills

All applicants for diver training should perform the

blood pressure medication) should be evaluated

following

on a case-by-case basis. The use of beta blockers

snorkels and with confidence and good watermanship:

increases the risk of

swimming

exercises without face masks, fins, or

bronchospasm and suppresses
•

the stress response.
•

Swimming

•

case basis.

Swim 300
sidestroke,

Hypertension should be considered on a case-by-

yards (274 meters) using the crawl,
and backstroke

Swim under water

for a distance of

50 feet

(15.2 meters) without surfacing

Hematological
•
•

Leukemia
brosis

•

•

or pre-leukemia manifesting as myelofi-

7.1.4

and polycythemia should be disqualifying.

Anemia

relatively disqualifying

is

and requires

Intoxication that has caused

Scuba Training

Although

NOAA

certification program,

case-by-case evaluation.
•

Stay afloat for 30 minutes.

Sickle cell anemia should be disqualifying.

methemoglobinemia

has

its

own

NOAA

diver training and

personnel often receive

basic scuba training before they

become

NOAA

diver

candidates. Regardless of the training organization,

should be disqualifying.

however, there are basic practices and procedures that
Gastrointestinal
•

Any

disorder that predisposes a diver to vomiting

should be disqualifying (including Meckel's

should be included

•

Unrepaired abdominal or inguinal hernia should

•

be disqualifying.

Active peptic ulcer disease, pancreatitis, hepatitis,
colitis,

cholecystitis, or diverticulitis should be dis-

qualifying until resolution.

diet controlled.

October 1991

competence that

will

— NOAA

•

and

efficiently.

Diving procedures, particularly those of a lifesaving

Diabetes mellitus should be disqualifying unless
is

a level of

Divers who can respond to emergency situations
and make appropriate decisions when faced with
problems under water
Divers who can execute assigned underwater tasks
safely

Endocrinological
•

who reach

Divers

permit safe open-water diving

sickness).

•

any scuba training program. For

di-

verticulum, acute gastroenteritis, and severe sea

•

in

example, any diver training program should produce:

it

nature, should be overlearned to ensure automatic
response

Diving Manual

in

emergencies, which reduces the likelihood

7-3

Section 7

of the diver losing control and panicking (Bachrach

and Egstrom 1986).
Although training courses vary widely among organizations with respect to length, content, complexity,
and water skills required, all courses should include

surface-support requirements in vessel diving; and

water entry and
•

definition of tasks, selection of equipment, selec-

tion of dive team, emergency planning, special
equipment requirements, and setup and check out

both classroom sessions and in-water training. The
core of a training program for working divers should
follow the guidelines discussed in Sections 7.1.4.1 and

exit;

Operations planning: objectives, data collection,

of support platforms;
•

Principles of air diving: introduction to

decom-

pression theory, definition of terms, structure

7.1.4.2.

and

content of diving tables, single and repetitive div-

7.1.4.1

ing principles, practical decompression table problems (including decompression at altitude), and

Classroom

calculation of air supply requirements;

Classroom lectures using multimedia presentations
•

should be developed to provide the candidate with as

much knowledge

as possible.

It

is

important for the

ments; hand and line signals; recall; water emer-

candidate to develop a general understanding of diving

and the

principles and the diving environment,

Diving procedures: relationship of operations planning to diving procedures; warning signal requiregencies; buddy teams; tending; precautions required
by special conditions, e.g., pollution, restricted

self-

confidence (but not overconfidence) necessary to operate

visibility,

safely in the field.

Formal training courses are only the
becoming a safe and efficient diver. With

first

step in

this in

or flying after diving; dive station setup and post-

mind,

dive procedures; work procedures for search and

diver training should expose the trainee to a wide vari-

recovery; salvage and object lifting; instrument

ety of diving-related experiences in addition to teaching the basics. Details of various diving systems
ancillary

equipment

will

deployment and maintenance; and underwater navi-

and

gation methods;

be learned as part of on-the•

job training. Topics to which working and research
divers should be exposed during basic

currents; "dive safe ship" requirements;

boating safety; dangers of diving at high altitude

Accident prevention, management, and

and advanced

resuscitation
training include:
•

(CPR), use of oxygen

resuscitators,

development of accident management plans, recov-

Diving physics: pressure, temperature, density, spe-

ery of victims and boat evacuation procedures,

buoyancy, diving gases, the kinetic
theory of gases, and the gas laws and their practi-

lung overpressure, and "diver's colic"), the indi-

recognition of pressure-related accident signs and
symptoms, patient handling en route to treatment,
introduction to recompression chambers and treatment procedures, and procedures for reporting accident investigations (see Sections 18 and 19); and
Diving environment and hazardous marine life:
tides and currents (surf; thermoclines; arctic, temperate, and tropical conditions); waves and beaches;
rip currents; and river, harbor, and marine life

rect effects of pressure (decompression sickness,

hazards.

cific gravity,

cal application in diving;
•

first aid:

basic principles of first aid, cardiopulmonary

Diving physiology and medicine: the anatomy and

mechanics of circulation and respiration, the effects
of immersion on the body, hypoxia, anoxia, hyper-

•

capnia, hypocapnia, hyperpnea, apnea, hyperthermia,

hypothermia, the direct effects of pressure (squeeze,

gas embolism, inert gas narcosis, oxygen toxicity,

bone

necrosis), breathing gas contaminants,

drown-

near-drowning, overexertion, exhaustion,
breathing resistance, "dead space," and psycho-

ing,

logical factors
•

such as panic;

Equipment: selection, proper use, and care of
personal gear; air compressors and compressor systems; operation and maintenance; tank-filling

procedures; requirements for testing and inspection of specific types of

cylinders);
•

7-4

and

air purity

equipment (including scuba
standards and testing;

7.1.4.2

Pool and Open-Water

A

program of work in the water that progresses from
pool to protected open water and then to a variety of
open-water situations is essential to diver training.
Students should be exposed to open-water conditions
while diving at night, under conditions of reduced
visibility, and in cold water (see Section 10 for details
of diving under special conditions). An understanding
of the proper use of mask, fins, and snorkel; surface
swimming; surface

dives;

underwater swimming; pressure

and rescue techniques

Diving platforms: shore, small boat, and large vessel

equalization;

platforms; fixed structures; safety precautions and

skin (breath-hold)

is

required to master

and scuba diving.

NOAA

Diving Manual

— October 1991

Diver and Support Personnel Training

hazardous, and work-

Experience and experimental data have shown that

must be

the diver should be trained to maintain a reasonably

competent swimmers in excellent physical condition.
The skin diver is subject to barotrauma of the ears and
sinuses, just as any other diver is; however, air embolism and related complications are a problem only if
the skin diver breathes air from a scuba cylinder, a
habitat, or an underwater air pocket. Since breathholding can cause serious problems, divers should

constant respiration rate with a nearly complete inha-

Breath-hold or skin diving

is

ing and research divers using this technique

lation

and exhalation pattern. This slow deep-breathing

pattern permits good air exchange at relatively low
flow rates. Keeping the flow rate at lower levels results

more comfortable breathing; higher

in

respiration rates

can cause discomfort and anxiety (Bachrach and Egstrom
1986).

thoroughly understand the potential hazards of prolonged

breath-holding under pressure.
Specific skills to be learned in a pool and open-water

program should include but not be limited

7.1.5 Umbilical
Umbilical diving

Dive Training
is

to:

also referred to as surface-supplied

diving. In umbilical diving, the diver's breathing gas
•

Skin diving

is

supplied via an umbilical from the surface, which pro-

skills

— equalization of spaces
— mask clearing and equalization
— snorkel clearing
— proper use of buoyancy compensator
— proper use of weight belt (including how
ditch
— proper kicks with and without
—distance swimming with skin-diving gear
— water
and surface dives

vides the diver with an unlimited breathing gas supply.

air

Preliminary selection procedures and criteria for
umbilical dive training are essentially the same as
those for basic scuba. In

NOAA,

divers applying for

umbilical training must be certified as advanced working
to

it)

fins

which requires the completion of at least 100
logged dives. Before qualifying as umbilical divers,

divers,

trainees should receive instruction

and training

in:

full

entries

•

The general purpose and

limitations of surface-

supplied (umbilical) diving;
•

Skin diving confidence

•

drills
•

— recovery of mask,
and
—clearing the ears
—one-finned kicks over a distance
— snorkeling without mask
snorkel,

fins

system;
•

Lifesaving

lar tasks

skills

•

— search and recovery
— proper rescue
— rescue techniques with and
compensator
— rescue
— in-water mouth-to-mouth

Use of accessory

tools

and equipment basic

to

umbilical procedures and specific to the particu-

•
•

Use of masks and helmets;
Assembling and disassembling of the gas supply

•

being contemplated;

Methods of achieving intelligible communication;
Equipment repair and maintenance;
Water entry, descent, and ascent procedures and
problems.

entries

without a buoyancy

When

initial

training

is

completed, an open-water

qualification test that includes both general diving

carries

techniques and actual working procedures should be
artificial

resuscita-

given.

tion

Qualification Test
•

Skills involving the use of

scuba equipment

— sharing
— "ditch and don" exercises
— mask clearing
— regulator recovery and clearing
—emergency ascent
breathing
—
—scuba
— buoyancy control
— gauges and other special support equipment
— scuba rescues.
air

To pass the qualification
demonstrate the ability
•

test,

candidates must

to:

Plan and organize an air surface-supplied diving
operation to depths between 30 and 50 fsw
(9.1 and 15.2 msw), including calculation of hose
pressure and air requirements and instruction of
surface personnel;

station

entries

life

October 1991

— NOAA

Diving Manual

•

Demonstrate ability to rig all surface and underwater equipment properly, including air supply,
mask/helmet, communications, and other support
equipment;

7-5

Section 7

•

•
•

Demonstrate proper procedures of dressing-in and

Variable- Volume

dressing-out, using the particular pieces of equip-

— Suit
preparation, and maintenance
— Emergency procedures blowups, weighting,
buoyancy control
—Control of operational problems
— Hypothermia/hyperthermia
—Accessories
— In-water training
— Cleanup and decontamination after pollutedselection,

ment needed for the working dive;
Tend a surface-supplied diver;
Demonstrate knowledge of emergency procedures
(these

may

differ for

for

each project or exposure) as

determined by the instructor or dive master;
•

Participate in at least two practice dives, as described

below:

— Properly
(3

enter water that

is

at least

msw) deep and remain submerged

10 fsw

water dives

for at least

Contaminated-Water Diving Training

30 minutes, demonstrating control of air flow,
buoyancy, mobility, and facility with communi-

—Protective systems
— Donning and doffing
— Buoyancy
— Hyperthermia
—Training tender
— Work performance while
— Decontamination procedures.

cation systems.

— Ascend and leave water a prescribed manner.
— Properly enter water that between 30 and
in

control

is

50 fsw (9.1 and 15.2 msw) deep and conduct

as a

work-related tasks.

fully suited

After successful completion of this
tor should evaluate the diver's

test,

the instruc-

performance and estab-

phased depth-limited diving schedule

lish a

Dry Suit Training

to ensure

a safe, gradual exposure to deeper working depths.

7.1.7

Detailed descriptions of umbilical diving equipment

Mixed-gas diving involves the use of a breathing
other than air; this mixture may consist of
nitrogen-oxygen, helium-oxygen, or oxygen and one
or more inert gases.
The curriculum for NOAA's mixed-gas training program includes coverage of the following topics:

and

its

7.1.6

use appear in Sections 5.2 to 5.2.4.10.

Special Equipment Training

how to operate and maintain
and umbilical equipment, divers

In addition to learning
diver life-support scuba

medium

may be

called on to use special equipment in the performance of their duties. In such instances, new techniques and procedures must be learned from divers
who are already experienced in their use, from technical personnel (such as

Mixed-Gas Training

•

Oxygen

•

Nitrogen-oxygen breathing mixtures

•

Depth/time

•

Central nervous system and pulmonary oxygen

partial pressure limits

limits for

oxygen during working dives

manufacturers' representatives), or

by test and evaluation. Examples of types of equipment that are used by divers and whose use requires
special training are: variable-volume suits; thermal

toxicity
•

Nitrogen/oxygen breathing media mixing procedures

•

Analysis of mixed-gas breathing media

•

Mixed-gas diving equipment (open-circuit systems)

protection diving suits; protective suits, clothing, support equipment, and breathing apparatus for diving in
contaminated water; photographic/video equipment;
scientific equipment; and underwater tools.

Many
cial

•

•

NOAA
circuit

addressed include:
•

Nitrox

I

NOAA Nitrox decompression tables
NOAA Nitrox residual nitrogen table
NOAA Nitrox surface interval table.
NOAA mixed-gas trainees attend classroom
•

I

•

I

—Search and recovery techniques
— Wireless communications
—
objects
—Ships husbandry
systems
— Underwater
— Pinger/sonar
—Underwater

•

I

television

locators

tools

equivalent air depths for open-

scuba

Operational Diver Training

Lifting of

7-6

Nitrox I no-decompression limits and
group designation table for no-decom-

pression dives

training programs prepare divers to use spe-

equipment and protective clothing. The topics

NOAA

repetitive

and then progress

to

sessions

open-water dives, during which

they use a nitrox (68 percent nitrogen, 32 percent
oxygen) breathing mixture. Divers enrolled in a commercial diving mixed-gas course or those being trained

by their companies receive classroom and open-water

NOAA

Diving Manual

— October 1991

Diver and Support Personnel Training

training in the use of heliox (helium-oxygen) breathing mixtures.
in

Heliox

is

a widely used breathing

deep mixed-gas diving and

in

medium

saturation diving.

For example, water boils at a higher temperature
under water than on the surface: 262°F (128°C) at
50.5 feet (15.4 meters) and 292°F (144X) at 100 feet
(30.5 meters); cooking procedures must be altered,
tat.

because burned food not only constitutes a

fire

hazard

7.1.8 Saturation Training

but produces toxic gases at depth. (For additional infor-

Although the basic requirements for saturation diving are the same as those for surface-based diving, there

(1984).)

are

ration usually

is

"home base" during

satu-

either a seafloor habitat or a diving

system (see Section

bell

ration diver needs a

17).

A

that need to be addressed

some important differences

during training. The diver's

mation on underwater habitation, see Miller and Koblick

For

this reason, the satu-

fundamental reorientation

to the

slight loss in

speech

occurs as a

intelligibility also

atmosphere

result of the denser

at depth.

The amount

of speech distortion depends on the habitat breathing

mixture and the depth. Other factors directly affecting the saturated diver or a habitat diving

program

environment. For example, the saturation diver must

include: the necessity to pay special attention to per-

constantly be aware that returning to the surface will

sonal hygiene, e.g., to take special care of the ears and

complicate, rather than improve, an emergency situa-

Because of the high humidity encountered in
most habitats, the growth of certain pathogens and
organisms is stimulated and recovery is prolonged.
Proper washing, drying, and care of diving suits is

This factor has specific implications with respect

tion.

to the selection

and use of certain pieces of saturation

diving equipment. For example, in saturation diving:

skin.

essential to prevent skin irritation or infections. Trainees
•

Weight

belts without quick-release

mechanisms

or weight harnesses should be used;
•

Buoyancy compensators with

to the use of toxic materials in a

oral inflation tubes

rather than a cartridge or tank inflation system

should be used;
•

A

for the repair of

when umbilical equipment

is

utilized;
filling

scuba

cylinders to avoid admitting water into the valves.

Because the consequences of becoming lost are so
program also should
include training in underwater navigation techniques.
serious, a saturation diving training

lines, string

highways, ripple marks,

suits)

and aerosol sprays.

should teach divers the procedures for making

ascending and descending excursions from the storage
depth. Special diving excursion tables have been

developed for excursions from the saturation depth.
These tables are designed to consider storage depth,
oxygen dose, nitrogen partial pressures, and other facTrainees should become familiar with these tables

tors.

and

their limitations.

A

Divers should be instructed in the use of navigational

such as grid

wet

Training for saturation diving from underwater habi-

in tropical regions;

backup breathing gas supply should

Extra precautions must be taken when

aids,

to the

use of scientific preparations but also to the use of

tats
self-contained

be used
•

closed-environment

system such as a habitat. This applies not only

normally harmless things such as rubber cement (used

Adequate diving suits should be worn because the
extended diving time involved in saturation may
cause chilling even

•

should be aware that there are restrictions with respect

unique feature of saturation diving

ability to

make upward

is

the diver's

excursions. However,

upward

topographical features, and navigation by compass.

excursions constitute a decompression, and divers must

Because compasses are not always accurate, divers
should be trained to use the compass in combination
with topographical and grid line information.
Training in habitat operations, emergency procedures,
and local diving restrictions usually is conducted on
site. Such training includes instruction in: communi-

be careful to remain within the prescribed excursion

cation systems; use of special diving equipment; habi-

resist

tat

support systems; emergency equipment; regional

topography; underwater landmarks; navigational grid

systems; depth and distance limitations for diver/
scientists;

This applies not only to the divers themselves

limits.

but also to certain types of equipment; for example,

camera

is

opened and reloaded

in a habitat,

if

a

an upward

excursion of 10 to 15 feet (3.0 to 4.6 meters) can cause
flooding because such equipment

is

not designed to

internal pressure. Students should be instructed

check all equipment to be used in a habitat to determine whether it is designed to withstand both internal
and external pressures.
to

and operational and safety procedures used

by the surface support team.

Other features related
need

to

to seafloor habitation also

be identified during saturation training.

Some

of these relate to housekeeping chores inside the habi-

October 1991

— NOAA

Diving Manual

7.1.9

Chamber Operator

Training

The operation and maintenance
chambers are

of recompression

a necessary part of a diving

program;

it

is

7-7

Section 7

therefore important to ensure that

all

personnel oper-

As an

often not practical.

is

(DMT)

alternative, a Diving

ating recompression

Medical Technician

include the following topics:

emergency medical
situations and can also communicate effectively with a
physician located at a distance from the diving site

chambers are properly trained
and certified as chamber operators.
A training program for chamber operators should

•

Introduction to hyperbaric chambers;

•

Chamber

trained in the care of

diving casualties can be assigned to the

The development

— Pre- and post-dive procedures
— Plumbing
— Controls
— Life-support and emergency procedures
— Breathing and communication systems
— Maintenance procedures

in-

of

emergency medical service

organizations began in the United States in the mid1970's in response to the need for improved national

emergency medical
fic

care.

The National Highway

Traf-

Safety Administration of the Department of Trans-

portation developed and implemented a

program to
Emergency Medical Technicians (EMT's) at vari-

train

ous levels of certification. These services, coordinated

Recordkeeping;

by the Department of Transportation, are offered and

Introduction to the physics of pressure;

Decompression theory and calculation of decompression tables;

Recompression theory and treatment

managed

at the state level.

Courses

in

various aspects of emergency medical

American
American Heart Association, and local
fire and rescue groups. Individuals successfully completing these courses are certified by the sponsoring
agency as having fulfilled the course requirements.
care are offered by organizations such as the

tables;

Red

Barotrauma;

Examination and handling of patients;
Emergency management of decompression
and air embolism;

sickness

Cross, the

may

Courses

lead to different levels of certification,

Inside tending procedures;
kit

national, state, local, or regional,

e.g.,

contents and use;

Review of case histories;
Hands-on experience with simulated treatments;

Chamber

An

(see Section 19.6.1).

setup and subsystems;

Chamber medical

site.

dividual so trained can respond to

and thus may

reflect different levels of proficiency.

In the late-1970's, the need for medical technicians

emergency treatment of diving caswas recognized; this specialized need arose

specializing in the

operation procedures.
ualties

because existing

EMT

training programs were heavily

oriented toward urban ambulance-hospital emergency

TRAINING OF DIVING SUPERVISORS

7.2

Many

organizations, including

NOAA,

the Navy, and

commercial diving companies, designate certain experi-

enced divers as supervisors.

NOAA

has four supervi-

sory diving categories: Line Diving Officer, Unit Diving Supervisor, Diving Instructor,

Each organization provides

and Divemaster.

training that

is

specifi-

cally related to the goals of the organization; however,
all

diving supervisors are required to have a broad

range of diving experience. In addition, every supervisor

must have the working knowledge

projects, oversee diving activities,

to plan diving

conduct inspections,

and investigate accidents. Diving supervisors receive
advanced training in dive planning, the use of special
equipment, first aid, communications, and accident
management.

systems.

The

medical technicians

interest in diving

grew with the development of offshore

oil

and gas

well drilling platforms. Experts decided that the most

workable solution to

this

need was

to cross-train

work-

ing divers as medics rather than to train medics to

working
by economic considerations, since using a diver as a medic
made it unnecessary to have a person standing by. The
National Association of Diver Medical Technicians
(NAMDT) was founded in 1981 and, by 1985, a number
of training organizations were approved to provide
DMT training. NOAA has adopted DMT training for
its medical personnel and has a representative on the
NAMDT Board of Directors.
The approved DMT training program is an extensive
303-hour course and includes training in the following
treat diving casualties. This choice to train

divers as medical technicians

was

also driven

areas:

7.3

DIVING MEDICAL TECHNICIANS

Although there are obvious advantages

in

Lecture (158 hours)

having

a qualified hyperbaric physician at a diving site, this

7-8

•

orientation,

anatomy, medical terminology, legal

problems

NOAA

Diving Manual

— October 1991

Diver and Support Personnel Training

support, shock, use of oxygen

ing casualties has increased.

In response to this need,

•

basic

•

systemic diseases and injuries

several organizations offer specialized training.

•

medical, environmental, thermal, diving, and de-

courses range from a series of lectures to more inten-

compression aspects

sive courses lasting several weeks.

•

equipment

•

life

handling, emergency com-

use, patient

drugs and fluids

Society, Inc., which

One

•

animal laboratory (optional)

the

is

located

in

of the most respected and comprehensive train-

gram offered by

autopsy (optional)

•

diving treatment, neurological examination

•

chamber operations

NOAA.

Started

the 3-week pro-

is

in

1977 with finan-

support from the Department of Energy and the

cial

•

hyperbaric

Bethesda, Maryland.

ing courses in hyperbaric medicine

and care, suturing

patient assessment

is

in

Undersea and Hyperbaric Medical

medicine

•

best source of

information on the availability of courses

munications

Laboratory and Practical Experience (115 hours)

The

These

cooperation of the U.S. Navy, this program has trained

The course

over 269 physicians to date.

includes train-

ing in the following areas:

Clinical Observation (30 hours)
•

mixed ambulance/emergency room experience.

DMT

training

may

based on the

number

but includes a
it

is

EMT

Level

I

diving physics
basic diving physiology

Program

fundamentals of

of important additions. Because

stress physiology

be hours or even days before medical help

oxygen toxicity

emergency diving situation, the DMT
must be capable of delivering more advanced support

arrives in an

than a medical technician

DMT's

ingly,

in

mothorax

air

an urban area. Accord-

saturation diving

commercial diving equipment
decompression tables

pneu-

stabilization, simple suture techniques,

embolism

vestibular problems related to diving

receive training in parenteral drug

administration, intravenous infusion techniques,

exchange
and behavior

inert gas

and

decompression sickness and treatment

other special procedures.

DMT's must

helium-oxygen tables and recompression treatment

be recertified every 2 years and must

attend 24 hours of lectures and serve 24 hours

in

recompression chamber operation and safety

an

procedures

ambulance/emergency room situation to maintain their
certification. Serving under the diving supervisor, the
trained DMT brings enhanced diagnostic and clinical
skills

to medically

DMT's

gas analysis systems
pressure exposures

and geographically remote worksites.

also have the ability to

orientation to the national Divers Alert

received from medical specialists belonging to organi-

Network (DAN)

Network

basics of diving accident

though these experts are
geographically distant from the scene of the diving
(see Section

recompression chambers

emergency treatment of diving casualties

implement expert advice

zations such as the national Divers Alert

in

hyperbaric oxygen therapy

19.6.1), even

management

case histories of diving accidents and treatment

polluted-water diving

accident or

illness.

treatment of near-drowning victims

7.4

A

evaluation and assessment of scuba diver injuries

HYPERBARIC PHYSICIANS

hyperbaric physician

cial training in the

is

and

illnesses.

a medical doctor with spe-

treatment of medical problems

Physicians trained

in

hyperbaric medicine are an

related to diving and/or elevated atmospheric pres-

important resource for the diver. Every diver should

Such a physician may be a general practitioner or a
specialist in any branch of medicine. In many cases,
the personal impetus to become an expert in hyperbaric
medicine derives from the fact that the physician is
also a diver. Historically, the U.S. Navy and U.S. Air
Force have been the primary sources of expertise and

learn the

sure.

trained personnel in hyperbaric medicine.

Because of the increase

in

the

October 1991

— NOAA

Diving Manual

cian

in his

of divers,

to treat div-

or her area. In the event of a diving accident

related to pressure, such as an

sion sickness,

it

is

essential to

embolism or decompreshave located a physician

trained in hyperbaric medicine before beginning the

Hyperbaric chambers are described in Section
and the treatment of diving casualties is discussed
dive.

number

however, the need for physicians trained

name, address, and phone number of the
nearest hyperbaric facility and/or hyperbaric physi-

6,
in

Section 20.

7-9

Section 7

7.5

RESEARCH DIVERS

Research diver training

number
tories.

is

offered by

NOAA

and

a

and the success of scientific diving are maintained
(American Academy of Underwater Sciences 1987).

of educational institutions and marine labora-

Although the course content and

style differ

Selection

7.5.1

with different organizations, the objective of such courses
is

either to train experienced divers in scientific tech-

niques and methods to enable

them

ter scientific technicians or to train
tists

to act as

underwa-

experienced scien-

the techniques and methods of underwater work.

in

In either case, the curriculum should include

advanced

instruction in diving physiology, uses of underwater

equipment, and a review of the potential hazards faced

by

Selecting individuals for research diver training
depends on the objectives of the particular course. The

acceptance of individuals for such training should be
based on need, academic background, personal moti-

and the

vation,

ability to pass certain

fitness requirements.

mon

If possible,

swimming and

individuals with

com-

objectives should be grouped together and trained

in a single class.

divers.

Each of these

Selection criteria should require research diverfactors should be related to the prob-

candidates to demonstrate evidence

of:

lems faced by diving scientists and their impact on the

conduct of underwater investigations. Diving safety
should be emphasized throughout the course so that on

•

Diver certification from a recognized organization

•

Satisfactory completion of a physical examination

completely com-

•

to concentrate their

•

Good
Need

energies on the work or scientific tasks at hand. This

•

Training

degree of competence can be achieved only

•

Training or equivalent experience
methods

completion of training the divers
fortable in the water

feel

and are able

if

the basic

diving skills are learned so thoroughly that routine

become

operations and responses to emergencies

•

physical condition
for the specialized training
in the basics of first aid,

Ability to pass diving and

CPR

including

swimming

in

research

skill

tests to

the satisfaction of the examiner.

automatic.

University research diver training programs have
historically lasted for a

minimum

of 100 hours and

Research divers must be comfortable

in the

water and

required candidates to complete 12 open-water dives.

know their limitations and those of their equipment.
To accomplish these ends, a series of pretraining tests

Admin-

are used to predict likely success in the diving envi-

In

1984, the Occupational Safety and Health

istration
in

(OSHA), which had promulgated

regulations

1978 governing commercial diving operations, spe-

exempted from these regulations those scienand educational diving programs that could meet
certain requirements. A research organization or
educational entity wishing exemption from the Federal OSHA standard must have in place a diving program that has developed a diving manual, has a diving

ronment. The following phases are included

in the

pretests:

cifically
tific

control officer

Phase

fins,

1.

2.

to fulfill

these requirements for exemption was originally de-

The

become

new

and

certification procedures. Individuals or organizations

wishing information about scientific diving programs

Academy

or snorkel

and

in the following

sequence:

Perform a 75 foot (22.9 meter) underwater swim

Perform a 1000 foot (304.8 meter) swim on the

Perform a 150 foot (45.7 meter) underwater swim,
surfacing for no more than 4 single breaths during the swim.

community

reflects the effectiveness of current diver training

completed within a

or side stroke.
3.

available.

safety record of the research diving

to be

surface in less than 10 minutes, using the breast

veloped at the Scripps Institution of Oceanography in
technologies and techniques have

is

on a single breath.

procedures for emergency diving situations. The pro-

the 1950's and has been updated since then as

— Swimming Pool

15-minute period and should be done without mask,

and diving safety board, and has developed

gram used by many research organizations

1

This series of activities

The 75

underwater swim simulates
emergency ascent, except that
the exhaling is omitted. The 1000 foot (304.8 meter)
surface swim simulates a swim back to the beach. The
foot (22.9 meter)

a 75 foot (22.9 meter)

Underwater
Sciences (947 Newhall Street, Costa Mesa, California
92627). As a result of the combined experience of

single breaths, simulates surf passage,

scientific diving organizations, a set of standards has

to

been developed

before the next wave.

should contact the American

7-10

of

to ensure that the high level of quality

150 foot (45.7 meter) underwater swim, surfacing for 4

where one has
surface, take a breath, and get back under water

NOAA

Diving Manual

— October 1991

Diver and Support Personnel Training

The candidates are then required

to

swim 75

Operational planning, including diver supervision,

feet

scheduling, and emergency plans;

(22.9 meters), dive to the bottom of the pool, recover,

and tow a person of similar

size

75 feet (22.9 meters).

First aid, including

CPR;

Diving accident management procedures;

Phase 2

— Open-Water Test
open-water swim involves
(304.8 meter) open-water swim and a dive

An ocean
1000 foot

or other

Underwater navigation and search methods, includmethods of locating, marking, and returning to

ing

a

research

to

sites;

the bottom in a depth of at least 15 feet (4.6 meters).

Collection techniques, including introduction to

This open-water exercise often reveals potential problems

sampling, testing, and harvesting systems, tagging,

that are not apparent

swimming

The

pool.

those screened by
Institution of

when

the candidate swims in a

diver training success rate

means of these two

tests at the

preserving, transporting of specimens, and data

among

recording methods;

Photographic documentation, including the use of

Scripps

Oceanography has been nearly 100

per-

cent (Stewart 1987).

7.5.2

for scientific investigations.

Curriculum

Research diver training should cover dives conducted

many

in as

different environments as possible. Addi-

tionally, students

should gain experience using a vari-

ety of different platforms, such as small boats, ships,
piers, docks,

and

jetties,

and should make water

entries

The curriculum should be

tailored to the local area

and the particular needs of the researcher. However,
the following outline identifies topics that are usually

•

A

in a

practical scientific diving course:

review of diving physiology and physics as they

relate to field operations;
•

Surface-supplied diving techniques, including
tending, communications, capabilities of surfacesupplied diving systems, and emergency procedures;

•

Small boat handling, including the uses and limitations of small craft as diving platforms, load
limits

and distribution, securing procedures, minor

field repairs,
•

•

legal responsibilities;

and securing of research equipment

Environmental hazards, such

as:

Training

element

equipment maintenance is an important
any diving program. Although fatal diving

accident statistics show that equipment failure

issuance of visual cylinder inspection stickers

The cylinder

inspection course covers the following

in the water;

diving

in

currents,

•

Reasons

•

Frequency of inspection;

wrecks, and under con-

for cylinder inspection;

•

Types of inspection;

•

Analysis of cylinder structure and accessories;

•

Criteria of inspection, e.g., wall thickness, material

and valve specifications;

Evaluation of cylinder interior and exterior;

Use of inspection equipment,

Thermal protection problems, including the use of
wet suits, variable-volume dry suits, and hot water
suits, and the advantages and disadvantages of

•

hardwire, and acoustic and diver recall systems;

— NOAA

Diving Manual

lights,

probes,

Detailed inspection sequence (this

is

an 18-step

process describing each step of a cylinder inspection);

Diver communication, including diver tending,

e.g..

flushing solutions;

each;

October 1991

The

tightly

is

controlled.

•

in

rarely

the course are certified as cylinder inspectors.

ditions of limited visibility;

and

is

ience, and premature dive termination. Only trained
and qualified personnel should perform maintenance
and repair of diving equipment, especially regulators,
scuba cylinders, and other life support systems.
NOAA and other organizations have instituted a
training and certification program for scuba cylinder
inspectors. The objective of these programs is to ensure
that uniform minimum inspection standards are used
at diving facilities. People who successfully complete

•

as caves, under ice,

•

in
in

the cause of death (see Section 19.2), equipment mal-

polluted water, blue water, restricted areas such

•

EQUIPMENT MAINTENANCE

topics:

Equipment handling, including safe use, field maintenance, and storage of diving and scientific
equipment;
Underwater rigging, including emplacement, moving,

•

and

7.6

function does cause near-misses, lost time, inconven-

under as many shore conditions as practical.

addressed

video, movie, and time-lapse photography

still,

•

and

The inspection

of a

minimum

of 10 cylinders under

the supervision of an instructor.

7-11

«

«

Page

SECTION

8

8.0

General

8-1

WORKING

8.1

Surface-Supplied Diving Procedures

8-1

DIVE

8.1.1

Planning the Dive

PROCEDURES

8.1.2

Selecting the Dive

8.1.3

Dressing the Surface-Supplied Diver

8-3

8.1.4

8-4

8.1.6

Tending the Surface-Supplied Diver
The Dive
8.1.5.1
Diver Emergencies
Ascent

8.1.7

Post-Dive Procedures

8-8

8.1.8

Umbilical Diving From Small Boats

8-8

8.1.9

Basic Air Supply Systems

8-9

8.1.5

8.2

Rates of Air Flow
Supply Pressures
Search and Recovery

8.4

8-2

8-4
8-5

8-7

8.1.10

8-9

8.1.1

8-10
8-10

8.2.1

Circular Search

8.2.2

Arc Pattern

8.2.3

Jackstay Search Pattern

8-13

8.2.4

Search Using a

Tow Bar

8-15

8.2.5

Search Without Lines
Recovery

8.2.6

8.3

8-1

Team

8-12

(Fishtail)

Search

Underwater Navigation
Underwater Tools

8-13

8-16
8-16

8-16
8-18

8.4.1

Hand

8.4.2

Pneumatic Tools

8.4.3

Hydraulic Tools

8-20

8.4.4

Electric Tools

8-21

8.4.5

Power Velocity Tools

8-21

8.4.6

Cutting and Welding Tools

8-22

8-18

Tools

8-20

8.5

Maintenance and Repair Tasks

8-23

8.6

Instrument Implantation

8-23

8.7

Hydrographic Support

8-24

8.7.1

Hazards

8-24

8.7.2

Locating and Measuring Least Depths

8-25

8.7.3

Resolving Sounding Discrepancies

8-25

to

Navigation

8.8

Wire Dragging

8-25

8.9

Salvage

8-26

8.10

8.11

8.12

8.9.1

Lifting Devices

8-26

8.9.2

Air Lifts

8-27

Diving

From an Unanchored Platform

8-27

8.10.1

Liveboating

8.10.2

Drift Diving

8-30

Underwater Demolition and Explosives
Underwater Photography

8-31

Photography

8-33

8.12.1

Still

8.12.2

8.12.3

8-33

8.12.1.1

Lenses and Housings

8-33

8.12.1.2

Light and Color

8-34

8.12.1.3

Selection of Film

8-38

Time-Lapse Photography
Motion Picture Photography
8.12.1.4

8.13

8-28

8-41

8-42

8.12.2.1

Selection of Film

8-42

8.12.2.2

Procedures

8-42

Special Procedures

Underwater Television

8-44

8-44

«

i

WORKING
DIVE

PROCEDURES
GENERAL

8.0

depths that do not require

to shallower

This section describes some of the techniques and procedures used by scientific and academic divers engaged

in

underwater objects,

routine underwater

of choice for underwater

ment of various types

to

supplied

air.

This

mode

is

8.1.1

also called umbilical diving.

may

in detail.)

of any dive depends on careful pre-dive

SURFACE-SUPPLIED DIVING

planning, which must consider the goals of the dive,

PROCEDURES

the tasks involved in achieving these goals, environ-

The surface-supplied

NOAA

by

5

Planning the Dive

The success
8.1

a lightweight diving outfit

describes diver and diving equip-

be used. (Section

work operations. The diving mode
work that requires the diver
remain submerged for extended periods of time is

maximum

protection from pollution, temperature extremes, or

gives

them

mental conditions (both surface and subsurface), the

air diving

mode

is

widely used

divers and by diver-scientists because
the flexibility they need to perform

it

many

different underwater tasks. In surface-supplied div-

breathing mixture

ing, the diver's

surface by

means

is

supplied from the

of a flexible hose; thus, divers using

mode have a continuous breathing gas supply.
The surface-supplied mode is generally used when

this

divers need to remain under water for an extended
period of time to accomplish the dive's objectives.

The

advantages of surface-supplied diving over scuba diving are that

it:

personnel needed to carry out the dive, the schedule for
the dive, the equipment needed to conduct the dive
safely and efficiently, and the availability of emer-

gency assistance. Figure 8-2 is a checklist that can be
used to evaluate environmental conditions that may
affect the dive.

For every surface-supplied dive, the dive supervisor
should complete this checklist (or one adapted to the
specific conditions of a particular dive) before decid-

and equipment needs. Different environmental conditions affect members of the dive team

ing on personnel

differently.

For example, divers are generally not affected

by surface waves except when entering or exiting the

•

provides greater safety;

•

permits dives to greater depths;

water; however, divers operating in very shallow waters,

•

permits divers to stay on the bottom for longer

in surf, or in

periods;

by wave action

•
•

•

provides thermal protection

(if

exceptionally large waves can be affected
at the surface.

Air temperature and wind conditions at the surface

diving in cold water);

may have

a greater effect

on the tender and other

permits communication between the diver and the

also

surface; and

surface support personnel than on the diver, because
these individuals are

provides an unlimited air supply.

Another advantage of the surface-supplied mode
that

it

surface conditions.

platforms, including piers, small boats, barges, and

The disadvantages of this mode, compared with
the scuba mode, are: (l) that the umbilical diver's
mobility and operational range are restricted by the
length of the umbilical; and (2) that a large amount of
ships.

equipment is required to support umbilical diving.
Surface-supplied diving gear includes both deepsea and lightweight equipment. When a diver-scientist
needs maximum protection from the physical or thermal environment or when the dive is deep (i.e., to
190 fsw (57 m)), the deep-sea diving outfit shown
Figure 8-1 is the diving dress of choice. For dives

October 1991

— NOAA

Diving Manual

more exposed than the diver to
is important to remember, how-

is

can be undertaken using a variety of support

in

It

ever, that the surface

crew should be able

to operate

with maximal efficiency throughout the dive, because

reductions

in

the performance of topside personnel

could endanger the diver.
Visibility at the surface

can affect the performance

and safety of the diver and the surface crew. For example, a diver surfacing under low- or no-visibility conditions

might not be able

to find the support craft.

The underwater environment can influence many
aspects of a dive, from crew selection to choice of
diving mode. All diving operations must consider:
•

depth;

•

bottom type;

8-1

^

Section 8

Figure 8-1

Surface-Supplied Diver
in Deep-Sea Dress

Helmet
Assembly
Adjustable

ill

Exhaust
Valve

.Jocking Harness

Air

/ Yvr^^rlrfu". ^^Front

Communication

Jocking
Strap

W

Hip Weight
>

—

Pocket

-i

Whip

Whip

Rear Jocking
Straps

iv*'

^S ii^^oidS.
P

Thigh Weight
Pocket

Umbilical

Dry Suit

Thigh Retainer

•Crotch
Jocking
Strap

Calf Weight

Pocket

,

Calf Retainer

Boot Safety
Straps

Boots

Source:

US Navy (1988)

•

temperature of the water;

ocean, and tidal currents vary with such factors as the

•

underwater

and

•

tides

time of year, phase of the tide, bottom conditions,
depth, and weather.
Underwater visibility and water temperature also have a

visibility;

and currents.

In addition, the presence of contaminants in the water

underwater obstacles, ice, or other
unusual environmental conditions can affect planning
for some dives.
Dive depth must be measured using two different
methods before the dive begins. To obtain an accurate
(see Section

11),

depth profile of the area of the dive, a series of depth

measurements must be plotted. Methods of measuring
depth that may be used include lead line sounding,

pneumofathometer, high-resolution sonar, or shipmounted fathometer. Depth readings on maps or charts
are useful for general screening purposes but are not
sufficiently accurate to

be used to measure dive depths.

Samples should be taken of the bottom
area of the dive; in
tions

some

in the general

instances, in-situ observa-

and

visibility

underwater conditions

in

major U.S. geographi-

cal regions, see Section 10.1.

8.1.2 Selecting

The

the Dive

size of the

Team

team needed

for a surface-supplied

number of divers on the dive team,
the type of equipment available, the dive's safety
dive depends on the

requirements, environmental conditions, dive depth,
dive mission, and the surface support platform availa-

The optimal number

of dive team personnel for a
and complex surface-supplied dive is six: a dive
supervisor, diver, standby diver, tender, standby tender, and timekeeper/recorder. If all members of the
team are fully trained, a job rotation system can be
ble.

large

can be made before the dive. Bottom conditions

affect a diver's mobility

major influence on dive planning. For a detailed description of

under water; a

maximum mobility, and the diver's
stir up so much sediment that visi-

used that permits

team members

all

sandy bottom allows

ing as divers; this approach allows for

movements do not

working time and

By comparison, working in an area
muddy and silty bottom can be dangerous, because
diver may become entrapped in the mud and usu-

bility is restricted.

with a
the

8-2

ically efficient.

The

dive supervisor

is

responsible for planning,

in a

aid supplies are available, conducts pre-dive briefings,

the surface-supplied scientist-diver

The

in-water

direction and velocity of river,

visibility.

Currents must be considered in dive planning, whether

river or the ocean.

maximum

thus both logistically and econom-

managing all dive operations; the dive
supervisor remains at the surface at all times. This
individual also determines equipment requirements,
inspects the equipment before the dive, selects team
members, ensures that emergency procedures and first

ally generates sufficient silt to interfere substantially

with

is

to take turns serv-

is

working

organizing, and

NOAA

Diving Manual

— October 1991

Working Dive Procedures
Figure 8-2
Predive Environmental
Checklist
her diving gear

complete,

good repair, and ready
must know both line pull
signals and voice signals and must respond to and
comply with instructions from surface personnel.

Surface

is

in

for use. In addition, all divers

Atmosphere

Sea Surface

Visibility

Sea State

Wave

Sunrise/Set

Moonrise/Set

Temperature

(air)

Humidity

The standby

Action:

is

required for

Height

Length

bility of the

size.

It

surface-

all

the responsi-

is

standby diver to be ready to provide
emergency or backup support to the diver any time the

diver

Current:

in

is

the water.

The tender

Direction

Precipitation

standby

supplied operations, regardless of

Direction

Barometer

must be as well trained and quali-

diver

fied as the diver; a

the

is

member

of the surface team

who

is

Cloud Description/Cover

Velocity

responsible for tending the diver while the diver

Wind

Type

the water. Every diver in the water must have a tender.

Direction/Force

Other:

Water Temperature

_

•

checks the diver's equipment;

•

checks the

•

dresses the diver.

Local Characteristics

Subsurface

Once
Visibility

Depth

Underwater:
degrees

depth

at

degrees

at

depth

degrees

at

depth

degrees

at

depth

feet at

depth

feet at

depth

in the water, the

tender takes care of

line.

In addition, the tender maintains

supervisor informed of the diver's progress. All ten-

On complex

dives, a standby tender

The standby tender should be
and should be instructed
It is

in all

may

be needed.

fully trained as a diver

of the required duties of

the standby tender's job to be ready to

tender or to replace him or her at any time.

The timekeeper may be dedicated

Obstructions:

depth

at

on the

assist the

depth

at

is

the tender.

Bottom Type:

Thermoclines:

is

ders should be fully qualified divers.

depth

Bottom

bottom

the diver

communication with the diver and keeps the diving

feet at

feet at

and

air supply;

the diver's lines to ensure that no excess slack or tension

Water Temperature:

to

keeping the

diver's time during the job or, on dives involving a

Current:

limited

Direction

Marine

Source

number

of dive

involve keeping an accurate record of dive

sibilities

Pattern

times and noting
dive.

Other:

Tides:

High Water
Low Water

Ebb Direction

On some

all

of the important details of the

dives, the dive supervisor acts as the

timekeeper.

time
/

team members, the tender may
The timekeeper's respon-

also serve as the timekeeper.

Life:

Velocity

time

Velocity

Flood Direction

_ Velocity _

8.1.3

Dressing the Surface-Supplied Diver

Surface-supplied divers use either a diving
Adapted from US Navy (1988)

a helmet,

monitors the progress of the dive, debriefs the divers,
prepares reports of the dive, and checks equipment and
diver logs at the completion of the dive.
diver(s)

must be qualified and trained

in the

equipment and diving techniques needed for the dive.
During the course of the dive, the diver must keep
surface personnel informed of the progress of the dive,
bottom conditions, and any problems (actual or potential).

Every diver

October 1991

is

responsible for ensuring that his or

— NOAA

Diving Manual

mask

or

and the supervisor and diver must decide

whether a dry

The

in

Before the diver enters the water, the tender:

Visibility

Underwater and Bottom

is

suit,

wet

suit, or

bathing suit

is

appro-

priate for a particular dive. Factors to be considered

when making

these choices include:

•

Personal preference;

•

Depth of the planned dive;
Nature of the work to be performed;

•
•

Length of the planned dive;

•

Environmental conditions (temperature of the water,
speed of current, underwater visibility, etc.); and

•

Condition of the water,

i.e.,

polluted or clean.

8-3

Section 8

Figure 8-3
Lightweight Surface-Supplied

Mask
The dressing procedures followed by the diver and
depend on the type of dress selected

or her tender

his
Steady Flow
Valve (defogger)

for

the dive.

At

least

one tender

assists in dressing a diver

wear-

ing a lightweight surface-supplied diving system (dry
suit) or a

wet

suit. If

a dry suit

is

to

be worn, the diver

applies a lubricant to the suit's zipper

and then, while

seated, inserts his or her legs into the suit.

The

diver

then stands and works both arms into the suit's sleeves.

The tender holds the breech ring while the diver
performing these procedures. Then the tender:
Wraps

is
'Dial-a-Breath"

"Adjustment knob

the harness chest strap tab around the left

shoulder strap and presses

it

into place;

Pulls the crotch strap to the front

and fastens the

weight belt latch;

Adjusts the waist belt and shoulder straps and
Waterproof

secures both rear jocking straps;
Inserts thigh

Communication
Connector

and calf weights and secures the

(Male)

thigh and calf restrainers;

Ensures that

air is available to the

the air supply valve

is

helmet and that

Source:

US Navy (1988)

opened;

Lowers the helmet into place on the diver's head
and aligns it with the lower breech ring lugs;
Presses the quick-release locking pins, slides

them

and ensures that all pins are locked;
Positions the umbilical and whips under the diver's
left arm and secures them;
Performs a communications check; and
into place,

stage or ladder.

diver and to prevent a

As

a

hand on

fall.

the diver enters the water, the tender pays out the

umbilical at a steady rate, being careful to avoid sharp
edges. Throughout the dive, the tender

out of the

Establishes the appropriate air flow.

The tender must always keep

the diver's lifeline close to the helmet to steady the

line; at

the

must keep slack
same time, the tender must be

careful not to pull the line taut. Maintaining approxiIf a

a

lightweight

mask (Figure

wet suit or bathing

suit,

8-3)

is

to be

used with

dressing procedures are

simpler than those described above. For divers wearing
a wet suit or a bathing suit, the tender assists the diver
to

perform the following

steps:

•

Don

•

Place the lower breech ring with neck

the harness;

dam

over the

mately 2 or 3 feet (0.7 to 1 m) of slack on the line
permits the diver the right degree of freedom and
prevents him or her from being pulled off the bottom

by currents or by the movement of the support craft.
Too much slack in the line interferes with effective line
communication between the diver and tender and
increases the likelihood of line fouling.

Throughout the

diver's head;
•

Secure the ring to the jock strap; and

•

Place the helmet on the diver's head and secure

any

line-pull signals

Figure 8-4 shows a surface-supplied diver dressed and
in a

wet

from the diver.

If

an intercom

it.

system
ready to dive

dive, the tender continuously observes

the descent line and monitors the umbilical to receive

suit.

is

not in use, the tender periodically signals the

diver (using line pulls) to ensure that the diver's condifails to respond to two pull
must be treated as an emergency
and the dive supervisor must be notified immediately.

tion

is

good. If the diver

signals, the situation

8.1.4

Tending the Surface-Supplied Diver
is the dive team member in closest com-

The tender

munication with the diver during the dive. Before the
dive begins, the tender checks the diver's diving dress,

paying particular attention to the valves on the helmet,
the helmet locking device, the helmet seal, and the
harness.

The tender then

dresses the diver and helps

the diver to position himself or herself on the diving

8-4

8.1.5

The Dive

Once

the diver

is

dressed and ready for the dive, the

tender helps the diver to prepare for water entry.

The

entry technique used depends on the staging area or

type of vessel involved

in

the operation. If a stage

used for diver entry, the diver should stand or

NOAA

Diving Manual

sit

is

squarely

— October 1991

Working Dive Procedures
Figure 8-4

Surface-Supplied Diver
In Lightweight Mask

and Wet Suit
The diver must equalize pressure

•

sinuses during descent.

When

both ears and

in

equalization

is

not pos-

must be terminated.

sible, the dive
•

If

descending

in

a tideway or current, the diver

should keep his or her back to the current so that
he or she will be forced against the descent

When

•

line.

the diver reaches the bottom, the tender

should be informed of the diver's status and the
diver should ensure that the umbilical assembly

is

not fouled in the descent line.
•

If

necessary, buoyancy and air flow should be reg-

ulated before releasing the descent line; adjust-

ments

made

to air control valves should be

in small,

cautious increments.
•

The

diver should attach a distance line

one

is

used) and should then proceed to the work area.

A

distance line should be used

when

(if

visibility

is

extremely poor and the diver cannot see the descent

from a distance.

line
•

After leaving the descent

line, the

proceed slowly to conserve energy.
for divers to carry

diver should

It

is

advisable

one turn of the umbilical hose

in

the hand.
Source:

US Navy (1988)

•

The

diver should pass over, not under, wreckage

and obstructions.
•

If

on the stage platform and maintain a good grip on the
rails.

If the diver

makes

a

moving against a current, it may be necessary
assume a crawling position.

for the diver to

jump

or roll entry into the

If the

•

water, he or she must maintain a grip on the face

mask

etc.,

while the tender maintains sufficient slack on the line

and

diver

the umbilical hose at the entrance to the confined
space.

When

the diver

is

positioned for descent, the follow•

various

members

of the dive team.

The tender must constantly inform the diver
bottom time. The diver should be notified
minutes

The diver should adjust

his or her buoyancy,
Whether the diver is weighted neutrally
negatively will depend on the dive's objectives.

necessary.

•

The tender should

be

made

in

the air supply fittings

and also should look for

or suit

must

before the diver's descent. The tender

should check for any leaks

air

bubbles.

No

diver should dive with malfunctioning equipment.

The tender should
ment

•

is

also re-verify that

all

a few
advance of termination so that the task

can be completed and preparations

if

re-verify that the air supply

are functioning properly. If not, corrections

in

of the

made

for ascent.

or

system, helmet (or mask), and communications

•

required to enter wreckage, tunnels,

air hose.

ing procedures, as appropriate, should be followed by

•

is

a second diver should be on the bottom to tend

If

the diver experiences rapid breathing, panting, or

shortness of breath, abnormal perspiration, or an unusual sensation of

warmth, dizziness, or fuzzy

vision, or

become cloudy, there is probably
carbon dioxide in the helmet. To get rid of

the helmet ports have

an excess of

this excess, the air flow in the

helmet should be increased

immediately by simultaneously opening the

air control

and exhaust valves.

equip-

functioning satisfactorily.

The diving supervisor should

give the diver per-

8.1.5.1

Diver Emergencies

mission to descend.
•

The
line.

diver should descend

The descent

down

rate used

a descent or "shot"

depends on the

diver;

should not exceed 75 ft/min (22.9 m/min).

however,

it

The

supply should be adjusted for breathing

air

— NOAA

A

surface-supplied diver's umbilical

may become

fouled in mooring lines, wreckage, or underwater structures, or the diver

may

be trapped by the cave-in of a

tunnel or the shifting of heavy objects under water. In

ease and comfort.

October 1991

Fouling

Diving Manual

8-5

Section 8

such emergencies, surface-supplied divers are in a
better position to survive than scuba divers, because
they have a virtually unlimited air supply and can
communicate with the surface, both of which facilitate

may

rescue operations. Fouling

result in fatigue, expo-

and prolonged submergence, and

sure,
sitate

it

may

also neces-

an extended decompression. Divers who are fouled

should:
•

Remain calm;

•

Think

•

Describe the situation to the tender;

•

Determine the cause of fouling and, if possible,
and
Be careful to avoid cutting portions of their umbilical

themselves are unsuccessful, divers

should call for the standby diver and then wait calmly
for his or her arrival. Struggling

make

actions only

remaining

and other panicky

the situation worse by using up the

supply at a faster rate.

air

After surfacing, blowup victims should not be allowed

resume diving. If a diver who has experienced a
blowup appears to have no ill effects and is still within
to

the no-decompression range prescribed by the tables,

m) and
decompress for the amount of time that would normally
have been required for ascent from the dive's working
he or she should return to a depth of 10 feet (3.0

The diver should then surface and dress, after
which he or she should be observed for at least an hour
for signs of delayed-onset air embolism or decompression sickness.

Blowup victims who are close to the no-decompression
who require decompression should first be
recompressed in a chamber and then be decompressed in
accordance with surface decompression procedures; if
the available surface decompression tables are not adequate, the victim should be recompressed in a chamber
to 100 feet (30.5 m) for 30 minutes and then be treated
in accordance with U.S. Navy Treatment Table 1A (see
Appendix C). If no chamber is available, conscious viclimit or

assembly when using their knife.
If efforts to clear

losing

depth.

clearly;

clear themselves;

•

method of ascent should never be used because

control of the rate of ascent can have fatal consequences.

tims should be treated in accordance with recompression

Blowup

Blowup

the uncontrolled ascent of a diver from

is

depth; this

is

a hazard for divers using either a closed

dress (deep-sea or lightweight helmet connected to a

dry suit) or variable-volume dry suit
equivalent).

(UNISUIT®

Blowup occurs when the diving dress

becomes overinflated or the diver loses hold of the botor descending line and is swept to the surface.
During blowup, the diver exceeds the rate of ascent
(25 ft/min (8 m/min)) that must be maintained to be
decompressed successfully at the surface. Accidental
inversion of the diver, which causes the legs of the suit
fill

with

air, also

may

result in uncontrolled blowup.

Accidental blowup can cause:
•
•

•

Cerebral gas embolism;

Decompression sickness; and/or
(if the diver's head

Physical injury

strikes

an object,

such as the bottom of a ship or platform).
Before descending, the diver must be certain that

all

exhaust valves are functioning properly. The diving suit
or dress should

fit

the diver well to avoid leaving exces-

sive space in the legs in

which

air

can accumulate;

air in

the legs of the suit presents a serious hazard, particularly with

variable-volume

suits.

Divers must be trained

under controlled conditions, preferably

in a

swimming

pool, in the use of all closed-type diving suits, regardless of their
suits.

Some

previous experience with other types of
divers have attempted to use a technique

called "controlled

8-6

blowup"

.

unconscious victims should be handled according to the

m

recompression table

in

Appendix

C

that

is

designed for

cases of air embolism or serious decompression sickness.

or

or suit

tom

to

procedures for interrupted or omitted decompression;

for ascent; however, this

Loss of Primary Air Supply

Although losing the primary
quent occurrence

air

supply

is

an infre-

surface-supplied diving,

in

it

does

occasionally occur. In the event of a primary air supply

malfunction or

loss,

the panel operator should switch

immediately to the secondary supply, notify the tender

and diver, and call for the termination of the dive.
(Secondary air supply systems on the surface are
discussed in Sections 4.2 and 14.5 for both air compressor and high-pressure cylinder air supplies.)
The use of self-contained emergency air supplies in
surface-supplied diving has significantly reduced the
hazard associated with primary air supply failure. In
an emergency, a diver equipped with such a supply can
simply activate his or her emergency supply and proceed

to the surface. Divers

faced with the loss of their

surface supply should close their helmet free-flow valves
to conserve air,

and the surface crew should be alerted
soon as it develops. If, because of

to the situation as

fouling, the diver

is

forced to cut the air supply

line,

a

check valve incorporated into the reserve manifold

The

diver

a

must immediately terminate the dive if it is necessary
to switch to the emergency supply; under no conditions
should the diver attempt to complete the work task.

fl

will

prevent loss of the reserve air supply.

NOAA

Diving Manual

— October 1991

Working Dive Procedures

when
self-contained emergency

the primary air supply fails

If

without a

a diver

is

diving

air supply, the

Loss From View of Descent or Distance Line
Occasionally a diver

diver can drop his or her weight belt (without removing

line or lose

the mask) and then ascend to the surface, exhaling

tance line

throughout the ascent to prevent

air

embolism.

A

diver

will

lose sight of the descent

contact with the distance
lost,

is

line.

If the dis-

the diver should search carefully

within arm's reach or within his or her immediate

with a fouled hose should release his or her weight belt

vicinity. If the

and harness (or harness attachment) and then remove
the mask by grasping it and pulling it forward, up, and
over the head. The surface-support team should han-

the tender should be informed and should haul in the

dle a diver

who

way

surfaces in this

blowup emergency, because

as a

pression sickness

is

in the

same manner

embolism or decom-

air

a possibility.

water

is

less

than 40 feet (12.2 m) deep,

umbilical assembly and attempt to guide the diver

back

to the

may

be hauled a short distance off the bottom.

descending

line.

In this situation, the diver

contact with the descent line

is

When

regained, the diver

should signal the tender to be lowered to the bottom
again. In water deeper than 40 feet (12.2 m), the tender

should guide the diver to the descent line

Loss of Communication or Contact with the Diver
contact with the diver

If

is

lost,

the following proce-

in a

system-

atic fashion.

dures should be implemented:
•

If

intercom communication

lost,

is

the tender should

immediately attempt to communicate with the diver

by
•

line-pull signals (see

is

it

generally best to terminate

the dive so that the problem can be resolved and
the dive plan revised.
•

If

the tender does not receive an immediate line-

pull signal reply

an especially serious hazard for divers

from the diver, greater strain

hull of a ship.

A

diver falling off a diving stage or work

platform wearing such equipment
to be injured

is

much more

likely

than a diver falling a greater distance

in

open water. The principal danger from falling is the
sudden increase in pressure, which may not be compensated for by the overbottom pressure of the air
supply; this could result in helmet or mask squeeze.
The diver and tender must therefore always be alert to
the possibility of a

fall.

Should the diver

start to fall,

the tender should take an immediate strain on the

be sent again. Considerable resistance to the ten-

umbilical assembly to steady the diver.

der's pull

may

fouled, in

which case a standby diver should be

If the

indicate that the umbilical line

is

it

is

still

attached to the diver but

continues to receive no reply to line-pull signals,

it

is

is

air pressure should

If a tear

develops

in a

variable-volume

suit,

the dive

tating to a diver. If a closed suit with the helmet
is

available, or

if

for

some

considered unwise to use one, the diver

available to assist with the ascent.

— NOAA

in

the water.

Diving Manual

is

torn in a

fall,

the diver should remain in an

upright position and ascend to the surface at a safe rate
of ascent.

Ascent
When the diver's bottom

8.1.6

time has expired or the task

has been completed, the diver should return to the

is

The following procedures should be used;
all

times to enter the water when divers wearing
variable-volume dry suits are

attached

ascent line and signal the tender to prepare for ascent.
It

thus essential that a standby diver be ready at

October 1991

and the

effect of water entering the suit can be severely debili-

must be pulled to the surface at a rate of 60 feet
(18.3 m) per minute or less, and the tender and the
dive team should be prepared to administer first
aid and recompression as soon as the diver surfaces. If the diver is wearing closed dress or a
variable-volume dry suit, pulling him or her to the
surface is likely to cause blowup unless another
diver

it,

be increased slightly to prevent water leakage.

standby diver should be dispatched

no standby diver

reason

faceplate does crack, however, the diver

should be terminated immediately because the chilling

to

immediately.
If

If the

should continue to wear

be unconscious. In

the diver should be
this event, the

assumed

The likelihood of a faceplate being cracked during a
fall when a modern helmet is being used is relatively
small.

tender feels sufficient tension on the line to

conclude that

•

is

should be taken on the line and the signal should

dispatched as soon as possible.
•

Falling

using deep-sea or helmet equipment to work on the

Section 14.2).

Depending on diving conditions and the arrangements made during dive planning, the dive may
either be terminated or continued to completion
(using line-pull signals for communication). In
research diving,

Falling

•

The tender should pull in any excess umbilical line
and exert a slight strain on the line; he or she

8-7

Section 8

•

should then exert a slow and steady pull at the

divers are chilled.

prescribed rate (generally 60 ft/min (18.3 m/min));

any equipment defects noted during or after the dive,

start a timer on the surface and
should then monitor this timer (along with the

and defective equipment should be tagged for corrective maintenance. The divers should then be debriefed
Divers should establish their
and the log completed.
own standard of care for their masks, depending on the
conditions of use. For example, using a mask in fresh
water requires different maintenance procedures and

The tender should

pneumofathometer)

to control the diver's ascent

rate;
•

diver controls his or her buoyancy by using

The

either a

buoyancy compensator or adjusting the

air in his or her closed- or

suit,
•

•

variable-volume suit

must be careful not

(the diver

to overinflate the

which could cause an accidental blowup);
line

cleaning frequencies than are required

used

in

seawater.

seawater, the exterior of the

a

mask

is

When

mask should be

diving in
rinsed in

microphones. The interior of the mask should then be
wiped clean with a cloth or sponge. An alcohol solution
is useful for cleaning and disinfecting the oral-nasal

or diving supervisor should inform the

may

be required for

When

decompression

is

mask. (Inhibisol® or similar solvents should not be
completed, the tender

assists

is

stored, even

Some masks
8.1.7

Post-Dive Procedures

if

the storage time

is

very short.

should be placed in the face-down posi-

water to drain from the face seal.
some types require additional maintenance.
For example, the interior of masks that are fitted with
a cold-water hood are difficult to clean and dry unless
the hood is first removed. After the hood is removed,
the mask should be turned inside out and the water in
the open-cell foam face seal should be squeezed out.
The interior of the hood and mask should be dried
tion to allow

Divers should be helped from the water and should
then be assisted by surface-support personnel in removing their equipment.

harm the acrylic port.) The
mask should be completely dry when the

used, because they will
interior of the

mask

The following procedures are

recommended:

Remove
Remove

the weight belt;

•

the helmet and secure the air flow valve;
Unbuckle and remove the emergency backpack;

•

Remove

the neckring assembly;

•

Unbuckle and remove the jocking

Masks

of

completely before reassembling. Installing a zipper
the back of the hood simplifies maintenance because

in
it

reduces the number of times the hood has to be removed.

belt.

Close the supply valve and vent the primary air

maintenance and repair
masks in accordance with
the manufacturer's instructions and the service man-

hose;

ual supplied with each mask.

Monthly
If the

•

when

of underwater activity also

The tender

the diver to board the support platform.

•

The type

fresh water after each dive, taking care not to flood the

long decompressions);

•

and tenders should report

during ascent;

requirements (a diving stage

•

divers

influences maintenance requirements.

The diver should continuously hold onto the

diver well in advance of his or her decompression

•

The

diving system

is

not to be used again that day:

(or between-dive)

should be performed on

all

Close the emergency air cylinder valve, open the
reserve air valve to vent the line, and close the

8.1.8 Umbilical Diving

From Small Boats

reserve air valve again;
•

•

•

Disconnect the primary air hose from the emer-

gency manifold;
Disconnect the hose from the helmet inlet and
disconnect the communication cable;
Place the helmet in an upright position, rinse external
surfaces with fresh water, and wipe

the interior,

then wipe
•

it

if

necessary, with a

them

dry; clean

damp sponge and

dry;

Rinse the jocking belt

in fresh

water and hang

it

up

to dry.

The

umbilical diving

is

fixed platforms, the
readily to small boat

small boats,

i.e.,

at

m), a bank of high-

is usually used to supply breathing
which enables the team to operate without an air
compressor and its accompanying bulk and noise. The

pressure cylinders

air,

number and size of the high-pressure cylinders required
depend on the size of the boat and on operational
requirements. For small boats, two or more sets of

divers should be observed for any signs of sick-

standard twin-cylinder scuba tanks can be connected

and warming proce-

by a specially constructed manifold that is, in turn,
connected to a high-pressure reduction regulator or

ness or injury caused by the dive,

dures should be

8-8

Although most surface-based
conducted from large vessels or
umbilical system can be adapted
operations. When working from
depths of 16 to 30 feet (4.9-9.1

commenced

as soon as possible

if

the

NOAA

Diving Manual

— October 1991

Working Dive Procedures

The umbilical

small gas control panel.

is

then con-

nected to the pressure side of the pressure reduction
In larger boats, air

unit.

may

be carried

m3

240- or 300-cubic foot (6.8 or 8.5

in a series

When
is

of
•

Of specified purity (see Table
Of adequate volume;

•

At the proper pressure; and

•
)

high-pressure

Regardless of the cylinder configuration used,

cylinders.

cylinders must be secured properly, and the valves,

all

•

manifold, and regulator must be protected to prevent
personnel and equipment damage.

The umbilical may

the boat. For the convenience of the tender, the
is

is:

1

5-3);

Delivered at a sufficient flow rate to ensure ade-

quate ventilation. Regardless of the type of system,

be coiled on top of the air cylinders or in the bottom of

municator

properly configured, either of these air sources

able to supply breathing gas that

is

it

imperative that

it

be

good

in

com-

repair, be

manned by

serviced at regular intervals, and be
trained personnel.

generally placed on a seat or platform.

Communications equipment must be protected from

Air compressors are discussed

When

in

more

detail in Sec-

weather and spray. Because small boats can only be

tion 4.2.

used to support shallow water work, the umbilical from

diving operations incorporates an on-line air compressor,

the boat to the diver

m)

45.7

in

depths to

length.
less

It

is
is

the air supply system for surface-supplied

usually 100 to 150 feet (30.5-

the general system configuration

generally wise to limit diving

shown

than 100 feet (30.5 m) when working

from a small boat.

When

Figure 8-5.

in

similar to that

is

surface-supplied diving

operations utilize a high-pressure cylinder system for
diver air supply, the general system configuration used

The diving team

for a surface-supplied dive

from a

is

the one

shown

in

Figure 8-6.

small boat usually consists of a diver, tender, and

standby diver. The tender, who

a qualified diver,

is

also serves as the supervisor on such dives. If properly

8.1.10 Rates of Air

The

qualified, all personnel can alternate tasks to achieve

maximum

The standby diver
second umbilical and mask or,

operational efficiency.

may

be equipped with a

as

frequently the case, be equipped with scuba; he or

is

to

which

rate at

Flow
air

must flow from the

air supply-

the diver depends on whether the breathing appara-

mask) is operated in a free-flow or
demand mode. With free-flow equipment, the primarytus (helmet or

she should be completely dressed and capable of don-

requirement of the air supply system

ning scuba and entering the water

capacity (in acfm) that will provide sufficient ventila-

ute.

A

in

less

than a min-

standby using scuba should be fitted with a

quick-release lifeline (readily releasable in the event
of entanglement).

Some

munication cable as a

divers use a heavy-duty

lifeline,

com-

which allows the standby-

diver and tender to stay in communication. This line
also constructed so that

it

may

be released readily

is

in

Many

divers consider high-pressure cylinder air supply

systems safer and more dependable than systems
incorporating a small compressor and a volume or
receiver tank, and some divers prefer to have a small
tank incorporated into the system to provide air for
surfacing in an emergency. Most experts agree that a
diver should carry a small self-contained emergency
scuba tank for use in the event of primary system
failure. An emergency supply of this type is mandatory
when a diver will be working around obstructions or
inside submerged structures.

8.1.9

depth to prevent the carbon dioxide

tion at

mask

or helmet

work

levels

By ensuring

gencies.

liters)

will not

all

circum-

exceed 2 percent. To compute

inspired

C0 2

,

the following equation should be used:

R = 6(Pa)(N)
where

R =

ventilation flow rate in scfm;

lute pressure at

working depth

in

ATA;

Pa

N =

=

abso-

number

of

divers to be supplied.

Example:

What

ventilation rate would be required for two

divers using lightweight helmets at 80 fsw (24.4

R =
R =
R =
For

6(Pa)(N)
41.04 scfm

demand equipment,

the air requirement for res-

maximum

Air compressors; and

piration

•

High-pressure cylinder systems.

flow rate under severe work conditions.

is

based on the

m)?

6(3.42)(2)

•

Diving Manual

capable of

is

under

the ventilation rate necessary to control the level of

basic types of air supply systems used for

— NOAA

level in the

stances, divers can be reasonably certain that the inspired

surface-supplied diving are:

October 1991

have a

limits at

that the apparatus

supplying at least 6 acfm (170

Basic Air Supply Systems

The two

from exceeding safe

it

normal
and during extremely hard work or emer-

carbon dioxide

case of entanglement.

that

is

instantaneous (peak)

The maximum

8-9

Section 8

Figure 8-6
Typical High-Pressure
Cylinder Bank Air Supply

Figure 8-5

Major Components of a Low-Pressure
Compressor-Equipped Air Supply System

System
Supply

Air

to Divers

Moisture

Back

Separation

.Pressure

^i+J Regulator
LP
Compressor

/Valve

/

D*0—

W

^^^^

Air Intake
to

J

I

~0-

Pressure
Regulator
(if

req)

Pressure Regulator

From
Secondary
Source

Volume Tank
US Navy

Source:

Divers

"C£<|_

Manifold

(1985)

Drain

'Valve

|

Drain

regulators).

Valve

The supply pressure must always exceed

the ambient pressure at the working depth to provide a
Source:

US Navy

(1985)

safety factor in case an accidental rapid descent

from

below the planned working depth must be made.

When
instantaneous flow

is

demand but

not a continuous

rather the highest rate of air flow attained during the

inhalation part of the breathing cycle.

A

diver's air

using a free-flow

mask

or lightweight helmet,

a hose pressure of at least 50 psi

water

less

than 120 fsw (36.6

is

m)

required for dives in

in

depth, and a pres-

sure 100 psi greater than ambient pressure

is

necessary

requirement varies with the respiratory demands of
the work level. Consequently, the rate at which compressed air is consumed in the system is significantly
lower than the peak inhalation flow rate.

for depths exceeding 120 fsw (36.6 m). In addition, a

Computing the rate of flow that the air supply system must be able to deliver for demand breathing
equipment is essentially the same as calculating the

weight helmets.

consumption rate

at

loss

through the valves of at least 10 psig should be

anticipated. Simple calculations give the supply pres-

sures necessary for most free-flow

For depths

less

light-

than 120 fsw (36.6 m):

Ps

depth (see Section 14.3).

masks and

=

0.445D

+

65

+

Pj

= supply air pressure in psig; D = depth in
=
absolute hose pressure (50 psi + 14.7 psi);
fsw; 65
=
pressure loss in system.
and Pj
where P s

Example:

What rate of flow will a diver require using a demand
mask and doing moderate work at 75 fsw (22.9 m)?

For depths greater than 120 fsw (36.6 m):

Cd =
Cd =
Cd =

RMV (Pa)
acfm) (3.27
3.6 scfm

(1.1

For demand equipment, the rate of

ps

ATA)
where 115
air flow

=

=

0.445D

+

115

+

P;

absolute hose pressure (100 psi

+

14.7 psi).

must meet

or exceed the diver's consumption rate at depth.

8.2
8.1.11

The

Supply Pressures
supply system must be capable at

SEARCH AND RECOVERY

Search techniques

all rely

on one

common

element: the

times of

adoption and execution of a defined search pattern.

delivering air to the diver at a pressure that overcomes

The pattern should commence at a known point, cover
a known area, and terminate at a known end point.
Search patterns are implemented by carrying out
search sweeps that overlap. To be efficient, the overlap

air

all

the water pressure at the working depth (overbottom
pressure) and the pressure losses that are inherent in

any surface-supplied diving system (hoses, valves, and

8-10

NOAA

Diving Manual

— October 1991

Working Dive Procedures

Table 8-1

Wind Speed and Current Estimations
should be minimal. The

initial

step in a search

is

to

define the general area and the limits to be searched. If

Wind Speed,

Wind Current,

being conducted to locate a specific object,

knots (m/s)

miles/day (km)

the search

the last

is

known

position of the object

is

the starting

open

1-3

(0.5-

1.5)

2

(3.2)

sea resulting from sea and wind currents, the local

4-6

(2.0-

3.0)

4

(6.4)

7-10

(3.5-

5.0)

7 (11.3)

11-16

(5.5-

8.0)

17-21

(8.5-10.5)

16 (25.8)

22-27 (11.0-13.5)

21 (33.9)

28-33 (14.0-16.5)

26 (41.9)

The

point for defining the search area.

wind condition

drift in the

time the object was

at the

lost,

and the

leeway (movement through the water from the force of
the wind) should be studied. Sea currents can be esti-

mated

for a particular area using current

NOAA

Tidal

11

(17.7)

Current Tables and Tidal Current Charts and the U.S.

Navy's current Atlas of Surface Currents. Wind currents can be estimated using Table 8-1.

The leeway generally

to 10 percent

calculated at

is

Adapted from

of the wind speed, depending on the area of the object

NOAA

(1979)

exposed to the wind and the relative resistance of the

The

object to sinking.

direction of leeway

is

downwind,

made around

sions are

40 percent off the wind vector. Calculation of the value

is

and direction of leeway

can be implemented using a variety of patterns,
depending on the search equipment, visibility, or number

highly subjective for objects

is

that float or resist sinking; however,

wind velocity

is

or the object

leeway has

if

the average

relatively low (under 5 knots (2.5 m/s)),

heavy enough

is

to sink rapidly, the

or no effect on the calculation of a

little

the

datum

except for boats that have a tendency to drift up to

located. Searching the area

point until the object

around the datum point

of search vehicles involved.

Systematic searching

is

the key to success.

A

good

search technique ensures complete coverage of the
area, clearly defines areas already searched, and

probable location.
After the vectors of water current, wind current, and

remaining to be searched. The visibilibottom topography, number of available divers,

identifies areas

leeway have been added vectorially and applied to the

ty,

known position of the object, a datum point is
defined. The datum point is the most probable position
of the object. Once the datum point has been defined,
the search radius around the datum point is selected.
The search radius, R, is equal to the total probable

and

error of position plus a safety factor, as defined by the

of the ship's position by normal surface survey meth-

following formula:

ods. This

last

size of the object(s) to

in selecting

the best

be located are prime factors

method

for a particular search.

There are two acoustic approaches to underwater
object location. The first is to traverse the area being
searched with a narrow beam fathometer, keeping track

approach is suitable for returning to the
known object that has high acoustic relief

position of a

R =

radius

and

= safety factor (between
C = total probable error
k

and

1.5)

is

When

receiver unit

R =

+ k)C

(1

total

probable error

is

a mathematical combination

of the initial error of the object's position (x). the

navigation error of the search craft (y), and the drift
error (d e ). The drift error is assumed to be one-eighth
of the total drift. The total probable error, C, is:

C =

(d e

:

+x

2

+y

2 )'/2

mount. The

using side-scan sonar, a transponder
is

towed either from the surface or a
left and

submersible. Acoustic beams are broadcast
right,

The

such

flat area,

second acoustic method involves the use of side-scan
sonar.

where

located in an otherwise relatively

as a wreck, significant rock outcrop, or a

and the signals received are processed

to present

a picture of the bottom on both sides of the transponder-

receiver unit.

Approximate object

mined by knowing the

position can be deter-

ship's position, heading,

and

speed, and the approximate position of the transponder-

receiver unit with respect to the ship.

Onboard microprocessors
necessary to produce

to control the

optimum

range/gain

display contrast are

Each factor included in the total probable error is
somewhat subjective. Selecting conservative values has

the use of microprocessors simplifies the task of the

the effect of enlarging the search radius; sometimes, a

observer and increases the effectiveness of a search. If

small search radius

October 1991

is

selected,

— NOAA

and repeated expan-

Diving Manual

beginning

to

replace manual adjustment of the gain;

more precise determination

is

necessary, one of the

8-11

Section 8

Figure 8-7
Circular Search Pattern
acoustic surveying methods described in Section 9.1.3

,,

—Descending
—

Line

If*

can be used. Underwater object location using acoustechniques involves divers only after the object has

tic

been detected. The following diver search techniques
have been useful for such purposes.

^

,

Marker Line
M7==4s=
==_-L
rft.

is

is

the circular search technique

is

is

is

reason-

recommended. Under

the least potential for entanglement.
to

^

"

/AD

V

be

made

First

Search Circle

Weight

IA

^-^«_
^>v

small, use of

such favorable conditions, a floating search line is
anchored to the bottom or tied with a bowline around
the bottom of the descent line and is used to sweep the
area. To determine when a 360-degree circle has been
made, a marker line should also be laid out from the
same anchor as the search line. This marker line should
be highly visible and should be numbered with the
radial distance from the anchor.
Where current is noticeable, the marker line should
be placed in the downcurrent position so that the diver
always commences the search from the position having
is

J

J

==:==

free of projections,

good, the object to be located

ably large, and the area to be searched

one circle

SS

Search

In conditions where the bottom

the visibility

VwTT^

\

^V

8.2.1 Circular

j

,

When more

Search Line

Descending Line Anchor

Second Search

Circle

Courtesy Skin Diver Magazine

Figure 8-8
Circular Search Pattern for

Two

Diver/Searchers

than

with tethered divers, the direc-

changed

tion of travel should be

at the

end of each

rotation to prevent the possibility of fouling lines.

The

many

circular search has

modifications, depending

on the number of divers and the thoroughness required.

The standard technique

is

to station

one or more divers

along the search line close to the center of the search

The marker line can be used to assign precise
The divers hold the search line and swim in a

area.

(A)

distances.

marker line, which ensures
360 degrees has been covered. The divers
increase the radius for the next search, moving out a
distance that permits good visual coverage. This procedure is continued until the outermost perimeter is
circle until they return to the

that a full

reached (see Figure

When

Previously

Searched

Area

8-7).

two divers are searching, search effectiveness

can be increased by having one diver hold the circling
line taut

and swim the outside perimeter of the area

to

be cearched while another diver sweeps back and forth
along the taut circling

line.

As shown

in

Figure 8-8A,

bounded by the
outside diver's path. The search starts and finishes at
the marker line. The search may be extended by the
pattern shown in Figure 8-8B, in which case the circling line is marked at the point where the outside
diver was previously stationed. The outside diver then
moves to a new position, farther out on the circling
the

line,

first

search will cover a

and the

inside diver

full circle

sweeps back and forth between

the marker and the outside diver's

8-12

new

position. Posi-

Source:

tions

may be changed

become

fatigued.

NOAA

(1979)

at regular intervals if the divers

Changing positions can be done

at

the end of each sweep by having the outside diver hold

NOAA

Diving Manual

— October 1991

i

Working Dive Procedures

moving out one

position after

visibility length; the

other diver then moves outside, taking up his or her

murky

water, using a weighted line

ble; if the lost object

moving

line, a pull

shaped so that

is

on the

secured with

a

descending

line

in

the

for a circular search.

same
The

is

conducted

diver descends to the bottom (using a weighted line,

be advisa-

necessary) and searches the immediate area. After

snag the

will

it

line will tell the diver that the

object has been found.

may

if

reporting to the surface, the diver again descends,
going downstream to the extended length of the

At

Circular search techniques also

is

manner described above

may

position for the next sweep. If the search
in

diver

this point, the diver

be used for

arc-type swing.

begins moving sideways

line.

an

in

As the diver circles in the pattern, he
some resistance on the upward swing of

diving through the ice in waters that have no current,

or she will feel

such as inland lakes and quarries. The following pro-

the arc.

cedure has been used successfully by the Michigan
State Police Underwater Recovery Unit (1978). When

who pulls in the line the distance of the diver's visibility. The diver then swings back along the bottom in the

the ice

covered with snow, a circle

is

formed

is

the

in

snow, using the under-ice entry hole as the center

When

this occurs, the diver signals the tender,

opposite direction until he or she again meets the resist-

ance of the current. The pattern

repeated until the

is

the snow indicates the area being searched and the
approximate location of the diver who is searching

back at the original starting point. This pattern
can also be used in open water, including rivers and
lakes, and can be conducted from bridges, boats, and
off the shore. The fishtail technique is shown in

under the

Figure 8-10.

pivot point.

The

radius of the circle

determined by

is

The

the length of line used to tend the diver.

ice.

within the

of the search

If the object

first

procedure

only one diver, with a

The
backup

entering the hole, the diver
line,

not recovered

is

and the other end

formed on the

is

is

is

in

The

held by the tender.

diver

If the object

surface and describes the underwater conditions.

The

diver then proceeds just under the ice to the full length

With the

of the line (approximately 75 feet (25 m)).

use of rope signals, the diver begins circling, keeping
the line taut and staying about 6 or 8 inches (15-20

cm)

below the ice. After the diver completes one circle
without encountering any resistance, the tender signals the diver to descend to the bottom. With the line
taut, the diver begins the first circle

on the bottom.

After the diver completes one circle, the tender

him

pulls

or her to a

The

(within the limits of visibility).
searching

in

a second circle,

until the diver again

After reaching the general vicinity of the object, the

diver standing by; before

secured by one end of the

not found directly below, the diver returns to the

and

variation on the arc pattern search can be used to

relocate objects in waters with fast-moving currents.

diver searches large areas of the river bottom by swinging

search of an object will go directly below the hole

nals the diver

A

is

circular pattern involves

and make a search of the immediate area.
is

sur-

continued until the complete

is

area has been searched.

in

on

marked-off area, a second circle that

slightly overlaps the last circle
face. This

circle

diver

diver

reaches the hole.

is

repeated

If the diver's

rudder, allowing the current to force

bottom

in

right (or left) until the line

repeated;

otherwise, the standby diver takes over and a second
is

becomes

swims

taut.

to the

The diver

then turns onto his or her right side, grasps the line

with the right hand (both hands are needed

very

in

strong currents), and stiffens his or her body, turning
at

an oblique angle so that the current sweeps

it

it

rapidly

As the arc slows, a conventional swimming
assumed and the diver swims upstream and
shoreward. When swimming against the current becomes
to the left.

position

is

hand,

turns on his or her left side, and repeats the procedure
in

reverse mode.

tom, the diver

As progress

slips

is

made

across the bot-

backward along the

making larger and larger

arcs.

The

depends on current velocity and

line,

gradually

size of the arc

line length.

If

the

up the
the pivotal point, relocates the anchor, and

line to

standby diver

initiating the

search, the diver has slack in the line and

ond hole

is

across the river

it

When

alternating directions.

object of search

cut in the ice and the procedure

attached to a heavy pivotal

tom, or a creeper. The diver's body can be used as a

physical condition continues to be satisfactory, a secis

line

difficult, the diver shifts the line to his or her left
sig-

new location
commences

and the pattern

widening arcs from a

object, such as an anchor, a stake driven into the bot-

is

not found, the diver returns

begins again.

designated. Figure 8-9 illustrates this

through-the-ice search technique.

8.2.3

Jackstay Search Pattern

In the jackstay search pattern, a rectangular search

8.2.2

The

Arc Pattern

(Fishtail)

Search

October 1991

in

Buoy

is

used to perform

lines

run from the bottom anchor weights to the sur-

water that has a current. The

face,

and a ground

arc pattern search technique

an under-ice search

and buoyed (see Figure

area

— NO A A

is

Diving Manual

laid out

line is

8-11 A).

stretched along the bottom

8-13

Section 8

Figure 8-9
Circular Search Pattern

Through

Ice

Courtesy

8-14

NOAA

Diving Manual

Clifford Ellis

—October 1991

Working Dive Procedures

Figure 8-10

Arc

(Fishtail)

Search Pattern

B.

Search

A.

in

Offshore Search

Waters

with Currents
Courtesy

Clifford Ellis

between the weights. The divers conducting the search

metal bar 4 to 10 feet (1.2-3.0 m) long that permits two

descend on the buoy

divers to be towed behind a boat (liveboating).

and search along the ground
line, beginning at one of the anchor weights. When the
searching diver reaches the other anchor weight, the
weight is moved in the direction of the search. The
distance the weight

line

moved depends on
weight is moved the

is

visibility;

if

area to be searched

is

marked

The

off with four diving flag

buoys, one at each corner, to form a square or rectangle.

The distance between

size of the area to

the buoys depends on the

be searched and the maneuverability

distance the

of the boat. After the buoys are in place, the divers

searching diver can comfortably see as he or she swims

grasp the tow bar and are pulled parallel to two of the

visibility

good, the

is

along the

line.

If visibility

is

poor, the line

only as far as the searching diver can reach.

is

moved

The searching

buoys

slow rate of speed. After the divers have

at a

passed the

last

buoy, the boat

is

brought about through

swims back toward the first anchor weight
along the ground line (Figure 8-llB). The length of the
ground line determines the area to be covered. The
jackstay search pattern is the most effective search

the center of the square and parallel to the buoys.

technique

then be

diver then

8.2.4

in

waters with poor

visibility.

Search Using a Tow Bar

The tow-bar partem

is

similar to the aquaplane

illustrated in Figure 8-21.

October 1991

— NOAA

It

method

involves the use of a

Diving Manual

second pass

is

made along

away. This pattern

is

continued until the buoyed area

has been searched completely.

moved

A

the buoys, one boat width

Two

to the far side of the

of the buoys can

second

set of

buoys,

forming another square. This technique is shown in
Figure 8-12. (The procedures and safety precautions
associated with liveboating are described in Section 8.10.1.)

8-15

—

\

Section 8

Figure 8-12
Searching Using a

Figure 8-11
Jackstay Search Pattern

6

Rectangular Search

Tow Bar

t

^\ Buoy

Buoy /"

N^Buoy
(

BuoyV

'

'

'

~~~—~rr^

\.Buoy

|.C J

Buoy

J

''^

I

|

'

'
;

Courtesy

'

J

I

Source:

NOAA

Diving

8.2.6

Search Without Lines
When conditions are such that

8.2.5

search lines cannot

be used, a search can be conducted using an underwater

compass. There are

many

search patterns that

will

ensure

maximum

tern

important. Divers should use the cardinal points

is

N, E,

coverage; however, simplicity of pat-

W — and

S,

the length of a side

intervals or 50 kicks

—and

Clifford Ellis

Pnjgram

—one-minute

should turn the same

way

each time.

Recovery

The method chosen to recover a lost object depends
its size and weight. Small items can be carried

on

directly to the surface

by the

diver, while larger items

require lifting devices (see Section 8.9.1).
is

used, the diver

ment

must attach

When

lifting straps

to the item being recovered.

A

a

lift

and equip-

line that

is

longer

than the depth of the water being searched and that has
a small buoy attached should be carried to the spot to

mark

the located object.

In addition to observing the usual safe diving practices, divers

conducting searches should consider the

following:
•

•

When

plastic-coated steel wire is used as a line
marker, a small pair of wire cutters should be
carried to permit escape from entanglement.
To prevent line fouling when two tethered divers
are used in search patterns, one should be designated as the inside diver; this diver always remains
under and inside the position of the other tethered

When

At

UNDERWATER NAVIGATION
present, all readily available diver navigation or

positioning systems rely on surface position for their
origin.

If navigational or geodetic positions

under water

were used, the origin would have to be extrapolated,
which would introduce an additional margin of error.
Recently, acoustic telemetry techniques, which use
microprocessor-controlled methods, have been applied to

diver.
•

8.3

advisa-

diver navigation. These systems can be used to track

ble to use contrasting materials for radius, bound-

from the surface and to guide them to particular
Newer methods will allow divers to take the system along to monitor their own position (Woodward 1982);
however, dead reckoning is still the most common form
of underwater navigation. This procedure has a long

ary,

untethered divers are involved,

and distance

of a diver

lines to

becoming

lost.

it

is

decrease the possibility

Polyethylene line pro-

vides a good contrast to plastic-coated stainless
steel wire

8-16

and

is

recommended

for

boundary

lines.

divers

locations.

NOAA

Diving Manual

—October 1991

Working Dive Procedures

Figure 8-13
Diver-Held Sonar

and is used because it is impractical for divers
and operate cumbersome and complex navi-

history

to carry

An

gation equipment.

acoustic-based navigational system

has recently been developed that uses a person's sensory
ability to differentiate the time-of-arrival of under-

water sounds at the two ears.

produced along

a

line, a

If

a sequence of sounds

is

person interprets them as

deriving from a moving sound source, just as a person

perceives the lights being sequentially turned on and

marquee

off on a theater

as moving.

A

diver can quite

accurately perceive the center of a sound array and

swim

to

when

diving in

from distances as great as 1000 feet (303 m).
This technique can be used in habitat operations and

Sonar
ity to

it

is

murky

water.

another method of increasing a diver's abil-

may

navigate under water. Divers

find carrying a
Courtesy Dukane Corporation

compact active sonar useful for avoiding obstacles.
Underwater diver-held sonars have been used with
some success for years (Figure 8-13). The effectiveness of
sonar operations

is

related directly to the level of a

many hours

diver's training;

of listening to audio tones

headset are required before a diver can "read" the

in a

tones.

When

using diver-held sonar, the diver

slow 360-degree rotation until the object

is

makes

a

located

and then notes the compass heading. The active range
of most diver-held sonars
the passive or listening

is

about 600 feet (182 m). In

mode, pingers or beacons some-

times can be detected as far

away

as

3000

feet

(909 m).

For shorter ranges, there are units that allow a diver

ahead and obtain a direct readout
feet for distances up to 99 feet (30 m) with a

For relatively short underwater excursions, however,

the compass, watch, and depth gauge are

when

activated, emit a high-frequency signal.

are the

used

in

companion

Pingers

a

in a

is

noted.

is

To swim

good compass course, the axis of the compass must be
A simple and reliable

parallel to the direction of travel.

method of achieving

this

that does not have the

to

to grasp this

is

for divers to

compass on

arm with

which the compass

Swimming

with the arms

it

extend the arm

in front of

hand

the other

them

(i.e.,

the

strapped) (Figure 8-14).

is

helps divers to

in this position

follow the desired course and, in low visibility, prevents

them from

colliding with objects. Practicing on

units to pinger locators; locators are

land by walking off compass courses and returning to

the passive mode. Pingers can be attached to

the starting point helps to train divers for underwater

any underwater structure, including:

navigation. Because the accuracy of a

compass

by the presence of

advisable to deter-

steel tanks,

it

is

is

affected

•

Habitats;

mine

a

•

Submersibles;

diver

swimming alongside and varying

•

Pipelines;

depth gauge or watch should not be worn on the same

•

Wellheads;

•
•

Hydrophone
Wrecks; and

•

Scientific instruments.

as the compass because
compass heading.

A

in

some

however, the sequentially activated acoustic array
to either pingers

dead reckoning.

— NOAA

the course.

may cause

A

a deviation in

D
T = S

cases,

have been as accurate as dead reckon-

system has been shown to be superior

October 1991

it

with a second

diver can calculate his or her transit time by using

locating underwa-

within the audible frequency range. In
single beacons

in a pool

the following formula to estimate distance:

with acoustic beacons that emit signals

ter structures

ing;

compass's deviation

arm
arrays;

Divers have had some success

or

com-

or her. Progress

timed with the watch, and the depth

arm

1982).

him

horizontal position in front of

in

cm) (Hall

a

along the line of bearing, holding the compass

and then

Acoustic pingers are battery-operated devices that,

the

still

pass bearing has been ascertained, the diver swims

to point the device

reported accuracy of 6 inches (15.2

Once

simplest navigational devices available.

where

T =
D =
S

Diving Manual

=

transit time in

minutes

distance to be covered in feet

speed of advance

in feet

per minute.

8-17

Section 8

Figure 8-14
Using a Compass for Navigation

A

swimming at a pace
maintained over a known distance and slightly
modifying the formula to:
diver can estimate speed by

easily

S

D
=T

For example, a diver traversing a 1000-foot (305 m)
course in 10 minutes

(30.5

is

m) per minute,

mile (1.85

km) per

swimming at a speed
or approximately

of 100 feet
1

nautical

hour.

Some underwater

topographical navigation aids that

can be used are underwater landmarks (and turns

made

with respect to them), the direction of wave ripples in
the sand, and the direction of the current (if

it is

known

change during the dive). Some
areas require the use of a transect line because they
lack distinct bottom features. Divers often use the
increase in pressure against their ears and masks or
changes in the sound of exhaust bubbles to identify
changes in depth.
that the current will not

8.4

UNDERWATER TOOLS

A

fundamental aspect of accomplishing work under
is the selection of proper tools and equipment. In
all operations, the relative advantages and disadvantages of power tools and hand tools must be considered.
The amount of effort that will have to be expended is
an important consideration in underwater work, and
power tools can reduce the amount of physical exertion
needed. Having to supply tools with power and to transwater

may be a substantial disadvantage.
The performance of divers under water is degraded

port them, however,

by several factors, including water resistance, diver
buoyancy, equipment bulk, the confined space environment, time limitations, visibility restrictions, and a

amount of reaction
force without adequate staging, hand grips, or body

diver's inability to provide a proper

harnesses.

A

diver's

land.

performance

compared with

significantly

Even a

may

therefore decrease

his or her

performance on

relatively simple task like driving a nail

can be difficult because of limited visibility, water
viscosity, and other environmental factors; however,
some tasks are easier to accomplish under water because
of the diver's ability to move easily in three dimensions. Because diver safety is a primary consideration
in any underwater operation, hazards such as electric
shock, excessive noise, and other potential causes of
injury must be taken into account when selecting underwater

lists

along with their

8-18

some common tools used under water,
sources of power and available acces-

J.

Cardone

Most pneumatic and hydraulic tools can be
adapted for underwater use. The information supplied
sories.

by the

manufacturer contains detailed use

tool's

specifi-

cations that should be observed faithfully.

8.4.1

Hand Tools

Almost

all

standard hand tools can be used under

water. Screwdrivers are generally available in three
configurations: the

machine

(or straight-slotted) type,

the phillips type, and the alien type.
alien screwdriver

only torque

is

required to operate

is

to

damage

When

and the linear

slip

out of the screw

the screw by twisting.

multipurpose tool can be
driver blade

it

is

screwdriver have a tendency to

head or

the three, the

minimum. Also, the alien
longer lever arm. The other types of

reaction force necessary

type provides a

Of

easiest for a diver to use, because

and a pair of

made by welding

pliers to

An added

tendency of the blade to
lihood that the blade will

NOAA

A

single

a screw-

an adjustable wrench.

using a hand saw under water,

follow a straight line.

tools.

Table 8-2

Photo by Bonnie

it

is

difficult to

complication

is

the

which increases the likebreak. Because it is easier for

flex,

Diving Manual

—October 1991

Working Dive Procedures

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8-19

Section 8

a diver to pull than push under water,

useful to put

it is

saw so that the sawteeth are oriented
toward the diver and the cut is made on the draw.
the blade in the

A

2- to 4-lb

used underwater

short-handled
tool.

easier to develop force

weight of a sledge
ting with a lighter

Because

it

is

effort

by pounding with the heavy
than by swinging and hit-

site in a

canvas bag

to the diver's belt with a line.

also can be attached to a descending line with a

down

this line to the

job

site

from

the surface. Tasks involving grinding, chipping, pounding, or

reaming with hand equipment are arduous and

8.4.3

tect

is

not practical unless the task

hand

bath before being turned on once to

To

Hydraulic Tools

closed-cycle power, are safer to use under water, have
little

or no depth limitation, are

much

lighter per unit

of power output, do not produce bubbles that obscure
the diver's vision, and require relatively

nance.

little

mainte-

As with pneumatic motors, hydraulic systems

have the capability

and stop rapidly, and they

to start

can be operated at different speeds.
Tools such as

(Figure 8- 15 A), impact wrenches

drills

pro-

(Figure 8-1 5B), chain saws, disc grinders (Figure 8-1 5C),

be rinsed with

and cable or pipe cutters usually are modified versions
of hydraulic tools designed for use on land. To convert
tools for underwater use, different seals are used,
internal voids are compensated to withstand ambient

small.

is

tools after use, they should

oil

Hydraulic tools are the most popular kind of tool
with working divers because they provide consistent

time consuming, and the use of hand tools for these
tasks

an

is

easy to lose or drop tools under water,

shackle and be slid

in

displace any water trapped in the tool.

than on land,

hammer.

and are then attached

the motor section; the tool should then be sub-

merged

commonly

hammer

they usually are carried to the work

They

a

is

Because considerably more

hammer under water

required to swing a
it is

hammer

fills

fresh water and lubricated with a protective waterdisplacing lubricant.

pressure, external surfaces are painted or coated with

8.4.2

a corrosion inhibitor, and dissimilar metals are insulated

Pneumatic Tools

from each other.

Although pneumatic tools are rarely designed specifically for use under water, they need little, if any,
alteration to be used in this medium. According to
Hackman and Caudy (1981), the power available in air
motors ranges from 1/8 to 25 hp, and loaded speeds
range from 40 to 6000 rpm; some of these tools have
even higher speeds. Most pneumatic tools require 90
psig of air pressure to operate, and they exhaust into
the water.

A

disadvantage of these tools

is

that they

To

facilitate the field use of hydraulic tools in areas

where hydraulic oil is not readily available or where
environmental restrictions prohibit the discharge of
oil, hydraulic tool systems are being developed that
use seawater as the working fluid in place of oil. The

Navy

has supported a program, called the "Multi Func-

tion Tool

System," that involves the development of a

seawater hydraulic grinder, band saw, impact wrench,

and rock

underwater use.

drill specifically for

exhaust bubbles that may disturb divers or impair
their visibility under water. In addition, the amount of
pressure available for power decreases at depth. Pneu-

that can be located at the

matic tools can be modified to include a hose attach-

These power sources are compensated

ment on the exhaust that

depths but require built-in batteries or an electrical

is

larger in diameter than the

supply hose. Often, the exhaust hose
the surface, where

it

is

routed back to

discharges to atmospheric pres-

Even with these modifications, surface-supplied
pneumatic power can be used only to depths of 100 to
150 feet (30.5-45.7 m). Although closed-circuit pneusure.

matic tools would not be as wasteful of energy at depth

have not been developed
because the entire system would have to be pressurized
or the tool would have to be designed to withstand
ambient water pressure. The extensive maintenance
requirements of pneumatic tools can be minimized by
using in-line oilers to meter oil automatically into the
as open-circuit tools, they

air

supply hose. After each day's diving,

poured into the

8-20

air inlet of the tool until

oil
it

should be

completely

Hydraulic tools require a power source at the surface or a submersible electrohydraulic power source

work

site

near the diver.
to operate at all

umbilical from the surface to run the motor.

normally operate at pressures from 1000

To

psi to

The

tools

3000

psi.

use them, divers usually work standing on the bottom

or on

some

structure.

When

working with these tools on

the side of a structure or in the midwater column, a
diver can use harnesses or a diver's stage for support.

The U.S. Navy has adapted and developed

a variety

of diver-operated hydraulic tools for construction

and

salvage work. These tools include:
1.

2.

An

abrasive saw (2000
by 1/8-in. thick blade);

A

grinder (2000

psi,

psi,

11

6-14 gpm, 10-in. dia.

gpm, used with

discs,

cups, or wire brush);

NOAA

Diving Manual

— October 1991

Working Dive Procedures

Figure 8-15

Underwater Hydraulic Tools
Hydraulic tools that minimize diver fatigue and discomfort should be selected. Most tools can be reconfigured or redesigned to increase diver comfort.
attention should be given to underwater

neering principles

the design of

in

human

new

tools.

More
engi-

Areas

where progress could be made include weight reduction, special grips and triggers, placement of handles
at the center of gravity or wherever they will best
counteract torque, and reduction of vibration and reaction forces.

Hydraulic tools are easy

to maintain.

They should be

rinsed thoroughly with fresh water after each use and

then be sprayed with a protective lubricant such as

WD-40.

Tools

8.4.4 Electric

Underwater

tools that operate

by

power have

electric

been designed, developed, and manufactured, but they
are seldom used.

The

AC

motor, stator, and control

electronics of such tools are potted in epoxy,

motor

tools require only a small umbilical,
limitation,

and are reasonably

Courtesy Stanley Hydraulic Tools

shock

persists,

have no depth
Although

light in weight.

ground-fault detector circuitry
electric

and the

water cooled and water lubricated. Electric

is

is

provided, the fear of

and most divers consequently

prefer to use hydraulic tools despite their greater weight

and support equipment requirements.
3.

A

come-along (1500

cable 1.5
4.

A

in.

psi,

2000

lb.

force,

moves

hurst tool (input of 5000 psi and .07

gpm, jaws

of tool open and close with force of 6 tons through

Power Velocity Tools

Power

velocity tools are actuated by the firing of an

explosive cartridge, which increases the pressure behind a

piston to accelerate a stud or a cutter into the

a distance of 32 inches);
5.

8.4.5

per stroke, used as a rigging aid);

Impact wrenches (2000 psi, 5 gpm, used for driltapping, or for make/break of nuts and bolts);
Linear actuators (10,000 psi rams, 8 ton pullcylinders, 10,000 psi cutters or 2 1/2 in. wire

piece (Figure 8-16).

Power

work

velocity tools are used to

attach padeyes, studs, and hollow penetrations

in

plate

ling,

6.

steel.

Different configurations are used to cut cable,

rebar, hydraulic/electrical umbilicals,

impact socket for loosening

jammed

and

to drive

an

Studs are

nuts.

rope, rebars, or splitting nuts);
7.

8.

A pump

(2000

psi, 5

gpm

hydraulic fluid; 100

available to penetrate steel that

400 gpm water flow, used for jetting, washing,
and dredging); and
Hose reels and different hydraulic power supplies.

(An excellent source

of information on the operation
and maintenance of the Navy's hydraulic tool systems

isNAVSEA
Some

1982.)

thick (0.64 cm).
in

The

cutters can sever

at least

is,

that operates on

for

2000

example,

a hydraulic

psi, 0.5 to 3.0

1/4-inch

diameter cables or 2-inch

(5.1

gpm, and

cm)
diameter

1.5-inch (3.8

cm)

in

composite umbilicals.

WARNING
Only Properly Trained Personnel

hydraulic tools have been designed solely for

underwater use. There

hammer

is

psi,

May Han-

dle Explosive Cartridges. Trained Divers Also

Should Use These Tools Only When The Proper
Safety Precautions Have Been Taken

develops a 40-foot-pound force per blow; output speed

ranges from

1

to

300 blows per minute. The unique

design uses compressibility of the hydraulic fluid to
generate and store the impact energy.

October 1991

— NOAA

Diving Manual

Power velocity

tools are well suited to

water work. Their weight

is

most under-

comparable

to that of

8-21

Section 8

Figure 8-16
Explosive Hole Punch

Figure 8-17

Oxy-Arc Torch

Courtesy Broco,

Inc.

Courtesy Battelle-Columbus Laboratories

metal being heated. The metal is heated to ignition
temperature by a hydrogen/oxygen flame, and pure
hydraulic tools, but they require no umbilical or power
line.

Some models

of underwater stud guns feature

by the diver. The
heavier duty models, as well as most cutters, require
that reloading be performed on the surface.

oxygen

Cutting and Welding Tools

Cutting and welding are often required both in sea-

water and

in

dry underwater enclosures or habitats.

Since habitat welding involves techniques and tools
similar to those of atmospheric welding, this

manual

addresses only cutting and welding tools that are used

then directed at the heated spot to start the

as a fuel gas for cutting,

barrels that can be replaced easily

8.4.6

is

cutting action. Although acetylene also has been used

at

it

is

considered unsafe to use

depths greater than 30 feet (9.1 m). Shielded metal-

arc cutting

is

a process in which metal

is

severed sim-

and physically pushing the metal out of
the kerf. An electric arc is formed between the electrode and the work piece to provide the heat for melting.
The process is used in situations where no oxygen is
ply by melting

available.
ting

is

Some

believe that shielded metal-arc cut-

superior to oxygen cutting on steel plates less

than 1/4 inch (0.64 cm) thick or when cutting brass,
copper, or copper-based alloys. Oxy-arc

is

used to cut

metal burns or oxidizes very rapidly. Electric current

up to 2 inches (5.1 cm) thick.
The most widely used underwater welding process is
shielded metal-arc welding. The weld is produced by
heating with an electric arc between a flux-covered
metal electrode and the work piece. The heat developed
by the arc causes the base metal parts, the core wire of
the stinger, and some of the flux covering to melt.
Other constituents of the flux decompose to gases,
which shield the molten metals somewhat from contamination. When welding under water, technique is
important and special training is required. Generally,
underwater welds are not as strong as surface welds
because of water quench and contamination. Also, it is
vitally important that the diver be aware at all times of

not required for oxy-hydrogen, but an air hose

the severe shock hazards associated with electric cut-

in seawater.

Underwater cutting and welding processes

emit toxic gases that

rise to the

surface and, since they

are heavier than air, collect in any low-lying confined
areas. Ventilation during
is

underwater cutting and welding

thus essential to protect both divers and surface

personnel.

The most popular cutting torch
ure 8-17); the process

is

is

oxy-arc (Fig-

learned with less training than

oxy-hydrogen, oxy-acetylene, or shielded metal arc
cutting.

The oxy-arc process uses

electric

power

to

heat the work piece to ignition temperature; a jet of

oxygen
is

is

required to

then directed at the heated spot and the

fill

the flame and to hold water

8-22

is

a shield cup around the tip to stabilize

away from

the area of

steel

ting

and welding processes. Metal helmets must be

insulated.

NOAA

Diving Manual

—October 1991

Working Dive Procedures

INSTRUMENT IMPLANTATION

8.6

WARNING

The proper implantation
Diver Training and Experience Are Essential
in Underwater Cutting or Welding

gations.

is

Instruments that are implanted on the sea

bottom include

8.5

of scientific instruments

important to the success of underwater scientific investi-

cameras, positioning stakes, radi-

lights,

ometers, recording current meters, thermistors, oxygen sensors, and acoustical devices. Factors affecting

MAINTENANCE AND REPAIR TASKS

the success of implantation are:

Maintaining and repairing equipment, structures, and
instruments under water requires

skill

and an under-

•

standing of the work to be done. In addition, underwater

maintenance should be performed only when envi-

sions, fragility,
•

ronmental conditions are acceptable.

The available power supply and instrument
out cables, or

(if

read-

self-contained) the frequency

divers should practice underwater tasks

with which the instrument's batteries must be

changed or the instrument must be serviced or

The time that
must be known
(or a

will

be needed to accomplish the task

to enable the diver to

major portion of

air supply.

it)

complete the task

replaced
•

within the constraints of the

For strenuous tasks, the work should be

divided into subtasks and several divers should take

its

to

Bottom conditions, the bearing strength of the

•

them out.
To accomplish underwater work, four task phases

are involved:

The alignment of the instrument in position,
height above the bottom, and its sensitivity
misalignment

turns carrying

bottom, anticipated currents, and the type of marine
life
•

The

Inspection of the work site and determination of

precise markings of instrument location and

methods used

the
•

size and weight, mounting dimenand attachment points

shallow water before attempting them in deep water.

If practical,
in

The instrument's

for recovery at completion of the

mission.

the condition of the equipment that needs mainte-

nance or repair;
•
•

The

Selection of appropriate tools;

cal

Performance of the repair or maintenance

task;

and
•

and weight of the instrument and

size

used and the techniques chosen to
to the site.

Reinspection

to

ensure that the work has been

accomplished successfully.

its

physi-

dimensions and fragility affect the type of anchor

may

move

the instrument

For small instruments, a concrete block

be an appropriate anchor.

The blocks can be

predrilled, fitted with fasteners on the surface,

moved
Most underwater maintenance and repair tasks that
is asked to perform are associated with the
inspection and repair of a ship's rudder, propeller, sea

a diver

chest, or cathodic protection system.

When

a diver

is

working over the side of a ship to perform a maintenance task, the ship's propeller should be locked out

and the rudder should be held

in

static

position.

The

appropriate international code flag should be hoisted.

Divers should be careful to avoid skin contact with
the hull of the ship on which they are working, because

to the site as a unit

and positioned.

and

In other

and instrument can be moved
and a diver can then position and

cases, the concrete block
to the site separately,

align the instrument in the water.

A

concrete block

anchor can be lowered directly into position using a
winch, or it may be fitted with flotation devices and
guided into position by a diver, who removes the
tion device

when

the anchor

is

flota-

in position.

For large instrument packages, anchors can be made
of metal piles that are driven into the bottom by a diver

using a sledgehammer or pneumatic impact

hammer.

marine

Steel pilings create magnetic anomalies that can affect

growth (barnacles, algae). These paints retain their
toxic qualities for months after the freshly painted

instrument readings; instruments should therefore be

toxic paints are often used on the hull to inhibit

used only after the effect of the pilings on the instru-

may

ship has been returned to the water.

ment's functioning has been calibrated. Pilings

Maintenance and repair tasks can be accomplished
more easily if a restraining system is used. Such a

grouted

system can be as simple as a

instrument installation and can be driven into the bot-

onto that

is

line for the diver to hold

attached to a convenient point or as elabo-

rate as a jacket with

magnets

or suction cups that

attach to a shear plate.

October 1991

— NOAA

face.

tom

in

Embedment anchors can
to secure the lines.

be used to stabilize an

Chains or wires equipped with

turnbuckles can be run over the instrument package

between anchors
Diving Manual

be

place with concrete supplied from the sur-

to secure the installation further.

The

8-23

Section 8

foundation package should be designed to accept the

therefore equip these instruments with automatic pinger

instrument package easily so that

devices in addition to marker buoys (see Section 8.3).
If a pinger-equipped instrument is believed to be

it

is

as easy as possi-

ble for the diver to attach the package.

foundation

When

the

complete, a line or lines should be run to

is

the surface to assist in lowering and guiding the instru-

ment

into place.

Many

underwater instruments require outside power to

operate and to transmit data to outside receivers. During the installation of instrument cables, a diver usually

is

required to anchor the cable at various points

along the cable run.

The

first

near the instrument package.

point of anchor should be

To reduce

and the
instrument. The diver should guide the instrument
cable around any rocks or bottom debris that might
abrade the cable covering. Anchors should be placed
a bight) of extra cable between the first anchor

frequent intervals along the length of the cable,

wherever the cable turns, and on each side of the cable
where it runs over an outcropping or rise in the bottom.

Cable anchors can either be simple weights attached

embedment

the cable or special

The alignment
alignment

tom

is

A

is

important to

simple technique to achieve

to drive a nonferrous stake into the bot-

A

then to hang a compass from the line or wire.

nonferrous stake

and

the compass indicates that the alignment

is

correct.

stakes and the attached line then act as the

reference point for aligning the foundation or instru-

ment.

A

tape

is

used to translate measurements from

the reference stakes and line to the foundation or the

8.7

necessary.

HYDROGRAPHIC SUPPORT

In hydrographic operations, divers can be used to con-

firm the existence and/or location of hazards to navi-

and measure least depths, and resolve
any sounding discrepancies identified by different
surface-based measurement techniques. When using
gation, locate

divers for this type of work,

is

it

essential to consider

the skills of the divers, water conditions, the nature of

the work, special equipment requirements, and the

Because hydrographic

availability of diver support.

important to mark the dive

site

it is

using buoys, electronic

pingers, or fathometers; this precaution

becomes

increas-

ingly important under conditions of reduced visibility

and high currents.

Hazards to Navigation

8.7.1

A
ing

significant portion of hydrographic support divis

Once

conducted

to identify

hazards to navigation.

the general location of a navigational hazard has

been identified,

When

Before selecting a location for an instrument, botconditions should be analyzed to identify the appro-

priate foundation.

The instrument

site

should be

reinspected at frequent intervals to monitor the condition of the instrument

ma-ine growth that

Unmanned

may

and

to clear

away sediment

or

affect instrument readings.

its

precise location can be determined

instrumentation

is

increasingly used for

Because many unmanned instruments are

self-

contained and expensive, they must be equipped with
reliable relocation devices.

the object has been found,

with a taut-line buoy and

be noted.

If the

depth

is

its

it

should be marked

geographic position should

shallower than about 50 feet

(15.2 m), a lead line depth should be recorded, along

with the time of notation.

Diving operations that are designed to prove that no

navigational hazard exists in a particular area are

long-term data-gathering and environmental monitoring
tasks.

is

using the search techniques described in Section 8.2.

instrument.

tom

long search

second

then driven into the bottom when

is

murky water when the divers are
surface supplied and use liveboating techniques (see
Section 8.10.1), particularly if the pinger is weak and a
especially well in

operations are frequently conducted in open water,

that has a nonferrous wire or line attached

The two

to

anchors.

of the foundation

successful implantation.

to the
approximate location; they can then descend and search
with a hand-held locator unit. This technique works

move-

either the cable or instrument will break the

cable connection, the diver should allow a loop (called

at

implantation, a surface receiver

from a boat can guide divers

unit operated

the possibility

that the cable will topple the instrument or that

ment of

lost in the vicinity of

Although surface or sub-

LORAN-C

extremely time consuming and require painstaking documentation of search procedures and location. The
reported location and geographic position of the hazard should be marked precisely; a taut-line buoy should

be used to mark the search control point.

Any time

the

common

moved, the move should be documented
and the geographic position of the new control point

relocation devices, at least for short-term implanta-

should be noted. Documentation of the search should

surface buoys (used in combination with

or satellite navigation systems) are the most

tion, these

buoys are subject to vandalism, fouling

ship propellors, and accidental release.

8-24

Many

control point

is

in

include the geographic position of control points, the

users

type of search, the equipment used, water conditions,

NOAA

Diving Manual

— October 1991

Working Dive Procedures

and problems encountered, what was found or not found,

statement describing the area that has been
searched and any area that may have been missed.

and

a

hazards associated with any wreck diving operation,
the wire itself poses a hazard. For example, if the wire
slips

on an obstruction,

could pin

it

diver;

a

if

the

strands of the wire are broken, the wire can cut a diver
severely;

Locating and Measuring Least Depths

8.7.2

it

When

Divers can be used to determine least depths accurately, especially in

such areas as rocky shoals, coral

and wreck sites. After the general location to be
studied has been identified, a diver is sent down to
mark precisely the least depth by tying off a line on the
bottom so that a buoy floats directly overhead. Care
reefs,

must be taken

to ensure that the lead line

marking

that the time of

is

recorded.

A

is

plumb and

taut-line

buoy

can be used to mark the geographic position of the
least depth so that it can be noted and recorded by
surface personnel.

and

if

a diver holds the wire and

an underwater obstruction needs

tigated, the support boat

must be

nearest the obstruction. After agreeing on

the discrepancies, and

mark

site,

resolve

in

swim to the buoy and descend to the
bottom wire. Depth gauges are checked, and the depth
of the obstruction is noted on a slate.
Because of forces acting on both the wire and the
upright to the buoy, the depth at the weight can vary
from its setting by as much as 10 feet (3 m). Once on
the bottom, the divers proceed hand-over-hand along
the wire, one behind the other, taking care to stay

procedure

is

to

effort to stay as

The recommended

"crab" into the current, making every

much above

the wire as possible.

WARNING
Divers Must Be Extremely Careful When
ing Inside the Bight of a Ground Wire

Work-

WIRE DRAGGING

Wire dragging

is

a

method

The method

involves deploying a wire between two ships and hold-

depth with weights ranging from 50 to
250 pounds (22.7-113.4 kg). The objective of this procedure is to tow the wire in such a manner that hydrodynamic forces induce an arc-shaped curve. As the ships
move through the water, the wire will snag on obstrucing

it

at

tions protruding

After arriving at the obstruction, wire depth

of ensuring that surface

ships can pass through an area safely.

above the depth of the drag. Divers

supporting wire-dragging operations are used to identify:

•

be difficult

reefs.

8.8

•

may

areas

such as rocky substrates, faulted or volcanic bottoms,

•

buoy

proce-

the site correctly. Dis-

crepant measurements are most likely to occur

and

all

dures, the divers

tends to push the diver into the bight.

of undersea features are dis-

crepant, divers can be used to inspect the

be inves-

because most drags are run with the current, which

Resolving Sounding Discrepancies

When measurements

to

tied off to the

outside the bight of the wire. This

8.7.3

pulls loose,

it

can sever the diver's fingers.

The objects on which the wire hangs;
The least depth over the obstruction; and
The highest protrusion that could be caught from
any direction.

recorded.

The

the obstruction; this procedure requires the divers to
leave the wire. If the obstruction

depth when they enter the bight. Once the least depth
is found, the divers record the depth and determine whether the high point could cause the ship to
hang at any point. If the object is intact or is a candi-

point

date for recovery, the divers select a suitable place to
tie

off a small buoy.

The buoy must be tied off inside
away when the drag wire is

the bight so as not to be torn

recovered.

The depth information recorded
the equipment involved
is

in

the removal of minor obstructions. Another

task performed by divers

verified by a

is

surface-tended pneumatic pressure gauge. Because

Divers also can identify underwater features that pose

assist

not substantial, the

is

divers should be several feet above the obstruction's

a hazard to fishing nets and trawling or ground tackle

and

is

divers then try to find the least depth of

is

assessing the areal extent

is

cumbersome,

this

technique

rarely used during the initial investigation.

tively

calm seas and slack current,

a lead line

In rela-

may

be

used to verify depth information.

of wreckage. If the least depth cannot be determined

Because divers following a wire do so

in single file,

it

accurately, the approximate depth needed for clear-

is

easy for one diver to lose track of his or her buddy.

ance

A

buddy-check should therefore be carried out every

is

sought.

Divers need to exercise extreme caution

when work-

ing around wire drag hangs because, in addition to the

October 1991

— NOAA

Diving Manual

50 feet (15.2 m);

this

procedure also

entanglement when there

is

poor

may

prevent diver

visibility.

8-25

Section 8

Figure 8-18
Salvaging an Anchor
With Lift Bags

NOTE
Wire-drag support diving should be done
only by experienced divers who are well
trained in the techniques and fully aware
of the hazards involved.

SALVAGE

8.9

Salvage of a ship or craft,

cargo, or

its

equipment

its

requires a knowledge both of the technical aspects of

recovery and the legal aspects of ownership of the
salved items and claims for salvage.
recovers a ship or craft or

its

ment with the owner must

A

salvor

who

cargo without prior agree-

file

a claim in the United

States District Court nearest to the port in which the
salved items are landed.

Salvage techniques vary considerably with the

size,

and condition of the item to be salved, the depth
of the object and seafloor conditions, and the equipment available to conduct the salvage. Salvage techvalue,

niques that are used

commonly

winch or crane, floating

lifts

are direct

lifts

Photo by Geri Murphy

using a

using a device to compen-

from the container; this will displace more water
and may increase the speed of ascent to an uncon-

buoyancy of the ship or craft, and
repairing and restoring the inherent buoyancy of the
sate for the negative

salved object

trollable rate;

itself.

Individual divers often salvage instruments or instru-

ment

arrays, anchors, or other small structures. In the

•

The weight

of the object in water

is

amount equal to the weight of the water

reduced by an
it

displaces.

majority of these cases, the diver simply carries the
item to the surface. In other situations, the diver atta-

ches a flotation device (Figure 8-18)

or, for

items, a line or wire that will facilitate a direct

heavy
lift

to

8.9.1 Lifting

Many

Devices

objects can be used as lifting devices, includ-

ing a trash can or bucket inverted and tied to the

the surface.

In

some salvage operations such

excavations,

it

may be

necessary to clear bottom sedi-

ment from around the item before
This procedure

is

as archeological

it

can be recovered.

necessary to ensure that the item

free of entanglement.

A

water

jet or air lift

is

commonly

used to clear away entangling debris (see Sec-

is

bag placed in a net bag, a 55-gallon oil
drum, or a commercially available lift bag (shown in
Figure 8-18). If the object is lying on a soft bottom, it
may be necessary to break the suction effect of the
mud by using high-pressure hoses or by rocking the

object, a plastic

object back and forth; a force equal to 10 times the

may be necessary to break it free.
Raising and lowering can be accomplished with
commercially available lift bags of various sizes and

weight of the object
tion 9.12.2).

When

working with heavy or overhead items with
under tension, divers must develop

cables, lines, or chains

lifting capacities or

a sixth sense for safety. Divers should avoid positioning

themselves or their umbilicals under heavy objects
that might fall or placing themselves above lines that
are under tension. The buoyancy or the weight of water
displaced from a container by the compressed air necessary to raise an object

is

equal to the weight of the

object in water plus the weight of the container.

It

is

important to remember that:
•

The container should be vented

•

The air will expand if the object is raised from the
bottom before all the water has been displaced

air

8-26

from rupturing

to prevent excess

it;

tubes.

One

with ordinary automobile

regular-sized inner tube will

tire
lift

inner

about

100 pounds (45.4 kg). The tube or tubes are rigged with
them together and with the

a short loop or rope holding

valves pointing toward the bottom. (The valve caps

and cores must be removed.) A rope loop is attached to
the object to be lifted and is then pulled down as close
to the object as possible, because inner tubes have a
tendency to stretch to about twice their original length
before lifting starts. An ordinary shop air nozzle with a
spring-loaded trigger

is

attached to a short length of

low-pressure air hose and

is

then plugged into the

low-pressure port of a single-hose regulator first-stage

NOAA

Diving Manual

— October 1991

Working Dive Procedures

mechanism. This device

is

attached to a separate air

cylinder for transport to the work
nozzle

The end

site.

of the

and pushed so
and the object

inserted into the tire valve opening

is

The tube

that air will not escape.

fills,

Care must be taken to leave the
valve open, because the expanding air on surfacing
rises

to the surface.

the object cannot be lifted to the surface directly

If

by winching or lift devices, the rise of the tide can be
used if a large vessel or pontoon is available. At low
connected tautly to the object and the

tide, lines are

surface platform; as the tide

rises,

the load rises with

it.

could burst a closed system. With practice, objects can

Every salvage project must be planned and executed
Novice divers should not attempt under-

be raised part-way to the surface and moved under

individually.

kelp canopies, etc., into clear water, where they can be

water salvage tasks for which they are not properly

surfaced and towed. Divers using this technique should

trained or equipped.

accompany

try to

the object to the surface and should

way expose themselves

not stay on the bottom or in any

drop or ascent path of the object. This technique

to the
is

8.9.2 Air Lifts

An

especially useful to biologists lifting heavy bags of

Although the innertube method works, commercially
for

lift

bags are preferred. These bags are designed

heavy duty use, come

from 100

to

20,000

lbs

in a variety of sizes

(45.4-9080 kg) in

and have built-in overpressure
valves.

They

ranging

and/or

dump

and readily trans-

also are lightweight

weighs only 6 lbs (2.7 kg), and a 1/2-ton-capacity bag
weighs only 14

mud, and similar materials from the holds of
some cases of
stranding, an air lift may be used to clear away sand

mud from the side of the vessel (Figure 9-39);
An air lift works on the pressure-differential princi-

and
ple.

Air

introduced into the lower end of a partially

is

submerged

pipe.

The combining

of air bubbles with the

liquid in the pipe forms a mixture that

is

less

dense

than the liquid outside the pipe. The lighter density

head pressure inside the pipe than outwhich causes the mixture to rise in the pipe. The
amount of liquid lifted depends on the size of the air
lift, submergence of the pipe, air pressure and volume
side,

lifting

an object, the

bag should be inflated

lift

Inflation should cease as soon as the object begins to
off the bottom.

rate of ascent
to lose control.

may

Because

expands as

air

it

rises,

Loss of control
tip

is

over

dangerous, and

when

it

it

used, and the discharge head.

the

increase rapidly, causing the diver

can cause the bag to

also

An

to the

bottom. The bag's

dump

valve, therefore,

should be used carefully to control ascent.

discharge pipe and a foot

The

size of the discharge pipe

ranges from approximately 3 to 14 inches (7.6-35.6

reaches the

surface, spilling the air out and sending the object

air lift consists of a

piece or air chamber.

in

back

mixtures of water, grain,

lift

results in less
lbs (6.4 kg).

slowly from a spare scuba cylinder or other air source.

lift

used to

ships during salvage operations. In

lifting capacity,

relief

portable, e.g., a bag capable of lifting 100 lbs (45.4 kg)

When

is

sand,

specimens.

available

air lift

done and the service intended. The air chamber
should be located approximately 20 to 30 inches
(50.1-76.2 cm) from the end of the pipe. Table 8-3

may

be used as a guide

charge pipe and

WARNING

air available

An

Do Not Use Your Buoyancy Compensator as
a Lifting Device While Wearing the Compensator

cm)

diameter, depending on the amount of work to be

in selecting the size of dis-

air line, taking into consideration the

and the job

to be done.

air lift operates as follows: the

submerged

in

the mixture

discharge pipe

to be lifted to a

approximately 50 to 70 percent of the

total length of

The air is turned on, and the lifting operation
commences almost immediately. Occasionally, considerthe pipe.

able experimentation
In addition to the type of

lift

bags shown

in

Fig-

amount of

is

necessary to determine the

air required to

operate the

lift

efficiently.

ure 8-18, special computer-controlled lifting systems

The use

of air lifts in archeological excavation

have been developed for large salvage jobs (Kail 1984).

described

in

These systems are relatively insensitive
velocities to be held constant

even for loads as great as

Such systems can be used

for

October 1991

8.10

emplacing and

retrieving heavy instrumentation packages as well as
for salvage.

is

Section 9.12.2.

to surface

weather conditions and permit both ascent and descent
15 tons.

is

depth of

FROM AN UNANCHORED
PLATFORM
DIVING

Diving from an unanchored barge, small boat, or
can be an efficient method of covering a large

vessel

— NOAA

Diving Manual

8-27

Section 8

Table 8-3
Selection Guide For Discharge Pipe and Air Line

Diameter of
Pipe, inches

Diameter

Compressed

of

3
4
6
10

Cubic

Gallons per
Minute

Air Line, inches

.50

50--75

.75

90- -150

1.25
2.00

210--450
600- -900

Feel: of

Air

15-40
20-65
50-200
150-400

Source:

area for search or survey purposes.

towed from a boat that
referred to as liveboating.

diver but the diver

is

is

When

a diver

is

under way, the technique

is

When

liveboating

is

(1979)

used, the following safety pre-

cautions are recommended:

a boat accompanies the

not attached to the boat and

being propelled by current alone, the technique
drift diving.

When

NOAA

is

is

•

boat should be equipped with a "jet

propeller.

There are procedures and safety precau-

tions that apply to both kinds of diving; these are

If possible, the

dive" propulsion system, which has no rudder or

called

•

If the

boat

equipped with a propeller, a propeller

is

cage or shroud should be fabricated to protect the

described below.

divers.
•

WARNING

A

communications system should be

practiced prior to diving.

When

Liveboating or Drift Diving, the Engines
of Both the Small Boat and Large Vessel (if
Any) Should Be in Neutral When the Divers
Are Close to the Boat or Are Entering or Leaving the Water

tow or descent
•

Liveboating
Some underwater tasks require great distances
covered in a minimum amount of time. These
include inspecting a pipeline, surveying a habitat

searching for a

lost

to be

tasks

Free-swimming divers are inefficient at carryand quicker methods of search or

survey are needed. Devices such as
sion units,

swimmer

to

Divers being towed should carry signal devices

from the boat and tow line.
Unless there is danger of entanglement, the divers
should carry a surface float to assist the boat crew
in tracking them. The float line also can be used
If diving

If diving

A

•

another method

of searching a large area. This technique

is

called diver

The boat should be equipped with

and vary their depth according to the contour of the
bottom, which allows them to make a closeup search of
the area over which the boat is traveling.

•

8-28

and

all

charts, radio,

and resuscitator, emergency

air sup-

equipment required by the Coast Guard

The boat operator should know the procedure
alerting the Coast Guard in case of an accident.

for

All personnel on board should be thoroughly briefed

on the dive plan.

One

Liveboat Divers Should Be Careful to Moniand Control Their Depth to Avoid Developing an Embolism

aid kit

for safe boating operations.
•

tor

with surface-supplied equipment, one

ladder or platform should be available for

ply,

towing; the divers hold onto a line attached to the boat

WARNING

on the bottom.

with scuba, two divers should be towed

boarding.

first
is

weather

become separated

the boat suited up and ready to dive.
•

increase diver efficiency.

Towing a diver behind a small boat

from the

diver should be towed while the other remains in

propul-

wet subs, or towed sleds may be used

line separate

together.
•

wide area, or any number of similar opera-

ing out such tasks,

A

may be employed.

for signaling the divers while they are
•

site,

instrument, observing fish popula-

line

conditions such as fog, in case they

8.10.1

tions.

up between

(whistle, flare, etc.) especially in adverse

•

tions over a

set

the diver and the boat, with signals agreed on and

and inexpensive method of liveboating
single towline with loops, a tow
bar, or a fluked anchor for the divers to hold. Divers
using such an apparatus should be towed at a comfortable speed that will not dislodge their masks. The
height above the bottom at which the divers travel is
practical

involves the use of a

NOAA

Diving Manual

— October 1991

Working Dive Procedures

controlled by the speed of the boat and the ability of

length of the towline from the position of the surface

the divers to arch their bodies and to plane up or down.

boat at the time of observation.

A

back to a
yoke with a short line for each diver works best. There
should be two crew members in the tow boat, one to
single towline, rather than a bridle, leading

operate the vessel and the other to watch for surfacing
divers and to keep the towline from fouling in the boat

In areas

may

where entanglement

not a problem, divers

is

wish occasionally to drop off the towline during

A

traverses to investigate objects of interest.

m)

(13.4

50-foot

return line attached to and trailing behind the

aquaplane can be used

to

permit a diver

who drops

propeller.

the sled to grasp the line and return to the sled.

The equipment necessary for towing divers is readily
available. The boat should have at least a 30-hp engine
and should be large enough to accommodate three or
more people and the diving equipment. A towline of
1/2 or 5/8 inch (1.3 or 1.6 cm) nylon line about
200 feet (61 m) long used with about 75 pounds

important for those

(34 kg) of weight permits divers to reach depths of
to

90 fsw (27.4 m). The towing weight should be

made

of two or three pieces of lead, steel, or concrete.

up

Three 25-pound (11.3 kg) lead

balls are ideal

are doing, especially
to

hang up on
1/2 inch (1.3 cm)

submerged objects. A return line of
nylon 50 feet (15.2 m) long should be tied to the
towline at the weights. Polypropylene line should not

be used because
trail

it

is

buoyant. The return line will

behind the towed divers, who hang onto the

towline at or near the weights.

Any time one

diver leaves the towline, the partner

should monitor the departing diver's actions until he or

made

she has again

contact with the return

line. If

the

may

aquaplane released by

sled or

downward by

Some tow

itself

and

have a small wire

rigs

built into the towline, with a

waterproof pushbutton

switch, so that the divers can

communicate by buzzer

with the tow boat.

One

of the best

methods of towing

divers, especially

they intend to drop off the towline,

arm

is

to

equip each

of the yoke with a large cork float, such as those

used on fishing nets or mooring pickup poles. The diver
merely straddles the cork and hangs onto the

The towing

pull

is

ahead.

line

then between the legs and not on the

hands and arms. Maneuvering by body flexing

easy,

is

and when the divers wish to leave the line they merely
release their grip and spread their legs, allowing the
cork to

rise rapidly to the

know

boat

surface to

let

the divers are off the line.

personnel

As soon

the

in

as the

cork breaks the surface, the boat stops, backs up along
the line to the cork (the boat

abandon the towline and both divers must surface

line to the boat),

must not

pull the cork

and hovers, with the engine

and

in neutral,

near the bubbles until the divers surface. The divers

Another liveboating method uses the aquaplane (Fig-

The simplest

ure 8-19).
tilted

is

the divers

they intend to drop off the line

A

diver fails to regain the return line, the partner must

together.

know what

boat to

continue planing

crash into the bottom.

because

less likelihood that a ball will

is

if

observe the bottom.

a diver

if

there

in the

off

It

downward

is

a

shown

that,

when

the tow. Experience has

dynamic

thrust

danger of losing the bubbles using

board

corresponding pull on the towing cable.

to counter the

The addition

version

or sideways, provides a

can then hand over samples, relate findings, and resume

of a broom-handle seat and proper bal-

that there
this

or no

little

is

method, because

the relatively slow towing speed of the boat allows the

cork to surface within seconds of being released.

The

ancing of the towing points permit one-handed control

cork should surface at a point very close to the place

of the flight path.

With an aquaplane, which can be
few hours from off-the-shelf materials, a
team of divers can be towed behind a small boat; as

where the divers dropped off the

made

not used and

in

a

with other towing methods, the

maximum

be such that the diver's mask

not torn off.

is

speed must

The

dive

team may operate either in tandem off the same board,
which requires some practice and coordination, or each
diver

As

may have
in

the

traverse (see Section

the diver keys observation to time.

10.16.5),

At the same time,

a

surface attendant notes the location of the tow boat or
escort boat as

it

line.

moves along the traverse, with horimarking locations versus time.

to be

is

a

lowered slowly and carefully overboard, so as not

to hit the divers below.

The towboat should stand by

vents the surface boat from being carried

at

away from

the survey area by current or wind.

The scope
and

in

of the towline

may

be as

much

as 10-to-l,

deep water this could place a diver far behind

Later, the position of the diver at times of recorded

earlier, the

observations can be determined by subtracting the

the diver

Diving Manual

is

chance that they are temporarily lost. In this case, a
standby buoy with an adequate anchor should be ready

the tow boat. If a weighted line

— NOAA

method

bubbles cannot be seen from the tow boat, there

zontal sextant angles

October 1991

If this

after the divers drop off a tow, their

the buoy until the divers surface. This technique pre-

a separate board attached to a yoke.

swimming

if,

is

is

used, as described

scope can be reduced to about 4-to-l.
a long distance

behind the tow boat,

If

a

8-29

Section 8

Figure 8-19

Aquaplane

for

Towing Divers

Source: iMOAA (1979)

safety boat

may be

used to follow the towed divers to

them if they become separated from the towline.
Whenever a towing operation is planned, regardless
of the equipment or method used, it is advisable to
assist

conduct a series of practice runs to determine the best

combinations of boat speed, towline-yoke length, and
diver-boat signals.

Although towing

is

a useful

way

of terrain, there are limitations

technique.

It

is

to

especially cautious to keep the umbilical clear, and
positive

may wish

The

system that
allows monitoring of the diver's communication. If
diver-to-surface communication is interrupted for any
reason, the engines must be stopped.
bridge also

to incorporate a

cover a great deal

and drawbacks

difficult to take notes or

to this

photographs

8.10.2 Drift Diving

while under tow, unless enclosed sleds are used. There

may

communications must be maintained between

the bridge on the large vessel and the tender.

be considerable drag on the body, so one should

Drift diving

area

when

is

used occasionally to cover a large

there are strong currents. Divers are put

hands should not be used for anything but holding on.

water upstream and drift with the boat, which
buoy with a clearly visible diver's flag. If the
operation must be conducted in heavy currents, divers

Sample bags, cameras,

should enter the water as far upcurrent as necessary

not carry bulky equipment either in the hands or on the

weight

belt.

Until the diver leaves the towline, the

should be attached to the

etc.,

towline with quick-release snaps.
to

The amount

of work

be accomplished and the equipment to be carried

can be determined

in

predive practice.

into the

trails a

and

drift

with the current, holding onto a line attached

to the drifting boat. Drift diving

only

when observers

should be carried out

in the drifting

boat can see the

Liveboating also can be used when surface-supplied

diver's bubbles. If the drift involves a large vessel, a

umbilical systems are provided.

Under such conditions,
must be slow (0.5-1.5 k (0.25-

small boat should be used to track the divers and to

the speed of the boat

pick them up.

As with

liveboating, drift divers should

0.75 m/s)), carefully controlled, and determined by the

carry appropriate signaling devices (see Section 8.10.1).

experience of the divers. Precautions must be taken to

During pickup, the boat operator should not (except
an emergency) approach the divers until the entire
dive team is on the surface and has given the pickup

avoid fouling the diver's umbilical in the propeller.

Generally, the propeller

is

covered by

a specially

in

The

constructed wire or metal rod cage, and the umbilical

signal.

"buoyed" so that it floats clear of the stern. When
liveboating from a large vessel, it may be desirable to
tow a small boat behind the vessel and to tend the
towed diver from the smaller boat. The tender must be

side the dive party on a

is

8-30

boat's operator should bring the boat along-

downwind

or downcurrent side,

and the dive tender should assist the divers aboard. In
all cases, the boat's motor should be in idle during
pickup, with the propeller in neutral.

NOAA

Diving Manual

— October 1991

Working Dive Procedures

WARNING

explosion, losing

its

intensity with distance.

pressure waves follow the

Liveboating or Drift Diving Should Never

Be

Conducted With Inexperienced Personnel

UNDERWATER DEMOLITION AND
EXPLOSIVES

Many underwater

Less severe

shock wave very

closely.

For an extended time after the detonation, there is
considerable turbulence and movement of water in the
area of the explosion.

8.11

initial

Many

factors affect the intensity

of the shock

wave and pressure waves; each should be

evaluated

terms of the particular circumstances

in

in

which the explosion occurs and the type of explosive

tasks require the use of explosives.

Several different types of explosives are available, and

involved.

Type of Explosive and Size of

the Charge.

Some

these can be applied in a variety of ways. Because

explosives have high brisance (shattering power

explosives are powerful and dangerous tools, they should

power at
long range, while others have reduced brisance and
increased power over a greater area. Those with high
brisance generally are used for cutting or shattering

be used only by trained personnel.

To achieve accurate

underwater applications, the explosive must

results in

be selected carefully and positioned properly.

immediate

in

the

vicinity of the explosion) with less

Explosives are used under water to remove obstruc-

purposes, while low-brisance (high-power) explosives

open new channels or widen existing ones, and

are used in depth charges and sea mines, where the

tions, to

to cut

through

or cables.

steel,

They

concrete, or

wooden

pilings, piers,

are also used to trench through rock or

coral.

Explosives suitable for underwater use include primacord, various gelatins, plastics, precast blocks,
liquids.

Such

and some

charges are relatively safe to use

if

the

target

may

not be in immediate contact and the ability

damage over

to inflict

a greater area

is

an advantage.

The high-brisance explosives therefore create a highlevel shock wave and pressure waves of short duration
over a limited area. High-power explosives create a
less intense

shock and pressure waves of long duration

manufacturer's instructions are observed and general

over a greater area.

safety precautions for explosives handling are followed.

sive to be utilized

Bulk explosives (main charges) generally are the most

use to estimate the type and duration of the resulting

stable of the explosive groups; there

shock and pressure waves. The principal characteris-

less stability

progressively

is

with the secondary (primers) and

tor (detonators/blasting caps) groups.

initia-

Initiators

and

tics

of the most

shown

tion are

in

The

characteristics of the explo-

need to be evaluated carefully before

commonly used
Table

explosives for demoli-

8-4.

secondary explosives always should be physically
separated from bulk explosives.

WARNING

WARNING
Only Properly Trained and Certified Personnel Are Permitted to Handle Explosives

An underwater

explosion creates a series of waves

that propagate in the water as hydraulic shock

waves

hammer") and in the seabed as
seismic waves. The hydraulic shock wave of an underwater explosion consists of an initial wave followed by
further pressure waves of diminishing intensity. The
initial high-intensity shock wave is the result of the
(the so-called "water

and liberation of a large volume of gas,

violent creation
in

the form of a gas pocket, at high pressure and tem-

perature. Subsequent pressure waves are caused by

Before Any Underwater Blast All Divers Should
Leave the Water and Move Out of Range of
the Blast

If a

diver must remain in the water, the pressure of

the charge a diver experiences from an explosion

must

be limited to less than 50 to 70 pounds per square inch
(3.5-4.9

kg/cm 2 ). To minimize

pressure wave effects,

up a position with feet pointing
toward the explosion and head pointing directly away
from it. The head and upper section of the body should
be out of the water, or divers should float on their back

a diver should also take

with their head out of the water.

rapid gas expansion in a noncompressible environment,

For scientific work, very low-order explosions are
occasionally used to blast samples loose or to create

which causes

pressure waves through substrata. Each use must be

a

sequence of contractions and expan-

sions as the gas pocket rises to the surface.

The

initial

dangerous;

it

high-intensity shock wave is the most
travels outward from the source of the

October 1991

— NOAA

Diving Manual

evaluated

in

terms of diver safety and protection. Bot-

tom conditions, the degree of the diver's submersion,
and the type of protection available to the diver can

8-31

Section 8

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Diving Manual

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— October 1991

4

Working Dive Procedures

Figure 8-20

Underwater Cameras
modify the effects of an explosion and must be considered

in

Divers also should be cautioned against diving
vicinity

A. Watertight

Camera

planning a dive involving the use of explosives.

when sub-bottom

air or

high electrical discharges

8.12

UNDERWATER PHOTOGRAPHY

Scientists can use three

in the

profiling using high-pressure
is

being conducted.

methods

to

document under-

water events: written records, tape recordings, and
photography/television. This section describes the use
of photography and television in underwater work.

Courtesy Nikon

Either diver-held cameras or remotely operated cam-

eras can be used, and each has certain advantages.

Diver-held cameras allow the photographer greater
mobility and permit

more precise positioning

B.

Standard Camera

in

Watertight Housing

in rela-

tion to the subject than can be achieved with remotely

controlled cameras.

On

the other hand, the remote

camera disturbs underwater subjects

than the pres-

less

ence of a diver, and such cameras can operate at depths
difficult for divers to reach.

8.12.1 Still

8.12.1.1

Photography

Lenses and Housings

A 35-mm

camera

is

a

good starting point

for under-

water photography; cameras of this type can then be
modified as necessary to meet task requirements.
categories of

camera can be used under water:

ments specifically designed

to

operate

Two
C. Motor-Driven

instru-

and Motor Winder Camera

in

Watertight Housing

the sea and

in

that have water-tight sealing, such as the Nikonos®, or

cameras designed for air use that are then housed in a
watertight casing (Figure 8-20). Cameras designed

underwater use are easily portable and are relacameras that have
been adapted for underwater use are more versatile
for

tively simple to use, while land-use

because they can be modified

The choice
water

is

of lens for any

easily.

camera

to be

used under

dictated by the required field of view and the

Because the distance from camera
must be short compared with that in air
(Figure 2-5), a photographer who wishes to photograph a
broad expanse must use a lens that has a wide degree of
clarity of the water.

to subject

A

coverage.
visibility
ity,

is

good rule of thumb

is

Ikelite

Underwater Systems

that photographic

only about one-third as good as eye visibil-

which means that

Courtesy

a wide-angle lens

is

an impor-

tant tool even in clear water.

Wide-angle lenses create optical problems

of water require that wide-angle lenses be corrected

before they are used under water; a correction for
underwater use can be designed into the lens formula

under-

(an expensive but effective approach), or corrective

used through a plane parallel port

ports can be placed in front of the lens. Attaching a

facing the water, these lenses produce distortions and

Plexiglas® dome (part of a hemisphere) and making
an allowance for closer focusing of the lens than is

water use.

When

color aberrations, narrow the angle of view,

sharpness at the periphery.

October 1991

— NOAA

The

in

and

lose

optical characteristics

Diving Manual

necessary

in air solves

the underwater wide-angle lens

8-33

Section 8

Figure 8-21
Basic Equipment for Closeup

and Macro Photography
Locking Screw

problem
ter

at lesser cost.

Several commercial underwa-

Support Rod

Wire Framer

housings have built-in corrective capabilities, and

Locking Screw.

sealed cameras can be fitted with lenses that range

from 15

to

mm in width.

80

Close-Up Lens

When

close-up photography of small objects is
required, a plane parallel port coupled with lenses of
longer focal length is useful. This type of photography

demands ground

9.25 Inches
(23.4 cm)

glass focusing for precise framing,

whisker sharpness of the image, a lens that can focus
closely on the object,

and

at least

one light source

Locking Knob

coupled to the camera. Plane parallel ports are helpful

when using

a longer lens

because they enhance the

telephoto effect without noticeably destroying the
sharpness or color quality of the picture. For example,

A

Locking Screw

/

i

the use of a Nikonos® close-up kit with a standard
35

mm

lens allows clear pictures to

be obtained

distance of 9.25 inches (23 cm); with the 35

Locking Screw
at a focal

mm

lens

must be 33 inches (84 cm). This
achieved through the use of an optically

alone, this distance

ability

is

matched auxiliary magnifier

lens that

is

Framer Bracket
A.

Closeup

placed over

Extension Tube

Lens

Wire Framer

the primary lens.

Another method of obtaining close-ups

is

macro

photography. This technique involves placing an exten-

between the camera's body and the lens to
A framer extension is attached
in front of the lens to ensure proper framing and focal
distance, which allows pictures to be obtained at distances as close as 2.5 inches (6.3 cm) from the subject.

sion tube

extend the focal length.

In addition to the high magnification,

raphy offers maximum color saturation, sharp focus
due to the strong flash illumination, and minimal sea
water color filtration because of the short focal distance (usually 3-7 inches (7.6-17.8 cm)). Figure 8-21

shows the basic equipment needed for closeup and
macro photography.

Unmodified off-the-shelf underwater cameras or
simpler housings for air cameras only permit a photographer-scientist to

work

in the

mid-distance range;

although useful data can be collected at this distance,
long distance, closeup, and

Courtesy Geri Murphy

macro photogB.

Macro

life.

In comparison, the ground glass focusing of the

housed camera and
ers to

its

longer lenses allow photograph-

work farther away from

their subjects.

The under-

water photographer must weigh the advantages and
disadvantages of each technique to determine which is
most suitable. An excellent series of articles comparing closeup and macro photography was recently
published in Skin Diver Magazine

(Murphy 1987-1988).

macro photography can

provide valuable additional information. Well-designed

and engineered housings for air cameras are heavier
and bulkier and require more maintenance than sealed
underwater cameras; however, housed cameras can be
more flexible and have a broader range of wide angle
and closeup capabilities than underwater cameras.
Another disadvantage of sealed cameras is that the
diver must work within a rigidly defined distance from
his or her subject and must rely on mechanical framing
rods to determine distance. Few fish will tolerate a
metal framing rod in their territory, and these rods
often cause unnatural behavior in fish and other marine

8-34

8.12.1.2 Light

and Color

Light and color go hand in hand in underwater pho-

tography (Figure 8-22). Color films balanced for either
daylight or tungsten light are relatively blind to the
color subtleties that the eye can distinguish within the

blue and green spectra of water.

When

light in shallow depths, filtration offers

sation.

A

using^ available

some compen-

color-correction filter (Table 8-5) over a

up enough so that a certain
amount of color is restored. The color red disappears at
approximately 22 feet (6.7 m), orange vanishes at
lens will break blue color

NOAA

Diving Manual

—October 1991

Working Dive Procedures
Figure 8-22
Diurnal Variation of
Light

Under Water

When

the sun

is

90° above the

is only reflected
by three percent as it enters the
water; nearly all the light will be
transmitted below the surface.

horizon,

0sable

its

light

Angle of Sunlight

Low-angle sunlight

is

nearly

totally reflected by the water's

surface.

Water

s

surface

Source:

NOAA

(1979)

approximately 40 feet (12.2 m), and yellow disappears

(Murphy

approximately 80 feet (24.4 m) of water, and no
filtration of the lens can restore it (Figure 8-23). Color

absorption and transmission of light under water, see

at

correction filters that selectively subtract ultraviolet
light

and correct the blue

readily available

(Murphy

shift

found

in

seawater are

1987). These filters, which

1987). For additional information on the

Section 2.8.
Artificial light

illuminates underwater situations and

also brings out the color inherent in the subject.

effective in water, artificial light

are designed and color-balanced for available light at

closer to the subject than

depths ranging from 15-50 feet (4.6-15.2 m), can be

The

attached to and removed easily from the camera while

under water. Because such filters subtract from the
of light reaching the film, however, slightly

amount

longer exposure times are required

October 1991

— NOAA

when they

Diving Manual

are used

To be

must be used much

would be necessary

in air.

and more powerful the light, the more it will
compensate for the inherent blue of seawater. By varying distance and power, different balances can be
obtained; a water-blue background with a slight hint
of color can be achieved as easily as brilliantly illumicloser

8-35

Section 8

Table 8-5
Color Correction

Figure 8-23
Selective Color Absorption
of Light as a Function of Depth
in Clear Ocean Water

Filters

(
Exposure

Underwater path
length of the

increase

Filter

light (feet)

1

CC
CC
CC
CC
CC
CC

.

2

.

5

.

8

.

12

15

05R
10R
20R
30R
40R
50R

1/3
1/3
1/3

2/3
2/3
1

For distances of greater than 15 feet (4.5 m), composite
the appropriate

number

stops

in

of

units

filter

filter

with

can be used.
Adapted from

NOAA

(1979)

nating the subject and completely obliterating the water
quality.

Many good electronic flash units are made for underSome offer an underwater wide beam for use
with wide-angle lenses, others a narrow beam that
may penetrate the water column more effectively. (For

water use.

a

list

of underwater strobe units, see Table 8-6.)

variance in exposure
is

when using

The

different strobe units

caused by:
•
•
•
•

The light beam angle;
The strobe reflector material;
The watt-seconds; and
The guide number of the strobe.

Most strobes designed

underwater use come with

for

an exposure guide (see Table

When

i

8-6).

using macro photography under water, divers

have a choice between manual and through-the-lens
(TTL) flash systems. Although each has its advantages
and disadvantages, the manual system is less expensive, has underwater quick-disconnect features, and
offers better exposure control. In general, the

system

is

manual

method for macro photograsystem does, however, have

The automatic TTL
some advantages. For example, because the length of
the flash is controlled by the amount of light reflected
from the subject back through the lens, the system
automatically compensates for varying distances and
phy.

reflectivity.

This system also provides a visual signal

confirming that the correct exposure was used. Auto-

TTL

systems can be switched readily to the
manual mode as needed; Table 8-7 lists some TTL
mini strobes that are suitable for macro photography.

matic

Tests should be
ous speeds.

It

is

8-36

amount

of blur caused by

of the camera during exposure.

Table 8-8 lists exposure compensations for underwater photography that should be used as a starting
point for work with adjustable cameras. These recommendations are based on the following conditions: bright
sunshine between 10 a.m. and 2 p.m., slight winds, and

availa-

other factors can significantly affect photographic

These shutter speeds should freeze

important to conduct tests before

advisable

possible.

movement

1/100 or 1/125 of a

before the dive to establish

when shooting with

ble light to use shutter speeds of
if

the action and reduce the

about 50 feet (15.2 m). The
degree of visibility, the amount of particulate matter
in the water, the reflective qualities of the bottom, and

made

correct exposures with any unit that uses films of vari-

second,

Derived from Church 1971
Derived from Church (1971)

the preferred flash

underwater

results,

visibility of

and thus

it

is

NOAA

Diving Manual

— October 1991

(

Working Dive Procedures
Table 8-6

Manual and Through-the-Lens
(TTL) Strobes for Closeup

Photography

Mfg.

Akimbo

Head

Weight

Model

Size

In Air

Subatec
S-100

6 x 3.5"

2.75

lbs.

Beam
Depth Beam
Tested Angle Spreader
500

ft.

96

No

Color

Temp.

Batteries

Removable

4,500 K

Rechargeable
Pack

Power No. of Recycle U/W Slave TTL
Modes Flashes Time Guide Mode Mode

Subatec
S-200 TTL

6 x 3.5"

2.75

lbs.

500

ft.

96

No

Removable

4,500 K

Rechargeable
Pack

Scuba
Helix

Helix

Ikelite

Ikelite

Whale Strobe
TTL

7 x 4"

Aquaflash
28

6 x 5"

Aquaflash
28 TTL

6 x 5"

Substrobe
150 TTL

10 x 6"

2.3 lbs.

165

ft.

65

Ikelite

Yes

4 AA
Dry Cells

5,600 K

(95)

II

3.8 lbs.

165

ft.

65

Yes

5,600 K

6

3.8 lbs.

165

ft.

65

Yes

5,600 K

10 x 6"

8

lbs.

lbs.

300

300

ft.

ft.

110

110

No

No

Nikon

SB-103

7

x4"

2

lbs.

160

ft.

65

Yes

5,500

Nikon

SB-102

8.5 x 5.5"

4.3

lbs.

160

ft.

79

Yes

Oceanic

3000 Master

See
& Sea

YS-150

See
& Sea

YS-100 TTL

9 x 5.7"

9.5 x 5"

6 x 4"

4.8 lbs.

5.4 lbs.

2

lbs.

300

350

200

ft.

ft.

ft.

110

100

65

No

No

Yes

Subsea

11 x

6"

8.5 lbs.

350

ft.

150

No

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

No

8

Full

130

7 sec.

32

1/4

450

2 sec.

16

Full

80

10 sec.

40

1/4

300

sec.

22

10 sec.

1

1

1

11

Full

80

1/4

300

1

150
300
600

6 sec.
3 sec.
2 sec.

22

125
250
500

6 sec.
3 sec.

32
22

2 sec.

16

130
450

12 sec.
4 sec.

24

sec.

5.6

1/4

1/2

4 AA
Dry Cells

Full

1/4

1/4

sec.

16
11

12

1/16

1,400

6C

Full

33

1/4

120
400

14 sec.

Dry Cells

5 sec.

16

1/16

1,200

2 sec.

8

350
650

3 sec.

22

sec.

16

100
200

5 sec.

22

3 sec.

16

5,500°K

Built-in

High

Rechargeable
Pack

Low

1

1

Removable

Full

Rechargeable
Pack

1/2

4 AA
Dry Cells

Full

130

12 sec.

1/2

12 sec.

32
22

12 sec.

16

1/8

250
450
900

12 sec.

11

150
100
50

175
250
325

5 sec.

22

3 sec.

16

5,400 K

(80)

Subsea
Mark 150RG

Yes

11

sec.

1/4

Graflex

Yes

2 sec.

1/4

Full

5,400 K

Yes

16

Removable

5,700 K

40

22

3 sec.

Rechargeable
Pack

(95)

No

4 sec.

1/2

K

Yes

150
250
350
500

1

1/2

Full

(95)

Yes

8

Removable

4,800 K

No

sec.

1/4

Rechargeable
Pack

4,800 K

225 TTL

AA

Yes

16

Dry Cells

6

(95)
7

AA

Dry Cells

(95)

No

22

3 sec.
2 sec.

1/8

Berry

No

4 sec.

1/8

Akimbo

No

150
250
350
500

1

1/2

Removable

5,500 K

Rechargeable
Pack

2 sec.

11

Courtesy Gen Murphy

starting to photograph; these variables can cause

exposures to vary by as

much

as 4 or 5 stops (see

Section 2.8.1.3).

strobe flash systems, flash bulbs (clear bulbs for dis-

tance and blue bulbs for closeups) can
effectively under water (Table 8-9).

still

be used

The longer water

effectively filters the clear bulbs with blue so

October 1991

— NOAA

be aware that the pressure

at great

depth can cause

bulbs to implode; divers have been cut

Although most underwater photographers now use

column

that the light balances for daylight film. Divers should

Diving Manual

bulbs

in

when changing

deep water.

Incandescent lights that are powered either by battery or by a topside generator

and that are a must

motion picture work can also be used

in still

for

photogra-

phy. Incandescent light does not penetrate water as

8-37

'

Section 8

Table 8-7
Through-the-Lens (TTL) Mini
Strobes for Automatic and

Manual Exposure

Manual

Angle

Beam

Color

Guide

Model

(diameter)

(degrees)

Spreader

Temp.

No.

Batteries

No.
Power
Time
Modes (seconds) Flashes

Whale Strobe
TTL

7x4"

65

Yes

5,600 K

32

4AA

Beam
Mfg.

Berry

Scuba

Helix

Ikelite

*

u/w*

Head Size

6x5"

Aqua Flash
28 TTL

Substrobe

MV

Full

7

1/4

2

(95 degrees)

II

5,600 K

Yes

70

6AA

40

1/4

No

65

"

10

Full

(95 degrees)

4.5 x 3.5"

Recycle

5,800

K

20

4

AA

1

5

Full

130
450

80
300

250

Depth
Tested
Extras

(feet)

Confirm

•

165

Signal
•

Test Fire

•
•

Slave
Confirm

•

Signal
Test Fire

•

Inter-

165

300

changeable
sync cords

SB-103

Nikon

7x4"

Sea &
Sea

YS-100TTL

5,500 K

Yes

65

4

24

AA

Full

12

130

1/4

4

450

1/16

1

1,400

(95 degrees)

Speedlight

6x4"

Yes

65

5,400

K

4

32

AA

12
12
12
12

Full

(80 degrees)

1/2

1/4
1/8

Confirm

•

160

Signal

130

•

Slave

250
450
900

•

Audio

200

Ready
Exposure

•

Calculator

Sea &
Sea

*

YS-50 TTL

6x3"

No

72

5,400 K

4

22

AA

10

Full

200

140

*U/W Guide Number based on ISO 50 film with strobe set on full power manual.
'Recycle times and number of flashes based on alkaline batteries. Rechargeable nickel-cadmium batteries produce faster recycle times but fewer flashes.
Courtesy Geri Murphy

Table 8-8

with brackets that permit them to be either mounted or

Exposure Compensation for
Underwater Photography

hand

held.

8.12.1.3 Selection of Film

Number

of f-Stops to

Depending on the quality of the documentation required

Increase Lens Opening

Over Normal Above-Water

Depth

Exposure

of Subject

Just under surface

6 feet

20
30
50

feet
feet
feet

1

m)
(6.0 m)
(9.0 m)
(15.0 m)

1/2f-stops

2 f-stops

(1.8

2 1/2 f-stops

3 f-stops
4 f-stops
Adapted from

NOAA

(1979)

by the diver/scientist, a wide variety of both blackand-white and color films is available (Table 8-10).
The sensitivity of film is measured according to an
American Standards Association (ASA) rating that
ranges for most purposes from 25 to 400 ASA. There
are slower and extra high-speed emulsions available
for special purposes and techniques.
Film is merely a base on which an emulsion of lightsensitive, microscopic grains of silver halide has been
placed. These particles react to light in various ways
that affect the following:

well as electronic or flash bulb light,

and these

lights

are also clumsier to use.

Lighting arms and brackets or extension cords allow

off-camera light to be placed

in

many

positions (Fig-

ure 8-24). Lights should not be placed on the camera

•

Grain, which

is

the clumping of silver halides.

High-speed film clumps more rapidly than slower
film, and enlargements show graininess more than
small pictures. Grain tends to destroy the sharpness

and

detail of a photograph, but

it

can be reduced

or increased in processing.

To obtain sharp

water directly can curtain off the subject matter and

tures, film of the finest grain

should be used, unless

increase backscatter. Underwater exposure meters, pri-

the light

marily of the reflected-light type, are manufactured

necessary.

lens axis,

8-38

because lighting suspended particles

in the

is

insufficient

NOAA

pic-

and a high-speed film

Diving Manual

is

— October 1991

Working Dive Procedures

Table 8-9

Underwater Photographic
Light Sources

Type of

Depth

Lighting

Limit(ft)

Noturol

50

100

to

Control

Accuracy

Light Subject

of Effects

Limiting

of Color

for the

Human

From

Visibility

Rendition

Eye as Camera
Will See If

Light

fair to

poor
(predominantly
green)

very good

scattering

absorptivity

fairly

good

very good

absorptivity

none

Flood

Ability to

Factors

Means

Duration

of

Power
Extent
Requirement of Use

Intensity

Determining
Exposure

good

meter

none

guide number
determined
by experiment

high

(sec)

Remarks

Scattering

continuous

good

at surface

general

but decreases

with depth
/ery

good

relatively low

continuous

scattering

(

general,

2

1

to2kw)

especially
at greater

depths

none

Flash bulbs

absorptivity.

good

fairly

poor

fair

1

50 to

1

100

guide numbers

h.gh

general

self-

scottermg

contained

replace
bulbs

battery

none

Electronic

absorptivity

good

foirly

poor

fair to

scattering

flash

very

good

1

1

1

2

000
000

very high

to

or

Diver must

general

Electronic

guide numbers,

self-

automatic

contained

flash

battery

probably

faster

is

better

than
regular
flash for

use under
water

Adapted from

•

Resolving power, which

the ability of the film to

is

hold fine details; resolving power
the

number

will

record distinctly.

is

measured

•

in

made from
be viewed

the finer the grain, the higher the resolving power.
•

Latitude

the over- and under-exposure toler-

is

ance of a film. Wide-latitude film is best under
water because a picture can be obtained even when
the exposure

film
•

this film,

and the resulting picture can

in its true

perspective shortly after the

Storage and
is

shelf-life.

The storage and

shelf-life

often an important consideration. For

atively high storage temperatures but

may

rel-

shift

with a 4 f-stop variance, while color transparen-

color with aging. Professional films, however, remain

cies of short latitude will tolerate only a

constant in color but must be stored under temper-

A

deviance.
ing

1/2 f-stop

wide-latitude film should be used

whenever a good picture

is

make

ature-controlled conditions.

necessary and bracket-

impractical. Color negative films, which are

is

used to

color prints, offer better latitude

A

fast

film,

such as Eastman Kodak Ektachrome

film that has an

ASA

value of 200, can produce very

than color reversal films, which are used to pro-

acceptable results, with good depth of field at moder-

duce color

ate light levels.

In low light conditions, the effective

ASA

be increased four times to

slides.

Color balance, which
film.

Films are

made

is

to

problem only of color
match the color temperaa

tures of different light sources-daylight, tung-

value

may

ASA

800.

although this film speed requires special processing
(see

Table 8-11). Black-and-white films are available

are color-balanced for outdoor use in sunlight and

ASA of 1200. As
ASA's are approached, however, black-and-white
films lose shadow detail during developing.
When taking underwater pictures with a flash or

for use with electronic flash systems.

strobe, both the f-stop generated

sten, strobe, etc. Processing

and printing greatly

affect the ultimate color balance.

Both color reversal

and color negative films are daylight

•

work under water.

example, over the counter films can withstand

white negative film will allow sufficient exposure

•

still

developed.

is

of film

not exact. For example: black-and-

is

used most commonly for

Slides or black-and-white or color prints can be

related directly to grain:

is

(1979)

Color reversal. Color reversal (positive color) film
is

of lines per millimeter that the film
It

NOAA

Contrast

the difference in density between darkest

is

shadow and
trast

is

brightest highlights.

Under water, con-

low because of the diffused

results, film with high contrast

light. For best
should be used

under water.

October 1991

films; both

— NOAA

Diving Manual

that can be processed to achieve an

higher

by the strobe or flash

and the available light (f number registered on the
light meter) must be considered. In this case, the aperture must be adjusted to accommodate the stronger of the
two light sources or a flash distance must be selected
that will equalize the natural and artificial light levels.

8-39

Section 8
Figure 8-24
Lighting Arms and Brackets
for

Strobe Systems

Hydro Vision International
Photo Cobra Flash Arm

Top: Sea

& Sea YS 100 TTL Strobe

Insert:

Sea & Sea Motormarine

Helix Aquaflush

Nikonos Speedlight SB-102 and SB-103

8-40

28TTL

Insert: Helix Universal

Slave Strobe

Courtesy Sea & Sea, Hydro Vision International, Nikonos®, and Helix

NOAA

Diving Manual

—October 1991

i

Working Dive Procedures
Table 8-10
Films Suited

Still

for

Underwater Use
Dayligh

Resolving

t

ASA

Film Type

Description

Sharpness

Grain

Power

high

very

high

Daylight Color

Eastman Kodak Ektachrome 64

A medium-speed

64

color slide film for

general picture-taking purposes, e.g.,

Daylight

macro, closeup,

Eastman Kodak Ektachrome 200

A high-speed

200

flash, available light

deep available

Eastman Kodak Ektachrome 400

A

400

very high-speed color slide

deep
Eastman Kodak Kodachrome 25

25

Daylight

Eastman Kodak Kodachrome 64

64

~

film for
(e.g.,

available light)

Moderate speed, daylight balanced
(e.g., macro photography)

high

A medium-speed

high

extremely

extremely

closeup,

(e.g.,

high

fine

color slide film for

general picture-taking

Daylight

high

fine

(e.g.,

light)

general picture-taking purposes

Daylight

very

high

color slide film for

general picture-taking purposes

Daylight

fine

high

fine

flash, available light)

Eastman Kodak Kodachrome 400

A

400

"

very high-speed color slide film for

extremely

very

fine

high

~

~

~

Slow-speed film for a very high degree
of enlargement

very

extremely

very

high

fine

high

Medium-speed

very

extremely

high

high

fine

very

very

high

fine

very

extremely

high

fine

general picture-taking

Daylight

deep

(e.g.,

available light)

Vericolor

II

S

100

Professional color negative film for
short exposure times (1/10 sec. or
shorter)

Black and White

Panatomic X

32

Plus-X Pan

Tri-X

film for general purpose
photography where a high degree of
enlargement is required

125

Pan

400

purpose film when the
enlargement required is

Fast, general

degree

of

medium

not great

Verichrome Pan

Medium-speed

film for general purpose
photography where a high degree of
enlargement is required

125

Note: Proper color balance occurs when colors are reproduced as they actually are. Making warmer or colder tones

cameraman. All color films should be exposed properly and have good
At more than ± Vfc stop, color reproduction differs noticeably from the original color.

aesthetic decision of the

±

1

/2

stop.

high

is

Adapted from

Infrared film has opened up new possibilities in underwater photography; however, because of drastic color

changes, infrared film
color documentation.

ASA
in

20

at

1/60 sec

feet (6.1

October 1991

at

yellow

filter

(1979)

should be used to exclude exces-

sive blue saturation.

starting at

ASA

8.12.1.4

an f-stop of 5.6 on a sunny

Many

m) of water

— NOAA

A

NOAA

not suitable for scientific

Kodak recommends

100, but underwater tests have

50 exposed

day

is

sure.

an

color acceptability at

shown

will give

Diving Manual

that

proper expo-

that

it

Time-Lapse Photography

is

biological

and geological events occur so slowly

neither possible nor desirable to record

them

8-41

Section 8

Table 8-11
Processing Adjustments
for Different

Speeds

Kodak

Kodak

Kodak

Kodak

Change

Ektachrome 200

Ektachrome 160

Ektachrome 64

Ektachrome 50

in

Film

Film

Film

(Daylight)

(Tungsten)

(Daylight)

Professional
(Tungsten)

800
400
Normal 200
100

640
320
Normal 160
80

250
125
Normal 64
32

200
100
Normal 50
25

the time
the first

developer by

+
+

5 1/2 minutes
2 minutes

Normal

—

2 minutes

For Kodak Ektachrome film chemicals, Process E-6.
Adapted from

continuously on film. Time-lapse photography, which

permits the scheduling of photographic sequences,

is

be able to swim in and out of scenes with as
unnecessary movement as possible.

To cover

the solution in such cases. This technique has been

should be planned.

An

and many other phenomena. It is particularly
useful for underwater studies, where, in addition to
investigating slow processes, the inconvenience and
cost of frequent site visits make other photographic

good amateur work

is

generally in one area.

techniques impractical.

for

Modern technology has

greatly improved underwacamera systems that are triggered automatically
by means of standard timing devices or by remote
command. The time-lapse interval (the time between
ter

photographs)

is

determined by the nature of the event

5 feet (1.5

(1979)

little

a single subject adequately, several dives

used widely for years for studying plant growth, weather
patterns,

NOAA

m)

average for topside shooting

m) used

1:5 (1 foot (0.3

in

for every

exposed). Photographers should consider

using a tripod

if

the objects to be photographed are
Artificial lighting

is

critical

motion picture work deeper than approximately 30

feet (9.1 m).

Surface-powered

cumbersome

lights are

but more reliable and longer-lasting than batterypowered lights. Ideally, a buddy diver should handle
the lights, which frees the photographer to concentrate
on filming techniques.

being studied, the available equipment, environmental
conditions,

and

cost.

The time

interval can vary

seconds or minutes to hours or even days.

of a long-term study using current technology
record being

made

from

8.12.2.1 Selection of Film

An example
is

the

of the scouring and erosion of sand

around offshore platforms and pipeline installations
during storms in the North Sea. In this instance, three
pictures per day were taken over a period of 1 month,
using a stereo-camera system (Photosea Systems Inc.
1984).

A

wide range of motion picture film
in

both 100 foot (30.5

in

tions of the film. This film also has a

broad range of

color correctability that can be applied during print-

and is faster and has more latitude than Eastman
Ektachrome Commercial 7252. Eastman 7294 also is
used frequently for filming at greater depths and on
ing

Because time-lapse systems remain unattended for
long periods, they must be thoroughly checked out for
reliability, leaks, buoyancy, and anchoring before
deployment. They must also be maintained and stored
carefully

when

not in use.

darker days because

it

has a higher

ASA

be processed as easily as 7291 can, and
quality that allows

it

Eastman Video News

Motion Picture Photography

Almost all motion picture cameras can be adapted
for underwater use; such cameras should be confined
in

rugged, reliable underwater housings that will with-

rating,

it

can

has a fine

it

be edited with 7291 scenes.
films 7239, 7240, and 7250 are
to

improvements over Eastman Ektachrome
8.12.2

available for

is

m) and
400 foot (121.9 m) rolls (see Table 8-12). Eastman
Color Negative Film 7291 should yield the best picture information in both highlight and shadow porunderwater photography

EF

(daylight)

7241 and Eastman Ektachrome EF (tungsten) 7242,
both with respect to speed and warmer tone (highlight)
characteristics,

which lend a pleasing overall effect

to

the photographs.

stand rough handling. All camera controls should be
outside the housing and should be as simple as possible.

The camera

also should be balanced properly to be

neutrally buoyant.

The underwater cinematographer

must position the camera himself or herself and must

8-42

8.12.2.2

Procedures

Because

all

film

is

sensitive to heat,

it

should not be

stored in the sun or in hot enclosures. In addition, film

should always be loaded in subdued

NOAA

Diving Manual

light.

Other pro-

— October 1991

Working Dive Procedures

Table 8-12
Motion Picture Films
Suited for Underwater Use

Film

ASA

Type

Description

Black and White
Reversal Eastman Plus-X 7276

.

.

.

50 Daylight

A medium-speed panchromatic

reversal film characterized by

a high degree of sharpness,

good contrast and excellent

tonal gradations

Reversal Eastman Tri-X 7278

.

.

.

.

A high-speed panchromatic

200 Daylight

lent tonal

Reversal Eastman 4-X 7277

.

Negative Eastman Plus-X 7231

.

.

.

reversal film that provides excel-

gradations and halation control

400 Daylight

A

80 Daylight

A medium-speed panchromatic

very high-speed panchromatic reversal film

negative film for general pro-

duction

Negative Eastman Double X 7222

.

A high-speed panchromatic negative

250 Daylight

latest

Negative Eastman 4-X 7224

.

advances

in

speed granularity

representing

film

An extremely high-speed panchromatic negative

500 Daylight

the

ratio

film

Color
Reversal Eastman Ektachrome
Commercial 7252 (Tungsten)

Reversal Eastman Ektachrome

EF7241

.

.

.

Daylight 16

w/85

A color

.

reversal camera film, balanced for dayintended primarily for direct projection
(after processing). However, satisfactory color prints can
be made if they are balanced properly

A high-speed color

.160

.

light

Reversal Eastman Ektachrome

.

.

.

w/85

.

.

.

1

.

.

.

filter

-

exposure,

A high-speed

color reversal camera film balanced for tungsten exposure, intended primarily for direct projection (after
processing). However, satisfactory color prints can be made
if they are balanced properly

80

A high-speed

color reversal camera film balanced for daylight
exposure, intended for use under low-level illumination
both for color news photography and for high-speed photography. Satisfactory color prints can be made if they are
balanced properly

60

Video News 7239 (Daylight)

Reversal Eastman Ektachrome
Video News 7240 (Tungsten)

reversal

originals from

(Daylight)

Reversal Eastman Ektachrome
EF 7242 (Tungsten)

camera

film designed to provide low-contrast
which color release prints (duplicates) of
good projection contrast can be made

filter

w/85 B

filter

=

80

.

.

.

.A high-speed color reversal
Satisfactory color

prints

film,

intended

can be made

for
if

use

in

daylight.

they are properly

balanced
Reversal Eastman Ektachrome

.

.

.

w/85 B

filter

=

250

.

.

.

No data

Video News High Speed 7250
(Tungsten)

Negative Eastman Color
Negative
7291 (Tungsten)

.

w/85

II

filter

-

64

A high-speed color negative camera

film designed for use in
tungsten light and in daylight with an appropirate filter. It
is characterized by accurate tone reproduction, excellent
image structure, and wide exposure latitude. Excellent
prints (duplicates) can be made from the original

Adapted from

October 1991

— NOAA

Diving Manual

NOAA

(1979)

8-43

Section 8

cedures to be observed when taking motion pictures

relief valves,

are:

external pressure

•

When

16-mm equipment, photographers

using

•

•

starting to film, the housed

down

to

m),

returned to the surface, and checked for leaks.

The camera should be held
if

feasible, a tripod

Protective shock-absorbing cases lined with

books,
•

and

camera floods in salt water, the best immediis to pack the equipment in ice and to

keep

frozen until

it

•

the value and length of each scene

are considered during the shooting.
•
•

Different distances, angles, and exposures of each
scene should be shot.

•

Scenes should not be rushed because the beauty of
the sea can be lost

•

Only a few special

when they

only

if

the photographer

is

If ice

camera should
it

in fresh

At the end of the day's work, all camera equipment
should be washed with fresh water.
When the camera and housing are removed from
the water, they should be placed in the shade immediately; this is especially true in the tropics, where
even a minimal exposure to the sun can cause heat

hurried.

effects should be used,

can be delivered to a repair

not available, the

is

be flushed thoroughly by immersing
water or alcohol.

The length of scenes should be varied (some short,
some long); this can be done in editing, but film
if

it

to

aid in the editing process.

can be saved

more informative than photography

of which contain errors.

ate action

Photogiaphers should overshoot at the beginning
to establish the scene

If a

many

facility.
•

foam

Actual underwater experience and experimenta-

as steadily as possible;

(custom-made or commercially

and end of each scene

Wearing a wool watch cap can keep water from the
from dripping into the camera during

tion are often

bought and heavily weighted) should be used.
•

WD

gear in a boat.
(9.1

•

•

camera main40 or

rubber are essential for transporting photographic

camera should
30 fsw

for

reloading.

meter.

be put in the water, taken

up

diver's hair

•

When

released.

equivalent, towels, etc.) should also be on hand.

real-time action.

•

is

basic tool kit should be set

tenance, and spare parts (0-ring grease,

should film at 24 frames per second (FPS) to achieve

At 24 FPS, most motion picture
cameras attain a shutter speed of approximately
1/50 of a second. Such a shutter speed is necessary
for interpreting f-stops when using an exposure

A

because the housing can flood when

inside the

and then

camera housing

to

damage

the film.

are exceptional and an integral

part of the picture.
•

The shooting
but

it

from
•

is

script should generally

be followed,

important to be flexible enough to deviate

it if

the situation so dictates.

most

UNDERWATER TELEVISION

Significant advances continue to be
ter television systems.

Photographers should know their cameras thoroughly
so that they can be used

8.13

effectively.

for the scientific

made

tion,

Procedures

Underwater photographers may find the following
hints helpful:
•

•

Overweighting with plenty of lead makes a diver a
much steadier photographic platform.

A

wet

suit protects against

even when
•

•

it is

rock and coral injuries

not needed for thermal protection.

and working diver with respect

to

hull inspec-

damage assessment, improving working procedures

and techniques, and diving safety. Excellent solid-state
underwater color systems now are on the market that

permit small, compact television cameras to be:
(l) held in the hand, (2) mounted on tripods, (3) worn as
an integral part of a diving helmet (Figure 8-25),
(4) mounted on manned submersibles, or (5) used as an
integral part of remotely controlled systems. Underwater video systems capable of operating at depths as

Photographic equipment should not be suspended
from lines on boats in a rough sea unless the line
has a shock absorber incorporated into it.

great as 35,000 feet (10,668

available. This

capability,

quality of cur-

To

rent video systems, has resulted in television replacing

the extent possible, photographic sequences

m) are now
when coupled with the high

The camera

photography as the method of choice for underwater
and technical documentation.
When selecting an underwater video system, it is
best to choose a system designed specifically for

housing should be taken up open, regardless of

underwater operation rather than to select a "surface"

should be planned before the dive.
•

underwa-

recording natural phenomena, conducting surveys,

documenting experimental procedures, ship
8.12.3 Special

in

These advances offer great promise

Cameras should be taken down

to a habitat

open

unless the housing has a relief valve; pressure pre-

vents cameras from opening at depth.

8-44

scientific

NOAA

Diving Manual

— October 1991

Working Dive Procedures

Figure 8-25
Video Recording Systems

A.

Handycam® System With
Underwater Housing
Courtesy Sony Corp.

C. Diver Using Underwater Video

B.

of

America

Underwater Housing With
Angle Lens Attached
Courtesy

Ikelite

Underwater System

System
Photo by Jim Churcn

October 1991

— NOAA

Diving Manual

8-45

Section 8

Figure 8-26

Commercial Underwater
Video System

Courtesy Hydro Vision International,

The

system packaged for underwater use. Surface television cameras normally operate at high light levels and

television Filming

often are not sensitive enough for underwater condi-

sive) as the selection of a

tions.

Further, surface cameras are sensitized to red

Inc.

selection of a lighting system for underwater
is

just as critical (and often as expen-

camera. Although quartz

iodide lights are often used for underwater work, their

mercury or thallium

light,

while underwater cameras for use in the open sea

lights are not as efficient as

have

maximum

charge lamps because quartz provides a high red spec-

the spectrum.

camera

also

is

sensitivity in the blue-green region of

The dynamic range of an underwater
critical if

under the broad range of

it

is

to

be used effectively

light intensities

commonly

encountered.

To achieve these underwater needs,

tral

output that

absorbed rapidly
is

seawater.

in

On

the

the only source that

produces enough red to allow good underwater color
filming.

specifically

is

other hand, quartz iodide light

dis-

Another alternative

is

a water-cooled quartz

halogen lamp that offers burn times of up to

3

1/2

designed low-light-level television cameras often are

hours at 100 watts at depths to 250 feet (76 m). Like

used; such cameras can record images at light levels as

cameras, underwater lights are designed to operate at

low as 0.0005 foot-candle at the camera tube while

depths of several thousand feet

maintaining a horizontal resolution of 500

meters). Specific factors to consider

lines.

In

addition to operating at low light levels, these cameras

can significantly extend the viewing range. Such sys-

tems offer great potential for working under conditions of low visibility, where the diving scientist needs
to observe or record the behavior of marine life without

(i.e.,

several hundred

when

selecting a

camera include the size and
location of the battery pack, burn and recharge times,
the size of the underwater beam angle, and an arm and
bracket mounting system. Rapid advances continue in
the development and miniaturization of videotape forlighting system for a video

either artificial light or the veiling effect of backscat-

mats. Miniature camcorders weighing less than 3 pounds

ter that occurs with lighted systems. In addition to the

(1.4 kg) have reduced the bulk of video systems

optical characteristics of video cameras, other impor-

permitted the use of high-quality 8

and
buoyancy control; type of viewfinder; automatic versus zone focusing; automatic exposure control with
manual override; and automatic white balance. Other
options to consider are built-in microphones, zoom
lenses, focusing for macro photography, housings, and
tant features to consider include: size, weight,

general ease of operation.

8-46

Underwater

DC, 115

and

mm video tapes.

TV

systems can operate from 12 volts
230 vac input power, which provides
to operate either from large or small

vac, or

the flexibility

diving support platforms.

As with other

television sys-

tems, data can be viewed in real time on the surface or

be stored for later viewing. The combination of a diverheld or helmet-mounted camera, a surface-based moni-

NOAA

Diving Manual

— October 1991

Working Dive Procedures

TV

good diver-to-surface communication system permits the diver to act as a mobile underwater
platform under the direction of the diving supervisor
or a scientist on the surface. This arrangement not only
permits real-time recording of events but greatly

detach, or service a

enhances diving safety by allowing the surface support

wireless communication.

team

narrative

tor,

and

to

a

monitor the activities of the diver continuously.

This monitoring can be done either at the

site

on the

surface or at a remote station or laboratory.

Computer microprocessing technology

also permits

means that
wide variety of data can be recorded, including

video camera. For the diving scientist, this
a

information on such things as environmental conditions,
weather, water conditions, and the results of experiments.

Underwater

TV

is

used

in a variety

(1) attached to submersibles, (2)

the monitoring

in

are obtained

of modes, including

lowered by cable for

mode

when

the

camera

is

manipulated by

a

diver using either umbilical diving gear with hard-

wire communications or a scuba diver with reliable

is

In

either case, the diver's

recorded on videotape, along with the picture.

Commercial systems are available

that are designed

as an integral unit, including a full face

on the output of the

digital displays to be overlaid

camera

or to carry the camera-light module. The best results

mounted

mask, helmet-

or hand-held camera, monitor, and complete

facilities for

two-way communications and videotaping

(Figure 8-26). Divers usually can work with cable
lengths up to 500 feet (152.4

m)

if

floats

and buoys are

used to reduce the drag and the possibility of fouling.

Underwater television technology has reached the stage
where it is preferable, in most cases, to underwater
photography.

Its

advantages include: on-the-spot evalu-

ation of results; instant replay;

communication with

use as a remote instrument, or (3) placed on or near a

surface support personnel both for safety and assis-

structure or habitat for long-term monitoring. Within

tance in the evaluation of results; and cost-effective

working depth limitations, divers

October 1991

— NOAA

may

be asked to attach,

Diving Manual

duplicate films.

8-47

<

(

1

Page

SECTION

9

PROCEDURES
FOR
SCIENTIFIC
DIVES

9.0

General

9-1

9.1

Site Location

9-1

9.1.1

9.1.2

Methods
Electronic Methods

9-1

Traditional

9-2

Underwater Surveys
9.2.1
Direct Survey Methods
Indirect Survey Methods
9.2.2
Underwater Photographic Surveys
9.2.2.1
Underwater Acoustic Surveys
9.2.2.2

9-2

9.3

Underwater Recording Methods

9-5

9.4

Biological Surveys

9-6

9.2

9.4.1

9.5

9.8

9.9

9.10

9.11

9.14

9-8
9-8

9.5.2

Benthic Organism Sampling

9-9

9.5.3

Airlift

Sampling
Midwater Sampling

9-1
9-1

9-12

Shellfish Studies

9-13

Collecting Techniques

9-14

Tagging and Marking Techniques
Botanical Sampling

9-17

9.8.1

Field Procedures

9-18

9.8.2

Collecting Techniques

9-18

9.8.3

Specimen Preparation and Preservation

Artificial

9-19

9-20

Reefs

9-22

Geology
9.10.1

Mapping

9-22

9.10.2

Sampling

9-26

9.10.3

Testing

9-31

9.10.4

Experimentation

9-31

Microphysical Oceanography

9-32

9.11.1

Emplacement and Monitoring

9.1 1.2

Planktonic Studies

9-33

9.11.3

Use of Dye Tracers
Water Samples

9-34

of Instruments

9-32

9-34
9-36

Archeological Diving

9-37

9.12.2

Shipwreck Location and Mapping
Shipwreck Excavation

9.12.3

Artifact Preservation and Salvage Rights

9-40

9.12.4

Significance of Shipwreck Archeology

9-40

9.12.1

9.13

9-4

Plankton Sampling

9.1 1.4

9.12

9-3

9.5.1

9.6.1

9.7

9-3

9-7

Estimating Population Densities

Biological Sampling

9.5.4

9.6

9-2

Capture Techniques

9-37

9-41

9.13.1

Nets

9-42

9.13.2

Seines

9-42

9.13.3

Trawls

9-42

9.13.4

Diving on Stationary Gear

The Use of Anesthetics

in

Capturing and Handling Fish

9-42
9-42
9-43

9.14.1

Response

9.14.2

Selecting an Anesthetic

9-43

9.14.3

Application of Anesthetics

9-43

9.14.4

Diver-Operated Devices

9-46

to Anesthetics

<

i

PROCEDURES
FOR
SCIENTIFIC

DIVES
9.0

GENERAL

Diving

is

widely performed

phenomena and

to

SITE LOCATION

9.1
to

observe underwater

acquire scientific data, and this use

To study any

map

a base

region carefully,

is

it

necessary to plot on

the precise location from which data will be

of diving has led to significant discoveries in the marine

obtained (Holmes and Mclntyre 197 1 ). This

method
that can be used to make valid observations and take
accurate measurements. Using equipment and techniques designed specifically for underwater use, the

important

diving scientist can selectively sample, record, photo-

of the seafloor, a scale of

sciences. In

some

instances, diving

is

the only

if

there

is

a

need

location several times during a study.

base

map depends

size of the area to

is

especially

to return to the

The

same

scale of the

on the detail of the study and the
be investigated. In geological mapping

water, and fish behavior studies, requires diving to be

inch to 200 yards (2.5 cm to
adequate for reconnaissance surveys. In
archeological and some biological studies, a much more
detailed base map, with a scale of
inch to 30 feet

used throughout the entire project, while other research

(2.5

may

contain the proper scale or sounding density,

make

graph, and

field observations.

Some

such as ecological surveys, benthic inventories

research,
in

shallow

require diving only as an adjunct to submersible,

remote sensing, or surface ship surveys. Regardless of
the project or the role that diving plays, marine research

using diving as a tool has been important in understanding

the ocean,

The
measured

its

organisms, and

its

dynamic processes.
is

minutes and seconds instead of hours

(unless the saturation diving

mode

is

used).

Long

underwater work periods necessitate decompression
times twice as long as the actual work time on the
bottom: the cost-effectiveness of scientific diving
therefore depends on how efficiently scientists can
perform their tasks. Efficiency under water requires
good tools, reliable instruments that can be set up
rapidly, and a well-thought-out task plan. Until recently,
there was almost no standardization of the equipment
and methods used to perform scientific research under
water, and in many cases the instruments, tools, and
techniques were (and

still

1

is

1

cm

to 9 m),

may

be required.

If existing charts

are) improvised by individual

meet the specific needs of the project.
However, now that the value of scientific diving has
been widely recognized, scientists are becoming concerned about the accuracy and replicability of their

it

do not

may

be

necessary to use echosounder survey techniques to
construct a bathymetric map of the bottom before
starting the dive. Gross features can be delineated and

bottom time used more efficiently

diving scientist or technician's working time
in

183 m)

good bathymetric

map

if

the diver has a

of the study area. If published

topographic charts are inadequate, the sounding plotted

on original survey boat sheets of a region (made by
NOAA's National Ocean Service) can be contoured
and will usually provide adequate bathymetric control
for regional dive surveys.

bottom traverses,

it

will

If the

survey plan requires

be necessary to provide some

means of locating the position of the diver's samples
and observations on the base chart.
Techniques used to search for underwater sites fall
into two general categories: visual search techniques
and electronic search techniques. The results from the
latter must be verified by divers after the specific site
has been located.

scientists to

data and results and are increasingly using statistically
valid

and standardized methodologies. Through neceswho want to work under water must be

sity, scientists

proficient both in their scientific discipline and as
divers, inventors,

The purpose

and mechanics.

of this section

is

October 1991

to

to describe

gather data.

— NOAA

The

some

of the

Diving Manual

Methods

great majority of diving

is

carried out in nearshore

waters where surface markers, fixed by divers over
strategic points of the

work

site,

may

be surveyed from

the shore using well-established land techniques,
including the theodolite, plane table, and alidade, or

from the

procedures used in diver-oriented science projects.
These methods are intended as guidelines and should
not be construed as the best or only way to perform
underwater surveys or

9.1.1 Traditional

or,

sea, using bearings

from a magnetic compass

preferably, measuring horizontal angles between

known

points with a sextant. Small, inexpensive, and
rugged plastic sextants are commercially available,
and techniques for using them are simple to learn.
Although sextants have limitations, especially when

9-1

Section 9

UNDERWATER SURVEYS

they are used from a small boat, they are generally

9.2

sufficiently accurate to be useful.

A

At the other extreme in terms of complexity is a site
relocation method used successfully by many scientists; in

landscape; these include direct and indirect surveying

method, lineups and landmarks on shore are sighted

this

visually, without the use of artificial aids. Basically,

once the

site is

located and the boat anchored over

it,

scientists take a number of sightings of various nearshore
landmarks (such as trees, hills, and power poles) and
align them visually so that when the boat is repositioned
the landmarks line up the same way. The only drawbacks
to this method are that the work must be conducted

near shore and the visibility must be good
the shoreside landmarks to be seen.

When

in

order for

survey

used during the

directly over the weights anchoring

lie

initial

them

the selected underwater features; the best plan

is

to

to

wait for a calm day at slack tide.
In

some cases

anchors
this

is

in

may

be advisable to leave the seabed

place after the floats have been cut away. If

contemplated, the anchors should be constructed to

rise slightly

may

it

above the surrounding terrain so that they

be seen easily on the next

of syntactic

foam may be

visit.

tied to the

Small floats made
anchors below the

surface with a short length of polypropylene line to aid
in relocation.

However, because biological fouling soon

obscures any structure used, expensive, highly painted

markers generally are not appropriate. Floating markers,

even

seen

if

they are small and badly fouled, usually can be

if

they protrude a short distance above the

surrounding substrate.

Once

system of markers

established and fixed relative to

is

methods

used to survey the underwater

is

methods. Direct methods require diver-scientists to
measure distances themselves, while indirect approaches
use photography or acoustic means to determine
distances, angles, and other features.

9.2.1 Direct

Survey Methods

With the exception of long distance visual triangulation, many of the methods used in land surveying can

several lineups

have been established and proven, they should be
diagrammed in a notebook that is kept in the boat.
These methods allow divers to establish the locations
of major features in the working area accurately. If
buoys are used for location, particular care is needed
to ensure that the surface floats

variety of

the transect, grid, or other

also be used

text

under water.

on surveying

A

review of a standard college

provide the scientist with some

will

basic surveying concepts, while

Woods and Lythgoe

(1971) give an excellent description and review of

methods that have been devised specifically for work
under water. In most diving surveys, distances are
measured with a calibrated line or tape. However,
measurements done under water seldom need to be as
accurate as those on land, and the use of an expensive
steel tape is unnecessary. Additionally, most ropes or
lines will stretch and should be used only if the
measurement error resulting from their use is acceptable.

A

fiberglass measuring tape that has a

of stretch and

is

marked

in feet

minimum

and inches on one side

and meters and centimeters on the other

commercially

is

come in an
frame with a large metal crank to wind the
tape back onto the reel. They are ideal for most purposes
and require no maintenance except for a fresh water
available (see Figure 9-1). These tapes

open

plastic

rinse and lubrication of the metal crank. No matter
what measuring method is used, especially if long
distances are involved, the lines or tapes must be kept

on reels to prevent tangling or fouling. In clear waters,
optical instruments can

and have been used

to

measure

permanent features on the shore, the diver should record

both distance (range finder) and angles between objects

the position of selected features within the working

for triangulation.

area in relation to the buoy array.

The

first

step in surveying any area

is

to establish a

horizontal and vertical control network of accurately

located stations (bench marks) in the region to be

mapped. Horizontal control
9.1.2 Electronic

Methods

a

Electronic positioning methods are excellent, but
they are also expensive. If cost

is

no object or extreme

accuracy of station positioning and marking

is

required,

map

is

the framework on which

of features (topography, biology, or geology)

to be constructed; such a control provides a

locating the detail that

is

means of

makes up the map. Vertical
and may be obtained

control gives the relief of the region

several highly sophisticated electronic ranging instru-

by stadia distance and

ments may be used.

Rough measurements can be made by comparing

Satellite positioning

equipment can

few meters of the desired
Loran equipment, although less accurate, is

vertical angles or

by

spirit leveling.

position a scientist within a

differences in depth using a diver's depth gauge, but

location.

measurements may be inaccurate

readily available at relatively low cost.

9-2

surface

is

if

the irregular sea

used as the reference point.

NOAA

Diving Manual

— October 1991

Procedures for

Scientific Dives

Figure 9-2
Figure 9-1
Fiberglass Measuring

Bottom Survey

Tape

in

Courtesy Forestry Suppliers,

High-Relief Terrain

Inc.

One method that has worked well in areas of high
where echosounders are not satisfactory is

relief

described below (Hubbard 1978).
•

Along a convenient axis (N-S, E-W, etc.), place
two permanent poles, one on either end of the
survey area.

•

Stretch a line between them to serve as a fixed
centerline.

•

At

Source:

by the

intervals prescribed

the irregularity of the terrain, place additional
poles identified by
a taut-line
•

some

buoy may make the

Lay out the

lines

sites

permanent grid

is

more

of

methods described

with respect to surface positions.

tie-in points.

If a

between the centerline

The

detail to

appear on the finished

poles.

terrain has significant relief, horizontal

changes can be measured by moving away from
each centerline pole, as shown

in

has been completed.

Figure 9-2.

In areas of significant terrain,

it

difficult to

is

maintain an accurate horizontal measurement.
Knowing the difference in depth (y) between the
two points (from a calibrated depth gauge or several

depth gauges) and the measured slope distance
(z),

the horizontal distance (x) can be calculated

is

located

is

located

first

and the

detail

is

located in a separate operation after the control survey

On

other surveys, the control and

the detail are located at the
•

map

by moving from the control networks (bench marks) to
the features to appear on the finished map. On some
surveys, the control

If the

Section 9.1.1 locates the site

in

visible.

desired, place poles at intervals

to those

(1979)

Determining the two end points of the centerline by the

perpendicular to the centerline

by using the centerline poles as

comparable

The use

sort of coding.

NOAA

and

size of the area

method

is

preferable

if

same time. The former

long-term observations are to

be carried out in an area, for example, around a
permanently established habitat. The latter technique
reconnaissance studies are being

is

preferable

in

remote regions or

if

in

made

areas that will not require the

re-establishment of stations.
easily using the formula:

x= V z 2

When

must be taken

Survey Methods

2
.

Indirect underwater surveying involves techniques

using a depth gauge over a period of hours,

tidal fluctuations

staff or

9.2.2 Indirect
y

into account.

bench mark should be established

A

reference

at the begin-

ning of the survey, and readings should be taken at the

that do not require the diver physically to

measure

angles and distances using tapes, lines, protractors,
etc.

Indirect underwater surveying currently

is

performed

using either photographic or acoustic methods.

reference during the period over which depths are being

measured

in the

survey area.

from each of the centerline

By going

poles, a

in either direction

complete Dathymetric

survey can be conducted with considerable accuracy.

October 1991

— NO A A

Diving Manual

Underwater Photographic Surveys
Obtaining reliable measurements by means of

9.2.2.1

photography

—photogrammetry—though

not as advanced

9-3

Section 9

under water as on land

—

is

a tool being used with

increasing frequency. Limited visibility

major drawbacks

is

one of the

in its application.

recording changes with time. Subtle changes

in

often recorded on sequentially obtained exposures of

the

same area

alone

is

or station can be missed

if

memory

costly systems can be used to

some of the problems

A

methods.

Photographs with appropriate scales in the field of
view can be useful in measuring objects on the seafloor

and

More complex and
avoid

that arise with these simpler

high-frequency sonic profiler (Figure 9-3)

can rapidly measure underwater

Such

1977).

not a factor, the sonic profiling

is

way

the best

(Dingier et

al.

and

beyond the means of most researchers.

technical support
If cost

sites

a device, however, requires electronic

method

is

by

far

of obtaining an accurate representation of

small-scale subaqueous bed forms.

relied on.

Photographic transects are useful in showing variations over an area or changes that occur with depth. In

the acoustic equivalent of direct trilateration. In

photogrammetry was conducted
because of the technical difficulties in producing

known

corrected lenses and maintaining altitude and constant

are interrogated sequentially from within their estab-

the past,

little

true

depth and because of the high relative

relief of

many

bottom features. However, improved techniques have
been developed that allow increased accuracy and
flexibility. Recent computerization of photogrammetric
plotting equipment has reduced technical difficulties
considerably.

To improve mapping for detailed archeological studies,
photographic towers may be used (Bass 1964, 1968;
Ryan and Bass 1962). The progress of excavation in

Acoustic Grid. This method of underwater survey

simplest form, three acoustic transponders are placed at
positions on the sea bottom.

lished

grid,

occurs

is

sound

in

and the time delay before each response

delay in time can be related to the distance between the

and each of the transponders.
Transponders are implanted and their positions are
determined using direct underwater survey methods.
interrogator

The

interrogator

produces a consistent series of photos that can be
compared easily when analyzing the data. The tower
ensures that each photo is taken from the same point of
view, thus simplifying follow-on dark room procedures. A

The process

however, a perspective view that requires

is

a small, hand-held directional sonar

device that has a digital readout of the time delay.
diver, positioned

is,

These transponders

measured and recorded. If the velocity of
seawater is known for that area and time, the

each area can be recorded with grid photographs taken
through a hole in the top of the tower. This approach

photograph

is

its

visually at the first transponder
is

The

above the point to be surveyed, aims
and takes three readings.

repeated for the other two transponders.

Ideally, the data are sent to the surface via

communications

an underwater

In the absence of this equipment,

link.

the data should be recorded on a writing slate attached
directly to the interrogator.

The accuracy

of this system

correction for the difference in scale and position of

can be increased significantly by using four or five

objects.

transponders.

A

series of stereophoto pair

photographs

may be

taken of sites for three-dimensional viewing under a
stereo-viewer.

More

important,

it

is

possible to

make

three-dimensional measurements from such photos.

The use

of wide-angle lenses, such as a

15-mm

lens,

permits detailed photographs to be taken that cover

from short distances. Bass (1978) recomand divided
into 6.6 foot (2 m) squares. These squares are then
excavated and photographed individually.
large areas

mends

that rigid metal grids be constructed

Because so many variables affect the velocity of
in seawater, errors in measurement can have a
significant effect on the resulting mathematical analysis. For example, sound velocity measurements in
very shallow water can be affected seriously by errors
in recording temperature. Accurate results depend on
keeping the salinity and temperature measurement errors
small enough so that the errors in velocity are below
sound

the inherent equipment-introduced errors.

More

sophisticated versions of the acoustic grid survey

system are available, and
directly.

Underwater Acoustic Surveys
Another method for conducting bottom surveys

9.2.2.2

involves the use of sonic location beacons (pingers).

These devices are particularly useful if there is a need
to return to specific locations. The system may consist
of small (the size of a roll of quarters) pingers, which
can be placed
receiver.

at the site of interest,

specific frequencies to differentiate

9-4

and a diver-held

The pingers can be tuned by the diver
between

sites.

to

many

of these read out range

Although more convenient

may

to use,

system

be created by variability in speed
of sound. Compact and reasonably priced sound velocimeters are now available that permit in-situ measureinaccuracy

ments

to

still

be used immediately as survey system correctors.

The acoustic
site is visited

grid

is

particularly valuable

when a

repeatedly to measure features that vary

over time, such as the motion of sand waves. Another

advantage of

this

system

is

its

internal completeness. If

the geodetic location of the site

NOAA

is

not important and

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-3

High-Frequency
Sonic Profiler
its

inherent mobility and flexibility are distinct advan-

tages except in situations where job requirements

make

the acoustic grid or one of the direct methods preferable.

Under

measurement

certain conditions, the phase

system can be more

fully utilized

if

diver towing tech-

niques are employed. In this case the position of the
diver relative to the support ship must be monitored

continuously, which increases both ease of operation

and accuracy. Combining the phase measurement system
with a good diver-to-surface communication system
results in

an excellent survey procedure.

9.3

UNDERWATER RECORDING METHODS

The

simplest and most widely used

method

for recording

data under water involves using a graphite pencil on

These records

a white, double-sided plastic board.

are sufficiently permanent to withstand normal handling
Photo

Tom Harman

during a dive. Since most divers use abbreviations
and shorthand in recording observations and species
names, however, the notes should be transcribed as

Wax

soon as possible.
only relative position and motion within the site are to

be measured, the acoustic grid

an appropriate method.

possible to relate the grid

It is also

geodetic

is

map

measurements

to a

at a later time.

which determines the position of an object relative
fixed network of transponders, phase

to a

measurement

systems are contained within the support ship except
mobile transponder. Three receiving elements

are located precisely with respect to each other on the

underside of the support craft; they are usually attached
to a

mast extended over the side of the

craft.

A

diver

places a transponder on the object whose position

is

to

be determined, and an interrogator located on the ship
queries the transponder.

A

phase analysis

by the receiver on the return signal, which
as deflection angle

and

is
is

performed
displayed

line-of-sight range to the object

with respect to the receiver element mast. The only
variable

is

velocity of sound,

which must be determined

by the method discussed previously.
scuba cylinder so that the position of the diver can

be monitored continuously by personnel
craft.

When

in

continuous communication

the support
is

available,

the diver can be directed through a geodetically fixed

survey pattern

if

This system

the ship's position
is

is

known

brittle

and break

in

corrode. Ordinary pencil lead can be cleaned off easily

wax smears and

often must

be removed with a solvent. Mechanical pencils are
unsatisfactory, since the metal parts will soon corrode.

The

best writing instrument

is

an off-the-shelf, readily

available plastic pencil that uses bits of sharpened lead

encased

in plastic butts.

Slates can be

made multipurpose by adding compasses,

rulers, or inclinometers (see

Figure 9-4). Because there

accurately.

suited to applications where a large

made under

water, a

list

of tasks to be undertaken and

the form to be used for

measurements should be

all

developed before the dive. These

lists

and tables may

be inscribed on the plastic pads. In some cases
desirable to retain the original records (this

important

in

is

is

the case of archeological drawings, for

instance); drawings then are

made with wax crayons on

or rubber bands.

There are several types of underwater

paper, including a fluorescent orange paper. Standard

formats can be duplicated ahead of time to facilitate

recording during a dive.

A

simple and inexpensive

technique for underwater data sheets

is

to

prepare the

sheets on regular typing paper and then have each
sheet laminated in the

same way

that drivers' licenses

disadvantage of requiring a surface-support platform.

good practice

Diving Manual

it

particularly

and other important identification are preserved.
Where precise measurements are to be made,

— NOAA

is

a risk of misinterpreting the often rather erratic notes

area must be surveyed or where there are only one or
two sites of interest. Although the system has the

October 1991

cold

water, and pencil holders have metal parts that will

waterproof paper attached to the plastic board by screws

Small transponders are available that can be strapped
to a

pencils are usually not satis-

become

with scouring powder, but

Phase Measurement. Unlike the acoustic grid method,

for a single

factory because they

for

two observers

to take

it

is

independent

9-5

Section 9

Figure 9-4

Multipurpose Slate
breathing noise and increases voice fidelity by picking

up sounds from the resonating chamber formed by the
rather than from the high-sibilance area in front
of the lips. Several commercially available masks are
equipped with demand regulators that can be used

mask

with standard scuba cylinders or with an umbilical air

When an umbilical is used, most diver-tender
communications systems can be wired to accept a tape
supply.

recorder so that both sides of the conversation can be
recorded. Regardless of the unit selected, divers should

practice using the system in shallow water until they

can produce

To

intelligible transcriptions routinely.

optimize recording fidelity and minimize distortion

and interference, cassette tapes of the highest quality
should be used. At present, commercial tapes are
Photo Robert

Dill

available that have 60 minutes of recording time on

each

side,

and

this capacity

generally sufficient for

is

most scuba missions. Maintenance

measurements and to check them with each other for
agreement before returning to the surface. If there is
disagreement, the measurements should be repeated.
Tape recording is another useful, although somewhat
specialized, method of documenting data under water.
The most satisfactory and reliable system includes a
cassette tape recorder as part of the hardwire two-way

in the

is

9.4

BIOLOGICAL SURVEYS

same requirements
and involve the same techniques as those described in

a self-contained unit carried by a diver

Section 9.2; however, some specific aspects should be

in

scuba mode. The position of the microphone and

way

which

Biological surveys generally have the

mentioned. Biological surveys are used for
placing

recorder.

the effects of ocean

in

especially important

O-rings, seals) to prevent corrosion.

waterproofed is critical in
determining the usefulness of an underwater tape

the

is

must be taken (checking

umbilical diving; the

communication system used
alternative

for tape recorders; special care

it

is

Some commercial systems

feature a special mouth-

piece unit into which a microphone

which the scuba regulator

is

built

and

to

many

poses, including determining the environmental

man-made

objects on the seafloor and assessing

dumping on marine

most marine environments,
ate the impact of

pur-

impact of

it

is

resources. In

not possible to evalu-

man-made changes without performing

attached. Standard

special baseline surveys designed to obtain specific

however, do not allow the lips to move
form anything more than simple words
or noises, which are usually intelligible only to the
speaker immediately after the recording is made. This is

information about the biota and the physical environ-

is

especially true for biologists giving long

cannot be obtained before the natural undersea envi-

mouthpiece

is

bits,

sufficiently to

names or

for scientists reading

lists

of scientific

numbers from instruments.

ment. To be meaningful, these studies must be

made

before structures are emplaced on the seafloor or material

discharged into the area.

When

baseline information

ronment has been altered by human actions, biological
surveys can be used to determine the incremental impacts

of subsequent activities.

NOTE

Baseline studies must be designed so that they can

The most

critical factor to consider in a voicerecording system for data gathering is the
ability of the diver to speak and enunciate
clearly enough to be understood and transcribed accurately.

be monitored at prescribed intervals. Control stations
placed outside the area being studied are necessary to

provide data on environmental changes occurring
naturally (e.g., seasonal effects).

The techniques of underwater
make

The

best equipment configuration

equipped with a microphone that
the immediate

9-6

mouth

is

is

a full-face mask,

located

away from

area; this position diminishes

biological surveying

involve establishing a standardized methodology to
the results of the survey quantitatively meaningful

and ecologically acceptable. This is done by choosing
stations at specific depth intervals along a transect
line and dropping an anchor at each station to serve as

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

the center of a circle of study. Quantitative observa-

made

tions are then

within the circle; general bottom

area; to the extent that the surfaces

from the horizontal, area

will

sampled depart

be underestimated, which

cause density to be overstated. This bias becomes

topography and biological features of the areas beyond

will

the circles are also noted.

particularly important as the scale of the surface vari-

The amount

of bottom area covered does not need to

ation approaches the scale of the distribution being

be the same for every station; water clarity and the

measured. Dahl (1973) describes a technique designed

complexity of the biota

study

to quantify the estimation of irregular surfaces in the

The poorer the visibility, the more restricted the
amount of bottom that can be surveyed. In West Coast

marine environment. Briefly, the technique consists of
making some simple height, frequency, and surface

will affect the size of the

circle.

regions and for sand stations having a limited macrobiota,

m)

a 10.2 foot (3.1

line

is

generally used to produce a

length measurements and then applying a surface index

formula to determine the surface area. The technique

323 square foot (30 m 2 ) area of study. In rocky areas,
where the biota is more diverse, a 7.2 foot (2.2 m) line

Thalassia, sand

can be used to define the radius of the circle of study.

reefs.

In addition, using tools such as plankton nets and
bottom cores, scientists can estimate the number of
plants and animals, take quantitative samples of life

organisms

is

who used

it

forms, and take photographs of general bottom conditions

ure 9-5). At each location sampled, the authors spent 10

and of each quadrat.

to

Environmental factors that must be considered when
surveying the establishment and growth of underwater

has been applied to coral reefs, benthic algal substrata,

A

and rubble zones, reef

crests,

and patch

simple method for estimating populations of sessile

described by Salsman and Tolbert (1965),
to

15 minutes

survey and collect sand dollars (Fig-

making observations, taking photographs,

and sampling population density. To facilitate counting
and to ensure a random sample, a counting cell was
by bending an aluminum rod into a square

communities include exposure to wave or swell action,
type and slope of substrata, water temperature, dissolved

constructed

oxygen and nutrient content, and extent of grazing.
Variations in the intensity and spectral composition of

counting squares also can be constructed using

light

under water also have a significant effect on plant

communities, but

it

is

often difficult to obtain accu-

measurements. The illumination

rate light

at or within

community can be obtained with accuracy

a given plant

only by actual in-situ light measurements; photographic
light

meters are not satisfactory for this purpose.

11.8 inches (30

As

tubing.

cm) long on each

side.

Inexpensive

PVC

divers approached the seafloor, they released

the square, allowing

it

to fall to the

bottom. The organ-

isms within this square were counted and collected for
procedure was then repeated

later size determination; this

at least

two more times

same method can be used
any

sessile

A

each location sampled. The

at

to take a

random sample

of

organism.

Underwater spectroradiometers, which are probably the
most effective means of measuring light in the sea,

operated fishrake (Figure 9-6).

are available. Submersible spectroradiometers have

obtain information on the small-scale distribution

been used

in

studies of photosynthesis

and calcification

device used for surveying epifauna
It

is

the diver-

has been used to

patterns and estimates of population densities of demersal

and invertebrates. The apparatus consists of a

rates of corals.

fishes

Most underwater investigators have used transect or
simple quadrat methods for the analysis of benthic
communities. A reasonable description of the change
in biota relative to depth and other factors can be

metal tubular frame fitted with a handle, a roller of

obtained by measuring the area of cover along a strip
or

band

transect.

Accurate quantitative data on standing

crops can best be obtained by collecting the entire

ground cover from
component species

a
in

quadrat and sorting this into
the laboratory for subsequent

rigid

PVC

tubing into which stainless steel wire "staples"

are fixed, and an odometer

of a plastic tracking

pushed along the bottom by a diver who makes
and other observations
on animals that occur within the path traversed by the
It

is

visual counts, size estimates,

roller.

In

some underwater

of animal behavior,

analysis.

made

wheel and removable direct-drive revolution counter.

it

is

situations involving observations

necessary to remain a reasonable

distance from the subject so as not to interfere with

normal behavior. Emery (1968) developed an underwater
telescope for such situations by housing a

9.4.1

Estimating Population Densities

When

estimating the biological content or density of

a given region,

account.

An

it

is

necessary to take surface area into

irregular surface can greatly increase the

October 1991

— NOAA

Diving Manual

PVC

rifle

scope

in

tubing with acrylic plastic ends. The underwater

scope described by this author functioned satisfactorily at

depths as great as 180 feet (55 m). An underwater
telephoto camera lens was used during the Tektite II

9-7

Section 9

Figure 9-5

Counting Square for Determining

Figure 9-6

Sand

Diver-Operated Fishrake

Dollar Density

j*

s

\s

/-Z

J^y\^~~^SF

/ ss.yy~~~--~~~A\)

gv
<

y

yyyy

copper

*

yy

REVOLUTION
COUNTER

pipe

PLASTIC ROLLER

Photo Art Flechsig

•MP"
Courtesy U.S. Navy

ably the most important practical one
ability to observe the

experiments to avoid interfering with animal behavior

(VanDerwalker and Littlehales 1971).
At the other end of the magnification continuum is
an underwater magnifying system (Pratt 1976). This
device, referred to as the Pratt Macrosnooper, has a
magnification power of seven and permits the diver to
study marine organisms too small to be comfortably
observed with the naked eye. It is a three-element lens
system designed specifically for use under water and

tiveness,

cm)

plastic pipe (see Figure 9-7).

are then drilled through the housing

is

mask

in use, the

Macrosnooper

faceplate. It should be cleaned

is

its

in

effec-

some cases, such as with
underwater sampling
considerably more effective than from
In

fish,

and magnitudes of the
and allows
one to decide whether the sampling site is
unusual or representative of a larger area.
With the less common species, it may be
particularly important to be able to make
repeated population estimates without imposing unnatural mortality by the removal
feeling for the types

errors associated with the sampling

to

held against the

and rinsed

of

the surface. Direct observation gives one a

permit the entry of water for equalization at depth.

When

the

improve the design or pro-

to

situ.

small demersal

Holes

and the spacers

and

cedure in

consists of three lenses with appropriate spacers inserted

into a 2 inch (5

make estimates

operation, to

is

sampling apparatus

carefully,

of individuals.

along with other diving equipment, after each use.
Soap, mineral, or fungus deposits, which

by an overnight soak
dry detergent,

may

may form on

Because a diver using marker buoys, stakes, or pingers

be removed

in either bleach, vinegar, or laun-

the lenses after prolonged

can return repeatedly to the same location, changes in
both environment and the biota can be followed for
considerable periods. In addition, changes can be imposed

use.

on the environment by selective removal of species, by
alteration of substrata,

9.5

BIOLOGICAL SAMPLING

Although a discussion of research design

and so on, and the effects of

these experimental manipulations can be followed in
for a

sampling

detail.

program

is outside the scope of this volume, careful
attention should be given to the implementation of

sampling methods. Chapters on the design of sampling
programs can be found in Holmes and Mclntyre (1971).

As Fager and

his colleagues

have noted (Fager

1966),

et al

9.5.1

Plankton Sampling

Planktonic organisms that live within 3.2 feet (1

m)

of

the bottom can be sampled with a skid-mounted
multilevel net apparatus that is pushed by a diver over
a

predetermined distance. Hand-operated butterfly

valves are used to isolate the collection bottles located

9-8

Underwater operations have several advan-

in the

tages over sampling from the surface for

ecological studies involving quantitative

Plankton sampling nets 11.8 inches (30 cm) in
diameter, with a mesh size of 0.08-0.12 inch (2-3 mm)

sampling or observations of behavior. Prob-

are used to collect plankton selectively in reef areas.

cod end of the

net.

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-8
Figure 9-7

Hensen Egg Nets Mounted on

Underwater Magnification System

a Single Diver Propulsion Vehicle

A. Optical

B.

System

Complete System

Photo William

carried out properly, there
net

is

reused,

it

is

no sample

loss.

L

High

Before a

should be turned inside out and back-

flushed.

Benthic Organism Sampling

9.5.2

Quantitative sampling of the epifauna can be accom-

plished by counting the animals within a randomly
located circle or square quadrat.
Photo Harold Wes Pratt

of brass,
Air-filled bottles also

can be inverted

appropriate

in

with grooves at 0.4 inch

The

areas to suck up plankton and water samples.

A

circle template,

movable arm may be constructed
with the center rod and movable arm marked

fixed center rod, and

(1

cm)

intervals (Figure 9-9).

position of an animal within the circle can be

Several methods of sampling plankton have been

defined by three numbers: the distance along the center

developed. Ennis (1972) has employed a method using

rod from a standard end; the distance from the center

two diver propulsion vehicles on which a 19.7 inch
(50 cm) plankton net was mounted. A similar method was
used during a saturated dive in the Hydrolab habitat
at Grand Bahama Island, when two 3.2 foot (1 m) long
Hensen egg nets were mounted on a single diver
propulsion vehicle that was operated at a speed of
about 2 to 3 knots (1 to 1.5 m/s) (Figure 9-8). At the
end of every run, each net should be washed separately
and the sample should be concentrated into the cod end
by holding the net up inside a trapped bubble of air
under a plastic hemisphere having an 18 inch (45.8 cm)
radius. The cod end should then be removed, and the

rod along the movable arm; and the half of the circle

contents of the net should be poured into a glass jar.

The

volume at
wrap should

be placed over the top of the jar to trap a small bubble
air.

The

and carried

jar

is

to a

then removed from the hemisphere

work area

at the base of the habitat.

The work area should be deeper than
that hydrostatic pressure will help to

from escaping.

A

the hemisphere so

keep the

syringe filled with formalin

pushed through the plastic wrap, the jar
immediately secured, and labeled.

October 1991

air

— NOAA

When

this

Diving Manual

is

bubble
is

then

capped,

procedure

is

To study

details

species, the "distance of the nearest neighbor" tech-

nique can be used. This method involves preassembling a
large, lightweight
it

metal or

PVC

at the appropriate location.

square and dropping

Within the square, divers

place short brass or plastic rods with fabric flags on

them

at

predetermined positions

in

relation to the

individuals of the species being examined. After the
positions of all individuals

have been marked, distances to

nearest neighbors are measured, and reflexives are
counted.

Samples of the substrate and infauna can be collected

jar should be filled, except for a small

the top, with filtered seawater, and plastic

of

within which the animal was observed.

of the distribution pattern of individuals of sedentary

with no loss of sediment or organisms by using a simple

coring device with a

widemouth sample container
The corer

jar) attached to the top (Figure 9-10).

pushed

a given distance, e.g., 2 inches (5

(a
is

cm), into the

aluminum plate is slipped
through the sand. The apparatus is inverted
sediment is allowed to settle into the jar. Once

sand, tipped slightly, and an

under

it

and the
all

sediment and organisms are inside the

attachment

is

removed and the

jar

is

jar,

the coring

capped.

9-9

Section 9

Figure 9-10
Coring Device
With Widemouth Container

Figure 9-9

A

Template

Determining
Benthic Population Density
Circle

for

Photo Art Flechsig

Another simple soft-bottom sampling device, esand meiofauna, is a

pecially good for small infauna

thin-walled coring tube of transparent plastic, the

diameter of which

is

based on a predetermined sample

designed to gather the desired substrate and organisms

most

efficiently.

Most organisms obtained by

this type

of device will be found in the top 3.9 to 4.7 inches (10 to

12

cm) of the sample. For ease of handling, the tube

should be at least 11.8 inches (30 cm) long and sealed
with rubber corks, one of which has a small hole drilled

through

it.

With both corks

off,

the tube should be

rotated carefully into the sand to the desired depth,

and the cork with the small hole should then be used to
cap the tube. While gripping the tube for removal, the
scientist's thumb should be held over the hole to create
a suction that keeps the sediment from falling out.
When the tube is free of the sediment, the bottom cork
should be inserted. Samples accurate to any depth can
be taken with this device, and depth lines can be marked
on the outside of the tube. To remove the core, the
scientist places a finger over the hole in the top cork,

removes the bottom cork, and allows the plug

To remove

to fall out.

discrete segments of the core, the plug

may

Photo Art Flechsig

Another coring device
samples of the infauna

is

for obtaining quantitative

a square stainless steel box

with handles and a screen covering one end (Figure 9-11). Its rugged construction allows scientists
forcibly to penetrate hard substrates, such as sand or
vegetated bottoms, as well as softer sediments. The
sampler, currently in use by

NOAA/NMFS divers, can
m 2 sample to a depth of

obtain a 0.17 square foot (1/64

)

be pushed out the end and cut into desired lengths or

9.1

quick-frozen in dry ice immediately upon surfacing

substrate to the desired depth, one side of the device

(to prevent

migration of animals) and later cut with

a hacksaw.

A

is

used for studying the depth

distribution of infauna. This corer samples an area of
1

(6 cm).

inches square (45

The corer

cm 2 )

to a

depth of 2.4 inches

consists of a square brass

box

fitted

with a funnel adapter at the top to accept widemouth

sample containers. The front side of the corer

is

slotted

to permit thin metal slide plates to be inserted to
separate the sample into five separate layers, which
can then be transferred under water to separate sample

containers.

9-10

excavated and the device

is

is

pushed into the
is

which the
To prevent any loss of

tilted over, after

corer and sample are pulled free.

multilevel corer

about

inches (23 cm). After the corer

sample, the diver holds the open end of the corer against

body while ascending. The contents are then
appropriate mesh size (Figure 9-11), washed free of most of the sediments, and the
residue containing the organisms is placed in jars of
preservative. A red dye (usually Rose Bengal) is added
to the preservative to facilitate the sorting and identihis or her

placed

in a sieve of

fication process.

A

Multiple Disc Sampling Apparatus for collecting

epibenthic organisms has been developed by

NOAA

Diving Manual

NOAA/

—October 1991

Procedures for Scientific Dives

Figure 9-11
Infauna Sampling

701

Box

1.2

mm 2

cm

Diameter

Stainless Steel

Mesh Screen
0701

mm 2

Mesh Screen

1.6

mm

Stainless Steel

Plug Sampler
Source:

NMFS

divers.

9.7 inches (24.6

Each
cm)

collecting unit consists of a disk
in

0.54 square feet (1/20

have been used

in

can bore into

it

or merely attach to

diameter with a surface area of

composition

m2

over long periods. In soft bottoms,

).

Various kinds of material

the construction of the disks (wood,

glass, steel, rubber, cement).

Rubber and cement

will

also determine

it,

NOAA

(1979)

and the rock's

resistance to erosion

its
it

is

useful to describe

sediment grain size and bottom configurations; deter-

minations of grain

size,

chemical composition, and

generally are superior substrates for most sessile
invertebrates. The disks are wired to a galvanized pipe

especially equipped to handle these tasks. Situations

frame placed on the bottom by divers. Individual disks

vary,

removed at intervals by divers who place a canvas
collecting bag over the disk and cut the wire holding
the disk to the frame. This procedure minimizes the

geological data.

are

the disks are filled with a narcotic solution (7.5%

chloride mixed

1:1

with seawater) for

hour and the disks are then preserved

in a

1

10 percent

formalin solution. Wiring disks rather than bolting

them

simplifies the operation

of corroded fastenings.

and eliminates the problem

The experimental design

—

col-

lecting frequency, substrate material to be tested, or

other epifaunal survey requirements

number

and it may be helpful to consult geologists for
recommendations on where to obtain the appropriate

organisms. Individual bags containing

loss of motile

magnesium

other physical characteristics are best done by scientists

— dictates

the

of disks to be used. Because of the large size of

disks, the epifaunal

assemblages that are collected by

9.5.3 Airlift

An

Sampling

airlift is

plastic pipe

a sampling device that consists of a long

equipped with a device

The

to

supply air at the

and organisms
and water, so
that they can then be emptied into a mesh bag of a
certain size (see Section 8.9.1). Large areas of soft
bottom can be collected in a very short time with this
device, and the samples can be screened through the
lower end.

airlift

carries sediment

to the top of the pipe in a

bag

in the process.

When

stream of

air

used with a diver-held scraping

method are more typical of those found on natural
substrates. However, only a portion of each disk is
examined and enumerated.
Some knowledge of geological techniques is helpful
when sampling. For example, on rocky substrates it is
important to know how to measure angles of inclines on

device, an airlift

overhangs or shelves, because

Although plastic bags have been used successfully
to sample swarming copepods and small aspirators
have been used to sample the protozoan Noctiluca,
animals in midwater must generally be collected using

this

this

many organisms

orientation of

angle influences the

(see Section 9.10.1).

Similarly, knowing the composition of the rock

important

in

is

determining whether or not organisms

October 1991

— NOAA

Diving Manual

is

also useful on hard substrates,

especially to collect the small organisms that tend to

escape when attempts are

9.5.4

made

to

"scrape and grab."

Midwater Sampling

9-11

Section 9

Figure 9-12

Use of a Hand-Held Container
to Collect Zooplankton
other techniques.

It

is

difficult to

sample even very

ftp'

*

•

~WM

small animals, such as the copepod Oithona, without

swim rapidly
and
readily
dodge
water
bottles,
short distances

disturbing them. Although small, copepods
for

nets, or aspirators. If nets must be used, they are deployed
most effectively by divers swimming the nets by hand
or guiding diver-propulsion units to which the nets are

attached (see Figure 9-8).
the

mouth of

No

^^y

objects should obstruct

the net, because even monofilament bridles

cause zooplankton to avoid nets.

The diver can

easily capture larger, less motile

zooplankton that range from several millimeters to a
few centimeters

in size,

such as the gelatinous medusae,

ctenophores, salps, pteropods, and chaetognaths,

by permitting the animals

to

swim

etc.,

into a hand-held

container, preferably of clear plastic or glass (see Fig-

ure 9-12). This

is

it

is

the

method of data

the preferred

for all aspects of laboratory

collection

y^w

marine research, because

way to collect these delicate animals without
damage that normally occurs even with the most
the

carefully handled net.

Estimating density of planktonic aggregations. For

many

kinds of organisms, density and distribution can

B^afl

be determined photographically without disturbing the

The use

aggregation.

of an

80-mm

lens

and extension

tubes provides a small measured field of view some
11.8 to 15.7 inches (30 to

Depth of

40 cm) from the camera.

field varies systematically

with f-stop (see

Photo Al Giddings

Section 8.13). Instructions for some underwater cameras

provide these calculations, but investigators can

make

own cameras by photographing underwater
targets at a series of known distances in front of the
camera with different f-stops and determining the
them

for their

depth of

field in the resulting

photographs. Density of

organisms such as copepods within swarms

by counting
i.e.,

all

within a

is

determined

of the animals in focus in the photograph,

known volume determined by area of field
field. When the number of organisms in

times depth of
focus

is

large, density

can be estimated by measuring

the distance from one individual to

its

closest in-focus

neighbor for each of some 20 individuals within a
single plane. These distances are averaged and the
density of the aggregation is estimated by entering this
average into the formula for close packing of spheres
or of isohedronic arrays. Use of the formula
1,000,000

cm 3 /0.589

x (average nearest neighbor's

distance in

Number

cm) 3

Density measurements for animals sparsely distributed

can be obtained more easily by swimming

Figure 9-13). Divers also

9-12

all

drift slowly

on a tether

drift rate

and counting the number of organisms that

pass through a grid in a specified time.

Replicated measurements permit the application of

most normal
ecology.

many

statistical

Some

statistics

procedures used

in quantitative

tests are of questionable validity

because

depend on presupposed patterns of normal

distributions, patterns that

may

dimensional arrays. Nonetheless,

not apply to three-

many

of the sampling

procedures used by the terrestrial ecologist may be
applied to underwater sampling. Biological oceanographers

now use

these

new techniques

frequently.

=

of organisms per meter 3

preferred because isohedrons pack symmetrically

along

may

with the ship and estimate densities by measuring the

9.6
is

line transects

between tethered buoys while counting the number of
animals that pass through a grid of selected size (see

three axes, whereas spheres do not.

SHELLFISH STUDIES

The use

of diving as a research tool to study lobsters,

crabs, scallops,

and other types of

NOAA

shellfish has increased

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-13
Use of a Plexiglas Reference Frame for
Estimating Population Densities in Midwater

ment. In addition, lobsters

than one-half pound

less

(0.22 kg) in size generally are not nocturnally active in

environment but are active

their natural

at night in the

confines of an aquarium tank. Lobsters spend most of
their first 3 years of life in a labyrinth of tunnels

projecting as

many

as 3 feet (0.9

m)

into the boulder-

rock substrate of the ocean bottom (see Figure 9-14).
Replicating this substrate

9.6.1

in

an aquarium

is

difficult.

Collecting Techniques

Many

shellfish (crabs, lobsters,

and clams) inhabit

tunnels and burrows on the bottom. Others (scallops,

and abalone) live in beds and reefs or creep
and rocks. When collecting shellfish,
divers should always wear gloves and carry catch bags.
oysters,

across the seafloor

Lobsters inhabit burrows, tunnels, and caves

in

shallow

and in ocean depths that are beyond the
range of surface-supplied diving. Those more than
one-half pound in size are nocturnal in their movements;
during daylight hours, they remain in their homes.
coastal waters

When

picked up, spiny lobsters and bulldozer lobsters

if grabbed around the
abdomen (tail), the tail can cut a diver's fingers. The
American lobster can be collected easily by grabbing

should be held by the back;

it

from the back, behind the claws. Lobsters can also be

grabbed by their ripper claws and held
Courtesy ^National Geographic Society
Photo Al Giddings

seconds;

for

l

to 2

held longer, their crusher claws will be

if

brought into action. Lobster claws should be inactivated

by banding or pegging before the animal is put in a
catch bag; this will prevent animals from crushing

commercial importance of these
and the difficulty of sampling these

as a result of both the
living resources

organisms effectively with conventional surface-oriented

equipment. In general, shellfish studies have been
directed toward the ecology of these organisms, their
behavior

in

relation to sampling gear, the efficiency of

sampling gear, and the potential effects of conventional

sampling techniques on the bottom environment and
its

fauna.

Historically,

more underwater studies have been

New

conducted on the American lobster of the

England

coast than on any other single species of shellfish. In
addition, extensive studies have been done in Florida

and California on the spiny lobster (Herrnkind and
Engle 1977, Marx and Herrnkind 1985).
Direct in-situ observation of lobsters

is

the most

each other. Lobsters frequently

will

autotomize (drop)

antennae and claws when handled; American lobsters
this especially during the winter months, when
water temperatures range between 28.5° and 34.0°

do

(-1.94°

and 1.1°C).

The conventional method

for commercial harvesting
and New England clawed lobster is the
wire or wooden trap. Divers should assess the efficiency
and design of this gear before using it, bearing in
mind that spiny lobsters move much faster than
American lobsters and are much more sensitive to

of the spiny

being disturbed.

Commercial crabs are found

in

waters ranging from

shallow estuaries to ocean depths that are beyond
conventional diving limits. Gloved divers can catch

them

easily

by hand with short-handled scoop nets and

when

way to study lobster ecology and behavior.
Comparative studies of lobsters in the laboratory-

tongs. Caution should always be exercised

aquarium environment have shown that

claws; depending on the size and species, such injuries

effective

is

altered significantly

when they

example, lobsters held
balistic,

in

but cannibalism

October 1991

— NOAA

is

their behavior

are in captivity. For

collecting crabs because they can pinch with their

can vary from

a cut

finger (blue crab or

Dungeness

captivity are highly canni-

crab) to a broken finger (stone crab or Alaskan King

rare in the natural environ-

crab).

Diving Manual

9-13

Section 9

Figure 9-14
Benthic Environment
of the American Lobster
coast states, and in the

North

Pacific.

They occur

and pilings,
and together, in large beds of thousands of individuals.
These sedentary shellfish are easy to collect by hand. A
individually, in clusters attached to rocks

Surface

pry bar can be used to collect samples that are attached.

Oysters can temporarily be piled loosely on the bottom

during harvesting.
Scallops live in bays, sounds, and ocean bottoms in

depths up to 328 feet (100 m). Density varies from one
or two individual scallops to dozens per square meter.

They

are collected easily by

piles of scallops
Distance from Shore (Meters)

100

the scallops

200

150

should not be

hand or scoop
left

may swim away.

Loose

net.

on the bottom because

Getting one's fingers

stuck in the shell of a live scallop

is

painful.

National Marine Fisheries Service

Abalone inhabit rocky coasts from Alaska to southern
They are nocturnal foragers of algae and

California.

Blue crabs

estuaries, bays,

and sounds

Atlantic Ocean.

When

fast

in

frightened, they will burrow

quickly into the bottom or

These

temperate waters of
the Gulf of Mexico and

live in the shallow,

swim away with

great speed.

rest

during the day at their "homespots" on a rock.

iron pry bar

can be used to pull them

An

and they

loose,

can sometimes be pried loose quite easily with a quick
motion.

swimming, pugnacious crabs can be collected

They can be
found partially buried and lying around shells and

9.7

rocks or walking along the bottom.

Tagging aquatic organisms can provide information on

easily with a short-handled scoop net.

Stone crabs inhabit burrows, depressions, and shell
houses in the coastal waters along the South Atlantic

and Gulf of Mexico
tongs

is

useful to

An

cm) pair of
extricate them from burrows and
states.

18

inch (45.7

TAGGING AND MARKING TECHNIQUES

many
tion,

aspects of underwater

including coastal migra-

life,

nearshore to offshore movement, seasonal

bution, and growth rate. Because tagging can

distri-

damage

the animal, the value of the information gained from a

shell houses.

Their claws can be brought into action
quickly and can easily crush fingers, so they should be

return should be carefully considered.

handled carefully. Stone crabs should be handled by

organisms:

their rear legs.

be captured and brought to the surface for tagging.

The Alaskan King crab lives in the cold waters of the
North Pacific Ocean and the Bering and Okhotsk Seas.
Young crabs (2 to 3 years old) inhabit shallow waters

collect fish for tagging.

in large "pods" of 2000 to 3000 individuals and migrate to
deeper water as they mature. Mature crabs (males
range up to 6.6 feet (2 m) and 22 pounds (10 kg))
migrate seasonally between deep and shallow water to

spawn. As the crabs walk across the bottom, divers can
collect

them by grabbing them

cautiously from behind.

Dungeness crabs are found

in shallow inshore,
and offshore waters from southern California
to Alaska and the Aleutian Islands; they live in waters
that are up to 328 feet (100 m) deep. These large crabs,
which range up to 9.4 inches (24 cm) across the back
estuarine,

and up

to 2.2

pounds

(1

kg) in weight, can

move

quickly,

occasionally even faster than a diver can swim. Individual

crabs can be captured from behind and placed in a

mesh bag,

if this is

done cautiously.

Oysters inhabit relatively shallow waters
bays,

9-14

and sounds

in the

There are two different methods of tagging marine
The animal can either be tagged in situ or

Figure 9-15 shows an electroshocking grid used to
Although more traumatic for
the organism, the latter method has the advantage of
allowing the animal to be weighed, measured, and

examined

in detail before release.

ble to take

measurements

in situ

Methods are

under water. Although

body dimensions can be measured under water, a
method for determining body mass (weight)
has not been developed.
Ebert (1964) described a fish-tagging gun that
satisfactory

inserted a standard dart tag into bottom-dwelling fishes

and which could be adjusted
scale thickness.

More

to

account for skin or

recently, the plastic

Gulf of Mexico, off the Atlantic

"T"

tag,

marking clothing (Figure 9-16),
has been used. The needle of the tagging gun is placed
against the organism and the tag is inserted into the
body tissue. With practice, the depth of tag penetration
originally designed for

can be controlled by the tagger. Because
in estuaries,

availa-

gun has many metal

parts,

it

this particular

must be washed and

oiled

carefully to avoid corrosion.

NOAA

Diving Manual

—October 1991

Procedures for Scientific Dives

Figure 9-16
Tagging a Spiny
Lobster on the Surface

Figure 9-15
Diver With Electroshock Grid

Courtesy Floy Tag and Manufacturing Inc

Courtesy Diving Systems International
Photo Steven M. Barsky

carapace, adjusted, and then crimped with a leader
sleeve.

Other methods of short-term tagging include

staining by injection or dipping with vital stains, fluo-

Lobsters have been tagged within their natural envi-

Tagging of oysters, scallops, and abalone can be
accomplished by attaching Petersen tags with glue or a

be marked with styrofoam floats, numbered

wire, painting the shell, using colored quick-setting

term (retained
dens

may

rescent dyes, or phosphorescent dyes.

shedding) tags and marks. Lobster

ronments with short-term
at

(lost

at

shedding) and long-

The

carefully to note specific locations. Color-coded tags

cement, or staining the shell with

may

be inserted into the dorsal musculature between

excurrent holes on abalone shells are very convenient

abdomen and thorax of the lobster with the aid of a
No. 20 syringe needle (Figure 9-17). A secondary mark

abalone has been reported by Tutschulte (1968). This

or 4

mm)

technique involves attaching a small battery-powered

mark

will

the

may

be

made by punching

a small hole (0. 1 6

in.

into one of the five tail fan sections; this

be retained through at least one molt and will permit
recognition of a lobster that has lost

Movements and

its

primary

locations of lobsters at night

tag.

may be

determined by using small sonic tags (pingers). These
tags are small (about 1.2 x 2.0 x 0.4

in.

or 3 x 5 x

1

cm)

and weigh only a few grams. Several types are available commercially. They operate in the general frequency
range of 70 kHz and may be picked up as far away as

m) on an open bottom and 60

1200

feet

when

the tagged lobster

When
kept

in

(363

is

mind

movements
shell are

its

to the shell.

for tagging

During the night, the

of the abalone with the light source on

recorded on sensitive film by a camera

Movement

fixed several meters above the seafloor.

of a

marked animal may be recorded

either as light

streaks (in time exposures taken with a
or as a

moving point of

still

light (in time-lapse

tography). Animals studied by this
to a constant, low-intensity light

method are subjected
and are not illumi-

havioral changes caused by unnatural light flashes

and the

affect overall behavior. In one

in

night diving; be-

are therefore probably eliminated with this method.

A

technique has been developed for tagging echino-

study, a significant alteration of the population dis-

derms (Lees 1968). This method involves

was noted during the course of several weeks
of capturing and tagging (Miller et al. 1971).
Long-term and short-term tags also have been used
by divers in crab population studies. Long-term dart
and spaghetti tags can be inserted at the isthmus of the
carapace and abdomen, the point from which the crab

tiny hole completely through the sea urchin

tribution

exits

when shedding. Short-term

to the legs or carapace.

tags can be applied

Carapace tags

for blue crabs

consist of an information-bearing plastic spaghetti

is

stainless steel line) that has

carefully
in a

holding device

its

The urchin

first

is

hole or crevice and placed

made from

diver to press the urchin
still

(11.4

Diving Manual

removed from

a weighted plastic bowl

lined with thick polyurethane foam; this enables the

drill

— NOAA

been strung with small

pieces of color-coded vinyl tubing.

A

October 1991

drilling. a

and inserting

an inert filament (monofilament line or high-quality

put around each of the lateral spines of the

tag with a loop of stainless leader wire at each end.

loop

camera)
cinema-

should be

required for direct observation
it

method

nated by the periodic flashes of high-intensity light

that the very presence of the diver

may

luminous beacon

A

m)

feet (18.4

in a crevice.

conducting a survey of lobsters,

tagging procedures

points of attachment for tags.

vital stains.

down

into the

during the drilling operation.

An

fitted with an 18-gauge, 4
cm) hypodermic needle is used to

foam

to hold

it

ordinary hand
1

/2-inch-long

drill

completely

9-15

Section 9

Figure 9-17
Tagging a Spiny Lobster

in

Situ

(Randall 1961). Spaghetti tags are

made

of soft tubu-

about 1/16 inch (0.16 cm) in diameter,
with monofilament nylon in the center. This type of tag
lar vinyl plastic

can be attached by running the

line

through the

fish's

back beneath the rear of the dorsal fin. Because this
type of tag can snag on rocks or coral, the method is not
recommended for reef fishes. Dart tags consist of a
vinyl plastic tube with a nylon tip and barb. They can
be inserted into the back of the fish with a hollow
needle so that the plastic streamer bearing the legend
trails posteriorly,

this

come

tend to
Source:

NOAA

(1979)

with a slight upward

tilt.

Although

technique permits fairly rapid tagging, these tags

via the first

loose

more

easily than those implanted

two methods.

Another method of tagging

finfish involves injecting

colored dyes subcutaneously (Thresher and Gronell

through the

test

and body

cavity. After the filament or

wire has been threaded through the needle, the entire
drill/needle assembly

slowly withdrawn, pulling the

is

1978). This technique has been used successfully in

studying the behavior of reef fish. The dye can
be injected via disposable plastic syringes and dispossitu for

wire through the body cavity and leaving wire and tags

able needles. Although several different dyes have been

on the urchin. The ends of the wire are then

used, plastic-based acrylic paints are the most satis-

in place

twisted together to form a loop, and the loose ends are

factory and apparently do not

trimmed.

cantly affect their behavior.

The same technique can be used

to tag sea

cucum-

can be pushed through by

bers, except that the wire

hand instead of with a drill. Animals tagged in this
fashion seem to be unaffected, and tags have been
known to last for 6 to 8 months. With sea cucumbers,
trimming the tags short

important because fish

is

may

otherwise nibble on the long loose ends.

Tagging

The

finfish requires special skill

size of the fish

will not

must be

and handling.

sufficient so that the tag

impair the ability of the fish to navigate,

forage, or avoid predators.

Lake (1983)

lists

several

guidelines for tagging finfish:
•

use barbless hooks to catch the fish

•

avoid the use of bait

•

don't tag fish that have been tired by a long fight

•

hold fish with a wet rag over their heads

keep

•

don't tag fish that are bleeding from the gills

•

tag during cold water season whenever possible

•

during tagging,

gills free

the water for

of sand and dirt

make

sure that fish are not out of

more than 60 seconds.

For small-scaled and scaleless species, the needle

from the

number of techniques have been used to tag finfish.
Three common methods involve Petersen disk tags,
spaghetti tags, and dart tags. Disk tags are about 3/8
or 1/2 inch (0.95 to 1.27 cm) in diameter and come in a
variety of colors. They can be attached to the back of

is

body surface, so
that the tip enters the skin, runs underneath it for a
short distance, and then emerges. This in-and-out
technique ensures that the tag is placed immediately
below the skin, the best position for producing a longlasting tag. Slight pressure should be placed on the
syringe to start the flow of dye (and ensure that the
needle is not plugged), and then the needle should be
pulled back under the skin and withdrawn. The smooth
motion results in an even line of color below the skin.
inserted

rear, parallel to the

For large-scaled species, the needle should be inserted
under the rear edge of a scale and moved gently from
is

applied to the syringe,

which causes a small pocket of dye to be deposited
under the scale. Acrylic paint tags inserted in this
manner have lasted as long as 16 months; durability
depends

in part

on the color of the paint.

Scallops have been

marked successfully using a quickcement (Hudson 1972). This

setting calcium carbonate

material meets four criteria:

A

the fish or signifi-

used, depending on the size of the species to be tagged.

side to side while pressure

•

harm

Two methods have been

tissue; 2)

it

is

1) it

does not

harm

living

easy to apply and readily visible; 3)

it

adheres to a wet surface and hardens under water; and
4) it makes a durable mark. The recommended mixture
for this purpose

is:

not be used on fish that will

seven parts Portland gray (or white) cement
(Portland Type II is best because it is formulated

the tag will

especially for use in seawater)

the fish with monofilament

9-16

line.

This type of tag should

grow to a large size because
cause pressure on the fish as it grows

•

NOAA

Diving Manual

— October 1991

Procedures for

Scientific Dives

Figure 9-18
Elkhorn Coral

Implanted on Rocky Outcrop
•

one part moulding paste

•

two parts builder's sand

(fine grain).

This mixture will start to harden

in 3 to 5

minutes (or

moulding paste is used). The materials
should be thoroughly mixed while dry, and three parts
of water should be added to 10 parts of dry mix. If
colored cement is desired, no more than 10 percent
additive by volume should be used, so that the strength
sooner

if

of the

cement

less

is

not reduced.

The

final consistency

should be similar to that of a firm putty.

To apply cement to a scallop, the organism should be
removed from the water and the upper valve should be
pressed into a soft sponge to remove excess water. A
small quantity of cement (about 1/2 cc for scallops 0.4
to 0.8 inch (10 to 20 mm) in shell height and 1 cc for
scallops 1.2 inch (3
lip

cm)

or larger)

is

placed near the

and then rubbed firmly across the

shell at right

angles to the ribs. This tightly grouts the depression

between the
over the

"A*

and leaves a thin coating of cement

Several quick

shell.

to distribute

shell

ribs

thumb

cement evenly out

to the lip so that

J.

Harold Hudson

new

growth can be measured accurately. Only enough

cement should be applied

Photo

strokes are necessary

relatively

deep habitats. The

sites

where most research

the inter-rib areas;

involving algal and angiosperm vegetation takes place

the upper surface of the ribs should be visible through

are shallow enough to be accessible with scuba equip-

the coating.

Marked

to

fill

scallops can be returned

ately to the holding tank,

immedi-

where they should be held

for several hours to allow further hardening. Scallops

marked in this way have retained this marking material
months or more.
The same type of cement has been used to transplant
live coral in reef areas and to mark large marine
gastropods and other delicate bivalve molluscs (Hudson

for 15

1978). Figure 9-18

shows a

living

elkhorn coral, Acropora

palmata, implanted on a rocky outcrop. Another method

marking marine organisms involves the use of
various dyes. Alizarian Red dye has increasingly been
found useful for making permanent growth line marks
in living corals and other invertebrates. The dye does
not harm the coral, and subsequent growth can be

for

measured

after the coral

sliced with a saw.

is

ment.

Wherever

stable substrates occur nearshore,

on rocky

beaches, in estuaries or bays, or on coral reefs, various

forms of plants

will develop.

As with

all

underwater

work, however, site-specific features limit and strongly
influence the choice of sampling method. Large-scale
biologic studies

may

include samples or catalogues of

plants, recorded with estimates of area covered.

may sometimes

Data

be combined for forms or species (crusts,

Iridaea spp., for example), depending on the need for

taxonomic precision. Large discrete

thalli,

such as

taxa of brown kelp, usually are counted. In some cases
only indicator taxa, selected on the basis of economic
value, dominance, or ease of identification or counting,

are of interest. Sampling programs that are designed

natural environments focus on both nearshore intertidal

abundance and distribution patterns of plants
sessile organisms are described in Sections 9.5.1 and 9.5.2.
Presence/absence data or estimates of abundance
are utilized for experimental studies as well as for
descriptive investigations. The methods employed for
these various objectives rely on sampling procedures

the region where sufficient

that have largely been adapted from terrestrial or

can penetrate the water to support the growth of

(Figure 9-19). Benthic algae can occur at depths greater

intertidal studies. Their applicability to subtidal work
depends on their efficiency under conditions where
time, mobility, and visibility are often severely limited.
These factors must be assessed independently for every

than 656 feet (200 m), but few species occur

situation.

to record

and other

9.8

BOTANICAL SAMPLING

Studies of benthic macroalgae and seagrasses in their

zones and depths. This
light

is

diverse and often dense associations of photosynthetic

organisms that grow attached

October 1991

— NOAA

to

bottom substrates

Diving Manual

in

these

9-17

Section 9

Figure 9-19
Algal Cover
of Rock Substrate
material into component species in the laboratory. These
specimens can then be dried, weighed, and reduced to

ash for analysis of organic content.

For ecological studies or census (.data, the size and
of quadrats to be used must be determined by

number

appropriate

tests,

such as species accumulation curves,

and researchers often find it advisable
somewhat larger than the minimal one

to use

to

an area

be confident

of establishing statistically significant differences

between samples.
Seasonal variations in the diversity and abundance
of plants
world.

and

To

is

very conspicuous in certain parts of the

get complete coverage of events in an area

to gain understanding of the natural cycles,

it

is

necessary to sample repeatedly throughout the year.

It

is

same

best to return to the

station to monitor changes

over time.
Photo

9.8.1 Field

Bunton

Procedures

As with any

ecological project, the objectives and

constraints of the study
sites

Bill

and the features of underwater

determine which techniques are appropriate. In

Some plants have a narrow temperature tolerance,
and these may act as indicator species because their
presence or absence suggests certain environmental
characteristics. North latitude kelp taxa, for example,
do not live in warm water and are not found in tropical
latitudes except where cold currents or deep cold water
provide suitable circumstances.

recent years, subtidal biological methods have been

summarized

in

books that draw on hundreds of scientific

and technical publications. These sources provide up-to-

9.8.2 Collecting

Techniques

date reviews of methods, as well as discussions of their

Before beginning a study that requires the collection

advantages and disadvantages. Accordingly,

of plants, an investigator should survey local environ-

the following paragraphs represent only a brief review

mental conditions so that he or she will know where
and how to sample. Most macroalgae require a hard
substrate for attachment, and the diversity of plants on

relative

of botanical field procedures.

Generally, underwater botanical sampling, whether
of data or specimens, depends on the use of transect
lines, grids,

haphazard ("random"

is

rock surfaces usually

far greater than in soft sediment

is

in fixed, systematic, or

or sandy areas. Pilings, shells, dead corals, barnacles,

rarely practical) positions.

shipwrecks, and mangrove roots are other places algae

and quadrats arranged

Recently, circular sampling designs have been found

are likely to attach. Marine vascular plants (seagrasses)

useful in sites of heavy surge, rough water, or low

follow the reverse pattern; most species

visibility.

grow on

soft or

In circular sampling, a radius-length line

sandy substrates, although some, such as Phyllospadix,

used to partition the

grow on the rocky shores of the western United States.
Frequently, seagrasses and larger algae themselves

attached to a central fixture

is

area and guide the diver. Underwater sites are usually
located on the surface by sighting or buoys and on the

provide substrates for a great array of smaller epiphytic

bottom by a variety of fixed markers. Data can be
recorded by notations on data sheets treated for
underwater use, by collections of organisms, photography, voice recorder, or television camera (see

plants.

Because benthic plants are attached to the substrate, a
tool

such as a putty knife, scraper, or knife

is

usually

appropriate for investigating marine plants. Studies

remove entire plants if these are required for
voucher specimens or for later study. Mesh bags or
small plastic vials with attached lids are useful for
holding samples. If plant samples are necessary for

methods seek,

identification, portions or selected branches are often

Section 9.3).

Methods

suitable for sessile animals are particularly

that rely on these
ferentiate

and

classify plant

in general, to dif-

communities and

to analyze

needed

to

adequate. If there

is

no reason for collecting material,

of productivity,

a non-destructive sampling or experimental design

standing crop data can be obtained by collecting the

can be implemented. If small thalli are needed for
laboratory examination, it is often more efficient to

the data to identify changes.

entire vegetation

9-18

As an index

from a given area and sorting the

NOAA

Diving Manual

—October 1991

Procedures for

Scientific Dives

Figure 9-20
Diver in Giant Brown
Kelp (Macrocystis) Bed
collect pieces of rock or substrates than to

remove and

handle plants during the dive.

When

several divers are involved in a study, a system

"unknowns" (specimens

for incorporating

be identified

that cannot

the field) should be included in the

in

planning stage. Vouchers for such data as well as for
all critical

taxa should be assembled and retained with

the raw data.
If

an investigator wishes to obtain a census of an

area, collections from diverse substrates should be

sampled. Because some plants

only in intertidal

live

or shallow water, while others live only in deep water,

made

over a broad depth range.
such as the kelp Macrocystis
(Figure 9-20), that may be 100 feet (30 m) in length,
with holdfasts 3 feet (0.9 m) in diameter and as many
collections should be

Data

as

for large plants,

400 or 500

based on in-situ

stipes, are usually

observations and measurements. Care should be exercised when placing several types of marine plants in
a

common

container, because plants that have extremely

high acidic content
in

may damage

other forms of algae

the container.

A

clipboard with waterproof paper and pencil for

notes and a field notebook should be used to record

data immediately after diving. Diving observations
should be recorded as soon as possible. Ideally, field
data should include notes on depth, substrate, terrain,

water temperature, current, visibility (clarity), con-

Source:

NOAA

(1979)

spicuous sessile animals, herbivores, the date, time,

methods used, and the collecting party.

If possible,

information on available light, salinity, and other
environmental factors should be obtained. Census data

become more
species

is

useful

i.e.,

abundance of each
whether common,

Many marine

species are incon-

if

the relative

at least estimated,

occasional, or rare.

spicuous, and these require careful microscopic exami-

increased surface area, which augments the current

output per unit of illumination; a system for easily
filters; and a sensitive ammeter
whose range can be altered by current attenuation

changing the colored
circuitry.

nation and identification in follow-up work.

measurements within a given plant
community can be obtained by using small, selfcontained light meters. The use of photographic light

9.8.3

meters that incorporate selenium photocells

be

Accurate

light

is

unsatis-

factory unless restricted spectral regions, isolated with

colored

are measured. This

filters,

system that responds differently

is

Specimen Preparation and Preservation

To determine the kinds of plants present, notes should
made on the collected specimens while they are still
fresh. Herbarium and voucher specimens can be made

because a sensing

from either fresh or preserved material. Plants prepared

wavelengths

soon after collection tend to retain their natural color

to different

being used to measure light that is becoming
monochromatic with depth. The introduction of colored filters in front of the meter greatly
is

better than those that have been preserved, because

increasingly

more than formalin does.
Although procedures for drying and mounting large
algal and seagrass specimens are described in many
easily obtained and standard guides, a few simple
procedures are described here. Most marine algae have a
gluelike substance on the outside of the cells that makes
specimens more or less self-adherent to most kinds of
paper. Standard herbarium paper will preserve a

reduces

added

its

to

sensitivity.

make

An

opal cosine collector can be

the system behave

more

like the plant's

terms of light absorption, but such
collectors can only be used in shallow, brightly lit
waters. The apparatus needed to make such measuresurface does

in

ments generally incorporates

October 1991

— NOAA

a selenium photocell of

Diving Manual

alcohol bleaches thalli

9-19

Section 9

collection permanently, but this paper
requisite for

making a useful

Formalin (2.5-5%)

set of

will preserve

is

not a pre-

voucher specimens.

small or delicate forms,

Samples obtained from many stations can be kept
separate bags in a single large storage

off,

or collector should be associated with every specimen

condition for several weeks

by

label,

with a numbered reference to a field book or

in

that can

be sealed tightly to prevent formalin from leaking out.

and permanent slides are useful for ongoing work.
Time and place of collection and the name of the study

data

drum

For shipping, most of the preservative can be drained

because the plants, once preserved, remain

An

in

good

they are kept damp.

if

method for preserving whole large
them for several hours or days

alternative

plants involves soaking

set.

There are standard herbarium methods for pressing
some special variations for marine algae.
The usual approach is to float specimens in large, flat
plants and

and to slide them carefully onto sheets of heavyweight herbarium paper. Using water, the plants are
arranged on the paper; the paper is placed on a sheet of
blotting paper and topped with a square of muslin or
other plain cloth or a piece of waxed paper. This is
covered with another blotter, and a corrugated cardboard "ventilator" is placed on top. Another layer of
paper plant cloth blotter cardboard is
blotter
stacked on top. When 20 or 30 layers have been stacked,
the pile should be compressed, using a weight or the
pressure from heavy rocks or from straps wrapped
around the plant press. The top and bottom pieces
trays

—

—

—

—

—

in a solution consisting

of 10 percent carbolic acid and

30 percent each of water, alcohol, and glycerin. Spec-

may be

imens thus preserved

dried and then rolled up

The

glycerin helps to keep the plants flexi-

ble indefinitely.

Another technique involves partially
newspaper (in the shade) and

for storage.

air-drying giant kelp on

beginning with the holdfast. Rolls

rolling the plants,

wrapped in paper, and left to finish
drying. Specimens so prepared can later be resoaked
are tied, labeled,

for examination.

one wet preserved specimen should be

If possible,

kept for each pressed specimen. This

is

especially impor-

tant for unidentified species, because taxonomic classification often

depends on

cell structure.

Some

small

plants can be preserved with general collections, but

boards slightly larger than the herbarium

delicate specimens should be isolated. Retaining small

paper and blotters are generally used. After several

pieces of rock with encrusting algae attached helps

hours (or overnight), the stack should be taken apart,

keep the plants intact. Coralline algae and rock-

should be

stiff;

and the damp blotters should be replaced with dry
ones. Many small algae dry in one day using this technique, but some, such as the large brown algae, may
take a full week to dry completely, depending on air
humidity.

The usual method

for preserving

specimens for

later

detailed examination and herbarium preparation

is

encrusting species require special attention. Articu-

may be pressed on paper and then
brushed with a diluted solution of white glue as an
alternative to older methods of storing in boxes.
Plants collected for particular purposes (electron
lated corallines

microscopic study, chemical analyses, culture inocula)

require special treatment.

It

is

important to

fix or

simple and effective. For each station, one or more

preserve such specimens as soon as they are removed

large plastic bags can be used to hold samples of larger

from seawater. Because algae are photosynthetic organ-

plants.

Small bags or

should be used for selected

vials

isms and the deleterious effects of surface light on

a

the pigment systems of specimens from subtidal habitats

solution of 3 to 4 percent formalin in seawater buffered

tablespoons of borax per gallon. Ethyl

can affect other metabolic processes, they should be
kept relatively cool and dark until placed in a killing

made up

(fixing) solution or

fragile or rare plants.

with

3

to 4

alcohol (70%,

The

best general preservative

with fresh water)

for longer storage. Plant

is

is

recommended

used for physiological work.

and animal specimens should

not be mixed.

Permanent
cies.

slides

may be made

One common method

clear corn syrup

of microscopic spe-

uses a solution of 80 percent

and 4 percent formalin. The

slides

9.9

ARTIFICIAL REEFS

Artificial reefs are

manmade

or natural objects in-

should be allowed to dry slowly; as the syrup dries,

tentionally placed in selected areas of marine, estua-

more should be added. The edges of the

rine, or

slide

can be

sealed with clear nail polish.

fish habitats.

Plants collected for histological study should be

preserved

in a

manner

that

is

appropriate for the

particular technique to be used. In

all

cases, preserved

specimens should be kept in a dark place, because
exposure to light causes preserved plants to fade.

9-20

freshwater environments to provide or improve

Much

of the ocean, estuarine, and fresh-

water environment has a relatively barren, featureless

bottom that does not provide the habitat that reef fish
need. Natural reefs and rock outcrops are limited; less
than 10 percent of the continental shelf can be classified as reef habitat.

Even

NOAA

if

rough bottom consists of

Diving Manual

—October 1991

Procedures for Scientific Dives

Figure 9-21
Fish Using Tires
as Habitat

Figure 9-22

An

Reef Complex

Artificial

Photo Dick Stone, National Marine
Fisheries Service

Source: Grove and Sonu (1985)

low-profile rock outcrops,
fish

it

can provide a habitat for

and invertebrates.

Properly sited and constructed artificial reefs can
provide the same

enhance

benefits as natural reefs.

fish habitat, provide

more

They can

accessible and high-

quality fishing grounds, benefit the anglers and eco-

nomies of shore communities, and increase the total
number of fish within a given area. Artificial reefs
function

in

the

same manner

as natural reefs.

They

provide food, shelter, spawning and nursery habitat,

and orientation

in

an otherwise relatively featureless

non-toxic solid wastes or surplus materials

have been used

in

the United States to build reefs

automobiles

junked

(Figure 9-21),

and

streetcars,

damaged concrete

materials, including gas and

Christmas

trees,

oil

and brush

reef materials in fresh water.

scrap

tires

pipe and building

rubble, surplus or derelict ships, and

tires,

and fiberglass-coated

tested in the United States.

used

commonly

Japan and Taiwan. Fish aggregating devices

in

these have been used for

many

years

in

in

the United States;

the western Pacific.

Although artificial reefs can enhance recreational
and commercial fishing opportunities, creating a successful reef involves more than placing miscellaneous
materials in ocean, estuarine, and freshwater environments. Planning
artificial

reefs.

constructed,

all

is

needed

to

ensure the success of

species at the reef sites. Species,

mean

als,

number

of individu-

and behavioral observations should

lengths,

be recorded on waterproof data sheets (see Section
visibility

4 feet (1.2

is

observations can be

made by two

m)
or

9.3).

or more, these

more

divers.

Each

observer makes counts by species for sections of the
reef,

and these are then totaled for the entire reef. The
obtained by all observers are averaged for a

totals

mean

species count of territorial and schooling fish,

cardinalfish, morays,

and certain groupers, the highest
is used. Although

count obtained by any one observer

the accuracy of fish population estimates varies with
visibility, species,

and time of day,

it

is

assumed

that,

conditions remain constant, the counts represent

if

population density. Photographs taken at intervals from
the

same

location also can be used to count and iden-

tify species.

In this case, the photo print should be

placed on a soft surface and a pin hole put through

each identified

fish;

the print should then be turned

over and the holes counted. Visibility should be meas-

ured after taking the picture to compare the areas
covered by different photographs.
Diver-biologists have used direct observation tech-

or part of a reef can disappear or break

niques to demonstrate that artificial reefs can be used

natural reefs in the vicinity.

October 1991

site

materials are improperly placed or

If

apart and interfere with commercial fishing operations or

damage

and any changes that occur over time are
important pieces of information to researchers and
managers. Also, diver estimates of reef fish populations can be made by direct counts of the number and

on the

grunts, and most porgies. For seclusive fish, such as

plastic units have been
Figure 9-22 shows an

(FAD's) also are becoming popular

of reef material

have been popular

recently, fabricated

reef complex. Fabricated units are

artificial

The charting

such as black sea bass, Atlantic spadefish, snappers,

piles

More

numerous other

documenting the suc-

in

structures. Rocks,

structures such as Japanese-style fish houses, concrete
structures,

cess of an artificial reef.

When

environment.

Many

Divers can play a key role

— NOAA

Diving Manual

augment productive natural
areas. They have also shown that
to

reef and rough bottom
these structures increase

9-21

Section 9

biomass within a given area without detracting
from biomass potential in other areas.

total

clinometer can be cemented to a clipboard or to a
plastic writing surface and a pencil can be attached
with rubber tubing; a plastic ruler can also be mounted

on the edge of the board (Figure 9-23). Other useful

9.10

equipment of a general nature might include: a

GEOLOGY

Diving

is

research.

still,

movie, or video camera; an assortment of small sampling

an invaluable

The advent

tool for

many

aspects of geologic

bags or

vials; lights;

9.10.1

Mapping

and small coring tubes.

of scuba in the late forties and

early fifties permitted easy access to the shallow

subaqueous environment for the

first

time.

The

results

of in-situ underwater studies soon began to appear in

niques generally are applicable to research in lakes

Three basic types of mapping can be accomplished
under water: bathymetric, surficial, and geologic.
Bathymetric maps display the depth contour of the
seafloor. Surficial maps show the two-dimensional
character and distribution of the material that comprises the seafloor, and geologic mapping projects a

and rivers.
The topics

on the seafloor.

the literature. Since that beginning, the scientific
applications of diving have increased to the extent that

many

geologists now routinely use scuba as a research
Although most underwater geologic research has
taken place in shallow marine waters, the same techtool.

categories

three-dimensional analysis of the rocks that crop out
in this section are

— characterization

grouped into two general

and experimentation.

Geological characterization includes mapping, sampling,

and testing parts of the underwater environment, while
experimentation deals with the real-time analysis of
specific geologic processes. Experimental geological
studies rely in part on information obtained from
characterization studies, but they go much further in
that they require extensive interplay between geology
and other disciplines such as biology or fluid mechanics.
Initially, underwater geologic research primarily
involved the characterization of existing conditions,
but such studies

now

routinely entail experimentation

Bathymetric mapping is best done from a surface
echo sounding equipment. Multibeam swath
sonar systems are available in hull-mounted and towed
fish configurations; although expensive, their accuracy
is unsurpassed. A diver under water generally cannot
match the range and efficiency, the accuracy of location,
or the precision of depth determination and recording
possible from a surface craft. However, in unnavigable
water, or when taking precise measurements of a highly
irregular bottom or of features too small to be resolved
from the surface, underwater mapping may be the only
craft with

practical

means

of compiling the bathymetry.

Bathymetric mapping can also be done

as well.

Although sophisticated methods have greatly expanded scientists' sampling abilities, careful observation is still the mainstay of most underwater geological
studies. In some projects, observations may constitute
the main data collected; in other cases, careful docu-

in detail

over

a small bottom area to determine the area's microrelief.

Small-scale bed forms are an example of an important
geologic feature too small to be resolved from surface
craft.

These forms develop

in

response to near-bottom

currents, and their presence indicates aspects of the

of

dynamics of the environment that otherwise may not
be readily apparent. Moreover, such features may be
preserved in the geologic record, where they are of

the most important elements of underwater geological

considerable use in deciphering ancient environments.

accurate note-taking, coupled

Scaled photographs of bed forms provide important

mentation

may

be important either to select sampling

sites later or to

place a chosen study site into the

larger context of

its

research, therefore,

surrounding environment.

is

with agreement on what was seen.

It

is

One

advisable to

supplement notes with a debriefing immediately after
the dive and to record debriefing results along with

information on shape and orientation. In mapping
features such as sand ripples, however, the geologist
needs to determine the average size of the bed forms

The small

size of the

bed

the underwater notes.

over a section of seafloor.

Although most research projects require specific
equipment, there are some basic tools that a diving
geologist should carry routinely. These include a compass, inclinometer, depth gauge, noteboard, ruler, and

forms, the nature of the sediment, and the fact that bed
or unidirectional currents create difficult sampling

These are small items, and many of
them can be combined into a single tool. For example,
a small, oil-filled plastic surveying compass with in-

Peterson's Wheel-Meter Tape Trianguiation Method.
This trianguiation method requires a wheel that is
mounted on a vertical shaft and that has a rim marked

collecting bag.

9-22

forms often are located

in

areas of strong wave-induced

problems.

NOAA

Diving Manual

—October 1991

Procedures for

Scientific Dives

Figure 9-23

Underwater Geological Compass
the table tops and the alidades are set on these.

Two

plane tables are placed on the bottom, one on each side
of the

and

site,

leveled. Initial sightings are

made on

a

previously selected reference or primary fixed control
point and across the site from one table to the other.

Lines are inscribed on each plastic drawing surface
with ordinary lead pencils and are then labeled. The
resultant vectors, plus a

between the two

measurement of the distance

points, establish the position of both

tables on a horizontal plane. If the tables are not at the

same

elevation, the relationship

a 19.7 foot (6
at the lower

m)

determined by placing

is

long calibrated range pole, weighted

end and buoyed

A

the lower table.

at the top with a float,

sighting

is

made from

on

the upper

plane, and the distance between the sighted point on

the length of the pole and the lower table provides the
Photo Robert

Dill

vertical elevation relationship.

A

diver

diver
in degrees.

locations.

The

shaft

is

driven into the bottom at selected

The 0-degree mark on the rim

aligned

is

A

meter tape, pulled out from the
top of the shaft, measures the distance to any point,
with the direction read on the wheel rim where it is
with magnetic north.

A

crossed by the tape.

around

it,

mounted

slightly larger wheel,

over and perpendicular to the

first

so that

it

can pivot

allows elevations to be calculated from

simultaneous readings of upward or downward angles.

site,

mans each

of the two plane tables.

moves the range pole from point

to point

and sightings are taken from each table and labeled

marker up or down the pole until he
from the diver manning
one of the plane tables. The distance is then measured
from that point to the object being positioned. The
plane table diver uses the horizontal element of the
cross hairs for this measurement. The efficiency of this
method is limited by the clarity of the water and the
diver,

who moves

a

or she receives a stop signal

requirement that three divers record each point.

Meter Tape Triangulation Method. This triangulation
method is preferable to Peterson's wheel method when
small areas need to be surveyed under conditions of
reasonable visibility. Although this method is time
consuming, it is inexpensive, requires little equipment
and only a few divers, and is especially adaptable to
level and uncomplicated sites. Control points at known
distances from each other are selected and marked on
the seafloor around the site. Horizontal measurements
with a meter tape made from two of these control
points to any object or point on the site provide the
necessary information for plotting the position on a

used by archeologists.

plane.

object within the frame.

is

a simple

Plane Table Triangulation Method. This triangulation

method may be used

in clear

position triangulation

and

for taking elevations.

plane tables are necessary.
table, three
is

movable

legs,

water or on land, both for

They

consist of a

and a weight.

A

Simple

wooden

simple alidade

constructed by combining a sighting device, a tube

Dumas Measuring Frame Method.
precision

frame

is

mapping

for small areas has

couplings.

The

and extension

leveled a few meters above a sloping site, and the

new sections into place. Using two
frame as tracks, a horizontal crossbar
mounted on wheels can be moved from one side of the
doubled by

fitting

sides of the

frame

to the other. This crossbar, in turn,

by a yoke holding a
the vertical pole,
centimeters.

The

is

traversed

The mobile crossbar,
and the frame are calibrated in
vertical pole.

vertical pole

is

adjusted to touch any

The coordinates of the point are recorded from three
measurements read on the frame, the beam, and the
elevation pole. The details around the point must be
drawn by a diver hovering over portable 6.6 foot (2 m)
grids placed directly on the site materials.

grids are divided into 7.9 inch (20

sides of the grids.

Diving Manual

m) square metal

extension couplings allow the size to be indefinitely

are designated by

— NOAA

16.4 foot (5

telescopic legs enable the frame to be

weighted base. Sheets of frosted plastic are then tacked

October 1991

A

This method of
been successfully

fitted with four telescopic legs

with cross hairs at each end, and a straightedge on a
to

third

on the

consecutively. Elevations are measured by the third

method of making measurements under
limited visibility conditions, using two divers equipped
with voice communication.
This

A

cm)

These simple

squares, which

numbers and letters marked on
The measuring frame is used to

the
fix

9-23

.

Section 9

the positions of the corners of the grid. Although this

method and the Dumas Measuring Frame method are
no longer used extensively, they

may

be useful

in certain

Merifield-Rosencrantz Method.

A

marker stakes has been
developed and tested by Merifield and Rosencrantz
(1966). Two divers are used for the survey. The procedure

of ground control reference

consists of the following operations:

rough sketch of the approximate locations of the
points to be surveyed is drawn on a frosted plastic sheet
for underwater recording. Using a tape measure, the
between the various points

determined.

is

A

work of measurements should be made, forming

a triangular net (three sides of all triangles); this

eliminates the need for

making angle measurements.

When possible, more than the minimum set of measurements should be taken. For example, if surveying a
square that has a point at each corner, all four sides
and both diagonals should be measured. One of these
measurements

nometry and a hand-held

scientific calculator.

The

is

redundant, but

it

a set of adjoining box cores (the basic box coring tech-

nique

shown

is

sediment

in

Figure 9-24). Because the surficial

box core

in the

may be

modified during the

when
Newton (1968) covered the

coring process, additional steps must be taken

surface relief

is

desired.

sediment surface with a layer of dyed sand followed by

A

lattice

vertical heights

unconsolidated sediment can be measured from one or

simple method of

determining the three-dimensional positions of a number

slant distance

True horizontal survey distances and

microrelief of a small section of seafloor covered by

circumstances.

1

3.

are then calculated from these data using basic trigo-

will

enable the divers

check the accuracy of the measurements and to
detect errors. (Errors can easily happen when a large
number of points is being measured.)

to

a layer of native sand to provide a protective covering

before coring. After the core was impregnated with
casting resin, the microrelief was obtained from slabs.

This type of box coring
is

is

not only time consuming but

also extremely difficult to accomplish under the

influence of strong currents.

Ripple height and wave length can be established
under water and, where closely spaced, the resulting
profiles

can be used to create a three-dimensional

of a section of the seafloor.

equipment used

The

map

sophistication of the

to establish ripple profiles differs greatly,

and the corresponding resolution of the data varies
accordingly. Inman (1957) used a greased "comb"
(Figure 9-25) to obtain a profile of the large ripples
that form in

medium and

coarse sand. In principle, this

technique should give a fairly accurate profile of the
2.

The

vertical height of each point

is

measured

using a simple but extremely accurate level.
is

A

stake

driven into the ground in the middle of the array of

points.

A

clear plastic hose with an inner diameter of

0.37 inch (0.95

cm)

is

fastened to the top of the central

end of the hose pointing down. The hose
should be long enough to reach the farthest point to be
measured. To set up the level, a diver first works all the
air bubbles out of the hose. The free end is held at the
stake, with one

end attached to the stake. The diver
then blows into the free end and fills the hose with air.
As it fills, the hose will rise and form an inverted "u" in
the water. The diver then swims to each point to be
surveyed with the free end of the hose. A measuring

same

level as the

is placed on the point and held vertically. The
end of the hose is placed alongside the stick and
pulled down until bubbles are seen rising from the
fixed end of the hose. When this occurs, the water level

stick
free

at the

measuring stick

fixed end,

and the

is

even with the mouth of the

vertical

measurements can be read

off the stick. If visibility conditions prevent seeing the

fixed end, the hose at the free end should be pulled

down

slowly until the water level remains steady with

respect to the measuring stick.

When

this occurs,

come out of the free end, even
keeps them from being seen.

will

9-24

if

bubbles

poor visibility

ripples as long as the spacing of the

comb elements

is

small compared with the ripple wave length. In practice,

the

comb

is

awkward

to use

because

it

has to

be

handled carefully to prevent grease from fouling divers

and equipment and

to ensure that the

adhered grains

are not lost before the trace can be measured. If visibility

permits, photographing a scaled rod laid transverse to

the ripples produces a quick but accurate measure of

wave length (Figure 9-26). To measure the small
form in fine sand, Inman (1957) laid a
Plexiglas® sheet on top of the ripples and marked off the
crests with a grease pencil. Using this method, ripple
heights could only be estimated, and the problem of
ripple distortion by the Plexiglas® was always present.
Furthermore, reliability decreases markedly when the
current velocity increases because of scour around the
sheet and the diver's inability to hold position long
enough to mark the Plexiglas®.
Underwater surficial mapping requires identification and delineation of the materials and features that
compose the seafloor. In a small area, this can be
accomplished more accurately by a diver at the
underwater site than by instruments from a surface
ripple

ripples that

craft. Surficial features

(such as rock outcrops, coral

unconsolidated sediment, and textural and
compositional variations in the sediment) must be

reefs,

NOAA

Diving Manual

—October 1991

Procedures for Scientific Dives

Figure 9-24

Box Cores (Senckenberg)

for

Determining Internal Structure

in

Sand

(^
y\

/
/ -V

/

BOTTOM

TOP

— Senckenberg boxes aligned in o series, shown here as normal
a northtrending shoreline (L). Box 81 is nearly completely emplaced boxes 82 and 3 partly emplaced. Spiral anchor screwed m sond
behind boxes provides stability and leverage for diver b — Box filled with sand bottom plate secured with elastic band Box sides were
taped together prior to sampling to prevent their spreading apart during emplacement c — Box on side in laboratory bottom pier
moved d — Upper side of box detached and uppermost 2 to 3 cm of sand removed by careful troweling, e — Metal tray inverted and

Taking and processing of sand box cores to identify internal structure, a
to

sand surface Orientation data transferred to tray f — Tray removed and sand leveled and dried. Orientation data ot
g — Sand within tray impregnated with about 120 cc of epoxy resin. When resin has set orientation data is transferred
the sand slab, h — Sand slob removed from tray, internal structure outlined by surface relief provided by preferential penetration o
through individual beds Orientation data on underside of slab
pushed

into

side of tray

Source:

identified,

and their distribution must be traced and

plotted to scale.

The problems of

locating underwater features accu-

and of covering a sufficiently large area can be
minimized by towing the diver-observer with a surface
rately

craft

to

NOAA

(1979)

In areas where the bottom can be seen clearly from
above water, aerial photographs are useful to establish
the general bottom configuration.

The

details can then

be completed under water (Figure 9-27). Geologic

equipped for precise navigation and communication

mapping of the rocks that compose the seafloor is best
accomplished by using seismic profiling techniques

To ensure accurate location of features,
mark the features with a float.

the identification of a rock unit or the location of the

with the divers.

the towed diver should

October 1991

— NOAA

Diving Manual

from a surface

craft. If

a specific question arises

—such

as

9-25

Section 9
Figure 9-25

Greased

Figure 9-26
Diver Using Scaled

Comb for

Rod and Underwater Noteboard

Ripple Profiling

'

m

/

/

'V
^*',-^.*B^.
Photo David

Klise

Photo David

—

direct underwater observamust be used to answer it. For example, a geologist
may need to know the attitude (strike and dip) of
sedimentary strata or of fractures, joints, and faults in

surface trace of a fault

Klise

tion

the rock.

The

strike of a rock

the bed would

bed

is

make when

plane on the earth's surface.

Dip

is

is

the compass direction that

with the bubble defines the dip and dip bearing.

projected to a horizontal

Some outcrops are located in water too deep to be
sampled by these methods unless the diver is operating
in the saturation mode. Where underwater sampling

To

fix

the orientation of

the bed, however, it is also necessary to know the dip.
The dip is the angle in degrees between a horizontal
plane and the inclined angle that the bed makes,
measured down from horizontal in a plane perpendicular
to the strike.

The other crosshair, which
now horizontal, defines the strike of the feature, and
the downward direction of the crosshair coincident
coincides with a crosshair.

cannot be done, a photograph of the outcrop that includes

considerable

For any kind of underwater mapping,

measured with a clinometer. These

prepare a base

relationships are illustrated in Figure 9-28.

Rock outcrops on

the seafloor

one in Figure 9-29) can yield a
amount of information.

a scale (like the

may be

located by

map on which

established features are

drawn

New

it

is

useful to

the outlines of previously
in indelible ink

on a

features can be sketched in

noting irregularities in bottom profiles, anomalous shoals

sheet of plastic material.

or reefs, or the presence of organisms such as kelp that

pencil on the base and, as they are confirmed, inked

normally grow on rocks. The rock outcrop

may

be so

onto the map.

encrusted by bottom flora and fauna that recognition
of features, such as stratification surfaces, fractures,

and

joint planes,

geologist

is

difficult.

In such cases the diving

9.10.2

must clean off the encrustations, search

Sampling

for

freshly scoured surfaces, or collect oriented samples in

Diving geologists sample everything from unconsoli-

the hope of establishing the three-dimensional fabric

dated sediments to surface and subsurface rock forma-

of the rock in the laboratory. In some areas, differential
weathering or erosion makes stratification surfaces
and fractures more readily visible under water.

directly in a few underwater situations, they usually

To measure

the attitude of planar elements in the

adequate compass with an
Underwater housings can be built for the
relatively large surveying compasses commonly used

tions.

Although standard land techniques can be used

must be modified
to

(or

new techniques must be developed)

cope with the underwater environment. Diving allows

which

when using

rocks, the diver needs an

selective sampling,

inclinometer.

boat-based methods. The diver sees exactly what

on shore.

A

hollow plastic dish almost completely

Filled

with fluid (plastic petri dishes work well) and marked
with perpendicular crosshairs on the

flat

useful adjunct to underwater mapping.

surfaces

The

placed in the plane of the feature whose attitude

be measured and rotated until the enclosed

9-26

air

is

dish
is

a
is

to

bubble

collected and

how

it

is

not possible

is

relates to other aspects of the

submarine environment. Compromised samples can be
discarded and easily replaced. Also, diving may be the
only way of sampling the seafloor in areas, such as the
high-energy surf zone, inaccessible to surface craft.

Rock sampling may be required
of an underwater geologic

NOAA

map

in the

compilation

or to answer other

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-27
Aerial

Photograph and Composite

Map

Courtesy U.S. Geological Survey

may

be

4-cylinder industrial motor, which limited the type of

they can be traced to a particular outcrop.

surface vessel used for support. Smaller units have

are the most reliable, although talus fragments

adequate

if

Breaking through the external weathered or encrusted
rind of a

submarine outcrop may be

water makes swinging a

hammer

difficult

because

impossible; a pry bar

or geological pick can be used in existing fractures or

can be driven against an outcrop with better effect.
Explosives may be practical in some cases but must be
used with extreme care (see Section 8.12). Pneumatic,
electric, or

work

hydraulic

drills

are available for underwater

(see Section 8.4).

diver-operated

drill

m) (Figure

used

9-30).

in

The

water depths up to 49 feet
drill

consists of a Stanley

hydraulic impact wrench (modified for consistent
rotation) that

surface.

The

is

been designed that
is

a

powered by

drill rotates at a

a hydraulic

maximum

pump

of 600

on the

rpm and

provides sufficient torque to core under any reasonable

Glynn 1976, Macintyre 1977).
recover cores roughly 2 or 3.5 inches

utilize

more portable

unit,

of Macintyre's original design, cores over 82 feet (25
in

(Halley

et

al.

1977,

Hudson 1977, Shinn

Marshall and Davies 1982, Hubbard

exposed

in

water

less

reefs, a tripod

is

diameter, using a double-walled core barrel.

October 1991

— NOAA

Diving Manual

drill

bag can be used
in place of the tripod. Using the habitat Hydrolab in
the U.S. Virgin Islands as a base, Hubbard and his
lift

coworkers (1985) were able to core horizontally into
the reef face in water depths of 98 feet (30 m). On such

deep operations, bottom time
a diver

in

1977.

al.

required to support the

(Figure 9-30). In deeper water, a

The

cm)

et

et al. 1985).

than 6.6 feet (2 m) deep or on

In addition to tending the

(5 or 9

m)

length have been retrieved with these newer systems

conditions (Macintyre and

unit will

5-10 hp motors. The result
weighing about 350 pounds

(159 kg), that can be operated from a small boat.
Although this approach reduces the flow rate over that

For use

Macintyre (1977) describes a hydraulically powered,

(15

Macintyre's original unit was powered by a Triumph

Samples broken directly from the outcrop

questions.

and

is

needed

to note

to

is

usually the limitation.

normal operation of the

drill,

monitor the progress of the coring

anything that would be useful

in

logging

9-27

Section 9

Figure 9-28
Dip and Strike
of

Figure 9-30
Coring in a Deep Reef
Environment With a Hydraulic

Rock Bed

Block diagram

due

east,

illustrating dip

and

shown by arrow; amount

Drill

strike. Direction of dip

of dip, angle abc. Notice

that arrow extends horizontally as

it would if placed flat on
a map. Direction of strike is north-south, shown by crossarm of symbol; it represents a horizontal or level line
drawn on inclined bedding plane.

Photo Holmes (1962)

Figure 9-29
Geologist Measuring
Dip (Inclination) of Rock Outcrop

Photo Eugene Shinn

The hydraulic

drill is also

useful in obtaining shorter

samples through large coral heads for the purpose of

examining internal growth bands.
single-walled barrel

is

A

fitted to the

larger diameter,

same

drill

and

is

used to remove a plug from the coral colony. Because

method is meant to be non-destructive, great care
must be taken not to damage the surrounding colony.
Some researchers have inserted a concrete plug into
the hole they have drilled to promote overgrowth of the
this

colony by algae.
Photo Larry Bussey

A

the core at the surface.

submersible drilling frame

can solve some of these problems when divers are working
in

deeper water. Adjustable legs allow deployment on

an irregular, sloping bottom. The frame securely holds

bag can be used either

the drill in place, while a

lift

place pressure on the

or to

drill

using a video camera, the

drill

and divers are needed only
cores.

9-28

lift it

out of the hole.

to

By

can be monitored remotely,
to set

up and recover the

The

drill

100

psi (7

that

is

(Figure 9-3 la), which can operate at about

kg/cm 2 ),

is

attached to a neoprene hose

fitted to the low-pressure port of the first stage

of a regulator, which

is

attached to a standard scuba

cylinder.

The

sample

forced up into the middle of a core barrel

is

drill bit is

attached to the

bit.

designed so that the core

This barrel, in turn,

sample when the barrel

is

designed to

removed from
the bit. The barrels containing the sample can be
removed, and new barrels can be attached by the diver
retain the core

is

under water. The best cores can be obtained by running

NOAA

Diving Manual

— October 1991

Procedures Tor Scientific Dives

Figure 9-31

Pneumatic Hand
A.

Drill

and Attachment

Drill

The sediment beneath the seafloor may have been
deposited under conditions markedly different from
those producing the surface sediment;
will

differ accordingly.

How

is

character

its

mud? How

containing interlayered sand and

sample

if so,

does one sample a sediment
large a

required to be representative of a specific

particulate trace component, such as placer gold, without

some component, such

biasing the sample by the loss of
as the finest or densest material?

Many

of these questions

have been addressed in conjunction with subaerial
sampling, and the techniques employed in this form of
sampling are applicable to underwater sampling as
well (Clifton et

X Ray

B.

Core

of

al.

1971).

Surficial samples taken with a small core tube circum-

vent

many sampling problems and permit

consistent collection program.

centimeters

in

a highly

Plastic core tubes several

diameter with walls a millimeter or so

thick are ideal and inexpensive.

Cut into short tubes
numbered and have

several centimeters long, they can be

rings drawn (or cut) on them 0.39 to 0.78 inches (1 to 2 cm)
from the base and top (depending on the thickness of
the sediment to be cored). Two plastic caps for each
Photo

Collin

W. Stearn

tube complete the assembly. The tubes are carried
uncapped by the diver to the collection site. A tube
is

the

at

drill

on the

maximum
make the

its

to

bit

penetration of the bit

motion of the

permit

it

to

is

carefully over the top of the tube. Its

A

in

diameter and up

cm) long have been obtained with

single 72 cubic foot (2

m

3
)

scuba cylin-

der is sufficient to drill 4 holes in the coral Montastrea
annularis at depths up to 23 feet (7 m) (see Figure 9-3 lb). Because this equipment is not designed for use
in salt

water, extra care must be taken after use to rinse

and clean

it

to avoid corrosion.

number

is

the full

break the core free and

cm)

sediment until the ring on the side

pressure

be removed from the hole. Complete
(1

into the

coincides with the sediment surface, and a cap

completed, a slight rocking

bit in the hole will

to 33.5 inches (85

method.

When

hole quickly.

unfractured cores 0.39 inch

this

maximum

speed, with

pushed

along with a description of the sample location.
or rigid plate
the tube

is

is

is

placed

recorded,

A

trowel

slipped under the base of the tube, and

then removed from the sediment and inverted.

The second cap

is

placed on the base, and both caps

are secured. This simple arrangement can be improved

by adding a removable one-way valve to the top end
and a removable core catcher to the bottom. These
items allow the diver to insert and remove the core
without capping it. Capping is done at a convenient
time,

and the end pieces are then transferred

to

another

tube for reuse.
Further details concerning

also present

An inexpensive alternative to a core tube is to cut
one end off a 50-cc disposable syringe and to use it
as a small piston core. The sampler is pushed into the
sediment while the syringe plunger is being withdrawn

problems. The collection technique used depends on

slowly to keep the sampler at the sediment surface.

this

technique can be found

in

Stearn and Colassin

(1978).

Sampling unconsolidated sediment generally
than sampling solid rock, but

it

may

the purpose of the study. For example,

if

is

easier

samples are

The plunger provides enough

collected for compositional or textural analysis, the

sampler

primary concern

losing

a larger entity.

is

On

to obtain material representative of

the other hand,

if

internal structure

or engineering properties are the goal, the sample should

be as undisturbed as possible (see Section 9.10.2).

number
For example, how

Collecting a representative sample creates a
of problems that

must be resolved.

deep below the surface should the sampler penetrate?

October 1991

— NOAA

Diving Manual

to

suction to permit the small

be removed quickly from the bottom without

any sediment. The sample can then be extruded
sample bag, or it can be kept in the core tube
by capping the tube with a small rubber stopper.
into a

Undisturbed samples of seafloor sediment are valuable for identifying internal structures, such as stratification or faunal burrows,

and

for

of certain engineering properties.

making measurements

Compared with

the

9-29

Section 9

brief view of the seafloor possible during a single dive,

to a stationary pole so that the piston

analysis of these structures provides a broader per-

sediment surface during coring can increase the penetration of this apparatus to several meters. Recently,

spective on processes through time. Internal stratifi-

remains at the

have constructed a coring apparatus that

cation, considered in light of sediment texture, can be

scientists

used to infer the strength of prevailing currents during

used a hydraulic jack hammer. The jack

The

hammer

is

orientation of cross-strati-

attached to one end of a section of 3 inch (7.6 cm) in

fication indicates the direction of the stronger currents in

diameter aluminum irrigation tubing cut into the

the time of deposition.

the system and

may

indicate the direction of sediment

The degree

transport.

to

which mixing by faunal

necessary lengths.

made by

The attaching device

press-fitting a collar to a

is

a slip-fit

standard jack

hammer

upper 6 inches

burrowing disrupts these structures is indicative of the
rate of production or stratification, which in turn reflects

chisel shaft. Slits are also cut into the

the rate of the occurrence of physical processes and/or

water. During operation, the entire device

the rate of sedimentation.

the water with an air bag or air-filled plastic garbage

cm) of the core tube

(15.2

to allow for the escape of
is

suspended

in

seafloor sediment also

can. Holding the core pipe in a vertical position, the

provide a basis for interpreting ancient sedimentary

diver releases air from the air bag and descends slowly

Internal structures of

modern

environments. Direct comparison of depositional features
in a

be

rock outcrop with those in an individual core

difficult

core. This

may

because of the limited view permitted by a

problem can be overcome,

to a degree,

by

taking oriented cores in an aligned series, which yields
a cross section that

is

comparable with that

in the

the trigger

oriented vertically,

is

pressed and the tube

is

is

jack-hammered
m) of penetra-

into the bottom. Generally, 19.7 feet (6

tion

attained in about 30 seconds. Experience has

is

shown that

loss

up

compaction is less than 10
29.5 feet (9 m) in length have been

due
to

to

The

obtained using this method.
collection of undisturbed samples from the

seafloor requires special coring techniques. Diver-

operated box cores have been used successfully to core
the upper 3.9 to 7.8 inches (10 to 20 cm).

removed are useful

in

muddy

at the

is

layer can be lost

or

sediments. With their

tops off, they can be pushed easily into the

the top

Cans

from which the bottoms have been

similar containers

mud

until

sediment surface level (the surface
the container is pushed below the

if

sediment surface). The opening at the top of the container
sealed by a screw cap or stopper after the can

emplaced

in the

is

sediment, and the sediment remains

intact as the core

is

withdrawn.

A

wedge-shaped or

spade corer permits the taking of somewhat larger

Cores can be taken

in

sandy sediment with a variety

of devices, ranging in design from very simple to quite

complex. Cores more than 6.6 feet (2 m) long can be
taken by driving thin-walled tubing several centimeters

diameter into the sediment. A simple apparatus
removable collar that can be attached
firmly to a 3 inch (7.6 cm) in diameter thin-walled

in

consists of a

irrigation pipe.
3 inch (7.6

welded

to

collar.

By

cm)
it is

A

pounding sleeve consisting of

inside diameter pipe with

a

two pipe handles

slipped over the irrigation pipe above the

forcefully sliding the pounding sleeve

onto the collar, a 3.3 to 6.6 foot

(1 to

2

m)

down

core can be

taken (the core tube must be long enough to allow for
the core and enough pipe above the collar to slide the

pounding

A

different type of apparatus used for underwater

coring

is

the vibracore, which relies on high-frequency

vibrations rather than pounding to push the core tube

through the sediments. The core tube
into the

bottom as possible and

is

is

driven as deeply

then extracted; dur-

ing extraction, the vibration source

is

turned

off.

Several excellent but costly commercial units are
available; a less-expensive unit can be constructed

by

attaching a simple concrete vibrator to the top of a
3 inch (7.6 cm) piece of irrigation pipe. The unit can be
powered by a small motor located in the support boat;
cores 32.8 feet (10 m) long have been taken with this

type of unit.

Subaqueous cores are saturated with water when

surficial cores.

9-30

ascertaining that the core tube

percent. Cores

outcrop.

is

tube makes contact with the bottom. After

until the

sleeve).

Adding a removable

piston attached

they are removed from the bottom and must be handled
carefully to avoid destroying them. For example, unless

may be washed from
removed from the water, be liquefied
by excessive agitation, or collapse during removal from
the corer. The careful geologist avoids these frustrations
by planning core retrieval and transport as an integral
great care

is

the corer as

taken, the sediment

it

is

part of the coring system.

Other types of geologic samples can be collected by
For example, gas escaping from seafloor seeps
may be collected more easily by a diver/scientist
operating at the seafloor site than by scientists working
from a surface craft. Hydrocarbons in the sediment can
be analyzed with greater precision when the samples
have been taken by divers. These containers can be
divers.

NOAA

Diving Manual

— October 1991

Procedures for

Scientific Dives

Figure 9-32
Diver Taking

Vane Shear Measurement
sealed immediately after sterilization, be opened under

water, and then be resealed with the sample inside
before being returned to the surface.

9.10.3 Testing

means determin-

In the context of this section, testing

ing

some variable of the sediment

in situ that

same sediment. For example,

the

cannot be

from a sample of
and Moore (1965)

identified accurately on the surface
Dill

modified a commercial torque screwdriver by adding a
specially designed vane to the shaft.
inserted carefully into the sediment,

The vane was
and torque was

slowly and constantly increased until sediment failure

occurred (Figure 9-32). From this simple
authors were able to determine the

They

strength of surface sediments.

test,

these

maximum

shear

also

measured the

"residual strength" of the sediment by continuing to
twist the dial after initial shear occurred.

equipment generally

is

because the diver has
test to

Use of

this

restricted to currentless locales
to

remain motionless during the

be able to operate the apparatus correctly and

accurately.
Photo Lee Somers

9.10.4

Experimentation

The underwater environment

a

is

superb natural

laboratory, and diving permits the geologist to study a

number

of processes in real-time experiments.

Most

studies of this type begin with a careful characterization

of the study area, followed by an experiment (usually
carried out over an extended period of time) designed
to explore the interrelationships
logical, physical,

among

geological, bio-

equipment such as sonic pingers (see Section 8.3) may
be needed under adverse conditions. Current technology has advanced to the point where Loran C navigation
systems can guide a boat to within less than 20 feet
(6.1 m) of a previously visited site. Such units are readily
available and can be used on small boats. Surface
buoys tend

to arouse the curiosity of recreational boaters,

who may tamper with

and chemical processes.

or even

remove them, and land-

The experimental technique may be simple or sophisticated, depending on the nature of the phenomenon

marks are seldom close enough

studied and the resources of the experimenters. Repeated

stakes at the actual site must be done carefully so as

observations at a selected site can produce

much

information on processes, such as bed-form migration
or bed erosion and deposition.

When

visibility permits,

real-time video, cinephotography, or time-lapse photog-

useful, especially

when

to the actual site to

visibility

not to alter the current flow

is

enough

to

be

Emplacing

poor.

compromise

experimental results.

Some experiments

involve the

emplacement

unattended sensors that monitor conditions

of

at specific

raphy produces a permanent record of an ongoing process

times or whenever certain events occur. The data from

that can later be analyzed in great detail. Monitoring a

such sensors are either recorded

with sophisticated sensors can, for instance, yield

by cable or radio

in situ or

transmitted

to a recording station. Relocation

is

quantitative information on the interaction of perti-

necessary to maintain or recover the equipment used

in

nent physical and geologic variables.

such experiments.

site

Since

making

many experimental

studies in nature involve

serial observations of the

experimental

site

may have

to

same

be reoccupied

Characterization studies will continue to be the main-

the

stay of underwater geologic research because most of

to continue

them can be completed without elaborate equipment.

site,

the study or to service equipment. Relocating the site

In-situ

and must be planned ahead of time. A
buoy, stake, or prominent subaqueous landmark may

become

can be

difficult

suffice in clear, quiet water, while

October 1991

— NOAA

more sophisticated

Diving Manual

experimental studies, however,
increasingly important as

cover the advantages they offer

will

more
in

undoubtedly

geologists dis-

answering funda-

mental questions about the geologic environment.

9-31

Section 9

Figure 9-33
Undersea Instrument

Chamber

MICROPHYSICAL OCEANOGRAPHY

9.11

Micro-oceanographers have so far not taken

advan-

full

tage of diving techniques; to date, in-situ measurements

and observations of water mass processes have not
been widely used. Turbulent cells, boundary layers,
and flow regimes have not been studied extensively.
Notable among published accounts are the studies of
visual indications of the thermocline, the use of

tracers to reveal flow patterns

and the study of

1971),

dye

(Woods and Lythgoe

waves and the formation
(LaFond and Dill 1957).
Hydrolab has shown that

internal

of bubbles in sound attenuation

Work by Schroeder

(1974)

divers can be used to do

in

more than emplace,

tend,

and

recover oceanographic instruments. Divers are the best

means of ascertaining the

measurements of the
The oceanographic
scientist today dives to implant instruments in the
active parts of the water column and to ensure that
these instruments are measuring the real underwater
scale of

physical nature of the water column.

world.

Table

9-1

summarizes some of the micro-oceano-

graphic variables and problems that involve the use of
divers in data collection.

As

better methodology develops,

the diver's role in micro-oceanography will expand.

(
9.11.1

Emplacement and Monitoring
of Instruments

The implantation, reading, and maintenance of
instruments and instrument arrays and the recovery of
samples and data are important jobs divers can perform in

oceanographic surveys. Instruments implanted at a
site to measure current flow, direction, or other phenomena may be damaged by marine growth or the
buildup of sand or bottom debris. If the instruments
are read remotely, these conditions

of the data

may

alter the validity

measured by the instrument. Divers should

routinely check the condition of implanted instruments to

Photo Morgan Wells

ensure that they are operating correctly.

Undersea laboratories are of great advantage
imental studies requiring the use of

many

in exper-

instruments

and dives of long duration. The Undersea Instrument
Chamber (USIC) provides a stable underwater housing for instruments that record oxygen, temperature,

pH, conductivity, and sound. The

light,

USIC

can be

entered by divers as necessary for data retrieval equip-

ment, calibration, and monitoring (Figure 9-33).

A

good diver-managed oceanographic instrumentation

program was carried out during a Hydrolab underwater habitat mission in 1972 (Schroeder 1975). The
objective was to evaluate a continuously deployed
shallow-water current and hydrographic monitoring
system. Divers set up thermometers, current meters,

9-32

pressure gauges for tidal measurements, and instru-

measuring depth, temperature, conductividissolved oxygen, and pH using a taut line
buoy array. Data were obtained by reading the instruments and/or by a direct readout display inside the

ments

for

ty, salinity,

habitat. When reading a vertical array of the thermometers, the procedure was to swim at an angle to the

top thermometer, read
line to

it,

and then

to

descend the buoy

read the remaining thermometers. The data

were transferred onto a slate secured to the anchor
weight of the buoy system. This procedure prevented
the aquanaut's exhalation bubbles from disrupting the
thermal structure.

NOAA

Diving Manual

— October 1991

(

Procedures for Scientific Dives

Table 9-1
Micro-Oceanographic Techniques

Variable

Temperature

Instrument/

Diving

Technique

Mode*

Thermometer array

as

Placement

Problems

Remarks

Taut-line buoy,

Where

Limited by bottom

pier, piling,

mometers. Pre and post use

time

oil rig.

calibration. Reduires

modes.

to position ther-

in

conventional

repetitive observation.

Recording
thermograph

Same

as above
but secure to
bottom.

C.S

Equipment flooding.

Relocation of

units.

Electronic failure.

Only one data point unless
multiple units used.

Remote readout

Same

C.S

as above.

Same

as above

Excellent for use

in

habitat.

Water samples

Salinity

C.S

Bottle rack

Number

carried by

Processing procedures.

of samples.

Dissolved

salino-

Same

as

for

Temperature, above

Remote readout

Same

as

tor

Temperature, above

Water samples

C.S

Oxygen

time

in

conventional

modes

diver.

Recording
meter

Limited by bottom

Bottle rack

Outgassing when brought

Best

carried by

to surface.

a habitat

Reverse vertical

Fouling of cables.

Excellent for

profiling using

Interface at surface.

habitat operations.

used from

divers.

Multiple

Remote readout

Same

as

for

Temperature, above

Recording

Same

as

for

Temperature, above

Remote readout

C.S

Sensor Unit

floats

and

pulley

system.

Currents

Recording

Same

as for Temperature,

above

Remote readout

Same

as for Temperature,

above

Recording (waves)

Same

as

Ambient pressure

S

Dye

Tides

studies

gauge

inside

for

Temperature, above

Gauge

inside

habitat.

habitat

"C = conventional diving
S = saturation diving
Source:

9.11.2 Planktonic Studies

NOAA

screw-type anchor or other anchoring device

(1979)

in

the

Diving techniques have long been an integral part of

lake bottom and attachment of a collapsed bag held in

experiments on the effects of controlled nutri-

a vertical position by a submerged float (Somers 1972).

in-situ

ent enrichment of phytoplankton
lations.

bags

at

and zooplankton popu-

Lake Michigan, divers implanted large plastic
various depths, which required placement of a

In

October 1991

— NOAA

Diving Manual

Divers could then insert a hose into each bag to
tate filling with lake water

facili-

and nutrient solutions.

After the filling process was completed, the divers

9-33

Section 9

disconnected the hoses and secured the

Water samples were taken
a hose and pump.
The role of zooplankton

filling tubes.

periodically by divers using

vidual vortexes rapidly lose their

own motion and

low the ambient flow. The pellets are sealed

proof polyethylene strips until needed. Three sizes,
in a coral reef

system was

each with the same aspect

ratio, are used: the smallest,

studied by divers working from the Hydrolab under-

described above, gives the most regular

water habitat during three saturation missions (Schroeder

only for about 5 minutes.

et al.

fol-

in water-

1973). Plankton samples were obtained by divers

in

The

wake but

lasts

largest, 0.24 inch (6

mm)

mm)

diameter by 0.09 inch (2.3

thick, can lay a

The speed

using small nets attached to a hand-held diver pro-

streak through the whole thermocline.

pulsion vehicle (see Section 9.5.1). Several variations

these pellets

this technique have been used and are described in
Schroeder (1974). To quantify the volume of water
filtered by the sampling nets, the area of the net mouth
was multiplied by the distance traveled. Samples were
preserved by pouring the contents of the cod end of
the net into a jar filled with filtered seawater and
sealing it with plastic wrap. The sample was then
preserved by injecting formalin through the plastic
by syringe and capping the jar immediately.
A second method of sampling zooplankton in inac-

zontal velocity encountered along any streak,

on

drop path

is

is

comparable

and their
means that the
cannot be determined from a single

often quite complex, which

velocity profile

photograph. Instead, the
layer

of

mean

shear across any given

obtained in successive frames of a timed sequence

is

still

of

to the difference in hori-

photographs or motion pictures.

The general procedure

is

as follows: after identify-

ing the area of interest by dropping a trial pellet, the

cessible areas, such as small caves in coral, involves a

photographer positions himself or herself above the
chosen level and then signals an assistant who is floating above and upstream to release a second pellet. As

suction system utilizing air from a scuba tank to create

the second pellet begins to

a vertical water current in a 7.9 inch (20

cm)

tube with a plankton net secured to the top.

When

used

capable of capturing even

fast-

properly, the device

moving small reef

is

plastic

fall,

the assistant increases

buoyancy, which permits the assistant to
move away from the dye streak without disturbing it.
Whenever possible, the assistant is positioned above
his or her

the sheet overlaying the layer being filmed; this sheet

fish.

movements from the dye. The
photographer then films the dye streak, keeping the
sun behind the camera to increase contrast.
Current can also be measured near the bottom by
using dye tagging techniques (Figure 9-34). Care must be
isolates the assistant's

9.11.3

Use

of

Dye Tracers

In addition to the

emplacement and monitoring of

instruments, divers have used dye tracer techniques to

measure currents, internal waves, thermoclines, and
various turbulent components of the water column
(Woods and Lythgoe 1971). Water masses tagged with
fluorescein dye can be followed and photographed to
provide an accurate measurement of current speed and
direction. If a point source of dye (a bottle full of dyed

taken not to kick up sediment or to create artificial

released into the current, accurate measure-

column, care should be taken to minimize the amount
of activity around the study sites to avoid unnecessary

water)

is

ments can be made at speeds lower than those of most
current meters commonly employed. To understand
the generation of turbulence inside a thermocline and
within the water column,

it

is

know both
shear. The most

necessary to

the density gradient and the velocity

vortexes by

swimming

in the

area during such studies.

Water Samples
When taking measurements

9.11.4

or samples in the water

mixing of the water column caused by vertical water
currents from the diver's exhaled bubbles. Instruments

should be placed well away and upstream of

all

bubble

activity.

to

Divers can collect bulk water samples by swirling

drop a tiny pellet of congealed fluorescein through the

large plastic bags through the water until filled, sealing

layer under study. Disk-shaped pellets, 0.12 inch

the mouths of the bags, and carrying the bags to the

convenient technique for laying a shear streak

(3

mm)

in

diameter and 0.6 inch (1.5

mm)

is

thick, are

particularly useful. These pellets are attached to a
light line

and dropped through

a thermocline.

The

dispersion of the dye by the ambient flow can then be

photographed.

The only disturbance

caused by
column is caused
by the formation of a small vortex wake, whose indito the existing flow

the pellet's passage through the water

9-34

Because large water samples are heavy, the bags
should be put into rigid underwater containers that are
then attached to the boom of the ship. The plastic bag
sampler can be modified to collect more precise water
ship.

samples by gluing or stapling a strip of wood or plastic
to each edge of the bag opening, so that it will extend

from the corner to about two-thirds the length of the
The remaining third of the open end is then

opening.

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-34

Dye-Tagged Water Being
Moved by Bottom Current
of the air-filled jar

is

buoyancy

sufficient to disturb the

of the diver, requiring constant attention to depth regulation

When

and distracting the diver from the task

at

hand.

standard ship-operated water samplers are used,

the divers and ship personnel can precisely position

and trigger the samplers under water.
It

is

measures of

difficult to obtain accurate

dis-

solved oxygen in seawater because the changes in pressure

which

to

y^>

a

sample of seawater

is

subjected as

it

is

brought to the surface affect the chemical nature of
the solution. Liquids and solids are relatively insen-

but dissolved gases are sensi-

sitive to pressure effects,
tive to pressure

as

/

if

taken up when the container

/
Courtesy U.S. Navy

the container

is

protected

raised through the water column, oxygen

is

it

changes. Even

may

be

opened on the surface.
To overcome this limitation, a sampler that is portable,
versatile, and inexpensive has been developed (Cratin
et al. 1973). This sampler and technique are equally
effective for operations from the surface or from an
ocean floor laboratory.

The sample

PVC

is

bottles (Figure 9-35) are constructed

mm)

folded back against one of the supports and lightly
closed with tape or a rubber band to prevent water

from

from entering the bag. To begin sampling, the diver
pulls the two mouth supports apart, breaking the tape
or rubber band, and opens the bag to form a triangular
mouth. The bag will fill entirely as the diver pushes it

provides a volume of about 0.24 quart (225 ml). Screw

forward.

The

diver then closes the supports, refolds the

end back against one of the supports, and rolls
the edge tightly toward the bottom of the bag to seal in
the water sample. Large plastic bags also can be filled
loose

using hand-operated pumps.

When

shipboard analysis

requires uncontaminated samples, new, acid-washed,
hand-operated plastic bilge

pumps can be used

to collect

1.9 inch (48

caps

made

tubing that

mm)

i.d.,

is

and

2.4 inches (60

4.7 inches (12

of plastic and fitted with

cm)

PVC

long,

o.d.,

which

inner linings

and rubber O-rings effectively seal both ends of
the sample bottle from their surroundings. A hole,
0.59 inch (15

mm)

in

diameter,

each sampler and a piece of

mm)

is

drilled into the side of

PVC

tubing 0.59 inch

rubber membrane
and over the small PVC tubing. When
taking large numbers of samples, a backpack designed
to fit over double scuba tanks is a useful accessory
(15

is

long

is

sealed into

it.

Finally, a

fitted into

(Figure 9-36).

A

samples.

Smaller water samples, up

to

1.06 quart

(1

L),

can

be taken with extreme precision using a plastic or glass
jar with a 2-hole stopper, one hole of

which

is

fitted

with a flexible sampling tube of selected length and
diameter. At the desired depth, the diver inverts the

unstoppered

jar,

The

stopper.

jar

purges
is

it

with

air,

and then

inserts the

place.

then righted and, as the air bubbles

out of the open hole in the stopper, the diver manipulates the

sample collection proceeds as follows: the open
i.e., without the screw caps, is moved to the
underwater location, tapped several times to ensure
complete removal of all trapped air, and one of the
caps is screwed on. A marble is placed into the sample
bottle and the second cap is then screwed firmly into
bottle,

sampling tube

to

vacuum

organisms, or detritus into the

jar.

the water sample,

After evacuating

all

To prevent oxygen from ongassing when
is

the sample

brought to the surface, two chemical "fixing" solu-

tions are

added

in

(hypodermic) needle

the following manner: a venting
is

placed into the

membrane and

the diver seals the jar by inserting the tip of the

.0042 pint (2 ml) of manganese (II) sulfate and alka-

sampling tube into the open hole of the stopper or by

potassium iodide solution are injected into the
by hypodermic syringe. (Special care must be
taken to make certain that no bubbles of air are present
in any of the syringes.) The bottle is shaken several
times to ensure complete mixing. (The dissolved oxygen
gas is converted through a series of chemical reactions

the

air,

swiftly replacing the stopper with a cap.

remains

in the

with water

when

air

tion

is

A

top of the sampling jar and

the stopper

is

bubble of
is

replaced

removed. Contamina-

generally insignificant. Bottles larger than

1.06 quart (1

L) are inconvenient because the buoyancy

October 1991

— NOAA

Diving Manual

line

bottle

9-35

Section 9

Figure 9-35
Diver Using

Figure 9-36

Water Sample Bottle

Water Sample Bottle Backpack

Source:

into a white insoluble solid

When

—manganese

III

NOAA

hydroxide.)

the samplers are taken to the laboratory, they

must be kept under water as added insurance against
leakage.

Once

in the

laboratory (with the bottle

water), a venting needle

is

inserted into the

still

Photo William

(1979)

under

membrane

L.

High

As more people have discovered the advenand monetary rewards of shipwreck diving, government resource managers and scientists have become
increasingly aware of the need to preserve and protect
artifacts.

ture

historic shipwrecks.

Although

this section deals primarily

with shipwreck

and .0042 pint (2 ml) of concentrated sulfuric acid is
added via a hypodermic syringe. The bottle is shaken
several times to ensure complete reaction. The sampler
is then removed from under the water, one of the caps
is carefully unscrewed, and known volumes of solution
are withdrawn. A knowledge of the volumes, concentrations of reacting chemicals, and other pertinent

archeology, research on prehistoric remains that are

data enables the analyst to calculate quantitatively the

than 10,000 years. Figure 9-37 shows a diver recovering

oxygen content
nique

is

seawater.

Use

of this sampling tech-

may

limited only by the depth at which a diver

safely work.

much

in

Oxygen

analysis of samples taken from

greater depths requires

more complicated and

expensive equipment that can be operated remotely.

under water is conducted for other purposes as well.
For example, extensive work has been done in Warm
Mineral Springs (Cockrell 1978) and Salt Springs
(Clausen 1975), Florida, to depths of more than 200
feet (61 m), to obtain information on the area's early
animal and human inhabitants, who date back more
Indian artifacts off the coast of California.

The

real

boom

in

archeological diving in the United

States has involved shipwrecks.
the

more

It is

estimated that, of

than 2.5 million certified recreational divers

in the country,

about 200,000 are wreck divers. In
more than

addition to recreational divers, there are

1000 active salvor divers

9.12

ARCHEOLOGICAL DIVING

20 years, diving methodology and technology have had an enormous impact on the scientific
development of underwater archeology in the Americas
(Burgess 1980). Archeological procedures developed

Over the

in the

in the

trained marine archeologists,

last

1960's for use on shipwrecks in the Mediterra-

country. Professionally

who number no more

than 100 in the United States, thus comprise the smallest

group of wreck divers.
It is estimated conservatively that there are well
over 100,000 shipwrecks in United States waters. Available data indicate that close to 90 percent of

known

shipwrecks on the Continental Shelf are located in
depths of less than 60 feet (18.3 m). Along some parts

nean by Bass (1966, 1970, 1972, 1975) and his associates have been adopted and modified by professional
archeologists in the United States to study both sub-

of the coastline, shipwrecks are clustered in large

many

bers within a few hundred meters of the beach.

merged

prehistoric

and

historic sites. Since then,

archeologists have conducted historical and/or anthro-

Thousands of recreaand professional salvors have also become
involved with wreck diving in their search for historic
pological research on shipwrecks.

tional divers

9-36

numMost

harbors and inlets are rich in shipwreck sites. The
rivers, estuaries, and navigable channels
waterway
also contain thousands of shipinland
of the
Great Lakes,
wrecks from

many

different periods.

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-37
Diver Recovering
Indian Artifacts

and grid mapping,
and photomosaic surveys, are well-known procedures
on land sites and are described in detail in archeologiartifact triangulation, plane table

cal publications (see Sections 9.2.1

method and theory

the

and

9.10.1).

Although

of underwater archeology are

similar to those used to conduct excavations on land,

operating procedures for mapping sites can be very

The best
modify these

different because of underwater conditions.

way

for archeologists to learn

techniques

how

to

by borrowing from the experiences of

is

marine biologists and geologists and by experimenting
with various methods to ensure that reliable descriptive data are obtained.

9.12.2

Shipwreck Excavation

Every

historic

shipwreck presents unique problems

with respect to the archeological methods required to

excavate.

The

depositional environment of each site

how shipwreck remains are to be uncovered and recorded in situ. No two wreck sites are
exactly the same. Shipwreck discoveries made since
largely governs

the early I960's along the coasts of Florida, Bermuda,

the Bahamas,
and throughout the Caribbean have
shown that ancient wooden-hull shipwrecks do not
stay intact for as long as formerly believed. Shallow

water shipwreck remains are subjected continuously to
the onslaught of the sea. Because the vessels' super-

structures are degraded by the impact of currents,
storms, and shifting overburden, visual remains often
Courtesy Diving Systems International
Photo Steven M. Barsky

9.12.1

Shipwreck Location and Mapping

Underwater archeologists use many of the same techniques and much of the same equipment as other marine
scientists.

The two principal methods

of locating

shipwrecks involve the use of visual search and remote

sensing techniques. Visual search procedures are
discussed

in

Sections 8.2 and 9.1 to 9.3. Within the

are not easily recognizable on the sea bed.

Before excavation,

a

1986).

number

make

objective of these techniques

to obtain reliable

that accurately reflect

of these

mapping techniques, such

October 1991

— NOAA

the horizontal

Many

as baseline offsets.

Diving Manual

and

unnec-

the operation

efficient

ples of the environmental

and

logistical

information

needed include:
•

Measurements of the bottom topography and

rates

of sedimentation to determine the type of excava-

equipment needed
Sub-bottom profiles to determine sediment layers

tion

relative to
•

Number
at the site

•

and stratigraphic relationships between different types
of artifacts within overall artifact scatter patterns.

more

Exam-

of different

The primary

sites.

measurements

essential to determine the

is

to avoid

•

techniques to survey underwater
is

it

essary expenditures, accidents, and mistakes.

shallow water shipwreck remains scattered over miles

Marine archeologists use

ship's

ballast

general character of the environment, which helps to

sophisticated with respect to locating and defining

(Mathewson 1977, 1983,

its

last

decade, remote sensing techniques have become highly

of open ocean

The

and lower hull structure, may be covered by tons of sand, mud, or coral.
Figure 9-38 shows a marine archeologist exploring the
wreck of the Golden Horn.
contents, along with

If

site,

and/or coring requirements

work days and best time of year

and the weather conditions

Movement
bility,

•

wreck or

of

work

to

to be expected

of suspended materials, underwater

wave

action, current,

visi-

and temperature

near shore, usefulness of shore area as land base.

work

area,

and

living area.

9-37

Section 9

Figure 9-38
Archeologist Exploring
the Golden Horn

cm)

3 to 14 inches (7.6 to 35.6

diameter greater than

cm) are very

difficult for individual divers to handle.

sand or

mud

When

needs to be removed from a wreck

larger diameter pipe

more

is

with a

in diameter, airlifts

8 inches (20.3

effective.

When

deep

site,

the

uncovering

fragile artifacts, particularly in the presence of large

amounts of organic matter, however, a 3 or 4 inch
(7.6 or 10.2 cm) airlift is essential. The principle of
airlift

operation

is

described in Section 8.9.2.
with water depth because

Airlift efficiency increases

the trapped air expands as

ascends

it

in the pipe; air-

lifts

are consequently not very effective in water depths of

less

than 15 feet (4.6 m). Exploratory test holes 6 feet

m) in diameter can be dug
cm) airlift in 45 feet (13.7 m)
of water to define the perimeter of a site. When
excavating around fragile artifacts, the airlift should
be used more as an exhaust for removing loose overburden
than as a digging instrument. Instead of using the
(1.8

m) deep and

10 feet (3

quickly with a 6 inch (15.2

suction force of the

airlift to

cut into the sea bed, divers

should expose artifacts by carefully hand-fanning the

bottom deposits into the

pipe. In this

way, fragile artifacts

can be uncovered without being sucked up the pipe.

Because even experienced divers

lose artifacts

pipe, the use of a basket or grate at the other
essential.

The most common problem with

up the
end is

airlifts is

drawn

that large pieces of ballast, coral, or bedrock get
into the

mouth

become jammed

of the pipe and

as they

ascend.

Water
Courtesy Diving Systems International
Photo Steven M. Barsky

jet

excavation involves the use of a highpump, a fire hose long enough to reach

pressure water

The nozzle should

the sea bed, and a tapered nozzle.

Before excavation,

all

possible information about

the attitude and extent of a shipwreck and

its

cargo

must be known. Once the preliminary survey has been
completed, a site excavation plan is formulated and
systematic layer-by-layer surveying and artifact
removal can begin. Care is needed to avoid damaging
the artifacts or removing them without documenting
their position; archeological excavation requires tech-

nique, appropriate equipment, and a great deal of
patience.

pingpong paddles to the application of large-diameter
prop washes, more commonly referred to as deflectors
or "mail boxes."

Each digging procedure has

its

own

advantages and disadvantages.
excavation involves the use of a long discharge

made of PVC or aluminum) and an air
manifold bottom chamber (Figure 9-39). Although
the size of the airlift can range anywhere from

pipe (usually

9-38

stabilize the hose.

The water

jet creates

a high-pressure

stream that can cut through and remove hard-packed
clays

and sand, but

its

use as an excavating tool

limited to situations where the water jet will not

is

dam-

age artifacts or the integrity of archeological deposits
before they are mapped.

The

venturi

pump excavation

technique, sometimes

referred to as a Hydro-dredge, involves the use of a

10 foot (3

Excavation methods range from hand-fanning with

Airlift

have small holes for permitting a backward thrust of
water to eliminate the recoil so that the operator can

m) length of metal
cm) in diameter,

(7.6 to 15.2

at the suction end.

A

or

PVC

that

is

tube, 3 to 6 inches
bent in a 90° elbow

hose from a high-pressure water

pump

on the surface

at the

end of the tube.

is

attached to the elbow juncture

When

high-pressure water flows

along the length of the tube, a venturi effect causes a

which draws bottom sediment into the tube
and out the other end, where it is discharged off the
suction,

site.

This excavation technique

is

ideal in shallow water,

particularly in areas that are not accessible to the large

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-39

Heavy Overburden

Air Lift

LOW
AIR

PRESSURE

COMPRESSOR

Courtesy:

October

1991— NOAA

Diving Manual

7ffV&%2)

NOAA

(1979) and Duncan Mathewson

9-39

Section 9

needed

vessels

to support airlifts or a

prop wash. In

9.12.3 Artifact Preservation

water over 50 feet (15.2 m) deep, a similar hydraulic
dredging tool called a Hydro-flo can be used by lowering it over the side and controlling it from the deck. As
with

underwater excavation

all

must be used carefully

tools,

hydraulic dredges

damaging

to avoid

artifacts.

horizontal discharge of the water thrust that normally
is

deflected downward. This

away the bottom sediment. As
successive overlapping holes are dug by shifting the
surge of water blows

position of the boat on

its

anchor

lines,

an archeologi-

to using the

ological tool

is

only the

first

step in enjoying the rewards of research, diving,

and

hard work.

divers, either

rule for preserving

wet

until

submerged

ever,

if

is

to

first

keep them
initi-

should consult local experts or publications on artifact

treatment (Murphy 1985). Special preservation procedures are required for iron and steel artifacts, including

the use of rust and corrosion inhibitors, acid treat-

ment, sealants, chemical and electrolytic reduction,
and encapsulation (Murphy 1985). Some of these techniques require soaking or treatments lasting weeks or

months, depending on the nature and size of the
fact.

arti-

Non-metallic artifacts must be preserved by the

In addition to preserving artifacts,

engine speed properly. At

it

is

essential that

the states and the courts establish the rightful owner-

very delicately from wreck sites

submerged bottomlands.

50 feet (4.6 to

Generally, the U.S. Government controls operations

damaging the archeological
It can do great damage, how-

on or under navigable waters, while the states own the

When

authority over most finds. Non-navigable waters are

in 15 to

of water without

integrity of the deposits.

them

uncertain about what to do, he or she

is

ship of artifacts recovered on

m)

artifacts

proper preservation procedures can be

ated. If a diver

slow speeds, the prop wash can remove overburden
15.2

by accident or by design,

recover valuable or historic artifacts, only to lose

prop wash as an effective arche-

to control the

Many

is

use of entirely different procedures.

cal picture of the artifact scatter pattern slowly emerges.

The key

and Salvage Rights

of submerged artifacts

because they do not take proper care of them. The

Prop wash excavation (also known as a "blower" or
"mailbox") involves a 90° elbow-shaped metal tube
mounted on the transom of a vessel (Figure 9-40). The
metal elbow, slightly larger in diameter than the vessel's propeller, is lowered over the propeller, where it is
locked into position. With the vessel anchored off the
bow and stern, the engines are started so that the
pushes the vessel forward

The recovery

the engines are raced for too long a time.

waters and their submerged beds, which gives them

owned

or are controlled by local gov-

operating a prop wash, experience and good judgment

usually privately

are needed to ensure that artifacts are not lost or

ernments. There are

damaged. It is essential to maintain good communication between the divers on the sea bed and the operator

of historical artifacts or the salvage of abandoned proper-

at the throttle to ensure safe, well-controlled excavation.

such activities must be aware of applicable laws, both

wash can be very effective in
defining the anatomy of a wreck site by determining
the extent of its artifact scatter pattern. Even in deep
sand, where it is impossible to record exact provenance
data, artifact clusters mapped as coming from the
same prop wash hole may aid in the interpretation of a
site. Marine archeologists in Texas, Florida, North
Carolina, and Massachusetts have successfully used
In proper hands, a prop

many

laws affecting the recovery

and these are often complex. Divers involved

ty,

to protect

in

themselves and their historical finds.

9.12.4 Significance of

The archeological

Shipwreck Archeology

significance of shipwreck sites

best determined by their physical integrity

potential for providing historical

and

is

their

and cultural data

that are not available elsewhere. Information that can

prop washes to excavate wrecks.

be gleaned from shipwreck sites includes: overseas

The use of flotation gear is an inexpensive and effective method of lifting. Lift bags are available in different sizes and forms, ranging from large rubberized

cultural processes; maritime life styles

bags and metal tanks capable of

tion of

lifting several tons to

cultural change;

European

and information regarding the evoluvessels and the development of New

small plastic and rubberized nylon bags for lifting

World shipbuilding techniques.

50 to 500 pounds (22.7 to 226.8 kg). Larger bags should
be equipped with an air relief valve at the top. For
archeological work, smaller rubberized nylon bags are

distributed on a

recommended; these

self-venting bags have a lifting

capacity of 100 pounds (45.4 kg) and are useful in

all

underwater operations. Lifting bags are described further
in

Section 8.9.1.

9-40

New World
and patterns of

trading patterns and maritime adaptation to

Like terrestrial
tial

sites,

random

historic shipwrecks are not
basis.

patterning of shipwrecks

is

The temporal and

spa-

primarily a function of

environmental factors, seafaring cultural traditions,
maritime technology, and socio-political variables.
Recent studies have demonstrated that the preservation potential for shipwrecks

NOAA

is

highest in areas of low

Diving Manual

—October 1991

Procedures for Scientific Dives

Figure 9-40

Prop Wash System Used
for Archeological

Excavation

LOOSE SHELLY SAND
.••U.Y.

Courtesy:

energy

(less

wave action) and/or high

rates of sedi-

mentation. Thus, a knowledge of oceanography and
aquatic geology is important when searching for sub-

merged artifacts.
Shipwrecks should be considered not only as cultural resources but also as a source of valuable
educational and recreational experiences. Wrecks to
be explored for recreational purposes should be situin clear water less than 30 feet (9.1 m) deep, have

ated

a visible hull structure,
boats.

Heavily disturbed

sites

physical integrity can.

how

teach students
cal operations

to

and be accessible by small
in

with

little

or no remaining

certain cases, be used to

perform underwater archeologi-

without distorting the archeological record

(Mathewson 1981). Similarly, heavily disturbed sites
and those of more recent date can be developed into
archeological parks to provide new underwater experiences for sport divers. By promoting such recreational
dive sites, user pressure on some of the more archeologically significant sites

October 1991

can be reduced.

— NOAA

Diving Manual

9.13

Duncan Mathewson

ANIMAL CAPTURE TECHNIQUES

A wide variety of devices is used by scientists and
commercial fishermen to aggregate, concentrate, or
confine aquatic animals. Trawls, seines, traps, grabs,

and dredges have
equipped
ior.

all

been used successfully by scuba-

scientists interested in

Diver-scientists

who

will

animal and gear behav-

be diving near such cap-

ture systems should train under simulated conditions

before participating in open-water dives. Marine

sci-

can help to improve the design of trawls and
other such equipment by evaluating its underwater
entists

performance, observing how animals behave in relaand then conveying this information to
equipment designers.
tion to the gear,

In the

FLARE

and Hydrolab undersea programs,

divers were able to observe fish near stationary traps

25 to 80 feet (7.6 to 24.4 m) below the surface for up to
8 hours per day (Figure 9-4 1) and to devise methods to
alter catch rates

and the species captured (High and

9-41

Section 9

Figure 9-41
Fish Trap

draw the bottom

closed,

which

seals off the fish's escape

route.

9.13.3

Trawls

Trawls are nets constructed like flattened cones or
wind socks that are towed by one or two vessels. The
net

may be

operated at the surface,

midwater, or

in

across the seafloor. Specific designs vary widely,

depending on the species sought.

A

plankton net having a 1.6 foot (0.5

may
Source:

NOAA

(1979)

be towed at speeds up to 3.5 knots (1.7 m/s), while

m)

a 202 foot (61.5

long pelagic trawl with an opening

40.3 by 10.5 feet (12.3 by 21.5
1

Ellis

1973). Divers from the National

Marine Fisher-

Service were also able to estimate accurately the

ies

populations of fish attracted to experimental submerged
structures during studies designed to develop

automated

fishing platforms.

9.13.1

of use. Divers working close to an active net (one which

being towed) can interfere with

is

cially

if

touch

it.

it

is

its

if

net

considered large

Any

is

contact does not appreciably influence
tion or operation.

if

or

direct diver

its

configura-

Plankton nets typify small nets both

and

in the

retain micro-organisms.

sea
4.5
(61

be opened horizontally by towing each wingtip
from a separate vessel, by spreading the net with a
rigid wooden or metal beam, or by suspending paired
otterboards in the water to shear out away from each

to entangle fish

when towed.

on Stationary Gear

Diving on stationary gear such as traps, gill nets,
and some seines presents few problems. Experienced
divers can dive either inside or outside the net to observe

it

lightweight web required to
At the larger extreme, hightuna seines often are 3600 feet (1098 m) long, with
inch (11.4 cm) long meshes stretching 200 feet
m) or more down into the water. Gill nets are designed

in physical size

water at

operation, espe-

they swim too near to

small,

filter

may

9.13.4 Diving
purpose, materials, and methods

in size,

m) may

knot (0.5 m/s). Figure 9-42 shows a trawl diver. Trawls

other horizontally

Nets

Nets vary

m) long
m) mouth opening

9.8 foot (3

attempting to push through the meshes;

webbing mesh and thread size vary, as do net length
and depth, in accordance with the size and species of
fish sought. Gill nets use fine twine meshes hung
vertically in the water between a corkline and a leadline.
The net may be suspended at the surface or below the
surface or be weighted to fish just above bottom and
across the expected path of migratory fish. Divers and
their equipment can easily become entangled in gill
net webbing, which is difficult to see in the water.

animal behavior or to carry out work assignments.
Divers must be alert to the entanglement hazard
presented by loose diving gear, such as valve pull rods,
valves, mask rims, knives, vest inflator mechanisms,
and weight belt buckles. A buddy diver can usually
clear the entanglement more readily than the fouled
diver. Fouled divers must avoid turning or spinning
around, which will entrap them in the web. It is
occasionally necessary for a fouled diver to remove the
tank, disengage the caught mesh, and replace the tank
assembly before continuing with the task

9.14

at

hand.

THE USE OF ANESTHETICS IN
CAPTURING AND HANDLING FISH

Anesthesia has been defined as a state of reversible
insensitivity of the cell, tissue, or organism. In connection with fish, the terms narcosis

and anesthesia are

often used interchangeably, although not

all

chemi-

cals characterized as fish anesthetics also act as nar-

9.13.2

Seines

cotics. Anesthetics

Seines are similar to

gill

nets in that a wall of

web

is

held open vertically in the water by the opposing forces
of a corkline and leadline; however, the seine
circle to confine fish within the

entangle the

fish.

leadline through

9-42

is

set in a

web rather than

to

Seines often have rings along the

which a

line or

cable can be pulled to

should be used for surgical inter-

vention or to perform other painful manipulations.
Fish anesthetics have been used in conjunction with a
multitude of operations, including capture, transport,
tagging, artificial spawning, blood sampling, moving
fish in aquaria, surgical intervention,

sessions.

There

is

and photographic

a wealth of published information

NOAA

Diving Manual

in

— October 1991

Procedures for Scientific Dives

Figure 9-42
Diver Checking Fish Trawl
pose concerned. In the absence of applicable data,

it

is

often advisable to conduct a preliminary experiment,

may

since even closely related species

same anesthetic

the

intolerance

Many

not respond to

same manner. Species-specific
has been demonstrated with some anesthetics.
in the

chemicals exhibit toxic effects that are unrelated

and these may be transitory
Some chemicals that exhibit toxic effects
long-term exposure may be satisfactory to use

to their anesthetic action,

or sustained.

during

for short-term anesthesia.

The therapeutic
used
Photo

Ian K.

Workman

in

TR = LC 50 /EC

ratio

is

EC =

the concentration necessary to provide the

desired level of anesthesia. Generally, a

and
of chemicals and

The use

on a wide variety

scientific literature

their applications.

more

TR

exercised to minimize this effect. The subsequent

which anesthetics have been

used must take this into account, because census and
other data are affected by the use of anesthetics.

TR, its usefulness is somewhat
The toxicity of the anesthetic

be considered.

A

given anesthetic

handle because of
potential, or

it

limited.
to

may

its

humans

may

Response

acute toxicity or carcinogenic

toxify fish flesh, rendering

gerous or fatal to eat. This

to Anesthetics

wild,

last

consideration

the

gills.

As

to the water,

which

is

know

in

simplified

which

is

where the fish will later be released
where fishermen might catch it.

may be important, and the stages of anesthesia
can vary with the anesthetic. As mentioned above,

it

usu-

evaluating the depth of the anesthesia.

A

levels of anesthesia,

devised largely from the work of McFarland

(1959) and Schoettger and Julin (1967),
in Table 9-2.

is

thetic

quinaldine generally cannot be used to induce the sedation stage,
lent to fish

and some chemicals are much more repelthan others. Other anesthetics may initially

cause an increase

in activity.

Several anesthetics have low solubility

presented

must

first

alcohol to increase their solubility.

and

ly,

pH, and

ness,

water temperature, salinity or hard-

state of excitability of the fish, as well as

may

be inconvenient, particularly

cost

in

water and

be mixed with a carrier such as acetone or

The response of a particular fish to an anesthetic
depends on a number of factors, including the species
size of fish,

to the

then taken up by

the fish proceeds into anesthesia,

scheme defining the

dan-

impor-

In addition, the specific responses of fish to an anes-

ally follows a series of definable stages that are useful

to

it

is

commonly

Fish anesthetics are administered most

by adding them

must

also

be dangerous to

tant in cases

9.14.1

of 2 or

considered desirable, but since time of expo-

the

surrounding environment, and extreme care must be
in

is

sure and a variety of other factors affect the validity of

of anesthetics does have an impact on the

monitoring of an area

the

concentration lethal for 50 percent of the specimens

and
the popular

sometimes

LC 50 =

evaluating an anesthetic, where

The need
in

field

to

premix

work. Final-

must be considered, especially when

large field

collections are concerned.

on the dosage and type of anesthetic. With some anesthetics, not all of the stages

mentioned

in

Table 9-2 are

observable; for example, with quinaldine there

is

gen-

Recovery begins
removed from the anesthetic bath and
untreated water, where recovery then

9.14.3 Application of
Rapid immobilization.

erally no definitive sedation stage.

when

the fish

is

transferred to

proceeds, usually

shown

in

Table

in

reverse order, through the stages

in

If

an anesthetic

high enough dosages, fish

idly for

may

capture or handling. The

to untreated

sprayed

9-2.

Anesthetics

in

is

administered

be immobilized rapfish

is

then removed

water for recovery. The chemical

may

be

the vicinity of the fish or added to a con-

tainer holding the fish, or the fish

may

be removed to a

separate bath, depending on the circumstances. Sev-

9.14.2 Selecting

an Anesthetic

Factors to consider

in

choosing an anesthetic are

purpose, toxicity, repellent action, ease of application,

and

cost. It

may

be helpful to refer to the literature to

choose a suitable anesthetic for the species and pur-

October 1991

— NOAA

Diving Manual

eral anesthetics that are unsuitable for sustained

anesthesia are satisfactory for rapid immobilization,

provided the exposure

is

of short duration.

Sustained Anesthesia. Under suitable conditions,

fish

can be sustained safely under anesthesia for several

9-43

Section 9

Table 9-2
Levels of
for Fish

Anesthesia

Stage

1

2

Description

Behavior

Unanesthetized

Normal

Sedation

Decreased reaction to visual stimuli and/or tapping on the tank; opercular rate
reduced; locomotor activity reduced; color usually darker.

Partial loss of equilibrium

Fish has difficulty

Total loss of equilibrium

3

for the species.

remaining

in

normal swimming position; opercular rate usually

higher;

swimming disrupted.

Plane

—Fish usually on side or back; can

1

still

propel

itself;

responds to tap on tank

or other vibrations; opercular rate rapid.

Plane 2 — Locomotion ceases; fins may still move but ineffectively; responds to
of peduncle or tail; opercular rate decreased.

squeeze
4

Does not respond

Loss of reflex

This

to

peduncle squeeze; opercular rate slow — often may be

erratic.

the surgical level.

Operculum ceases

Respiratory collapse

5

is

minutes unless

fish

to

move; cardiac arrest (death)

revived

in

will

occur within one to several

untreated water.
Source;

days. Choosing the proper anesthetic with regard to
toxicity
is

and

stability

is

Before the anesthetic

critical.

administered, the fish should be starved for 24 to

48 hours to prevent regurgitation of food.

To perform surgery on captured

fish, it is

head should be immersed

in

an anesthetic bath

For longer term
surgery, more sophisticated procedures are required.
One successful system employs two water baths, one
containing untreated water and the other the anesthetic solution. The level of anesthesia can be controlled carefully by selectively recirculating water from
the baths over the fish's gills. Steps should be taken to
maintain the oxygen content near the saturation level
and the ammonia concentration at the minimal level.
Filtration may be required to maintain water quality
(Klontz and Smith 1968).
Recovery. To revive fish in deep anesthesia, it may
be necessary to move them gently to and fro in their
normal swimming position. It is helpful to direct a
gentle stream of water toward the fish's mouth, which
for the duration of the procedure.

provides a low-velocity current over the

gills.

It is

not

advisable to use a strong current or to insert a hose
directly into the

mouth because

this

(Houston

et al.

in fish after anesthe-

1971). During this post-treatment

period, additional stress

may

result in mortality

and

simplest to

then be placed in a trough or other restraining device,
its

sia

(1979)

should therefore be minimized.

anesthetize the fish to the surgical level; the fish should

and

than a week, have been observed

NOAA

may

cause, rather

than alleviate, hypoxia. The water in which the fish

is

NOTE
Anesthetics administered to food fish must
be approved by the Food and Drug Administration, and those using anesthetics are
advised to be thoroughly familiar with all
pertinent regulations. Violations of these
regulations carry severe penalties.
Tidepools and Ponds. Anesthetics are useful when
collecting fish in tidepools.

The water volume

in the

pool must first be estimated, and then the desired dose

of anesthetic

the fish

is

are

untreated water as quickly as possible.
to collect fish

As

calculated and added to the pool.

become immobilized, they

It

removed
is

from tidepools as the tide

because a moderate amount of surge

to

desirable
is

rising,

in the pool helps

to flush anesthetized fish out of crevices,

and diluting

the pool water with incoming water will prevent the
killing of

specimens that are not going to be collected.

With the proper anesthetic and dose, the mortality of

being revived must be of good quality.

uncollected specimens can be reduced to a negligible

Some species recovering from certain anesthetics
may undergo violent, uncontrolled swimming move-

level

ments, and steps must be taken in such a situation to

can be collected with anesthetics. Quinaldine (10-20%)

prevent self-inflicted injuries. For example, this

used widely for this purpose. One-half to 1.05 quart
(0.5 to 1 L) of the solution is generally used for each

usually the case

when

is

the yellowtail Seriola dorsalia

recovers from quinaldine anesthesia. Various physiological changes,

9-44

some of which may

persist for

more

(Gibson 1967, Moring 1970).
Reef and Shore. Many species of reef and shore

collection. Species susceptibility

is

fish
is

highly variable.

For example, angelfish and butterflyfish are highly

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

Figure 9-43
Slurp Gun Used
to Collect Small Fish
susceptible, squirrelfish are moderately susceptible,

and moray

The

eels are highly resistant.

effectiveness

of the anesthetic also varies with the physical situation

and experience of the collector.
at least somewhat repellent, and

as well as the skill

Most anesthetics are

the fish usually need to be in a situation, e.g., in small
caves, short crevices, or under rocks,

where they can be

confined within the anesthetic's influence for several

The anesthetic

seconds.

squeeze bottle

is

usually dispensed from a

in sufficient

quantity to immobilize or

partially immobilize
tion.
in

The

fish

specimens on the

first

applica-

can then be collected with a hand net

the case of small specimens, with a

gun (Figure 9-43).
A power syringe

is

or,

manual "slurp"

permits the diver to deliver the anesthetic at closer
range to more species of

fish

than can be done using a

this delivery

more expensive anesthetics

system

may make

the

practical to use for collecting.

Sedentary specimens can sometimes be collected by
slowly trickling a light anesthetic dose

toward them. Fish

in

some non-repellent anesthetics

fish

to ensure that the

emerges.

system for collecting garden eels of the
Taenioconger species, which were previously difficult
is

bilized small sharks

and

ratfish with this technique,

while Harvey (1986) has used

it

A

piece of clear plastic, 6.6 feet (2 m)
placed over the area of the eels' burrows and

moray

eels

Coral heads.

It

usually

is

advantageous

to enclose

coral heads with a loose-fitting net before applying the

anesthetic.

Some

hawkfish reside

species of fish such as wrasse and

in coral at

night and can be collected

easily at that time with the aid of anesthetics.

Large-scale collections.
lect fish

One technique used

over a large portion of a reef

is

to col-

to enclose the

desired area with a seine and to administer a large

enough quantity of anesthetic

to immobilize the enclosed

population rapidly. Divers should work as a team to
recover the fish because of the danger of the divers

becoming entangled
Handling large
tured by hook

in

the net. Procedures to free

fish.

may be

in

ing

advance.

Sharks or other large

cap-

fish

immobilized by spraying a strong

anesthetic solution directly over their

1

weighted down along the edges with sand. Approximately 1.05 quart (1 L) of 13 percent quinaldine

to collect

and jacks.

Aquarium have developed

a successful

square,

much promise. Harvey, Denney,

Marliave, and Bruecker (1986) have successfully immo-

entangled divers should be planned

Scientists at the Scripps

to collect.

dart gun, shows

downstream

burrows are often difficult to
collect with anesthetics because the burrows are so
deep that the fish cannot be reached by discharging
anesthetic from a squeeze bottle. Attaching tubing,
such as a piece of aquarium air line, to the bottle may
provide an adequate extension to reach into the burrow. The anesthetic should have repellent qualities
that will cause the fish to emerge, because otherwise
the fish might become anesthetized in the burrow and
remain out of range. A noxious chemical can be added
to

National Geographic Society

available that allows oral anes-

thetics to be delivered through a probe. This device

squeeze bottle, and

Photo

gills

before bring-

them aboard. Gilbert and Wood (1957) used

000-ppm

a

tricaine solution successfully in this situation.

Transportation. Anesthetics have been used, with

solution in ethanol

conflicting results, to immobilize fish during transit.

area

The

is applied under the plastic. The
undisturbed for 20 minutes, after
which the sedated and immobilized eels are gathered
is

then

left

gently by hand.

colony

may

A

single collection in a well-developed

more than 20 eels. This technique can
other burrowing species, although the

yield

be applied to

dosage and time of exposure

may have

to be varied.

Fish can also be anesthetized by injection. Although

effectiveness of this approach depends on a

of fish, temperature, time in transit, preconditioning

of fish, and water quality. Since most fish can be

transported successfully without the use of anesthetics,

information on the appropriateness of using anes-

thetics during transit should be obtained

earlier attempts at collecting fish with projectile-

literature or

mounted syringes were

procedure.

limited in their success, a recently

developed technique utilizing Saffan®, a veterinary anesthetic,

administered by a laser-sighted underwater

October 1991

— NOAA

Diving Manual

num-

ber of factors, including the type of anesthetic, species

from the

by experimentation before attempting the

Summary. The use of anesthetics as collecting agents
aquarium fish is controversial, primarily because

for

9-45

Section 9

Conventional methods of capture such as seining,

of concern about the delayed toxicity of the anesthetic

A

agents.

survey of the literature indicates that, in the

and long-lining are not appropriate

trawling,

majority of species experimentally subjected to repeated

turing fish around coral reefs, and a

anesthetization, delayed mortality

techniques must be used instead.

negligible. Pro-

is

number

An

for cap-

of special

array of suction

fessional aquarists at Scripps

Aquarium, Steinhart

devices called slurp guns has been on the market for

Aquarium, and other

have also demonstrated

some

that

many

institutions

other species that have not yet been subjected

can be collected safely and

to formal experimentation

powered either by rubber tubing,

diver using a slurp

gun (Figure 9-43)

pulls the trigger,

drawing the plunger back and sucking a large volume

handled without significant mortality.

Most aquatic

time. These are

springs, or other means. After cornering a fish, the

biologists concerned with collecting

of water in through a small opening and thus pulling

agree that judiciously applied anesthetics are useful

small fish (1-3 inches (2.54-7.6 cm)) into the gun.

However, the misuse of these chemicals, especially if widespread, can be very harmful. For
example, the practice of using sodium cyanide to collect aquarium fish, which is sometimes done in under-

fish are

collecting agents.

developed countries,

human

is

ill-advised

and other organisms

among

readied for another shot.

is

to the fish,
in a hole, to

and the need
capture

to corner the fish, usually

it.

Glass or plastic bottles also

in the vicinity.

Recommendations. Tricaine® (MS-222) is a highly
powder that is easy to

proved to be a successful anesthetic in a
wide variety of applications under a broad range of
conditions in both fresh water and seawater, and there
use. It has

an extensive literature on its properties and use.
Tricaine® is a good choice where sustained sedation or
surgical-level anesthesia is required, but high cost

of

captured, the necessity for the diver to be very close

the fish

soluble and virtually odorless

The disadvantages

slurp guns are: the small size of the fish that can be

in

and has resulted

deaths, as well as high mortality

gun

The

then moved into a holding container, and the

small

fish;

however, fish

may be

may

used to entrap

react to the pressure

wave created by the moving jar and swim away. All
bottles must be flooded fully with water before being
submerged.

A

better technique than the bottle

is

the

use of a piece of plastic core liner or plastic tube with a
screen across one end, which can be slipped over fish

is

generally precludes

its

It

is

of low solubility in water

and

is

generally

withdrawn and placed

As discussed

hol before use in water. Quinaldine

is

not useful where

the goal, and

is

it

should not

be used for major surgery or other painful procedures

because

it

is

a poor pain killer. Liquid quinaldine can

be converted readily to a water-soluble
greatly facilitates

its

use.

When

salt,

which

a mixture of the salt

combines the desirable properties of both chemicals and is
and tricaine

is

prepared

in

proper proportions,

it

effective at lower doses than either alone. Propoxate®

and

its

analog Etomidate® are two relatively new and

highly potent fish anesthetics that have potential as

anesthetics for fish collection. Table 9-3 shows the

commonly used fish
mended dosages.

anesthetics, including their recom-

if

in

may
may be

to attract fish, or divers

herd fish into the net. Once entangled, fish

dissolved in acetone, ethyl alcohol, or isopropyl alco-

sedation-level anesthesia

Divers on the bottom can also use small
Animals such as sea urchins may be broken

easily.

nets.

up and placed near the net

use as a collecting agent.

Quinaldine has been used widely to collect or handle
fish.

more
gill

bags or wire cages.

earlier, fish traps

may

also be effective

baited appropriately and placed at a proper point

either on the

bottom or

in the

water column. Divers can

then remove fish from the trap and rebait

it

while

it

remains on the bottom.

Deepwater

can be caught on hook and

fish

line

and

reeled to 60 to 100 feet (18.3 to 30.1 m), where divers

can insert hypodermic needles into those with swim
bladders and then decompress the fish. There is an 80
percent recovery rate on many species of rock fish

when

this

technique

bottom. The fish

is

used.

A

dip net fastened to the

is

useful in collecting fish near the

may

be pinned against a rock or sand

end of a pole spear

bottom, taken out of the net, and placed in an appropriate container; again, needle decompression

may

be

helpful.

Many larger
may be

fish

such as rays, skates, or harmless

caught either by hand or by a loop of
heavy monofilament line on the end of a pole (such as a
snake stick). Electric fish and rays should not be taken
sharks

9.14.4

Diver-Operated Devices

The capture

Some

of live fish poses no special problems for

and maintain discrete
and roam widely.
Diurnal variations may also cause the fish to change

with metal poles or rods because of the shock potential

regions, while others live in schools

(see Section 12.4).

their habitats during a 24-hour period.

gloves.

divers.

9-46

fish are territorial

Invertebrates

A

may

be collected by divers wearing

pry bar, screwdriver, putty knife, or diving

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

Table 9-3
Fish Anesthetics

Dosage

(varies

Common

with species,

Anesthetic

Benzocaine*

Qualities

temperature,

Powder,

25-100 mg/L

etc.)

soluble

Use

Remarks

References

Immobilization,

Widely used

Caldarelli

deep anesthesia

in

in

medicine; safe

ethanol

and

effective

with

fish.

Low

potency;

Chloral

Solid, soluble,

hydrate

inexpensive

1-4

g/L

Sedation

not widely used.

McFarland 1959
McFarland 1960
Bell

Cresols

mix

Liquid;

50:50 with

20-40

mg/L

for

Collection

1986

human

Cresols have

1967

Howland 1969

undesirable

immobilization

acetone to

toxic effects;

facilitate

para-cresol

solution.

the most effec-

is

tive isomer.

mg/L

High potency;

Amend

analog of

Limsowan

propylene

Propoxate®;

1983

glycol.

longer seda-

Make

Etomidate 5

1

solution

percent

2-10

Immobilization

in

et

al.

1982

et al.

tion times

and

safer than

quinaldine and

MS-222

mixture.

Methylpentynol

Liquid.

0.5-2 ml/L

Sedation or deep

Widely used but

Bell

(Oblivon®,

moderately

1500-8000 mg/L

anesthesia

less desirable

Klontz and Smith

Dormison ')

soluble

Phenoxyethanol

Oily liquid

0.1-1

ml/L

than other

1968

anesthetics;

low potency.

Howland and
Schoettger 1969

Used

Klontz

with salmonids.

and Smith
1968
Bell 1967

Collection,

Good

Thienpoint and

immobilization

agent.

Immobilization

(2-phenoxye-

frequently

thanol)

Propoxate®

Crystalline;

(McNeil R7464)

1-4

mg/L

soluble

1967

collecting

Niemegeers 1965

Howland 1969

Quinaldine
(Practical

grade)

Widely used

No

soluble with

for collection,

state;

difficulty; dis-

immobilization

analgesic;

Oily liquid,

solve

October 1991

in

5-70 ml/L

10-50

sedation

poor

efficacy varies

percent acetone,

widely with

ethanol, or

species and water

isopropyl alcohol

characteristics;

to facilitate

long exposures

solution.

toxic.

— NOAA

Diving Manual

Schoettger and

1969
Locke 1969
Moring 1970
Gibson 1967
Howland 1969
Julin

9-47

Section 9

Table 9-3
(Continued)

Dosage

(varies

Common

with species,

Anesthetic

Qualities

temperature,

Quinaldine

Crystalline

15-70

sulfate

solid

(QdS0 4

Remarks

References

Collection,

Prepared from

Allen

immobilization

liquid quinaldine

1973

and has same

Gilderhus, Berger,

properties.

Sills,

Use

etc.)

mg/L

)

and

Sills

Harman

1973a

Rotenone®

Powder

or emul-

0.5

ppm

sion

Ichthyocide;

Used

occasionally

fish

used

water ponds.

for

collecting

to salvage

from fresh-

Limited use

seawater

Tate, Moen,

Severson 1965

in

for

live collecting.

Sodium
cyanide

Solid

DO NOT USE

Used

in

Philippines

Styrylpy-

White powder;

ridine (4-

soluble

20-50

mg/L

Dangerous to humans;
causes high

and elsewhere

mortality

for collecting

fish.

Immobilization,

Not widely used

Klontz and Smith

deep anesthesia

but a successful

1968

in

anesthetic.

styrylpyridine)

Tricaine®

(MS-222,

tri-

caine meth-

mg/L

White crystalline

15-40

powder; readily

sedation

soluble

40-100 mg/L

for

for

deep anesthesia
100-1000 mg/L

anesulfonate)

Immobilization,

Expense bars

deep anesthesia;
most widely used

use

used extensively

anesthetic

in

its

for collecting;

Klontz and Smith

1968
Bell

1967

surgery, fish

handling,

for rapid

transport.

immobilization

Urethane

Carcinogenic

DO NOT USE

Immobilization,

Carcinogenic.

Wood 1956

deep anesthesia

Mixtures of

Powder, readily

Various, e.g., 10:20

Immobilization,

Combines

MS-222 and

soluble

ppm QdS0 4 MS-222
equals 25 ppm QdS0 4
80-100 ppm MS-222

deep anesthesia

properties of each

Sills,

anesthetic;

1973b

QdS0 4

:

or

desirable

Gilderhus, Berger,

Harman

combination can be

used

in

lower

concentration than
either anesthetic

alone.

Source: Donald Wilkie

9-48

NOAA

Diving Manual

— October 1991

Procedures for Scientific Dives

knife

may

be useful

their substrate.

may

be placed

bags. Vials

and

in

removing some specimens from

Delicate animals such as nudibranches
in

separate plastic jars, vials, or ziplock

jars should be

open

at the

beginning of

either a scoop,

which has

a line inscribed

given volume, or a cylinder

aluminum,

made

showing a

of plastic, stainless,

or other material that can be forced into

the soft substrate.

A

simple cake server or spatula can

the dive but be completely filled with water before

be inserted from the side to provide a closure as the

being returned to the surface.

core of sediment

Traps are effective for crabs, lobsters, and, occasionally, octopus. Nylon net bags are more easily used
for collecting than bottles or plastic bags. Animals
that are neutrally buoyant will float out of the bottle or
plastic bag when it is reopened to add another specimen.
Animals that live in the upper few centimeters of
sediment or sandy bottom may be sampled by using

October 1991

— NOAA

Diving Manual

is withdrawn from the bottom. The
diameter of the cylinder should be such that it fits

snugly over the mouth of the collecting bottle so the
material can be forced into a labeled jar.

Nylon or other plastic screens can be obtained in a
mesh sizes. These may be tied over ends of
plastic tubes as a sieve or be sewn into a bag to be used
variety of

to hold

sediment samples.

9-49

(

Page-

SECTION
DIVING

10

10.0

General

UNDER

10.1

Geographic Regions

SPECIAL
CONDITIONS

10-1

Northeast Coast

10-1

10.1.2

Mid-Atlantic Coast

10-2

10.1.3

Southeast Coast

10-3

10.1.4

10-3

10.1.7

Gulf of Mexico
Northwest Coast
Mid-Pacific Coast
Southwest Coast

10.1.8

Central Pacific Ocean

10-6

10.1.9

Arctic and Antarctic

10-6

10.1.10

Tropics

10-6

10. 1.1

Diving

10.1.5

10.1.6

10.2

10.3
10.4

10.5

10-1

10.1.1

1

in

Marine Sanctuaries or Underwater Parks

From Shore
10.2.1
Through Surf
10.2.2
Through Surf on a Rocky Shore
10.2.3
Through Shore Currents
10.2.4
From a Coral Reef
Diving From a Stationary Platform
Diving From a Small Boat
10.4.1
Entering the Water
10.4.2
Exiting the Water
Fresh Water Diving

Diving

10-3

10-4
10-5

10-7
10-7
10-7

10-9

10-9

10-10

10-10
10-1

1

10-12
10-12

10-13

10.5.1

Great Lakes

10-13

10.5.2

Inland Lakes

10-14

10.5.3

Quarries

10-14

10-14

10.9

Open-Ocean Diving
Cave Diving
Cold-Water Diving
Diving Under Ice

10.10

Kelp Diving

10-22

10.11

Wreck

10-23

10.12

Diving at High Elevations

10.6

10.7
10.8

10-17
10-19
10-21

Diving

10-24

10.12.1

Altitude Diving Tables Currently in Use

10-24

10.12.2

10-25

10.12.3

Comparison of Existing Tables
Recommendations for Altitude Diving

10.12.4

Calculations For Diving at Altitude

10-25

10.12.5

Correction of Depth Gauges

10-26

10.12.6

Hypoxia During Altitude Diving

10-27

10.13

Night Diving

10.14

Diving

10-25

10-27

Dams and

Reservoirs

10-28

10.14.1

Diving at

Dams

10-28

10.14.2

Diving at Water Withdrawal and Pumping Sites

in

10.15

River Diving

10.16

Diving

From

10-30
10-31

a Ship

10-32

10.16.1

Personnel

10-32

10.16.2

Use and Storage of Diving and Related Equipment

10-32

10.16.3

Safety Considerations

10-33

10.16.4

Using Surface-Supplied Equipment

10-33

10.16.5

While Underway

10-33

(

DIVING

UNDER
SPECIAL
CONDITIONS
10.0

The

GENERAL

ber.

characteristics of underwater environments, such

and type of marine life, vary
significantly from geographic region to region and
influence the amount and type of diving work that can
be carried out under water. The following paragraphs
describe the diving conditions most typical of U.S.

as temperature, visibility,

coastal

and other areas and provide an overview of the

visibility increases.

Water temperatures near the surface during the spring
and summer, when a substantial thermocline exists,
range from 50 to 70°F (10 to 21 °C). Temperatures at
100 feet (30.5 m) range from 48 to 54 °F (9 to 12'C).
During the winter months, the temperature of the water

column

diving characteristics of these regions.

the New England
temperature decreases and underwater

As one progresses north along

coast, water

is

essentially

homogeneous, with temperatures

reaching as low as 28.5 °F (-2°C). Subzero air temperatures

WARNING

and strong winds cause wind

volume dry

Diving in an Unfamiliar Region, Information About Local Conditions Should Be
Obtained From Divers Who Are Familiar With
Local Waters. A Checkout Dive Should Be
Made With a Diver Familiar With the Area

When

suits

low

Wet suits and variablehave become standard for winter

diving in the Northeast (see Section 5.4).

Underwater visibility is primarily a function of sea
and vertical turbulence in the water column. In
the Northeast, horizontal visibility of 50 to 80 feet
state

(15 to 24.4

m) may occur

occasionally throughout the

year, usually in connection with

10.1

chill factors as

as -70 to -80 °F (-57 to -62 °C).

GEOGRAPHIC REGIONS

For purposes of discussion, the coastal regions are
classified as shown on the following table. The principal characteristics of

calm

a land mass or to estuaries or harbors

each region are described

in the

following sections of this chapter.

seas.
is

Proximity to

associated with a

because the load of suspended

decrease

in

visibility

material

in

the runoff from the land mass and the

processes associated with the mixing of fresh and salt

water greatly elevate turbidity. During the summer,
biologically caused 'red tide' conditions

lowering visibility to less than

1

may

occur,

foot (0.3 m). Coastal

waters within the Gulf of Maine have an average range
Area Encompassed

Region

in visibility of
visibility

Rhode

in

Northeast Coast

Maine

Mid-Atlantic Coast

Southeast Coast

Rhode Island to Cape Hatteras
Cape Hatteras to Florida

Gulf of Mexico Coast

West Coast

Northwest Coast

Subarctic Alaska to Oregon

Mid-Pacific Coast

Northern and Central California

(see Section

Southwest Coast

Point Conception to the

extend as

to

Texas

Northern Baja Peninsula
Central Pacific

Ocean

Hawaiian and Leeward Islands

and Antarctic
Caribbean and Florida Keys

Polar

Arctic

Tropics

Cape Cod averages

10 to

15 feet (3.0 to 4.6 m).

Island

of Florida to

25 to 35 feet (7.6 to 10.7 m), while

waters south of

Several species of brown algae comprise the large
kelp of the

New

England

coast. Unlike the kelp of

California, these kelp do not form surface canopies
10.11).

much

New

England kelp occasionally

m) off the hard ocean
bottom and, although they look impenetrable, they do
as 25 feet (7.6

not in fact present a significant entanglement hazard.

Generally, these algal plants are sparsely distributed

and seldom project more than 6
from the bottom.

to 8 feet (1.8 to 2.4

m)

New England coast are primarily
and generally do not exceed 0.5 knot
(0.25 m/s). Faster currents may be encountered in
channels and in river mouths. Divers should be cauCurrents along the

10.1.1

Northeast Coast

Diving

in

northeastern waters

tidal

is

an exciting and

chilling experience. Generally, the best diving condi-

tions in

terms of water temperature, sea state, and
visibility occur from June through Octo-

underwater

October 1991

— NOAA

Diving Manual

in origin

tious in the waters off the
cially

when diving

in

New

England coast, espe-

strong currents and cold water,

10-1

Section 10

because of the potential for overexertion. The surf

in

Water temperatures on the surface range during the

modest compared with the surf in California, but it is especially hazardous along rocky, precipitous coastlines such as the coast of Maine. Shortperiod waves as high as 5 to 10 feet (1.5 to 3.0 m) can
create very rough and turbulent sea states along these
coasts and can push divers into barnacle-covered rocks.

summer months from 72-75 "F (22-24 °C) and from

this region

is

Hazardous marine animals. Relatively few species of
and invertebrates

fish

in the

New

waters off the

England

coast are potentially harmful to divers. Sharks of several species are occasionally seen, but they are generally not

harmful to divers (see Section

12.3.1).

and blue shark; occasionally, the
shark

filter-feeding basking

mistakenly identified as a dangerous shark.

is

The torpedo ray (electric ray) (see Figure 12-19), cownosed ray, and stingray are found off southern New
England (Cape Cod and south). Documented divershark or diver-ray encounters are relatively rare along
the

New

England

coast.

The most bothersome

fish in this region

is

the goose-

which may weigh as much as 50 pounds (23 kg)
and grow to 4 feet (1.2 m) in total length. It is the habit
fish,

of the goosefish to

lie

partially buried on the ocean

floor waiting for unsuspecting 'meals' to pass by. This

fish is

approximately one-half head and mouth and

one-half
startle

tail.

The

sight of a goosefish

another bottom-oriented creature that

by fishermen and divers

for

when bothered. The

its

is

The

to

many fishermen have

wolffish

is

highly respected

strength and aggressive-

wolffish's six large canine

tusks are capable of inflicting considerable

discovered

when

damage, as

trying to boat

is

The green

sea urchin, which has

many

stout spines

that can easily puncture a rubber wet suit, can also
injure divers. Unless the tip of the urchin's spine
surgically

trapped every summer. This pool or

summer water on the entire
Tidal and wind movement of

contains the

cell

coldest

eastern continental

shelf.

cold bottom water

can cause a significant and sudden change

tom temperature of the water

A

off the

New

removed from the

diver's flesh,

it

will

is

cause

may last for months or
found in very dense
concentrations on hard substrates to depths of 50 to
60 feet (15.2 to 18.3 m).
a painful 'lump' under the skin that

The green

sea urchin

is

in the bot-

Jersey coast.

chief characteristic of the mid-Atlantic water

summer

the thermocline.

The

rapid

decrease in temperature at the thermocline

may

cause

column

in the

is

an unsuspecting and unprepared diver enough discomfort to abort the dive.

Plankton gathered at the ther-

mocline also can decrease the light so drastically that
artificial lights occasionally are needed in water depths
beyond 70 feet (21.3 m). In the Cape Hatteras area,
eddies from the Gulf Stream often bring warm clear
water to the coast. Bottom temperatures are warmest
in October and early November after the cold bottom
water mixes with the warmer upper layers. Winter
temperatures in the northern range drop as low as 35 °F
(2°C) near shore and are relatively homogeneous
throughout the water column, with slightly warmer

temperatures on the bottom.

Underwater
October, when

visibility
it

is

common

is

best during Septemberto

be able to see for

tances of up to 60 feet (18.3 m).

Many

dis-

of the inshore

waters of the northern area and the waters near the

major estuaries, such as the Hudson and Chesapeake,
have poor visibility throughout most of the year. Visibility

can range from

m)

to 15 feet (4.6

in these areas,

but improves with distance offshore. Tides

this species.

years.

mid-Atlantic Bight (Montauk Point, N.Y. to Cape
May, N.J.), a large bottom 'pool' of cold winter water

even a seasoned diver, but these fish do not

generally attack unless they are provoked.

ness

enough

is

proximity to the shore, and general location. In the

These

hammerhead,

are the mako, dusky, tiger, great white,

40-60 °F (4-1 6 °C) on the bottom, depending on depth,

large changes in visibility for as
(4.8

km)

much

may

cause

as 3 miles

offshore near bays and rivers.

Tides and currents. Strong tidal currents can be
expected in the Chesapeake Bay, parts of the New
York Bight, off the outer banks of North Carolina, and
in

Long Island Sound. Diving

especially hazardous

of low visibility and

if
is

in these areas

can be

the diver becomes lost because

swept away from the planned

exit area.

Waves. Long-period open ocean waves

in the

mid-

Atlantic are generally not hazardous to divers, although

10.1.2 Mid-Atlantic

Waters

Coast

characterized by low visibility and cold bottom temperatures.
flat

Bottom topography generally

consists of

sand clay or gravel and occasional low-relief rocky

outcroppings.

York-New

10-2

Wrecks are found frequently

Jersey coasts and off

squalls can cause quick 'chops' that may be a
problem. Waves pose the greatest danger to divers
attempting to dive off the end of a rock jetty in a

summer

off the coasts of the mid-Atlantic states are

off the

Cape Hatteras.

New

end of a
by a
wave. The surf in these waters is generally moderate,
and most beaches are composed of sand rather than

moderate

to

heavy

surf; divers too close to the

jetty can be picked

up and thrown

NOAA

into the rocks

Diving Manual

— October 1991

Diving Under Special Conditions

which makes entry from the shore relatively easy

rock,

there are often sharp boundaries between water masses

for divers.

in the

Although sharks are numerous off the coasts of the
mid-Atlantic states, there have been few diver-shark
encounters. However, divers carrying speared fish

ties.

have been molested by sharks, and divers are therefore
advised to carry fish on a long

especially in

line,

murky

m) above

(0.3-0.6

the bottom, and

if

1-2 feet

hug the

divers

bot-

tom contours they can work without interference from
the current. However, the tending boat operator must
be aware of the current differential and must establish
a reference for the diver's position to prevent the boat

water.

As

water column that have different current veloci-

The current generally slows about

in the

Northeast, the goosefish

is

probably the

most troublesome marine creature for divers.
Divers swimming close to the bottom to see their way
in murky water often inadvertently place a hand or
foot in the mouth of a goosefish lying camouflaged on
area's

from being carried away from the dive

site.

Dropping

a

well-anchored buoy over the side at the beginning of
the dive

is

a good

means of

establishing such a refer-

ence. Carefully monitoring the bubbles of the diver

is

Some means

of

extremely important

type of diving.

in this

the bottom and thus run the risk of being bitten. Sting-

diver recall must be established in case the crew on the

abundant in estuaries, especially
during the summers in the Chesapeake Bay, that maximum protection against them is necessary.

surface boat loses sight of the diver's position (see

ing jellyfish are so

Section 14.2.2).

10.1.4 Gulf of
10.1.3

Southeast Coast

For the most part, the waters off the coasts of the
southeastern states are tropical.

Warm

and can reach as high as 75

prevail

27 °C) during the

summer months.

temperatures

to 80°

In the

F (24

to

most north-

ern portions of this region of Georgia, South Carolina,

Mexico

Water temperature in the Gulf of Mexico drops to a
low of about 56 °F (13°C) during the winter months
and rises to about 86° F (30°C) in the summer. Visibility offshore is generally good to excellent and may
even exceed 100 feet (30.1 m) around some reefs. Underwater

visibility

near shore

near river outfalls,

in

is

poor, particularly in areas

bays and estuaries, and off some

and southern North Carolina, less tropical conditions
prevail. Water temperature during the summer in this

beaches. Occasionally, a mass of clear offshore water

about 70°F (21 °C). In the area just south of
Cape Hatteras, the Gulf Stream passes close to land,

ity

area

causing the water temperature to be

than

it

warmer near shore

During the winter, water temthe southernmost areas remains 65 to 70 °F

in

(18 to 21 °C); in the more northerly waters, however,

temperatures drop as low as 50 °F (10°C). In the tropi-

and subtropical waters of the Southeast, there are a

vast

up

to

inshore and increase the near-shore visibil-

75 feet (22.9

number

Mobile,

should

be of concern to divers. At times, strong

still

the gulf are generally negligible but

may occur around

offshore oil platforms, and
knowledge must be relied on in this situation.
Weather conditions and running seas are unpredictcurrents
local

able in the gulf. Unforecasted storms with 6- to 12-foot

good

is

(1.8 to 3.6

m)

seas have curtailed diving operations in

to excellent in
this region of the

the offshore areas; closer to shore, however,

25 to 30 feet (7.6 to 9.1 m), and

in

it

country

in the past.

drops to

harbors and bays,

it

can be poor. Farther north, both offshore and nearshore
drops drastically and averages 20 to 25 feet

10.1.5

Northwest Coast

Diving activities

in the

northwest take place off the

coast of subarctic Alaska and extend to areas offshore

(6.1 to 7.6 m).

When

in regions southeast of

in

of different species of marine animals.

Visibility in southern waters

visibility

m)

Alabama.
Currents

to the south.

is

perature

cal

may move

is

diving at the boundary of major oceanic cur-

Gulf Stream, special care

from Oregon. Water temperatures

in

subarctic Alaska

eddies that occasionally spin off the main mass of

3°C) during the winter
months and average 45 to 50° F (7 to 10°C) during
the summer. Divers in these waters must give serious

moving water. Extra precautions also must be taken

consideration to their choice of diving dress so that

because of the meandering nature of the current's edge;

dive duration

rent systems such as the

must be exercised because of the episodic turbulent

relatively quiet water near the

change

to

edge may suddenly

water with a current velocity of

more. Dives

in

1

knot or

boundary regions must be planned

to

anticipate high current speeds, and appropriate surface support must be provided.

October 1991

— NOAA

As

the diver descends,

Diving Manual

range from 34 to 38 °F

is

to

not affected by the cold. During the

winter, temperature
so that

(l

some bays,

and wind conditions may combine
and near-shore waters freeze

inlets,

over.
Visibility in

Alaskan waters varies drastically from

place to place and from time to time.

The

best visibility

10-3

Section 10

occurs along coastlines and in the Aleutians, where

may

it

range, at best, from 40 to 80 feet (12.2 to 24.4 m).

bays and

Visibility in the waters of

straits is usually

throughout the year. Visibility usually

from 5 to 25 feet
beaches and from

(1.5 to 7.6

At any location, visibility may
become temporarily limited by storms or phytoplank-

Puget Sound waters.

ton blooms. Late each spring in southeast Alaska, the

dictable. This

visibility in the

the water

upper 30 to 40 feet

m)

(9.1 to 12.2

of

column may be near zero because of phyto-

plankton, but below that layer the water
clear (visibility of 40 feet (12.2
this deep, clear

water

is

m)

may

be very

or more). Although

Currents
very low

may

in certain areas
is

is

low, ranging

in coastal

70 feet (0 to 21.3 m)

to

15 to 30 feet (4.6 to 9.1 m).

m)

water near
in

protected

be strong and unpre-

especially true in river diving,

visibility

where

can cause orientation problems. Logs,

stumps, wrecked automobiles, fishing hooks and

lines,

and other bottom trash also pose distinct dangers
divers working in Alaskan rivers (see Section 10.15).

to

often dark because of the

shading effect of the overriding low-visibility water,
there is usually sufficient ambient light to work.

10.1.6 Mid-Pacific

Currents and tides are strong and unpredictable in

The mid-Pacific

Coast

coastal region includes the waters

subarctic Alaskan waters. Tides are extremely heavy

of Northern and Central California.

and can cause currents as high as 10 knots in narrows.
Currents also vary significantly and have been observed

north, the best diving conditions in terms of underwa-

to

change direction within a period of minutes.
Much of the Alaskan coastline is steep and rocky;

many

areas are too steep to allow divers either to enter

ter visibility as well as

From San

Francisco

water temperatures generally

occur from June through September.

From San

Francisco

south to Point Conception, good diving conditions

may

continue through December.

From San Francisco
summer temperatures

and exit points must be careMost sections of coastline
are accessible only from boats. During times of heavy
seas or swells, many near-shore diving locations become

48 to 56 °F (9 to 13°C). Fall and early winter temperatures vary from 52 to 60 "F (11 to 16 °C), and late

completely unworkable.

winter and spring temperatures from 45 to 54 °F (7 to

or leave the water. Entry

fully selected before a dive.

Alaskan waters harbor

relatively

few hazardous marine

A

13 °C).

north to the Oregon border,

generally range from about

thermocline generally exists at depths from

m) during

organisms. Those that cause divers the most trouble

20

are the urchins, barnacles, and jellyfish, with their

summer. The difference

and stings.
Dense beds of floating kelp can cause some problems
for divers, especially during surface swimming. Sharks

peratures during this period ranges between 2 and

and whales are common but are rarely, if ever, seen
under water and generally do not influence diving activity
in any way. The presence of killer whales, which are
common, is an exception to this general rule.
Although no known diver/killer whale encounters
have taken place in Alaska, general caution should

waters.

potential to cause punctures, abrasions,

keep divers out of the water
to

if

these animals are

be near. Steller sea lions are very abundant

known
some

in

areas of Alaska; although there are no reports that
these animals have ever
fornia sea lions

harmed

sea lions are large, fast,
divers, they

divers in Alaska, Cali-

have been known to injure

and

agile

divers.

Because

and are attracted

to

can disrupt an otherwise routine dive. In

addition to being a psychological distraction, the activity

40 feet

to

(-17

and gloves,

Underwater

wet

suit,

a necessity

and

5°F

including hood,

when

diving in these

varies quite drastically through-

summer

Oregon border,

to winter.

late spring

m), increasing to 30 feet (9.1 m) in the fall. From
Santa Cruz north to San Francisco, visibility ranges
from 5 to 15 feet (1.5 to 4.6 m) in the early spring and
summer, 10 to 25 feet (3.0 to 7.6 m) in late summer and
6.1

fall,

early spring.

10-4

late spring

surface and bottom tem-

From Fort Bragg
and summer underwater visibility ranges between 10 and 15 feet (3.0 and
4.6 m). In the late summer and fall, underwater visibility
increases to about 15 to 25 feet (4.6 to 7.6 m). During
to
the winter and early spring, visibility decreases to
10 feet (0 to 3.0 m). South of Fort Bragg down to San
Francisco, visibility ranges from 10 to 20 feet (3.0 to
to the

iments and a reduction of

Farther south, in the waters off Washington and
Oregon, water temperatures range from about 43 to
60 °F (6 to 16 °C) over the year in protected areas such
as Puget Sound. In open ocean waters, depending on
the water masses moving through, temperatures ranging from 40 to 60 °F (4 to 16 °C) may be encountered

is

in

full

visibility

out the area from

of sea lions often causes serious roiling of bottom sedvisibility.

A

and -15°C).

boots,

12.2

to

(6.1

and

visibility

to 10 feet (0 to 3.0

From

m) during

the winter and

Point Conception to Santa Cruz,

ranges from 15 to 25 feet (4.6 to 7.6 m)

during the late spring and
50 feet (4.6

to 15.2

m)

summer and from 15 to
and may occasionally

in the fall

reach 100 feet (30.5 m) near Carmel Bay. During
winter and early spring, one can expect visibility to

extend 5 to 20 feet (1.5 to 6.1 m). The main factors

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

controlling underwater visibility in this area are the

60's (10 to

huge plankton bloom, which occurs during upwelling
in the spring and summer, and the dirty water condi-

deal of mixing in the upper layers and discrete temper-

caused by rough seas and river runoffs during the

thermocline at 40- to 60-foot (12.2 to 18.3 m) depths

tions

16°C). In

fall

and winter there

a great

is

ature zones do not exist. However, a distinct

summer

winter and early spring.

causes a sharp temperature drop that should be con-

Three species of surface-canopy-forming brown
kelp occur on the Pacific coast. From Monterey
algae

sidered

—

—

dominant kelp

north, the

is

the bull kelp. This particu-

forms large beds but, because of

lar species

its

struc-

same entanglement hazard

ture, does not pose the

to

dive planning.

in

Horizontal visibility under water ranges from 5 to
10 feet (1.5-3.0

as

much

islands.

The

North of Point Conception, surf conditions are probably the most important consideration in planning a

m)

of the mainland coast to

m) around

the offshore

best visibility conditions occur in the late

summer and

divers as the giant kelp (see Section 10.10).

m) along much

as 100 feet (30.5

fall.

underwater

During spring and early summer,
is generally less (30-50 feet

visibility

(9.1-15.2 m)) around the islands, at least in part because

can expect
most areas even on calm days, and on rough days it is
not uncommon to see waves 10 feet (3.0 m) or more
high. Divers should always scout the proposed dive

of prevailing overcasts and heavy fogs. Winter storm

area before going into the water to determine the safest

material from storm drains and river mouths.

2- to 3-foot (0.6 to 0.9

dive. Divers

surf

in

conditions and rain runoff can reduce the visibility to

zero for miles along the mainland coast, because the

prevailing long-shore current distributes suspended

Shore conditions along the mainland coast of south-

area of entry and, in case conditions change, to choose

ern California range from sand beaches to high pali-

alternate exit sites (see Section 10.2.1).

Long-shore currents and tidal currents are

and tend
nia.

On

to

be severe

in

common

northern and central Califor-

very windy days, divers should watch for strong

currents around headlands, off rocky shores, and near

common

sade

cliffs.

Ocean access from these areas

is

often

impossible, and a careful check of charts and maps,

supplemented by

preliminary site

a

recommended before

visit, is

initiating a dive.

highly

The offshore

along beaches

islands generally are accessible to divers only by boat.

Hazardous marine animals. As in other areas, divers
must watch for sea urchins, jellyfish, and rockfish, but

land coast and on the windward sides of the offshore

reefs.

Rip currents are very

and

coves (see Section 10.2.3).

in

shark attacks

in this

Moderate-to-heavy surf prevails along the entire main-

area are not

common.

In the last

15 to 20 years, fewer than 2 dozen shark attacks involving

islands. Under certain weather conditions, the normally
calm leeward sides also may present hazardous diving

conditions.

divers have been recorded; however, diving around the

Currents and tides are not of prime importance

Farallon Islands, Bodega Bay, Tomales Bay, and off

the southwest coastal region, although there are local

San Francisco
water

visibility

is

is

not

recommended except when under-

ideal.

Stingrays and electric rays are

in

exceptions. Currents around the islands, especially during
tidal

may

changes,

The

attain speeds of 3 to 4 knots (1.5 to

and

also found in the mid-Pacific coastal region (for appro-

2 m/s).

priate precautions, see Section 12.4).

currents can be observed both topside and under water

all

There are five ecological reserves in this area, where
animals and plants are protected: Point Lobos State

direction

relative strength of nearshore

by watching the degree and direction of kelp layover.

Hazardous marine organisms

in

this region include:

Reserve, Point Reyes Seashore area, Salt Point State

sharks (especially around the offshore islands) such as

Marin County
San Francisco, and Del Mar Landing in Sonoma
County. Divers should consult with the park authori-

the blue, horned, swell, angel, and leopard; whales

Park, Estero de Limantour Reserve in

north of

determine the boundaries of these marine reserves

ties to

and the restrictions that apply

to

(including killer whales);
jellyfish.

moray

eels; sea urchins;

and

Divers should be aware of the habitats, appear-

ance, and habits of these species (see Section 12).

Sewer

them.

outfalls are

common

along the mainland coast,

and direct contact with sewer effluent should be avoided
10.1.7

Southwest Coast

The waters

Point Conception to the northern Baja Peninsula. Water
temperatures range from 50 to 60 °F (10 to 16°C) in
winter and 55 to 70 °F (13 to 21 °C) in summer, with

some
ing

localized areas

much

made

colder by upwelling. Dur-

of the year, temperatures at depths below

100 feet (30.5 m) are fairly stable

October 1991

— NOAA

The outfall discharge point may occur
from a few hundred feet to several miles offshore, in
from 60 to several hundred feet (18.3 to several hundred meters) of water. The effluent sometimes rises to

(see Section

of the Southwest include the area from

in the 50's

Diving Manual

and low

1

1

).

the surface in a boil characterized by elevated temperatures, paper
If

and other debris, and an unpleasant odor.

diving must be conducted in outfall areas, precau-

tions

such as immunization, use of full-face gear, and

10-5

Section 10

scrupulous post-dive hygiene must be observed (see

and coral abrasions are the most

Section 11 for polluted-water diving procedures). Most

injury.

No

license

needed

is

common

types of

to harvest fish or crusta-

be identified on the surface by a boil or by an orange-

home consumption; however, game laws in
most states place season and size limitations on some

and-white striped spar buoy anchored near the pipe

species.

outfall discharge points are

marked on charts and can

ceans for

terminus.

As

Northern California, ecological reserves that

in

have various restrictions have been established

in the

California Department of Fish and

Game

is

the best

source of information about the location of these reserves

and any
waters

them.

restrictions that pertain to

Diving

The two most important

factors to be considered in

and antarctic environments are the effects of
cold on the diver and the restricted access to the surface when diving under ice. These topics are covered in
arctic

northern Mexican (upper Baja California)

detail in the sections dealing with diving in cold

similar to that in lower southern California.

(Section 10.8) and diving under ice (Section 10.9).

in

is

and Antarctic

10.1.9 Arctic

southwestern coastal region. The local office of the

However, Mexico imposes heavy fines and impounds
Mexican waters without
proper permits; permits can be obtained through the
Mexican government or from Mexican customs officials in San Diego.
the boats of people diving in

Temperature in arctic waters can be as low as 28 °F
(-2°C), but the air temperature and its associated
chill factor may be more limiting to divers than the
cold water

Often, surface temperatures as low as

itself.

-40 to -50 °F (-40 to -46 °C) are reached, with accom-

panying wind velocities that bring the

chill factor to

temperature equivalent to -100°F (-73°C) or
10.1.8 Central Pacific

Ocean

The
Hawaiian Archipelago, which
The major

islands are:

lesser

less.

a
In

such conditions, protecting divers from the extreme

most accessible diving in this area

Hawaiian Islands and the

water

is

around the

consists of the major

known Leeward

Islands.

Hawaii, Maui, Kahoolawe, Lanai,

Molokai, Oahu, Kauai, and Niihau.

The Leeward

Islands

are a group of rocks, shoals, and islets that are rem-

cold

is

paramount both before and

the problem
is

is

then both wet and chilled.

conducted under the
in a

after the dive, although

greater after the dive because the diver

ice,

When

diving

being

is

the dive should begin and end

heated shelter positioned over the entry hole.

If

such a shelter cannot be positioned over the hole, one

nants of ancient islands and seamounts that extend

should be located within a few steps of the entry point.

from Kauai to Midway Island. They are all wildlife
reserves and generally are inaccessible except to government personnel or authorized visitors.
The average water temperature around the major
islands is 76 °F (24 °C) and changes very little with the
seasons. Underwater visibility is almost always excellent, ranging from 50 to 100 feet (15.2 to 30.5 m) or
more. Currents can sometimes be a problem in channels and near points and may reach speeds of up to
3 knots (1.5 m/s). High surf is also a potential hazard
and may vary widely with the seasons.

The heated

make shore

from all the
islands, but rocks, surge, and surf must always be
considered when planning entries and exits (see Section 10.2.1). Since drop-offs occur very near shore and
It

is

possible to

continue for several hundred feet,

entries

it

is

an airplane parked nearby

When

exposed

to

may

extremely

low air temperatures for longer than a few minutes,
divers should

Gloves

wear heavy,

(in the case of

warm water

be flooded with
effects of air

the water.

loose-fitting

and

to forestall the chilling

comfort

to provide greater initial

Hot water can be carried

tainers such as

hooded parkas.

dry suits) or entire wet suits can

in

in insulated con-

thermos jugs.

In polar regions the marine species of concern are
seals, walrus, killer

whales, and polar bears.

A

predive

reconnaissance by an experienced observer will indicate
to

if

any of these animals

is

in the vicinity or

is

likely

cause a problem (see Section 12.5).

easy to get into

deep water quickly after making a shore entry. Caution

interior of

satisfy this requirement.

must always be exercised when making

repetitive

10.1.10 Tropics
Tropical waters provide the most interesting envi-

because underwater

dives.

ronment

Although most forms of dangerous marine life can
be found in Hawaiian waters, they are uncommon.
There have been a few recorded shark attacks over the
years, but they are extremely rare and usually involve

usually excellent and marine

although the waters

swimmers

a storm, during plankton blooms, or from silting near

10-6

or surfers. Eel bites, sea urchin punctures,

for diving,

ity in tropical

more. There

waters
is

little

is

life

visibility is

abounds. The

generally 50 feet (15.2

m)

or

variation throughout the year,

may become murky and

NOAA

visibil-

Diving Manual

silty after

— October 1991

Diving Under Special Conditions

Water temperatures hover around 70° F

shore.

during the winter months and
(28 °C)

in

Marine

(21 °C)

be as high as 82 °F

may

shallower waters during the summer.
life

to divers.

contours or features, or triangulation methods using

known shore

When commercial

abundant, and some forms are dangerous

is

Sharks thrive

tions should be taken

waters and precau-

in these

when they

A

are sighted.

wide

variety of poisonous marine animals (jellyfish, scorpionfish, sea snakes) also

abounds (see Section

positions should be used initially in locat-

ing a dive site.

diving operations are being con-

OSHA

ducted from shore without a boat,
played at the dive location.

entry conditions permit,

If

during the dive (see Section 14.2.4).

in

set aside for the

also advisable

signaling the shore in an emergency. These flares pro-

vide a quick
or

work

purpose of preserving

means of accurately

locating a diver on

the surface (see Section 5.6.8).

sanctuaries or underwater parks. These marine sanctu-

have been

It is

equip each diver with a day/night signal flare for

to

10.1.11 Diving in

aries

them

divers should carry and/or tow the flag with

12).

Marine Sanctuaries or
Underwater Parks
Divers may on occasion dive for recreation

regulations

require that the international code flag alpha be dis-

Entering the water from a smooth, unobstructed
is relatively quiet poses no

shoreline where the water

or restoring recreational, ecological, or esthetic val-

problem. Most lakes, rivers (where currents near shore

Examples include the Key Largo National Marine
Sanctuary, Biscayne National Park, John Pennekamp
Coral Reef State Park in Florida, and Buck Island in

are not swift), bays, lagoons, quarries, and ocean coast-

ues.

(where surf

lines

negligible) have shorelines of this

is

type.

the Virgin Islands National Park.

Marine sanctuaries are

built

around distinctive marine

resources whose protection and proper use require

Entering the water even through moderate surf when

comprehensive, geographically oriented planning and

management but do
people.

It

is

not necessarily exclude use by

important when diving

in

these areas to

follow the rules and regulations established for sanctuary management. Accordingly,

when conducting workmarine sanctuaries

ing or scientific dives in designated

and parks,
ties

DIVING

lines

tially

A

hazardous operation.

conditions should be

made

is

a difficult and poten-

careful analysis of surf

and,

if

conditions are con-

sidered too severe to allow safe passage to open water,
the dive should be terminated.

WARNING

FROM SHORE

diver should expect to encounter a wide variety of

conditions

burdened with diving equipment

important to check with local authori-

is

before beginning operations.

10.2

A

it

Through Surf

10.2.1

when entering

Before Diving Through Surf From an Unfamiliar Beach, Local Divers Should Be Consulted About Local Conditions

the water from shore. Shore-

vary greatly, and diving from a particular shore

requires individual preparation and planning.

Before entering the water, divers should observe the

Before entering the water from shore, special atten-

surf.

Waves

equipment checkout. Since diving equipment is often placed on the
ground near the water, small dirt particles may have
entered a space in the equipment that requires a per-

with

little

tion should be given to the predive

fect seal or has a close tolerance.

amount of

Even the smallest

dirt in a regulator or reserve valve

may

traverse vast expanses of ocean as swell,

modification or loss of energy. However, as

the waves enter shallow water, the motion of the water
particles beneath the surface

is

altered.

When

a

wave

enters water of a depth equal to or less than one-half of

wavelength,

its

orbital

it

is

said to "feel bottom."

The

circular

motion of the water particles becomes

ellipti-

with depth. Along the bottom, the particles

cause a serious air leak or a valve malfunction. Extra

cal, flattening

care must be taken to ensure that diving equipment

oscillate in a straight line parallel to the direction of

is

wave

kept as free from dirt as possible.
If the dive

from shore

underwater location,

it

is

is

to

be

made

to a precise

mark

marker buoy or surface

float.

floating on the surface, however,

diver to see; therefore,

October 1991

A

the

wave

feels

bottom,

and

its

done by using
small marker buoy

into

water whose depth

may

be difficult for a

compass bearings, underwater

— NOAA

travel.

the spot

advisable to

clearly at the water surface. This can be
a

As

Diving Manual

the

steepness increases.
is

its

As

wavelength decreases
the

wave

crest

moves

approximately twice that of

wave height, the crest changes from rounded to a
more pointed mass of water. The orbital veloc-

higher,
ity

of the water particles at the crest increases with

10-7

Section 10

Figure 10-1

Schematic Diagram of Waves
in the Breaker Zone

A
(4)

diver standing on the shore

backrush;

beach

(5)

and looking seaward would observe and

face; (6) inner translatory

waves;

(7)

note: (1) Surf zone; (2) limit of uprush; (3) uprush;

inner line of breakers, (8) inner bar;

(9)

peaked-up wave;

(10) reformed

wave; (11) outer translatory waves; (12) plunge point; (13) outer line of breakers; (14) outer bar (inner at low tide);
(15) breaker depth, 1.3 x breaker height; (16) waves flatten again; (17) waves peak up but do not break on this bar at high tide;
Adapted from US Army Corps of Engineers (1984)
(18) deep bar (outer bar at low tide); (19) still-water level; and (20) mean low water.
oscillatory

increasing

wave

height. This sequence of changes

is

the prelude to the breaking of the wave. Finally, at a

depth of approximately

when

1.3

times the wave height,

more
the wave becomes

wave

the steepest surface of the

than 60 degrees from the horizontal,

inclines

unstable and the top portion plunges forward.

The

are good, the diver should begin

swimming seaward on

the surface, using a snorkel. If heavy sets of waves are

encountered, it may be
and to swim as close to
bottom is rocky, divers
grasping the rocks; on

necessary to switch to scuba
the bottom as possible. If the

can pull themselves along by

called surf

a sandy bottom, a diver can
thrust a knife into the bottom to achieve the same

(Figure 10-1). This area of "white water," where the

purpose. Ripples on a sandy bottom generally run par-

waves finally give up their energy and where systematic water motion gives way to violent turbulence, is
called the surf zone. The surfs white water is a mass of

used to navigate through the surf zone by swimming

wave has broken;

this turbulent

form

water containing bubbles of entrapped

is

air;

these bub-

normal buoyancy of the water.

bles reduce the

Having

broken into a mass of turbulent foam, the wave continues landward under

beach face,

this

its

own momentum.

momentum

swash. At the uppermost limit,

Finally, at the

an uprush or
the wave's energy has

carries

it

uprush must now return seaward as backwash,

ment

of water

is

to the sea. This

i.e.,

as

seaward move-

generally not evident beyond the

surface zone or a depth of 2-3 feet (0.6-0.9 m).

By watching

the surf for a short period of time, water

entry can be timed to coincide with a small set of
waves.

When

ready to enter, the diver should approach

the water, fully dressed for diving.

to the face,

and place the snorkel

in the

mouth. With

one hand on the faceplate, the diver should then turn

around and back into the water with knees slightly
bent and body leaning back into the wave. If conditions

10-8

somewhat obliquely

to shore,

and they can be

perpendicular to them. Divers entering with a float
it behind them on 10 to 30 feet (3.0 to 9.1 m)
and should be aware of the possibility that
turbulence may cause the line to wrap around a leg,

should pull

of line

arm, or equipment.

WARNING
Divers Near the Surface Should Not Hold Their

When a Wave Is Passing Overhead
Because the Rapid Pressure Drop at the
Diver's Depth When the Wave Trough Passes
Overhead May Be Sufficient to Cause a Lung

Breath

Overpressure Accident

At the water's edge,

the diver should spit on the faceplate, rinse and adjust
it

or

into

diminished. The water transported landward in the
current flowing back

allel

Swimming over breakers should not be attempted.
As breakers approach, the diver should duck the head
and dive under and through them. Diving at the base of
the wave is advantageous because the water molecules
will carry the diver up behind the wave.

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

A group of divers may make a surf-entry in buddy
teams and meet beyond the surf zone at the diver's
flag. Once safely through the surf, all equipment should
be checked. Even a moderate surf can knock equipment out of adjustment or tear it away.
Sand may have entered the mask, regulator, or fins
after the diver has passed through the surf. Divers
should take time to remove the sand before continuing
the dive.

cause

it

in

the exhaust valve of a regulator can

to seal improperly, permitting water, as well as

enter the mouthpiece

air, to
fins,

Sand

though only mildly

when

Sand

inhaling.

irritating at first,

in the

may cause

carried back toward the shore and then kick seaward

wave

after the

When

passes.

exiting on a rocky shore, divers should stop

wave conditions

outside the surf zone to evaluate the

toward the beach on the backside

and should then

exit

of the last large

wave of

the

wave

As momentum from

a series.

divers should kick or grasp a rock to

lost,

is

avoid being carried seaward by the backwash. Divers

should maintain their position, catch the next wave,

and thus move shoreward, exercising caution over

slip-

pery rocks.

a

painful abrasion by the end of a dive.
Exiting the water through the surf involves performing

same procedures used to
order. The diver should wait

enter, except in reverse

the

just

seaward of the surf

for a small set of waves.

When

the diver should begin

swimming shoreward (while

a set has been selected,

keeping an eye on the incoming waves) immediately
after the passage of the last of the larger waves.

The

Through Shore Currents

10.2.3

In and adjacent to the surf zone, currents are gener-

ated by

approaching waves (and

1)

and 4)

tides.

When waves

angle, a longshore current
allel to

approach the shore

common

progress toward the beach. Using this assisting wave

current

increases

swim toward the beach until
reaching waist-deep water. At this point, while there
is still enough water for support and balance, divers

2) increasing

The

should pivot around, face the waves, and plant their

(0.5 m/s).

feet firmly.

The

diver should then stand up, and, bend-

and hips enough

When

back out of the water.
should position

them

to avoid

it

velocity

3) increasing

velocity

angle

of

along straight beaches. The

with

the

breaker

1)

breaker

to

height;

the

and 4) decreasing wave
of longshore currents seldom exceeds
beach

Wave

slope;

shore;
period.
1

knot

fronts advancing over non-parallel

bottom contours are refracted

cause convergence or

to

maintain balance,

divergence of the energy of the waves. In areas of

exiting with a float, divers

convergence, energy concentrations form barriers to

down current

to

or push

becoming entangled

in

it

ahead of

the towline.

As

soon as the divers are out of the water, they should

remove their fins.
knocked over by surf action after standing up,

turn; only then should they
If

an

the beach within the surf zone. Longshore

currents are most

ing at the knees

at

generated that flows par-

is

smaller waves breaking behind will assist the diver's

action, the diver should

bottom

surf); 2)

contours and irregularities; 3) shoreline geography;

the returning backwash, which

is

deflected along the

beach to areas of less resistance. These currents turn
seaward in concentrations at locations where there are
'weak
gaps

points,'

in the

extremely large water accumulations,

bar or reef, or submarine depressions per-

divers should not try to stand again but should let the

pendicular to shore, and form a rip current through the

waves carry them onto the beach. Hands and

surf (Figure 10-2).

fins

should

be dug into the bottom to prevent being swept seaward

by the backwash.

On

reaching shore, the divers should

crawl out of the surf on their hands and knees.

10.2.2

Through Surf on a Rocky Shore

Before entering surf from a rocky shore, divers should

evaluate wave conditions and should not attempt to
stand or walk on rocks located in the surf zone. Instead,

divers should select the deepest

wave of

backwash of the

last

and enter the water; the backwash should carry the diver between the larger rocks.
Every effort should be made to swim around the rocks
large

a series

rather than over them. Divers should stay in the small

deeper channels between rocks and maintain a prone

swimming

position facing the next

They should kick

October 1991

oncoming wave.

or grasp a rock to keep from being

— NOAA

Diving Manual

The

volume of returning water has a retarding
incoming waves. Waves adjacent to the
rip current, having greater energy and nothing to retard
them, advance faster and farther up the beach. Rip
currents may transport large amounts of suspended
material. A knowledgeable and experienced diver can
use rip currents as an aid to swimming offshore. A
swimmer caught unsuspectingly in a rip should ride
the current and swim to the side, rather than swimming
large

effect on the

against the current. Outside the surf zone the current

widens and slackens, which permits the diver

to enter

the beach at another location. Rip currents usually
dissipate a short distance seaward of the surf zone.

Most shorelines are not

straight.

Irregularities in

the form of coves, bays, and points affect the incoming waves, tidal

movements, and current

patterns.

When

preparing for beach entries and exits, a diver should

10-9

Section 10

Figure 10-2

Near-shore Current System
break up the wave action sufficiently to allow passage
over the inside calm area without difficulty. If a channel can be located that will allow passage through the

should follow

reef, the diver

deep water.

it,

submerged

if

possible,

passage cannot be
located, the diver should approach the edge of the reef,
into

If a satisfactory

wait for a wave to pass, and slip over.

\

4

MassTranspo

\

*~ Longshore
Current

Shore Line

can be used. In addition,

Curren t

all

possible before entry.

line,

under

equipment

required equipment can be

transported by vehicle directly to the dive

Ladders should be used

is

site.

to get as close to the

Any approved

water as

entry technique,

such as stepping, can be used safely for heights up to
Source: Baker et

al.

(1966)

not

(0.9

take wave approach, shoreline configuration, and currents into account. Entries
to avoid high

waves and

and

exits should

to take

be planned

advantage of current

movements. Divers should avoid dives that require
swimming against the current and should never undertake a dive from an ocean beach without considering
these factors. Hypothetical beach configurations,

approaches,

wave

and current diagrams are shown

in

The roll-in method shown in Figure 10-4
recommended for heights greater than 3 or 4 feet
to 1.2 m) above the water. Immediately prior to

10 feet (3.0 m).
is

submerged obstructions. Floating debris is
common around a pier, and pilings often rot or break
off just below the waterline. Divers should not
into

jump

an area that has not been examined beforehand or

where the water

is

not clear enough to see to the depth

of the intended dive.
If the dive is to

be conducted from an ocean pier or

other high platform and no ladder

Figure 10-3 to aid divers in planning beach-entry dives.

check for floating

entering, the diver should carefully

debris or

is

available,

gear can be lowered into the water and divers can

heavy

make

a shore entry with a snorkel, equipping themselves

10.2.4

From a Coral Reef

with scuba at pierside. If conditions

Diving operations from a reef should be planned,
possible, to take place at high tide

when water

if

covers

the reef. For a diver wearing equipment, walking on a
reef

is

hazardous. Footing

is

uncertain, reefs are gen-

pocked with holes, and areas that look
break under a diver's weight.

erally

solid

may

impossible, using a small boat

is

a shore entry

When

swim-

ming under a pier or platform, divers should be submerged whenever possible to avoid contact with pilings, cross-supports, and other potentially hazardous
objects.

When

exiting the water onto a pier or platform, the

diver should stop at the ladder to

(The ladder should extend 3

NOTE

make

advisable.

to

remove

his or her fins.
1.2 m) into
awkward and

4 feet (0.9 to

the water.) Climbing a ladder with fins

is

dangerous and should be avoided unless the ladder

Coral shoes or hard-sole neoprene boots
should be worn around coral.

In

some

instances, there

side of the reef

swimming. In

10-10

may

be an area on the shore

where the water

is

deep enough for

this case, the outer side of the reef will

is

designed specifically for use with fins (see Figure 10-5).

Tanks and other cumbersome equipment should also
be removed and tied securely to a line and be hauled up
after the diver reaches the top of the pier. Piers and
docks often contain fishing lines, and care must be
taken to avoid being hooked or becoming entangled in
these lines.

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

Figure 10-3

Shore Types and Currents

R

'

'

is

}

'/
J

Xy
Small Deep Coves

Points
Rip Currents

Rocky Cove

-

Sand Bar - Sandy Beach

Reefs
E

Heavy arrows

indicate direction of

wave approach; dashed

=

entry;

X

—

- Rip Current

exit.

lines represent path of currents, while direction

is

shown by

light

arrows.

Source:

10.4

A

DIVING

small boat

FROM A SMALL BOAT

is

probably the most

common

•

larger solid-hulled vessels.

A

in

(1979)

cold or inclement weather

for the dive party en route to the dive site and,

surface-

back to shore
Be maintained properly and in good repair
Carry a diver's flag (see Table 14-2).

after the dive,

support platform used by divers with self-contained

equipment. Configurations and types of small boats
vary greatly and range from small inflatable boats to

Provide some shelter

NOAA

•
•

boat used as a platform

Small boats used to tend divers can be either anchored

should:

When anchored, the boat should be
downstream of the site for easy access when
divers surface, and a surface float should be streamed
off the stern. Even anchored boats need to be able to
move immediately in case an incapacitated diver must
be recovered; a buoyed anchor line facilitates a quick
getaway. The operator in the boat should keep a constant watch on the diver's bubbles, and great care

or unanchored.
•

•

Be equipped with a means for divers to enter and
leave the water easily and safely
Be seaworthy and loaded within the capacity

recommended by

the manufacturer for the expected

water conditions
•

Be large enough

to

accommodate

all

members

of

the dive party, the diver's life-support equipment,

and any special equipment being used
of the dive

October 1991

in

support

positioned

should be taken to stay clear of divers
gear.

— NOAA

Diving Manual

When

if

an engine

is

in

tending without an anchor, the operator

10-11

Section 10

Figure 10-4
Entering the Water Using the Roll-In

Method

Source:

Figure 10-5

wale and rolling into the water

Transom-Mounted Diver Platform

distance

is

NOAA

considered best

(1979)

if

the

not greater than 3 to 4 feet (0.9 to 1.2

m)

(Figure 10-4).

The

is

diver should examine the area to be

entered to ensure that

it

is

on the gunwale

clear, sit

facing the center of the boat with both feet inside, and
lean forward to counterbalance the weight of the equip-

ment.

When

ready to enter, the diver should simply

sit

up, lean backward, and let the weight of the diving

equipment carry him or her over the side. A second
method of entry is the 'step-in' method, which is generally used when entering the water from a larger boat.
The diver should step onto the gunwale, bend slightly
forward at the waist, and step off into the water.

When

entering the water using these methods, the

diver should always hold the face

mask

firmly in place.

Also, any required equipment that cannot be carried

conveniently and safely should be secured to a piece of
line,

As

hung over the

side,

and retrieved after entry.

a general rule, the diver should always enter the

water slowly, using the method that

NOAA

Source:

should drop the divers off upstream of the
boat should then remain downstream of the

site.

site

(1979)

The

during

least physical

will result in the

discomfort and disturbance to equip-

ment. Each diver should determine the method best
suited to various water conditions.

operations. Drift-diving with a surface float provides

an effective method for keeping the boat

in position for

pickup.

10.4.2 Exiting the

When

general rules to
10.4.1

Entering the Water

Entering the water from a small boat can be accomplished safely by several methods. Sitting on the gun-

10-12

Water

exiting the water into a boat, there are two

remember and

follow. First, exiting

actually begins while the divers are

still

submerged.

While ascending, divers should look upward continuously
to ensure that the boat is not directly overhead and

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

Figure 10-6

Side-Mounted Diver Platform
that they will not strike

arm over

when

it

the head during ascent

Exhaling during the ascent
will alert

will

surfacing. Holding an
is

also a

good practice.

produce bubbles, which

surface personnel that the diver

is

ascending.

Second, after surfacing, the diver should not attempt
to enter the boat

wearing tanks or other heavy equip-

ment unless the ladder is strong enough to handle the
combined weight of diver and equipment. The diver
should remove the tanks and obtain assistance from
someone in the boat or from another diver in the water
before climbing aboard. Rails extending above the
sides of the boat are useful as handrails to support the

diver as he or she climbs into the boat.

Probably the most widely used method of returning
to a small boat

is

via a diver's ladder.

Ladders also

provide a secure point for divers to grasp while they are
still

the water.

in

A

ladder

may

be built

in

many

con-

Source:

NOAA

(1979)

figurations but should have these general characteristics:
•

It

should extend below the surface of the water 3 to

4 feet (0.9 to 1.2 m), providing a place for the diver
to stand and hold on while removing equipment.
•

should be strong, well built, and capable of

It

being securely fastened to the side so
shift

when subjected

it

will not

to the action of the seas

diver comfortably.
•

It

should be angled away from the boat to permit

It

the boat and suspended just below the surface of the

A

diver can

swim onto

the platform,

sit

securely

while removing equipment, and then stand up and step

A hand- or arm-hold should
portable, easily stored platform
(Figure 10-6) can be constructed from either wood or

safely into the boat.

should have rungs that are

Modifying conventional ladders

flat

and wide.

to fit small boats

be provided.

A

is

unsatisfactory because these ladders are closed on both

sides

assisting a diver into a small boat

the use of a platform rigged to the stern or the side of

water.

easier ascent.
•

Another method of
is

should be wide enough to accommodate the

It

motor, so the diver can pass unhampered on the other
side.

and

the diver's weight.
•

The ladder should extend about 30 inches (77 cm)
below the water's surface to allow diver access. The
ladder should have a handle only on the side next to the

metal.

by rung support shafts, are difficult to climb

FRESH WATER DIVING

with equipment, and hang too close to the boat to provide

10.5

sufficient toe space.

There are thousands of square miles of fresh water

Figure 10-5 shows a ladder that

is

designed to allow

a fully equipped diver to re-enter a small boat with
safety

and ease even

in

strong currents.

The most impor-

tant features of the ladder are lack of side supports

('open step' design),

its

slope,

and

positioned on the transom of the boat.

its

ability to be

With

a ladder of

the open step type, divers can use the inner sides of

and can then step
onto the rung from the side. The angle between the
shaft and the transom should be 35 to 40 degrees.
Positioning the ladder on the transom (the strongest
part of the boat) is particularly important in rivers
because the boat partially protects the diver from the
their feet to locate the ladder rungs

force of the current

ladders positioned on the side of the boat are used, the

may push

October 1991

The

five

in

Great Lakes alone have a

total area of 95,000 square miles (2,460,500 sq km),
and the two-thirds of these lakes that lie within U.S.
boundaries represent almost half of the fresh water

acreage

in the

country.

Basic techniques for diving in lakes, rivers, and quar-

much like those used in ocean waters. Howevsome differences should be noted. For example,

ries are

er,

depth gauges are calibrated for seawater density, and
adjustments must be

made

to achieve

accuracy

in

fresh

water (see Section 10.12. 5). Buoyancy requirements
also are

somewhat

different for fresh

and

salt water.

and because the diver can climb

out of the water parallel to the current. If conventional

current

the United States.

the diver sideways.

— NOAA

Diving Manual

10.5.1

Great Lakes

Great Lakes divers need

to

be aware of the tempera-

ture changes that occur with changes in depth and

10-13

Section 10

season. In a typical fresh water lake, the upper layer

Old

cables, heavy equipment, electric cables, rope,

(epilimnion) temperature generally ranges between

fishline, fishing lures,

55 and 75 °F (13 and 24 °C) in late summer. However, the

lake bottoms.

waters below the thermocline (hypolimnion) approach
the temperature of

maximum

density for fresh water,

39.2 °F (4°C). Consequently, divers working below the

thermocline, which averages 60 feet (18.3
lakes in late

summer, must plan

to use

m)

in these

buoyancy con-

and thermal protection.
During the winter months, the water temperature in
the Great Lakes ranges between 32 °F (0°C) near the
surface and 39.2 °F (4°C) on the bottom; during this
period, a significant portion of the Great Lakes is ice

Many

and even old cars are often found on
lakes have never been cleared of

trees, barns, houses,

water towers, and other objects.

The bottom sediment

of lakes

is

easily stirred up, as

is

sediment that has settled on lake-bottom trees or brush.
Divers should stay off the bottom as much as possible

and move slowly when forced

to

work on the bottom.

trol

covered. Occasionally, divers are required to

2 to 16 inches (5.1 to 40.6
tions, collect

ice to

work under

make

observa-

samples, or maintain scientific equipment.

Diving under ice
special techniques

taken only

cm) of

when

is

particularly hazardous, requires

and equipment, and should be under-

absolutely necessary (see Section

10.9).

Divers and surface support personnel operating in the
lakes

may

be subjected to atmospheric temperatures

of -30 °F (-34 °C), with wind chill factors approaching

-100°F(-73°C).
Underwater

visibility in

the Great Lakes ranges from

m)

less

than

Lake Erie. Visibility is influenced by
local precipitation and runoff, nutrient enrichment,
biological activity, local bottom conditions, and diver
foot (0.3

in

activity. Significant seasonal variations also

occur

in

these waters.

From September

Artificial

to

December, storms and severe

wave conditions can be expected

water systems such as reservoirs and flooded

strip mines, gravel pits, or stone quarries are

popular

some areas, they represent the only
and in other regions they are used

spots for diving. In

place for diving,

primarily for diver training. Quarries usually are deep;
their water originates

from seepage

in the

surrounding

water table. For this reason, the water usually

is

low

in

nutrients and significantly colder than water in areas

primarily fed by runoff. As the water near the surface
warms up during the summer months, a sharp thermocline is created that must be taken into account when
dressing for a quarry dive. Quarries are used frequently as

dump

about 100 feet (30.5 m) in Lake Superior to
1

10.5.3 Quarries

sites for old cars

and a variety of junk, and

quarry divers must beware of becoming snagged on
sharp metal or monofilament

sediment

10.6

is

stirred

up and

line, especially

visibility is

when

the

reduced.

OPEN-OCEAN DIVING

Researchers have recently become interested
and sampling pelagic organisms directly

in observing

in the

open

Great Lakes.

ocean instead of collecting specimens using such con-

Divers working offshore at these times must use sturdy

ventional techniques as Niskin® bottles, grabs, or nets.

in the

and monitor weather forecasts. Because swift
currents may be encountered in rivers and straits
connecting with the lakes, Great Lakes divers must use
considerable caution and be properly trained in the
vessels

techniques of diving in currents (see Section 10.15).

However, because open-ocean

(also

termed blue-water)

diving does not provide a fixed frame of reference,

divers performing open-ocean dives

may become

disoriented because they have a reduced awareness of

depth, buoyancy, current, surge, other divers, marine

organisms,

or, occasionally,

even of the direction of the

surface (Heine 1985). Special techniques have there-

10.5.2 Inland

Lakes

Other lakes in the United States vary from clear
mountain lakes with low sediment input to reservoirs,
sediment-laden rivers, and glacial lakes, which usu-

When planning a lake
bottom terrain is as important a consideration as
underwater visibility. Lakes may have vertical rocky
ally

have a milky appearance.

dive,

sides,

rocky outcrops, ledges, and talus slopes, or they

may be sedimentary and composed primarily of old
farm land. Algal blooms often occur in lakes during
the warmer months and may completely block the light,
even at shallow depths. Thermoclines also occur, and
temperature and underwater

10-14

visibility

may

vary greatly.

fore been developed to aid the diver operating in the
open ocean to carry out scientific tasks safely.
Blue-water diving is usually done from a small boat
to facilitate diver entry, exit, and maneuverability and
to minimize the 'sail' area, which reduces drift and the

consequent dragging of divers through the water. Even

when operations
vessel, a small

are being conducted from a large

boat should be used to tend the divers

because wind and surface currents often carry a larger
boat away from the actual dive

site.

Open-ocean dive teams generally consist of a boat
operator (who remains in the boat), a safety diver, and
as

many

as four or five working divers. After reaching

NOAA

Diving Manual

—October 1991

Diving Under Special Conditions

Figure 10-7
Down-line Array for

Open-Ocean

Diving

100 feet (30 m) long,

the dive site, a downline about

loaded with 5 to 10 pounds (2.3 to 4.5 kg) of weight and

knotted at specific depths,

passed from the boat

is

through a surface float and lowered to serve as a safety

(Figure 10-7). This line

line for the divers

then

is

secured to the surface float and to the small boat.

m)

4-foot (1.2

sea anchor

is

A

frequently used to reduce

caused by wind; the anchor can be attached to a

drift

loop in the downline at the surface float or to a separate
float to

keep

from collapsing and sinking if the wind
it is useful to drop a small

it

To mark

dies.

the dive site,

open jar of fluorescein dye into the water. The vertical
column of dye emitted as the jar descends will be
distorted by currents, giving a visual display of the
current pattern in the water

column

Because of the absence of any
the inherent danger of drifting

ocean divers are tethered

(see Section 9.8.2).

visible reference

away

or

down,

all

and

open-

at all times to the safety line

an underwater trapeze. The trapeze can be configured

via

Adapted from Hamner (1975)

from any bar or ring that accepts clips and shackles
easily. Figure 10-8 shows examples of three types of
than to the tether),

trapezes that have been used for this type of diving.
In conventional diving,
in

buddy

swim

divers

together;

it

diver's body,

can be released by pulling
which ensures that

it

away

it

will release.

open-ocean diving, however, the safety diver serves

buddy diver

as the

shown

in

for all of the divers

Figure 10-7,

all

on the team. As

divers are tethered to the

trapeze by means of lines approximately 30 to 50 feet
(9.1

to 15.2

underwater

To avoid

m)

long; the length of the line

visibility

depends on

and the task being undertaken.

kinking, tethers should be braided lines.

good rule of thumb
to

from the

is

A

WARNING
Tethers Should Not Be Attached to a Diver's
Weight Belt, Because Ditching or Losing the
Belt Would Add Excessive Weight to the Trapeze Array

to restrict the length of the tether

about 50 to 75 percent of the nominal underwater

(Heine 1985). The exception to this
the safety diver's tether, which should only be

visibility distance

rule

is

about

3 feet (0.9

m)

they understand the diving signals, especially the

long.

Because tethers of a fixed length tend

droop and

to

become tangled, they should be designed
taut at
ling.

all

times,

which also

to

remain

facilitates line-pull signal-

This can be achieved by weighting the end nearest

the safety diver with a 4 to 8 ounce (113 to 227
fishing weight.

The

Before starting a blue-water dive, all equipment
must be checked and the divers must all be sure that

gm)

tether then passes freely through

tug signals, that will be used.
the water

down

first,

but

all

The

line-

safety diver enters

of the divers usually descend

the line together to connect the pivot ring to the

vertical line

and

to

prepare the tethers. During the

dive, the safety diver monitors the tethers, keeps a

lookout for hazards, and supervises the dive.

The

safety

the metal loop on the end of a swivel clip (Figure 10-8);

diver maintains visual contact with the other divers

these clips are attached to the trapeze, which

near the safety diver. Thus, as the working diver swims

and can attract their attention by tugging at their
tethers. The boat operator can signal the safety diver

away from

the safety diver, the tether pays out smoothly,

by pulling on the vertical

when

the diver returns, the tether retracts as the

team can communicate and be alerted to ascend at any
time during the dive. A good practice is to have each
diver run the tether through the palm of one hand so

and,

weight sinks. In conditions of low
lines

is

located

visibility, tether

can be shortened by tying a knot on the weight

side of the tether, thus shortening the length available
to

pay

out.

nected to

The other end of the tether should be
the diver's buoyancy compensator or

separate harness. If the quick-release shackle
to the diver's

is

conto a

attached

buoyancy compensator or harness (rather

October 1991

— NOAA

Diving Manual

line.

In this way, the entire

that the line-tugs can be detected easily.
diver can
line to

move

any of the knotted

thus control the

The

the pivot ring up and

maximum

down

The

stops, as required,

depth of

all

safety

the vertical

and can

of the divers.

safety diver can also terminate the dive or send

10-15

Section 10

Figure 10-8

Three Multiple Tether Systems (Trapezes)

Used

for

Open-Ocean

Diving

Brass Snaps

Working Diver's Tether

Bottom Weight

Running
Counterweight
Source: Rioux, as cited

in

Heine (1985)

Stainless Steel

Attachment Ring

Swivel Snaps

Working Diver
Tether Line

Knot

in

Line

Running Counterweight

Polypropylene Washer
Safety Diver Tether Line
(

Source:

)) Small Coated Weight

Hamner (1975)
Source: Coale and Pinto, as cited

10-16

NOAA

Diving Manual

in

Heine (1985)

—October 1991

Diving Under Special Conditions

any diver up

if

the situation warrants such action.

Divers can ascend at will by signalling their intent to

temporary safety diver. There must always be someone
acting as safety diver (Heine 1985).

As with any

the safety diver, unclipping their tethers at the pivot
ring,

and ascending the vertical

line to the boat.

If

away from

can be attached

it

depth as the

line

is

is

to the line at the appropriate

deployed, which makes

it

unneces-

Any

equip-

ment hung on the downline should be positioned above
the trapeze and safety diver, and the weight of the
equipment must not be so great that it overweights the
downline. Divers working below the trapeze must be
careful to avoid entanglement in the weighted tethers,

which would envelop the safety diver in a cloud of
bubbles and reduce his or her ability to see. If a second
line is deployed for equipment, it must be separated
clearly from the safety line and should not be used as
for tethers.

and

In addition to diving, safety,

scientific equip-

ment, most open-ocean divers carry a shark
Section

According

5.7).

to experienced

at the University of California at

Twenty percent of

Readers

should consult a specialized open-ocean diving man-

hung on the

sary for the divers to carry the equipment.

an attachment

specialized diving, open-ocean diving

requires individualized training and practice.

ual for further details about this type of diving.

the boat.

scientific or diving equipment

downline,

is

when ascend-

important that the divers hold the downline
ing so that they do not drift

It

billy (see

blue-water divers

Santa Cruz:

the blue water dives

all

performed by our group

in the central

10.7

CAVE DIVING

Cave diving
performed

To

holes.'

is

in

a specialized

form of diving that can be

both inland fresh waters and ocean 'blue

scientists,

caves offer new laboratories for

research. In cave diving, the emphasis should be placed on

developing the proper psychological attitude, training
in

specialized techniques and

life

support systems,

dive planning, and the selection of an appropriately
trained

buddy

diver.

WARNING
Only Experienced and Specially Trained
Divers Should Undertake Cave Diving. Openwater Experience Is No Substitute for Cave
Diving Training

north

and south Pacific gyre systems and the eastern
tropical Pacific were aborted

due

to the

persistent presence of sharks, specifically

oceanic white tip sharks. In

were spotted

first

all

cases they

by the safety diver. This

The cave diving environment
because

it

is

alien to

humans,

involves both the underwater environment

and the limited-access, limited

visibility,

confined space

environment typical of caves. Examples of the special

may

be encountered

cave diving are:

underscores the value of the safety diver

hazards that

and a routine abort plan and the

the absence of a direct and immediate ascent route to

utility of

the surface, the sometimes instantaneous loss of visi-

the shark billy (Heine 1985).

bility

Divers generally work

in

an area upstream of the

because of

silting or failure of the diver's light,

the divers and the downline, and generally monitors

and the entanglement and impact hazards associated
with being in a confined, enclosed area. These and
other factors all have an effect on the psychological
composure of divers and their ability to cope with
stressful situations. Improperly trained divers, unaware
of the hazards unique to cave diving, often panic and
drown when they encounter situations that are in fact
normal for the cave diving environment. It is impera-

the progress of the dive. During the course of the dive,

tive that divers

the safety diver maintains contact with the divers by

tude before they consider conducting a cave dive.

periodically tugging on the divers' tethers to ensure

pletion of a standard scuba diving course does not

trapeze,

in

which allows them

samples and

to collect fresh, undisturbed

to stay in a single area in sight of the

As they perform their tasks, the divers
make visual contact with
diver. The safety diver constantly monitors

safety diver.

scan their surroundings and
the safety

the surroundings, checks for sharks, keeps an eye on

that they are comfortable, their air supply

and they are responding
If a

is

adequate,

to pull signals appropriately.

diver requires minor assistance, the safety diver

signals another diver to go to his or her aid. Before the
safety diver

or she

becomes involved

must

first signal

October 1991

— NOAA

in

helping another diver, he

another diver to act as the
Diving Manual

develop the proper psychological

prepare a diver for the special perils faced

in

atti-

Comcave

diving.

Before taking a course

in

cave diving, the diver-

student must have enough open-water experience to
feel

psychologically and physically comfortable under

water. Because their lives

may

one day depend on the

10-17

Section 10

Figure 10-9
Safety Reel Used

in

Cave Diving

quality of instruction received, persons contemplating

taking a course should select one taught by a mature

and nationally

A

certified cave diving instructor.

good

cave diving course should include prescreening of potential divers, at least

100 hours of training in underwater

work, and instruction in line safety, the elements of

buddymanship, dive planning, equipment handling, and dive theory. Three. basic rules of
buoyancy

control,

must be adhered

safe cave diving that

to

by every diver

are:

(1)

Always use a continuous guideline

(2)

Save two-thirds of the

total air

to the surface.

supply for returning

to the surface.

(3)

Carry

at least three lights during the dive.
Source:

A common
silt.

hazard

To minimize
swim

trained to

buoyancy

A

cave diving

in

and

cave diver's link to the

Temporary

safety and navigation.

lines are the

consist of a safety reel

and

most

line.

suitable safety reel should feature a line guide,

A

drum,

buoyancy chamber, a good turns ratio, and be capable
of carrying approximately 400 feet (122 m) of
1/16 inch (1.6 mm), 160-pound (72.6 kg)
(3.2
line.

test to

1/8 inch

mm), 440-pound (199.6 kg) test braided nylon
The reel should be neutrally buoyant, compact,

and rugged (Figure

Standard cave diving life-support systems should
include:

line are the

surface and survival. Several kinds of lines are used for

commonly used and

(1979)

cave divers must be specially

silting,

horizontally and to maintain proper

at all times.

safety reel

NOAA

the presence of

is

10-9).

Large

reels

and

double tanks
double manifolds

two regulators
submersible pressure gauge

buoyancy compensator with automatic

inflator hose

depth gauge

watch
decompression tables
wet or dry suit
safety reel with line

lines create

lights

extra drag for the diver

When

and require extra exertion.

running a safety

should maintain tension.

line,

The

compass

the diver with the reel
slate

line

should be tied within

surface light, and safety wraps should be

made

pencil.

approxi-

mately every 25 feet (8.3 m). The line should be centered in the cave as much as possible. The reel-diver is
first

in

and

last out.

The buddy

is

responsible for

The larger capacity double-tank arrangement recommended for cave diving has an 'ideal' or double-orifice
manifold. This system manifolds two tanks together

common

gas supply and uses two regulator

unwrapping the safety wraps on leaving the cave and

with a

for providing light for the diver tying or untying the

adaptors. If one regulator

line.

Physical contact with the line should be avoided

except when visibility decreases. In some cases, cave

tion without interruption

permanent lines for mapping or to permit a more complete exploration of a cave. Novices
should use temporary lines and should not attempt to
follow permanent lines unless they have a thorough
knowledge of the cave. The technique for laying and
retrieving a safety line is unique to cave diving and
should be practiced until it becomes second nature,
because it could save one's life in a total silt-out,
where there is a complete loss of visibility. It is impor-

cylinders.

One

5-foot (1.5

m) hose

divers will use

tant to

remember

that in cave diving the safety line

not a tow line and should not be used for support.

10-18

is

fails,

that regulator

may

be

shut off while the second regulator continues to func-

and with access

to both gas

of the regulators also should have a
so that divers

may

share their gas

supply when maneuvering out of tight situations.

Although the need

for lighting in cave diving

obvious, the lighting taken on cave dives

is

adequate for safety. Each diver must carry at
lights,

is

often not
least 3

with the brightest being at least 30 watts. Backup

can be of lower wattage, but they must also be
dependable and of high quality.
All cave diving equipment must be checked and
rechecked by each member of the dive team before

lights

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

submersion
ation,

to

ensure proper functioning, ease of oper-

and diver

During

familiarity.

smooth

this time, the

Two

types of diving dress have been used with suc-

cess under severe thermal conditions: the hot-water

which provides a continuous flow of preheated

operation of backup equipment should also be verified

wet

and the dive plan should be reviewed

water to the diver, and the variable-volume dry suit,
which allows the diver to control the amount of air in

for the last time.

The maximum recommended number of cave
per team

three.

is

divers

Larger groups cannot handle the

integrated 'buddymanship' necessary to maintain the

constant contact so essential

in

cave diving. For fur-

ther information about cave diving, readers should

Cave Diving, Box

write to the National Association for

14492, Gainesville, Florida 32604, or the National

Cave Diving

Speleological Society's

Oak

low

Section, 3508 Hol-

Place, Brandon, Florida 3351

1.

suit,

the suit and thus

its

wet

suit

presented

is

Except for the hot-water wet

tion 5.4.)

more

insulating capability. (A

detailed description of these suits

in

Sec-

no dry or

suit,

provides complete protection of the diver's

hands for long periods. As the extremities become cold
and dexterity is lost, the diver becomes less efficient

and should terminate the dive. The use of heavy insulating socks under the boots of a wet or dry suit will
help to keep the feet warm.

Hands should be protected

with gloves or mittens having the fewest possible digits;

10.8

COLD-WATER DIVING

Diving

in

cold water

associated with several equip-

is

ment problems not found

in

warmer

waters; the major

Most single-hose

difficulty involves the regulator.

regulators have a tendency to freeze in the free-flow

extreme

position after approximately 20-30 minutes of

cold-water exposure. However, several models are avail-

and that use a

able that are designed to resist freezing
special antifreeze-filled housing system.

The standard

double-hose regulator rarely develops this freezing
problem.

If a

regulator begins to freeze up, the dive

should be aborted immediately.
freeze-up

is

about to occur

is

An

early sign that

the presence of ice crys-

tals

on the tongue. Second-stage freeze-up

ally

caused by moisture

in

is

that the diver's

Divers must be careful

seawater through their noses,

because introducing very cold water into the mask
often causes divers to inhale involuntarily.

Keeping the diver's body warm

is

The standard foamed-neoprene wet

suit has

10-10).

been used

29 °F (2°C) water for dives lasting longer than an
doubtful whether the divers on these

dives were comfortable or thermally safe.

drawback of wet

suits

over, the diver

wet and

is

that,

is

A

major

by the time the dive

will therefore

is

probably con-

body heat even after leaving the water.
Further, the loss of foam thickness with depth drastically reduces the efficiency of any wet suit for cold
tinue to lose

water diving

much below 60

October 1991

— NOAA

from the head can be reduced by wearing a

second well-fitted neoprene hood over the regular

suit

hood. Wearing a knitted watchcap under the hood of a

dry suit
If the
suit's

is

cap

especially effective in conserving body heat.

pushed back

is

far

enough

to

permit the

face seal to seat properly, the diver's head will be

kept relatively dry and comfortable. With a properly
fitting suit

kept

and

warm and

If divers

all

can usually be

seals in place, a diver

dry, even in cold water, for short periods.

and members of the surface-support crew

feet (18.3 m).

Diving Manual

maintained in the best possible condition, dry suit
underwear should be kept clean and dry, and all seals
and zippers should be inspected and repaired (if necesDuring the dive, divers should
body heat.
Dives should be terminated immediately if the diver

sary) before the dive.
exercise as

much

as possible to generate

begins to shiver involuntarily or experiences a serious
loss of

manual

dexterity.

Once involuntary

shivering

begins, the loss of dexterity, strength, and ability to
function decreases rapidly (see Section 3.4). After leaving

the most impor-

tant requirement in cold-water diving (Figure

is

loss

warm

recommended.

also

water exposure can be greatly reduced. Suits should be

relieve this condition temporarily.

it

Heat

is

the exhaled breath, which

mask is more likely to fog or freeze in cold water, which
means that a non-irritating defogging agent should be
applied to the mask before diving. Partially flooding
the mask and flushing seawater over the faceplate will

hour, but

water just before the dive begins

follow certain procedures, the adverse effects of cold-

Another cold-water diving problem

in

they provide. Filling the gloves or mittens with

gener-

is

then condenses and freezes on the metal parts.

to avoid inhaling cold

manual dexterity associated with the use
is overridden by the added warmth

the loss of

of gloves or mittens

the water, cold-water divers are often fatigued, and,

because heat

loss

from the body continues even after

removal from cold water, such divers are susceptible
hypothermia. Flushing the wet suit with

warm

to

water as

soon as the diver surfaces has a comforting, heatreplacing effect, although such flushing can cause additional

body heat

loss unless

it

is

done cautiously.

must be provided that allow the diver
a comfortable, dry,

and

so that he or she

can regain

relatively

warm

lost

to

Facilities

dry off

in

environment,

body heat (see

Section 3.4.4). Divers should remove any wet clothes
or suits, dry off, and then don

warm

protective clothing

10-19

Section 10

Figure 10-10

Water Temperature Protection Chart

/7=\\

°F

*"tVpl£

Normal Body Temperature 98°F (3rC)

35—

Unprotected Diver

Average Skin Temperature 93°F

(34°C)

Unprotected Diver
Uncomfortably Cold 88°F

(31 °C)

Shivering 86°F

(30 C)

^
^
^

^|

—

Rest mg

90

Working

30—

Diver Will

Overheat

Unprotected
Diver

Comfortable
During
Moderate

Unprotected

80
25

—

Diver At
Rest Chills In

Work
Wet

1-2

or Dry Suit
Diver's

20

—

—

Hours

70

Underwear
Or Wet Suit
Required
Pain 60°F

(15°C)^

Dry Suit
Required
Over 60'; Wet

'

f.

60

15-

Suit For Short
Duration Dives
Less Than 60'

10

—

Death Within One Hour 40°F(5°C)^

5

—

Unprotected Diver

50

—

40

Hot Water Suit
Or Variable
Volume Dry
Suit Required

30

Fresh

^

Water

<4

Sea

Freezing
Point

Water

5

Protection Usually

—

Needed

Heated Suit

Source:

10-20

NOAA

Diving Manual

US Navy

(1985)

—October 1991

Diving Under Special Conditions

Figure 10-11
Diver Tender and Standby
Diver in Surface Shelter
as soon as possible. In cold-water diving situations
that require repetitive dives,

it

is

even more important

conserve the diver's body heat, to maintain an
adequate fluid balance, and to select the diving dress

to

carefully.

and nutrition are essential to providing cold-water divers with the energy necessary for
this type of diving. A diver should have a minimum of
6-8 hours of sleep before the dive. Care must be taken
to avoid dehydration, which can interfere with the

Adequate

rest

body's thermal regulatory mechanism. Careful planning is thus of the utmost importance in all cold-water
diving.

WARNING
If a Diver Is Extremely Cold, the Decompression Schedule Should Be Adjusted to the
Next Longer Time

UNDER

DIVING

10.9

ICE

In addition to the problems and limitations of diving

water (see Section 10.8), there are specific
precautions that must be taken when diving under ice.
in cold

Diving under ice

is

extremely hazardous and should be

Photo Doug Eiser

done only by experienced divers who have been carefully trained.

Most

ice diving

is

done from large and relatively

flat

surface ice sheets that are stationary and firmly frozen
to the shore.

Even

at

many

locations

miles from the

nearest land, these ice caps often offer a stable work-

However, diving from drifting or broken
dangerous and should only be done as a last
resort. When the ice cap is solid, there is no wave
action to the water; however, divers must constantly be
on guard because the current beneath the entry hole
can change quickly and dramatically without producing any noticeable effect on the surface. In most cases,
the absence of wave action produces good underwater
ing platform.

ice

is

although under-ice diving operations conareas characterized by river runoff or heavy

visibility,

ducted

in

plankton

may

be associated with conditions of reduced

visibility.

To
drill

enter the water through ice, divers should

mine

and water depth. If conditions are
the area around the site should be cleared

snow and the

approximately

3

size of the entry

by

5

fully dressed divers to

If

no shelter

works

first

site to deter-

ice thickness

satisfactory,

of

through the ice at the

a small hole

is

determined.

m)
accommodated
be

feet (0.9

by

1.5

hole of

allows three
at

one time.

used, a triangle-shaped entry hole

the diver's tasks, so that they will understand the diver's

movements and be able
gency.

A

— NOAA

Diving Manual

to

respond quickly

in

an emer-

safety line should be tied to the diver (not to

the equipment) and the other end should be tied firmly
to a large fixed object

on the surface. Excursions under

the ice should be well planned,

and the distance

to be

away from the entry hole should
be kept to a minimum; under normal circumstances,
this distance should be limited to 90 feet (27.4 m) and
should be extended to as much as 250 feet (45.7 m)
traveled under the ice

only in unusual circumstances. Longer under-ice excursions

make

it

difficult for the diver to get

back

to the

entry hole in an emergency and increase the difficulty
of searching for a lost diver. If divers

distances under the ice,
for

emergency

ascend

to the

tain positive

conserve

best.

October 1991

A

In all diving operations under ice, there should be
one surface tender for each diver and at least one
standby diver (Figure 10-11). While the diver is in
the water, the tender must be attentive both to the
diver and surface conditions, such as deteriorating
weather or moving ice. Tenders should be briefed on

air,

exits.

travel long

additional holes should be cut

Divers

overhead

must

lost

under the

ice cover

ice should

immediately, main-

buoyancy, relax as much as possible
and wait for assistance.

to

10-21

Section 10

WARNING

divers

from the wind and, together with a small porta-

ble heater, can provide relative comfort in these severest

Divers Lost Under the Ice Should Ascend to
the Ice Cover and Wait Calmly to Conserve
Air. They Should Not Search for the Entry
Hole

of diving conditions.

10.10

KELP DIVING

Kelp is found
and temperate

in

dense beds along

many

of the colder

coasts of the world. In the United States,

To

aid the diver to return to the entry hole, a bright

these plants are found along the shore regions of the

light

should be hung just beneath the surface. For

west coast. Kelp beds or forests are widely diversified

it is

both geographically and as a function of depth and

usually the only item required beyond those used in

temperature. Different varieties grow in different zones
and support an incredible variety of sea life. Kelp will
attach itself to practically any substrate (i.e., rock,
concrete, steel, wreckage, etc.) and will often form a
treelike structure, the base of which is a rootlike holdfast that provides a secure anchor and a home for many
organisms. There is generally an area of open water

night diving under ice, this light

is

a necessity;

day-time operations. However, since cold water shortens the

life

of batteries,

homing beacons and strobes

should be checked before use. Because direct ascent to
is impossible when under the
means of determining direction often is

the surface

ice,

a rapid

critical. In

shallow water, detours are often necessary to circumvent the 'keels' (thickened areas) built up beneath the
Also, because of the absence of waves, there are no

ice.

ripple patterns on the

bottom

to aid in orientation.

these reasons, the use of a tether

For

absolutely essential

is

under-ice diving.

in

If there

is

a failure in an ice diver's primary breath-

between the stipes originating from one holdfast. A
diver can swim between the stipe columns just as a
hiker can walk between the trunks of trees in a forest
on the land. Hollow floats or pneumatocysts are found
at the base of the blades or fronds on many of the
larger, longer kelp plants.

These

floats

cause the fronds to

tem, notify the buddy diver, and exit to the surface

up and keep the stipes relatively upright. The
floating fronds form a canopy when they have grown

with the buddy diver. Because buddy breathing

sufficiently to reach the surface. In

ing system, the diver should switch to the

ficult in cold water, all divers

backup
is

sys-

dif-

should practice buddy

breathing before making excursions under the

ice.

Octo-

pus regulators should not be used in cold water as

buddy breathing because the

float

many

instances,

this rapidly growing canopy becomes very dense and

can be several feet thick on and near the surface. The
canopy will usually have thin spots or openings located

stage

randomly throughout the area, and these thin spots or

of these regulators tends to freeze up. If a diver's

openings provide entry and exit points for divers. These

exposure suit tears or floods, the diver should surface

thinner areas are easily seen from below the surface

immediately, regardless of the degree of flooding,
because the chilling effects of frigid water can cause

because the light penetration

thermal shock within minutes. Surface-supplied tethered

light area exhales, the rising

substitutes for

diving
tions

is

becoming more popular

because

it

in

first

under-ice opera-

eliminates the need for safety lines and

navigation lights and provides unlimited

air.

The

full-

face masks or helmets of most surface-supplied diving

systems provide additional protection for the diver's
face and provide the capability for diver-to-diver and

under such a

bubbles usually float the

kelp outward to form an opening that
large to enable the diver to surface.

exercised

when

the diver's head

may

is

sufficiently

is

Care should be

out of the water,

back and fill in the hole and
surround the diver. Although the kelp will not actually
wrap itself around the diver, divers who twist around
because the kelp

float

These added features
must be weighed carefully against the burden of the
added logistic support required to conduct surfacesupplied diving. If the advanced dry suits now availa-

and struggle may become entangled. Training

ble (see Section 5.4.5) are used, the surface-supplied

snag and tangle

diver can spend long periods under the ice in relative

diver

diver-to-surface communication.

safety
If

for

and comfort.

more than

1

is

constructed over the entry hole (Figure 10-11). Such a
shelter will protect both surface support personnel

10-22

diving

and

is

and

necessary to master the

skills to

in kelp

make

entries

exits easily.

Equipment that

is

not relatively streamlined can

in the kelp

becomes entangled,

that kelp

scheduled to last
or 2 days, a tent or shed should be

an under-ice dive operation

much

in these areas is

better; in addition, as a diver positioned

is

it

and cause problems.
is

If the

important to remember

designed to withstand the pulling force of

wind, waves, and currents and consequently that the
tensile or stretching strength of the plant

is

very great.

Divers wishing to break a strand of kelp should fold
to

develop a sharp angle

NOAA

in the stipe. Pulling

Diving Manual

it

on the

—October 1991

Diving Under Special Conditions

may

kelp will result in frustration and

Nicking the kelp with a sharp object

cause panic.
separate the

will

streamlined surface to the kelp, since anything that
extends out from the body

will

Swim

probably snag.

kelp easily, but using sharp objects such as knives

fins

needs to be done with care because of the proximity of

The

end of the strap on the inside rather than the outside of
the buckle. Taping the loose end of a strap to the main

way to get free is to remain calm and to pull the
away carefully with a minimum of movement.

diving knife on the inside of the calf rather than any-

regulator hoses and other critical paraphenalia.
easiest

strands

When

working from a boat,

it

best to anchor in an

is

opening so that the wind or current

will drift the boat

back on the anchor line to a second opening in the kelp.
Divers may also anchor outside the kelp and swim in to
do their work.

If

anchor

full

be

will

the boat

is

anchored

in

the kelp, the

of kelp that must later be removed

with adjustable heel straps should have the loose

portion of the strap

Entry through the kelp

making

is

best accomplished

by finding

a feet-first, feet-together entry

rather than a headfirst or backroll entry that could
easily lead to entanglement.

through the canopy and into

Once through

important to get
the open water between
It

is

the surface canopy, the diver

can swim with comfort in the forestlike environment.
As the diver swims along, it is important to watch for

bags, and tools of

making an opening. When the diver
surface, the arms should be raised over

approaches the

the head so that any kelp that

may

be encountered can

be moved to the side easily as the diver moves upward
into the hole that has

been opened. Once on the sur-

face, the diver should stay in the vertical position

and

should not turn around; this helps to avoid entanglement. Submerging can be accomplished easily by either

exhaling and sinking or raising the arms overhead,

which forces the body deeper down into the water.
Smooth and slow movements make this maneuver easy
and

safe.

The

diver

who wishes

to travel

on the surface of a

kelp bed to get back to the shore or boat has several
choices. If the diver

is

desired location.

Each

step

move

streamlined

game

kinds should be organized to

all

it

is

remember

that kelp floats

and

that,

possible to achieve flotation by using

Under windy

the kelp for support.

conditions, divers

should approach the stern of a small boat to avoid
being pressed by the boat's

movement

into the kelp

and

becoming entangled.

The various forms

may grow so that the taller
may be found growing over a

of kelp

kelps such as Macrocystis
forest of

Pelagophycus

canopy of kelp

(or elk kelp). This

will further

reduce the

second lower

light level but

be easier to swim through than the surface canopy.

All kelp beds are influenced by wind, currents,

may disappear from

surge, and major beds

view

in

a swift current because they are held

45-degree angle. This has

its

and

surface

down

at a

advantages because the

kelp will stream with the current and thus

may

be used

as a navigational aid during the dive.

Achieving comfort and efficiency

in

diver along

who

is

kelp diving

Having

the result of training and practice.
equally well trained

is

a

is

buddy

also extremely

important.

10.11

WRECK

Wreck

diving subjects the diver to

DIVING

hazards that are found

in

cave or

many

of the

same

ice diving. In the past

easy to

20 years, wreck diving has evolved into an activity

in steps to the

requiring both specialized equipment and training, par-

sufficiently skilled,

use a series of breath-hold dives to

in a

present minimal problems.

will

bles to assist in

Wearing the

fashion and that inflated buoyancy compensators,

the light areas that signal the thinner areas in the kelp

bed. Surfacing slowly permits a diver's exhaust bub-

solution.

through the kelp or over the kelp

in a pinch,

a thin area and

good

also a

where on the outside of the body is also a snag reducer.
Kelp divers should remember that they want to move

Divers should also

surgically.

the stipes.

is

it

is

requires the diver to sur-

ticularly in the case of

deep wreck diving. Regardless

face through an opening in the kelp and to take a

of purpose (lobstering, artifact collecting, photogra-

breath or two

phy, or exploring), true wreck diving involves the diver

in

preparation for the next step. Another

useful technique, often called the Kelp Crawl, resem-

entering the wreck.

and involves keeping the body on
the surface above the kelp canopy and using the arms

enclosed space of the wreck that necessitates the addi-

bles the 'dog paddle'

to pull the diver across the top of the kelp as the diver's

make

narrow

body across
the top of the floating kelp canopy. The arms should
reach across the kelp in an extended position and then
the hands should grasp the kelp and press down as the
body is pulled over the kelp. It is important to present a
fins

a

October 1991

flutter kick to slide the

— NOAA

Diving Manual

It

is

the act of penetrating the

equipment and training.
Most intact wrecks are at depths

tional

in

excess of 80 feet

(24.4 m), because those in shallower water have been

destroyed either by storms or because they were
navigational hazards. After arriving on the bottom at
the wreck site, the first team of divers must check the
anchor of the boat for security and to ensure that the

10-23

Section 10

anchor

line will not chafe.

ally has fair to

however,

visibility

good

may

The path

visibility.

wreck usu-

the return trip,

be reduced dramatically because

the divers have stirred up the
(rust)

into a

On

silt

from the walls and exposed

and ferrous oxide
steel plates of the

wreck. The reduced visibility and the confusion and
anxiety caused by the

many passageways,

entrances,

chambers, bulkheads, and tight spaces require that
wreck divers use a penetration line such as a braided
1/8-inch (3.2 mm) nylon line on a reel. The line should
be tied off at the wreck's entrance, payed out during
entry,

and reeled

in

during return. If the line

is lost

cut, the diver should pause, allow the silt to settle,

or

and

regain his or her composure before attempting to return to

10.12

DIVING AT HIGH ELEVATIONS

The U.S. Navy Standard Decompression Tables,
No-Decompression Table, and Repetitive Dive Tables
were calculated and validated on the assumption that
the diver started from and returned to an ambient
atmospheric pressure of

1

atmosphere absolute (ATA).

Consequently, these tables do not account accurately
for dives

conducted from ambient environments hav-

ing pressures less than
corrections are

now

1

ATA. Two

sets of tables or

use for calculating diving sched-

in

Boni/Buehlmann tables
and the Cross corrections, as modified by Bell and
Borgwardt. These are described below, and represent-

ules for altitude diving: the

ative dive profiles based on these tables are

compared.

the entrance. Placing the faceplate of the underwater
light into the silt will

reduce the ambient light level

adapt partially to the
darkness. This will facilitate the detection of any surface light coming into the passageways and thus aid in

10.12.1 Altitude Diving

the identification of possible exit paths.

and

and allow the diver's eyes

to

Because of depth, the use of twin scuba cylinders,

Currently

in

The Boni/Buehlmann
sion,

his colleagues

Tables

Use
tables were developed

by Boni

(1976) and include no-decompres-

decompression, surface interval, and residual

together with a pony bottle with a separate regulator,

nitrogen (called the 'repetitive timetable') tables for

recommended as standard wreck diving equipment.
some instances, a spare air supply and regulator

each 1,640 feet (500 m) of altitude up to 10,496 feet

is

In

should be placed outside the wreck. These precautions
are necessary in case the diver

becomes entangled

or

needed unexpectedly. During wreck
diving, entanglement may be caused by objects such as
monofilament fishing line, fish nets, collapsed bulkheads, or narrow spaces. A bag containing appropriate
tools for artifacts, liftbags, and an upline should be
carried to reduce the risk of entanglement that prevails if this equipment is carried by or attached to the
diver. Most instrumentation can be strapped to the
underwater light; a set of decompression tables may be
decompression

is

attached to the light housing, reducing the amount of

equipment carried by the diver but
ready access to the tables

if

still

decompression

permitting
is

required.

Although a diver inside a wreck may be tempted to
breathe in the air pockets produced by previous divers,
this practice should be avoided because the partial
pressure of oxygen in these pockets is usually quite low
and hydrogen sulfide may be present.
The water temperature around a wreck is usually
low, and divers must therefore dress properly. Variablevolume dry suits or 1/4- to 3/8-inch (6.4 to 9.5 mm)
wet suits should be used in water temperatures of 50 °F
(10°C) or less (see Section 5.4). Extreme caution must
be taken not to snag the suit or equipment on the sharp
objects commonly found in wrecks, such as decayed
wooden decks or corroded metal bulkheads, because
these hazards are frequently overgrown by algae, sea
polyps, or other marine growth.

10-24

(3,200 m).

The

The

results of

feet (2,000 m) have
wet dives (Boni et al. 1976).

tables to 6,561

been tested on humans

in

94 non-repetitive dives

to depths

between

52 and 98 feet (15.8 and 9.1 m) and for bottom times as
long as 40 minutes were reported. The results of 184 dives
under approximately the same conditions were also
reported by these authors. No symptoms of decompression sickness of any kind were observed during these
278 dives. These tables require a routine decompression stop for 3 minutes at 6.6 feet (2 m) for dives

within the no-decompression limits. Consequently,
dives used for testing the tables included a

all

decom-

pression stop for 3 minutes or longer.

The Cross

corrections to the U.S.

Navy tables were
Navy decom-

developed to convert the standard U.S.

pression tables to tables that could be used in altitude

method was first developed in
1965 by Dr. Jon Pegg but was never published. A
similar set of corrections was later developed by H. J.
Smith, Jr. (Cross 1967) and was subsequently published
in greater detail (Cross 1970). The Cross method involves
determining a theoretical ocean depth (TOD) by multiplying the dive depth by the ratio of the atmospheric
pressure at sea level to that at the altitude at which the
dive will be made. The TOD and the actual bottom
time in the U.S. Navy tables are then used to determine the altitude diving schedule.
The theory of the Cross corrections has been examined in detail (Bell and Borgwardt 1976); the correction factors used in the Cross tables do not apply to the
diving. This adjustment

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

Table 10-1

Comparison of Differences in
Time Limits (in Minutes of
Bottom Time) for No-Decompression Dives
used

critical tissue pressures

On

safety criteria.

in

the

Navy

tables as

the other hand, in the cases studied,

the Cross corrections always 'failed' on the conserva-

Measured
Depth
(ft)

tive,

i.e.,

safe, side.

ter research

University of California underwa-

teams have used the Cross corrections as a
in California lakes and in Lake Tahoe,

guide to diving

Nevada

(elevation

6200

(1890 m)). Diving sched-

feet

ules used have included procedures for
repetitive dives per

day

up

to three

USN

Cross

Boni/Buehlmann

Tables

Tables

Tables

(min)

(min)

(min)

60

+

60
40

40

15

80
100

25

6 (+ 3 at 2 m)

25

10

4

120

15

5

(

3 at 2 m)

+ 3 at 2 m)
Decompression
(

depths of 130 feet (39.6 m).

to

Both no-decompression and decompression dives have
been conducted; no reported cases of decompression

In this

6000

example, dives are assumed to take place

feet

an elevation

at

of

(1829 m).

sickness have occurred in several hundred dives.
Adapted from

10.12.2

Comparison

of Existing Tables

2.

A

comparison of the no-decompression limits given
by the two altitude correction methods and the U.S.

Navy

tables

is

shown

in

Table

As this
Navy

10-1.

shows, both the Cross corrections and the

3.

table

those predicted by the

Boni/Buehlmann

(1979)

altitude of the dive site or the next greater

altitude

is

found

in the top

The entry corresponding

row of the

table.

to the intersection point

of the depth row and the altitude column marks

tables

the

yield no-decompression limits that are longer than

in

The

NOAA

"theoretical ocean depth"

(TOD), which,

according to the assumptions of the Cross theory,

although

yields a probability of decompression sickness

both cases the no-decompression limits are less than

equivalent to that for the altitude and measured

tables,

those that apply to sea level.

depth of the dive.

There have been no reported cases of decompression

4.

The

TOD

and the

total

bottom time, including any

sickness in divers using the Cross corrections on dives

residual nitrogen time accrued from repetitive

from an altitude of 6200 feet (1890 m). The Cross

dives, are then used with the U.S.

corrections therefore appear to be safe. Several labo-

The

ratories are continuing to study this problem, but at

be for a sea-level exposure. Each time a dive is
planned, the TOD equivalent is substituted for

this

time the true bends threshold for these tables has

not been established. Consequently, altitude diving,

and particularly decompression altitude diving, should be

that
5.

performed using conservative assumptions and special
precautions to ensure access to emergency treatment.

dive schedule

Navy

calculated exactly as

tables.

would

it

measured depth.

The ascent
shown

6. If

is

in

rate at altitude

Table

must be reduced, as

10-2.

a decompression dive

is

conducted (which

is

not

recommended), the depth of the decompression
10.12.3

Recommendations

stops

for Altitude Diving

recommended for general
use within the no-decompression limits. Although
The Cross

corrections are

decompression dives have been conducted using the
Cross corrections, they have been relatively few and
have not involved depths greater than 130

from an elevation of 6200
decompression dives

feet

at altitude

feet (39.6

m)

(1890 m). In general,

should be avoided.

must

also be corrected, as

shown

in

Table

10-2.

Example:

Two

dives are to be conducted at an altitude of
6000 feet (1829 m) on a no-decompression schedule.
The first is to be to 80 feet of fresh water (ffw) (24.4 mfw)
for 20 minutes; the second to 60 ffw (18.3 mfw) for
25 minutes. Find the surface interval required to complete the dive schedule in

minimum

time.

Solution:

10.12.4 Calculations for Diving at Altitude

The Cross

correction tables, as modified by Bell and

Borgwardt, are shown

in

Table 10-2. This table

identical to that presented by Cross
that

it

has been modified to

and rate of ascent. The table
1.

is

is

970), except
(
account for fresh water

— NOAA

used as follows:

Diving Manual

10-2, the theoretical

ocean depth

in

fsw

(ffw) (24.4

mfw)

in a lake

whose surface altitude

is

1

The depth of the planned dive is found in the
column on the left marked "Measured Depth."

October 1991

From Table

that corresponds to a depth of 80 feet of fresh water

97 fsw (29.6 msw) and that for a depth of
60 feet of fresh water (18.3 mfw) is 73 fsw (22.2 msw).

6000

The

feet

is

sea-level

decompression table (Appendix B) must
msw) and 80 fsw

therefore be entered at 100 fsw (30.1
(24.4 msw), respectively.

A

20-minute dive

to a

TOD

10-25

Section 10

Table 10-2
Theoretical Ocean Depth (TOD)
fsw) at Altitude for a
Given Measured Diving Depth

(in

i

Measured

Altitude in feet

1000

Depth*

2000

4000

3000

TOD
10
20
30

10
20
29

40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250

39
49
59
68
78
88
98
107
117
127
137
146
156
166
176
185
195
205
215
224
234
244

10
20
30
40

10

11

11

21

22
33
44
54
65
76
87
98
109
120

23
34
45
56
68
79
90
102
113
124
135
147
158
169

31

42
52
63
73
84
94
105
115
126
136
147
157
168
178
189
199
210
220

51
61

71
81
91
101

111
121
131

142
152
162
172
182
192
202
212
222
233
243
253

131
141

231
241

5000
fsw

in

12

252
262

261

271

281

272

282

293

9
18
27

9
17
26

34
43

51

9000

10000

63
76
88

73

85
97
109
122
134
146
158
170
182
195
207
219

101

114
126
139
152
164
177
190
202
215
227
240
253
265
278

231

243
255
268
280
292
304

14
27

13

26
39
52
66
79
92
105
118

51

61

152
164
176
187
199
211
223

234
246
258
270

8000

13
25
38

24
36
49

141

192
203
214
226
237
248
260

7000

at Altitude

12
23
35
47
59
70
82
94
105
117
129

152
163
174
185
196
207
218
228
239
250

181

6000

41

55
68
82
95
109
123
136
150
164
177

131

144
157
171

184
197
210
223
236
249
262
276
289
302
315
328

291

303
316

14
28
43
57
71

85
99
113
128
142
156
170
184
199
213
227

191

205
218
232
245
259
273
286
300
314
327

241

255
270
284
298
312
326
340
355

341

Stops
10

10
20
30
40
50

10
19

9
18

31
41
51

10
20
30
40
49

29
38
48

28
37

46

35
44

62

59

57

55

53

21

8
15
23
30

41

8
16
24
32
40

49

47

8
16

25
33

«

7
14

7
15
22

21

38

29
37

28
35

46

44

42

Ascent Rate
60

is not gauge depth. Table takes into account the effect of water density. The zero feet altitude column is for
a freshwater lake at sea level. According to Bell and Borgwardt (1976), these tables are theoretically correct (although
they do not account for seasonal or daily barometric changes) but are still untested.
Adapted from Bell and Borgwardt (1976)
*

Measured depth

diving

in

of 100 fsw (30.1
tive

for a

msw)

places the diver in the

F

repeti-

group (Appendix B). The no-decompression limit
TOD of 80 fsw (24.4 msw) is 40 minutes (Appen-

dix B). Therefore, the diver can have no
15 minutes of residual nitrogen time

second dive; the diver

move from

the

F group

is

in the

to the

C

C

when

had taken place
will

maximum

be passing through on the

elevation the diver

trip out.

more than
starting the

repetitive group.

10.12.5 Correction

To

group requires 2 hours

Neither

gauge

actual depth.

is

often

Depth Gauges

nor capillary depth gauges pro-

oil-filled

25 minutes. In high-altitude diving, the

dive

off

vide accurate depth indications

and 29 minutes.
A dive schedule for an altitude dive at 6000 feet
(1829 m) would therefore be 80 fsw (24.4 msw) for
20 minutes, 2 hours and 29 minutes of surface interval
time, followed by a 60-fsw (18.3 msw) dive for
last

at the

Oil-filled

when used

at altitude.

depth gauges are designed to read

pressure of

1

ATA. At reduced atmospheric

feet at a

pressure,

the gauge will read less than zero (unless there

is

a pin

that stops the needle at zero); in the water, such a
will give a

reading that

is

shallower than the

The depth readings can be corrected by

followed by a trip through mountain passes at an elevation

adding a depth that

higher than that used in the calculation. In this event,

the atmospheric pressure at the altitude site and

it is

good practice

10-26

to calculate the last dive as

though

it

1

ATA. Table

is

equal to the difference between

10-3 shows

NOAA

mean atmospheric

Diving Manual

pressures

—October 1991

4

Diving Under Special Conditions

Table 10-3
Pressure Variations with Altitude
Accordingly, special precautions and extra plan-

light.

ning are required for night dives.
Altitude,

Pressure,

Pressure,

Pressure,

ft

mmHg

psl

atm*

Oil-filled

760.0
732.9
706.7
681.2
656.4
632.4
609.1
586.5
564.6
543.3
522.8
502.8
483.5
464.8
446.6
429.1
412.1
395.7
379.8
364.4
349.5

1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
16000
17000
18000
19000
20000

14.70
14.17
13.67
13.17
12.70
12.23
11.78
11.35
10.92

2.37
3.53

10.51

9.73
9.35
8.99

8.64
8.31

7.97
7.66
7.35
7.04
6.76

night to have correct marking lights that are clearly

6.75
7.73
8.72
9.67
10.58
11.47
12.35
13.16
13.98
14.76
15.54
16.25
16.96
17.67
18.28

0.500
0.479
0.461

light

is

recom-

Predive checks are particularly important at night,

because the limited

precludes even a cursory

visibility

inspection of equipment once in the water. Night diving in fog or heavy rain should be avoided because

it is

easy for the diver to lose sight of the lights on the dive
boat or those carried by other divers.

Each diver should carry
charge sufficient to
pated for the dive.
the diver in

NOAA

light or small strobe

mended.

U.S. standard atmosphereSource:

chemical

attached to the anchor line or downline

(1979)

A

last

a reliable diving light with a

longer than the time antici-

second

light

advisable, because

is

common. The light should be secured to
a manner that permits the illumination of

failure of lights
*

A

can see under water.

5.70

0.521

which case other steps are approIt is also important at

liveboating, in

visible to other vessels in addition to a light the divers

4.61

0.772
0.743
0.715
0.688
0.662
0.636
0.612
0.588
0.565
0.542

The boat

priate (see Section 8.10.1)).

1.22

0.801

especially critical at night.

is

must be secure before the diver enters the water (except

ft

when

1.000
0.964
0.930
0.896
0.864
0.832

10.11

Anchoring

gauge
correction,

is

A

watches, gauges, or navigational aids.

chemical

light

should be taped to the snorkel or tank valve for under-

and the corrections necessary

at various altitudes
oil-filled

for

Because of the reduced density of the

trapped

in

the capillary gauge at altitude, less water pressure

is

air

required than at sea level to compress the air to a given

volume. As a

water and surface

The

gauges.

result, the capillary

gauge

will indicate a

depth greater than the actual depth. Because of the
question about the accuracy of these gauges, a meas-

visibility in

case the dive lights

fail.

team should be careful to maintain dark adaptation before and during the dive (see
Section 2.8.2). Every effort should be made to avoid
shining diving lights directly into the eyes of crew
members, both before and during the dive. Once in the
water, it is easy to keep track of a buddy's light at
entire night dive

night; however,

one diver

may

occasionally lose another

because the glare of the light being held prevents seeing

ured downline should be used.

the buddy's light. In this case, the divers should turn
off or otherwise shield their lights momentarily, adjust

10.12.6

A

Hypoxia During Altitude Diving

diver surfacing from an altitude dive

from a breathing gas
sure
low.

is

As

which the oxygen

in

relatively high to

an atmosphere

may

a result, the diver

is

moving

If a

partial pres-

in

buddy's

their eyes, locate the

ately turn their lights

which

it

is

experience symptoms of

hypoxia and breathing difficulty for a period after the

team

is

left

and then immedi-

light,

back on.

with only one light, the dive should

be terminated. Lights

may

also be used to signal the

surface; sweeping the light in a wide arc over the head
is

the standard 'pick

me

up' signal.

At

night, a whistle

or chemical flare should also be carried in case of light

dive (see Section 3.1.3.1).

failure.

Shore entries are more hazardous

10.13

NIGHT DIVING

Night diving exposes the diver

to

an entirely different

aspect of the underwater world. Marine

more

or less

colors than

abundant and appear

is

familiar to the diver during the

may

be

to be of different

day may appear changed

to the extent that orientation

October 1991

life

the case during the day. Areas that are

landmarks may be

difficult

— NOAA

at night

because

such features as rocks, algae, holes, waves, and rip
currents are not easily seen. Entries from boats, piers,

and locating familiar

even with good

Diving Manual

artificial

and other surface platforms require special caution so
that the diver avoids hitting objects on or below the
surface.
If

a shore exit requires a particular approach because of

in-water obstacles, two shore lights in a line can serve
as a navigational aid for divers.

When

possible, experi-

enced night divers should be buddied with novice night

10-27

Section 10

Making

divers.

the entry at dusk rather than at night

reduces some of the problems of night diving.

When-

ever possible, the area to be dived by night should

first

such operations are undertaken at altitudes

in

tions (see Section 10.12).

be dived by day to provide the divers with entry and
exit experience.

If

tion.

excess of 1000 feet, divers should take special precau-

Three major conditions must be considered when

dams

planning dives at

in the

northwest (or any other)

region:

NOTE

Water temperature

(1)

(2) Visibility

Decompression diving is more hazardous at
night than during the day and should be
avoided if possible. To be conducted safely,
night decompression dives need considerable advance planning.

Flow

(3)

velocities.

Water temperatures may vary from

slightly

ing in winter to almost 80 °F (27 °C) in

above freez-

summer. Divers

should be protected from the elements before diving

and during surface intervals

in

both

warm and

cold

seasons, because of the potential for heat exhaustion or

Most research diving
when rivers
and melting snow and fish migrations

hypothermia (see Section
In night decompression diving, lights

decompression

line are

marking the

necessary to ensure that the

divers conduct their in-water decompression near the

dive boat or other platform. Divers operating in a

decompression mode should not swim out of sight of
lines or lights that will

pression line

guide them back to the decom-

and dive platform.

dams occurs during

at

from rains

swell

occur.

The

spring runoff produces low underwater vis-

DIVING IN

from

silt

[0-0.6

Hydroelectric

dams

across rivers in the northwest United

States incorporate bypass and collection systems for
the protection of migrating fish species such as salmon

and steelhead trout (Figure 10-12). Because fish passage research is conducted at many of these dams,
NOAA and other scientist/divers are often required to
inspect, maintain, install, or retrieve research gear
such as flow meters and fish guidance and passage
devices. If time and circumstances permit, a shutdown
and de-watering of turbine intakes, gatewells, and fish
ladders is the safest and most efficient manner for
performing work on dam bypass and collection facilities. However, safe and efficient diving operations can
be performed within and on the upstream and downstream faces of dams even when these are
ing.

The agency operating the dam

inspector

who

still

operat-

supplies a diving

coordinates such dives, because strict

cooperation between the divers and the powerhouse
operations staff

is

mandatory

to ensure proper clear-

ances for turbine shutdown and flow gate closures.

10.14.1 Diving at

The

Dams

safety aspects of diving at

to those prevailing in cave,

dams

are comparable

wreck, and over-bottom

in the

carried by flooding waters. In

in clear water, the

DAMS AND RESERVOIRS

m]

Snake River)
warmer months,
algae blooms may cause low underwater visibility. Even
ibility (e.g., 0-2 feet

sediment disturbed by divers reduces

visibility so that the

10.14

10.8).

the spring freshet,

small amount of natural light

penetrating the gatewells

is

reduced. Although diving

minimally effective, the problems
associated with low visibility at dams can be overcome

lights are only

by careful planning, studies of the blueprints and plans
dam, and familiarization with the research devices

of the
to

be used during the dive. Objects can be recognized

by touch and orientation maintained, even in zero underwater visibility, if the diver is familiar both with the
gear and the dam's structures. The velocity of the flow

and the force of the suction through screens or orifices
dams can be eliminated or controlled by coordinat-

at

ing the diver's actions carefully with

dam

operations

personnel before the dive.

When

bypass systems become fouled or clogged by

sometimes are required

river debris, divers

dam

gatewells to clear the system's orifices.

to enter

The

haz-

ards of gatewell diving can be reduced by taking ade-

quate precautions to ensure that the influence of suc-

caused by the large hydrostatic head,

tion,

is

avoided

which eliminate
the need for buoyancy compensators, should be worn to
avoid the danger of loose equipment becoming caught
(see Section 5.4). Procedures are much the same as
those for umbilical diving, whether the diver is using
surface-supplied air or scuba cylinders. At a miniat the orifice.

mum,

Variable-volume

suits,

a tender line to the diver should be used for

diving,

contact and signals, although hard wire communica-

dam
dam

and many of the same procedures are used in
diving. Predive planning by the dive team with

personnel will help to ensure a safe diving opera-

transport the diver to and from the orifice level and the

10-28

tion

is

preferred.

A

diver cage should be provided to

NOAA

Diving Manual

— October 1991

Diving Under Special Conditions

Figure 10-12

Cross Section of a Typical Hydroelectric
Dam in the Northwestern United States

Courtesy George

Swan

Figure 10-13 shows a diver ready to be lowered into a

be performed in much the same manner as they are
conducted when diving amid pools and boulders in

dam

rivers with relatively fast currents (see Section 10.15).

dam, and

intake deck of the

a safety diver

gatewell. Procedures to shut

system immediately

in

the event of an

be coordinated with the

dam

down

is

required.

the bypass

emergency should

operations controller before

Work

on fish ladders (Figure 10-14) should be
performed during off-season when the number of
upstream adult fish runs is low and water flows can be
cut off for a period of time, which permits the task to
in

the open

impractical, and diving
plete the task.

diving tasks must be performed on the upstream

dam, turbines and/or spillway gates must be

shut down. Adjacent units should also be shut

the dive.

be completed

When

face of a

Flows

air.

is

On

rare occasions this

is

then the only way to comladders appear quite turbulent

in fish

when viewed from above; however,

baffles or weir walls

safety

and

to

reduce flows near the work

can be transported

to

and from the

the intake deck of the

and crane.

A

level of

dam by means

down

station.

for

Divers

work and

to

of a diver cage

boat or floating platform also

is

useful for

the safety (standby) diver and equipment. Diving on

the

downstream face of

a

dam

is

handled similarly;

flows are shut off to avoid sweeping the diver off station.

Divers should avoid water contaminants, such as

are regularly spaced perpendicularly to the flow, and

spilled

the water flows either over the top of each weir or

routine operation and maintenance of

through large rectangular orifices located

byproducts generated by underwater cutting and welding.
These contaminants can become concentrated in confined areas such as gatewells, where the water level
may be 5 to 20 feet (4.6 to 6. m) below the deck of the
dam. Before starting or continuing a dive, any contaminant discovered should be eliminated from the dive

of the baffle wall.
walls,

(2.4

flows

as

When
high

8.0

as

mps) may be encountered

with the orifices but
to either side or

may

at

the base

diving in pools between baffle
feet
in

per

second

be as low as 1.0 fps (0.3 mps)

above the

line of the orifice.

By using

safety lines and exercising caution, diving tasks

October 1991

— NOAA

(fps)

areas directly in line

Diving Manual

may

petroleum or lubrication products used

1

dams

in

the

or gaseous

1

site.

10-29

Section 10

Figure 10-13
Diver Protected by

be Lowered

Into

Figure 10-14

Cage and Ready

Dam

A

to

Fish

Dam

Gatewell

in

Ladder at a Hydroelectric
the Northwest

Courtesy George

Courtesy George

Swan

water opening; (2) a pierlike structure set out from the
shoreline that supports turbine pumps; (3) a combination pier/vault created

by closing

in the

area under a

pier with driven sheet piling or other material;

10.14.2 Diving at

Pumping
The impact

Water Withdrawal and

(4) a simple

Sites

single intake line extending to a depth

of water withdrawal on populations of

juvenile fish in the

Columbia Basin of the northwest

Swan

arrangement of a

water elevation.

Some

pump

and

or siphon with a

below the low

vaultlike structures

may have

trash rack bars in front of the fish screening.

A good

those seeking permits to install and operate water with-

and stable work boat serves as the best diving
sites and expedites diver travel between sites, but divers should be
careful when entering the water from a small boat.
Some sites with enclosed fish screens must be accessed
by ladder or small crane. For such a diving task, tanks,
weight belts, masks, and fins are lowered by lines to the
divers once they are in the water; this procedure is

drawals to

reversed after the dive.

United States

Water

is

a major concern to fisheries agencies.

withdrawn from the Columbia and Snake
Rivers via pumps and siphons and is then used for
is

irrigation, industrial applications, drinking water, ther-

mal cooling,

fish

and

wildlife propagation,

and other

domestic needs. Before water can be withdrawn from
these rivers, the U.S.

ly,

Army Corps

of Engineers requires

install fish protective facilities. Periodical-

divers are required to inspect fish screens at water

withdrawal

sites to

monitor the condition of the screening

and the status of compliance with established

fish

screening criteria.

Several basic types of water withdrawal sites are

common:

10-30

(1) a vaultlike structure with a screened under-

platform for accessing most withdrawal

Diving
safely

if

in

and around pump intakes can be performed
and the neces-

certain hazards are recognized

sary precautions are taken. In general, intake velocities

are not high enough to present a suction hazard,

although pumps should be shut down,

if

possible.

To

perform an inspection during the pumping season,

NOAA

Diving Manual

—October 1991

Diving Under Special Conditions

however, the approach velocities
ured while the

pumps

may have

to be

meas