Rebreathers: Minimizing Risks O2-CCRB

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CLOSED CIRCUIT OXYGEN APPARATUS

MINIMIZING RISKS FOR IMPROVED EFFICIENCY

Gregory S Sanders

U S

Rsh and Wildlife Service

2140 Eastman, Suite 100

Ventura, CA 93003

and

Fred Wendell

California Department of

ish

and Game

213 Beach Street

Morro Bay

I

CA 93442

The use of closed-circuit oxygen

underw ter

breathing

pp r tus

rebreathers has been limited

y

inherent risks associated with oxygen diving.

Advantages over other diving modes in applications where efficiency is enhanced

y

bubble-free environment has led to an increase in closed-circuit apparatus use

y

non-military divers.

he

California Department

of

ish nd Game and the U.S. Fish

nd Wildlife Service are using closed-circuit apparatus in lieu

of

conventional scuba

to

capture sea otters

(Enhydra lutris)

along the California coast.

With

proper training and

strict operational guidelines, closed-circuit apparatus may be used safely for scientific

div ing applications. However, operational needs must justify the use

of

this

equipment.

EVOLUTION O CLOSED·CIRCUIT OXYGEN APPARATUS

An engineer named Henry Fleuss has been credited with developing the first fully

independent diving apparatus (Sweeney 1955). His apparatus was a simple closed-circuit oxygen

rebreather consisting of a full face mask with two breathing tubes running to a breathing bag worn on

the diver s back. Oxygen was supplied to the bag by a copper tank filled to a pressure of 30 atm

(about 315 kg/cm

[450 psi]). The diver s exhaled breath would pass into the bag where carbon

dioxide was removed by rope yarns soaked in a solution of caustic potash. The cleaned gas was

then recirculated to the diver to be rebreathed.

Fleuss first tested his apparatus in 1879 (Dugan 1965). He succeeded in staying submerged

in a tank a few feet underwater for over an hour. His first open-water dive was in Wootten Creek, Isle of

Wight. Medical texts of that time stated that breathing pure oxygen could cause excitabil ity

a

feverish rise in body temperature. (Paul Bert s classic, La Pression Barametrique, describing

oxygen toxicity was published that same year, but Fleuss was apparently unaware of it.) To reduce the

potential risk of breathing pure oxygen, Fleuss filled his breathing bag with air before diving into the

creek. He then added oxygen with a hand valve

as

the volume in the bag diminished. During the

course of the dive, Fleuss reached a depth of 5 m At some point, he voluntarily turned off his oxygen

supply to see what would happen. He immediately became unconscious and was hauled to the

surface by friends who had attached a safety line to him before the descent. Fleuss appears to have

suffered from a gas embolism. He survived and was diving again within a few weeks.

Fleuss apparatus was commercially developed by Siebe, Gorman and Company, and was the

precursor to mine-safety devices, respirators used by firemen, submarine escape apparatus, and the

closed-eircuit oxygen rebreathers used by underwater swimmers in World War II

Sir Robert

H

Davis perfected the Fleuss apparatus in 1915 (Doukan 1957). The Davis

p://archive.rubicon-foundation.org

CLOSED CIRCUIT OXYGEN APPARATUS

MINIMIZING RISKS FOR IMPROVED EFFICIENCY

Gregory

S

Sanders

U S

Fish and Wildlife Service

2140 Eastman. Suite 100

Ventura. CA 93003

and

Fred Wendell

California Department of Fish and Game

213 Beach Street

Morro

ay

93442

The use

of

closed-circuit oxygen

underw ter

breathing apparatus

rebreathers has been limited

y

inherent risks associated with oxygen diving.

Advantages over other diving modes in applications where efficiency is enhanced

y

bubble-free environment has led

to

an increase

in

closed-circuit apparatus use

y

non-mifitary divers. The California Department

of Fish

and Game and the U S Fish

nd

Wildlife Service areusing closed-circuit apparatus in lieu of conventionalscuba to

capture sea otters

(Enhydra lutris)

along the California coast.

With

proper training and

strict operationalguidelines. closed-circuit apparatus may be used safely for scientific

diving applications. However. operat ional needs must justi fy the use

of

this

equipment.

EVOLUTION

OF

CLOSED·CIRCUIT OXYGEN APPARATUS

An engineer named Henry Fleuss has been credited with developing the first fUlly

independent diving apparatus (Sweeney 1955). His apparatus was a simple closed-circuit oxygen

rebreather consisting of a full face mask with two breathing tubes running to a breathing bag worn on

the diver s back. Oxygen was supplied to the bag by a copper tank filled to a pressure of 30 atm

(about 315 kg/cm

[450 psi]). The diver s exhaled breath would pass into the bag where carbon

dioxide was removed by rope

yarns

soaked in a solution of caustic potash. The cleaned gas was

then recirculated to the diver to be rebreathed.

Fleuss first tested his apparatus in 1879 (Dugan 1965). He succeeded in staying submerged

in a tank a few feet underwater for over an hour. His first open-water dive was in Wootten Creek. Isle of

Wight. Medical texts of that time stated that breathing pure oxygen could cause excitability

or

a

feverish rise in body temperature. (PaUl Bert s classic. La Pression Barametrique, describing

oxygen toxicity was published that same year, but Fleuss was apparently unaware of it.) To reduce the

potential risk of breathing pure oxygen, Fleuss filled his breathing bag with air before diving into the

creek. He then added oxygen with a hand valve as the volume in the bag diminished. During the

course of the dive, Fleuss reached a depth of 5 m At some point. he voluntarily turned off his oxygen

supply to see what would happen. He immediately became unconscious and was hauled to the

surface by friends who had attached a safety line to him before the descent. Fleuss appears to have

suffered from a gas embolism. He survived and was diving again within a few weeks.

Fleuss apparatus was commercially developed by Siebe, Gorman and Company, and was the

precursor to mine-safety devices, respirators used by firemen. submarine escape apparatus, and the

closed-eircuit oxygen rebreathers used by underwater swimmers in World War II

Sir Robert H. Davis perfected the Fleuss apparatus in 1915 (Doukan 1957). The Davis



International Pacifica Scientific iving 99

Submarine Escape Apparatus was designed solely as a life-saving device intended for rescue of

submariners trapped in sunken vessels. In 1936, the Italian Navy built and tested an underwater

electric torpedo designed to carry two divers equipped with the Davis apparatus (Dugan 1965). The

divers, called charioteers, could sneak through torpedo nets and fasten explosives under anchored

ships. Through trial and error, the charioteers became an impressive secret weapon at the beginning

of World War II. Not only did the closed-circuit oxygen apparatus allow the divers to remain underwater

for extended periods of time, but the device was also quiet and produced no telltale bubbles that

could alert

an

enemy to the divers presence. Other countries soon followed the Italians lead and

developed teams of underwater saboteurs.

The United States Office of Strategic Services pioneered the use of closed-circuit oxygen

rebreathers by American forces (Butler 1985). Divers used

an

oxygen rebreather designed by Dr.

J Lambertson called the Lambertson Amphibious Respiratory Unit (LARU). The U.S. Navy has

continued to use oxygen rebreathers for its Underwater Demolition (UDT) and Sea Air Land (SEAL)

Teams. The LARU was replaced by the Emerson-Lambertson Underwater Breathing Apparatus

(Emerson Apparatus), and in the late 1970 s, the Emerson was in turn succeeded by the German

made Dreager LAR V

Closed-circuit oxygen apparatus was used recreationally as early as 1939. Captain J Y

Cousteau, co-inventor of the aqualung, built a rebreathing apparatus using a gas mask, a canister of

soda lime, a small oxygen bottle, and a length of motorbike innertube (Cousteau 1950). His initial

dives with the oxygen rebreather proved to

be

nearly fatal. On two separate occasions, Cousteau

became unconscious underwater and nearly drowned. He quickly lost interest in oxygen diving.

Recreational d ivers used oxygen rebreathers through the 1950 s. Most recreational

rebreathers were either manufactured in Europe

or

were homemade using mine-safety equipment

and military surplus materials. During the late 1950 s and early 1960 s, the open-circuit air scuba

developed by Cousteau and Gagnan (1943) quickly gained in popularity, and closed-circuit oxygen

scuba was eventually discontinued by recreational divers. Diving with air greatly extended dive

depths and did not require caustic carbon dioxide absorbents. Oxygen toxicity concerns were traded

for potential decompression sickness and inert gas (nitrogen) narcosis.

Oxygen toxicity was not clearly understood by early closed-circuit oxygen divers. They knew

that oxygen became toxic at depth, but there was no agreement as to what maximum depth an

oxygen rebreather could be used. Several safe diving depths were proposed, ranging from

7 5·

m

25

- 100

ft

By

the 1950 s, most texts limited oxygen diving to a maximum depth

of

10.6 m

35

ft).

Hans Hass, an Austrian diver and early underwater explorer, used closed-circuit oxygen

rebreathers for scientific applications and underwater photography. From 1942 to 1953, he and his

companions logged about 2000 hours with oxygen rebreathers on expeditions in the Mediterranean,

the Red Sea, the Azores, the Caribbean, and the Galapagos (Hass 1975). He generally used a safety

limit of 20 m 65 ft), but occasionally made dives as deep as 33 m (100 ft). His dive team experienced

two fatal diving accidents. One was attributed to heat and overexertion, combined with a pre-existing

heart condition, that led to heart failure while diving at 2 m. Another diver apparently succumbed to

anoxia after entering the water without properly purging air from his rebreather apparatus.

In The Unsinkable Sea Otter, one in a series of films documenting underwater life, J Y

Cousteau s dive team used closed-circuit oxygen rebreathers to film sea otters. Sea otters allowed

the bubble-free divers to approach them closely underwater. Some even accepted food offered by

the divers.

In the late 1980 s, biologists from the California Department of Fish and Game and later the

U.S. Rsh and Wildlife Service began using oxygen rebreathers to capture sea otters. Divers used a

rebreather, underwater vehicle, and specialized trap to capture unwary sea otters resting on the

surface. Captures facilitated research efforts, and were required for an experimental translocation of

sea otters. Oxygen rebreathers continue to be used for this purpose.

88

tp://archive.rubicon-foundation.org

nternational acificaScientific iving 99

Submarine Escape Apparatus was designed solely as a life-saving device intended for rescue of

submariners trapped in sunken vessels. In 1936, the Italian Navy built and tested an underwater

electric torpedo designed to carry two divers equipped with the Davis apparatus (Dugan 1965). The

divers, called charioteers, could sneak through torpedo nets and fasten explosives under anchored

ships. Through trial and error, the charioteers became

an

impressive secret weapon at he beginning

of World War II. Not only did the closed-circuit oxygen apparatus allow the divers to remain underwater

for extended periods of time, but the device was also quiet and produced no telltale bubbles that

could alert an enemy to the divers' presence. Other countries soon followed the Italians' lead and

developed teams of underwater saboteurs.

The United States Office of Strategic Services pioneered the use o closed-circuit oxygen

rebreathers by American forces (Butler 1985). Divers used an oxygen rebreather designed by Dr. C.

J Lambertson called the Lambertson Amphibious Respiratory Unit (LARU). The U.S. Navy has

continued to use oxygen rebreathers for its Underwater Demolition (UDT) and Sea Air Land (SEAL)

Teams. The LARU was replaced by the Emerson-Lambertson Underwater Breathing Apparatus

(Emerson Apparatus), and in the late 1970's, the Emerson was in turn succeeded by the German

made Dreager

LAR

V.

Closed-circuit oxygen apparatus was used recreationally as early as 1939. Captain

J

Y.

Cousteau, co-inventor of the aqualung, built a rebreathing apparatus using a gas mask, a canister of

soda lime, a small oxygen bottle, and a length of motorbike innertube (Cousteau 1950). His initial

dives with the oxygen rebreather proved to be nearly fatal. On two separate occasions, Cousteau

became unconscious underwater and nearly drowned. He quickly lost interest in oxygen diving.

Recreational divers used oxygen rebreathers through the 1950's. Most recreational

rebreathers were either manufactured in Europe

or

were homemade using mine-safety equipment

and military surplus materials. During the late 1950's and early 1960's, the open-circuit air scuba

developed by Cousteau and Gagnan (1943) quickly gained in popularity, and closed-circuit oxygen

scuba was eventually discontinued by recreational divers. Diving with air greatly extended dive

depths and did not require caustic carbon dioxide absorbents. Oxygen toxicity concerns were traded

for potential decompression sickness and inert gas (nitrogen) narcosis.

Oxygen toxicity was not clearly understood by early closed-circuit oxygen divers. They knew

that oxygen became toxic at depth, but there was no agreement as to what maximum depth an

oxygen rebreather could be used. Several safe diving depths were proposed, ranging from 7.5 - 33

m 25 - 100 ft

By

the 1950's, most texts limited oxygen diving to a maximum depth of 10.6 m

35

ft .

Hans Hass, an Austrian diver and early underwater explorer, used closed-circuit oxygen

rebreathers for scientific applications and underwater photography. From 1942 to 1953, he and his

companions logged about 2000 hours with oxygen rebreathers on expeditions in the Mediterranean,

the

Red

Sea, the Azores, the Caribbean, and the Galapagos (Hass 1975). He generally used a safety

limit of 20 m (65

ft

but occasionally made dives as deep as 33 m (100 ft). His dive team experienced

two fatal diving accidents. One was attributed to heat and overexertion, combined with a pre-existing

heart condition, that led to heart failure while diving at 2

m.

Another diver apparently succumbed to

anoxia after entering the water without properly purging air from his rebreather apparatus.

In The Unsinkable Sea Otter, one in a series of f ilms documenting underwater life, J Y.

Cousteau's dive team used closed-circuit oxygen rebreathers to film sea otters. Sea otters allowed

the bubble-free divers to approach them closely underwater. Some even accepted food offered by

the divers.

In the late 1980's, biologists from the California Department of Fish and Game and later the

U.S. Fish and Wildlife Service began using oxygen rebreathers to capture sea otters. Divers used a

rebreather, underwater vehicle. and specialized trap to capture unwary sea otters resting on the

surface. Captures facilitated research efforts. and were required for an experimental translocation of

sea otters. Oxygen rebreathers continue to be used for this purpose.



Sanders

Wendell: Closed circuit Oxygen Apparatus

oday the closed-circuit oxygen rebreather is used primarily fo r military operations

Recreational use

is

virtually non-existent, and scientific applications are limited to very specialized

projects.

EVOLUTION CLOSED CIRCUIT OXYGEN PP R TUS

FOR SE OTTER C PTURES

The sea otter, Enhydra lutris is a small marine mammal that inhabits near-shore environments

of the North Pacific rim Figure 1). Individuals generally range from 20-40 kg in weight and 120-140 cm

in length Riedman and Estes 1990). Sea otters were hunted nearly to ext inct ion shortly after their

discovery by European explorers. By 1911, only remnant populations remained. Today, sea otter

populations in Alaska have recovered well. In California, sea otters number about 2,000 animals, and

are currently listed as a threatened species under the Endangered Species Act. Research into their

life history and behavior has prompted researchers to develop means of capturing and tagging otters.

Currently there are three methods by which the majority of sea otters are captured. hefirst

requires the use of a fast boat, a skilled boat operator, and a capture person with a long-handled dip

net.

he

boat runs at high speed towards an otter resting on

the

surface, and the capture person

literally dips the animal out of the water. This method generally favors capture of juvenile males that

are found resting in open water outside of kelp beds.

he second

method uses f loating entangl ing nets s imi lar to g il l nets

used

by fishermen.

Using nets is not without risk to the otters. The nets must be monitored closely to prevent drowning

or injUry of captured animals. Non-target species such as seals, sea lions,

or

sea bi rds may also be

captured.

Figure

A sea otter resting in a kelp bed.


Sanders


Today the closed circuit oxygen rebreather is used primarily fo r military operations

Recreational use is virtually non-existent, and scientific applications are limited to very specialized

projects.

EVOLUTION CLOSED CIRCUIT OXYGEN PP R TUS

FOR SE OTTER C PTURES

The sea otter, Enhydra lutris is a small marine mammal that inhabits near-shore environments

of the North Pacific rim Figure 1). Individuals generally range from 20-40 kg in weight and 120·140

cm

in length Riedman and Estes 1990). Sea otters were hunted nearly to ext inct ion shortly after their

discovery by European explorers. By 1911, only remnant populations remained. Today. sea otter

populations in Alaska have recovered well. In California, sea otters number about 2,000 animals, and

are currently listed as a threatened species under the Endangered Species Act. Research into their

life history and behavior has prompted researchers to developmeans of capturing and tagging otters.

Currently there are three methods by which the majority of sea otters are captured. The first

requires the use of a fast boat, a skilled boat operator, and a capture person with a long-handled dip

net. The boat runs at high speed towards an otter resting on the surface, and the capture person

literally dips the animal out of the water. This method generally favors capture of juvenile males that

are found resting in open water outside of kelp beds.

The second

method uses f loat ing entangl ing nets similar to gil l

nets used by

fishermen.

Using nets is not without risk to the otters. The nets must be monitored closely to prevent drowning

or

injUry of captured animals. Non-target species such

as

seals, sea lions,

or

sea birds may also be

captured.

Figure A sea otter resting in a kelp bed.



International Pacifica Scientific Diving...

The third method uses divers to sneak up under otters resting on the surface usually in a kelp

bed. This method is somewhat more selective and is discussed in more detail below.

In Califomia sea otters are generally associated with kelp forest Macrocystis and Nereocystis

communities. Aside from foraging interacting with other otters and grooming otters will spend

significant periods of time resting. Often resting sea otters will wrap themselves in a kelp bed canopy

and sleep. Divers may take advantage of this behavior to sneak up under an otter and capture it.

Captures of sea otters using divers was pioneered by the California Department of Fish and

Game. Early attempts used a metal basket-shaped framework that supported a net that could be

pursed closed to trap an otter. This device was later refined with the basic design intact and is today

called the Wilson trap Figure

2

named after its inventor Ken Wilson a Department of Fish and Game

biologist. The first dives were made using two divers using standard air scuba. A long pole was

attached

to

the Wilson trap. The divers pushed and pulled this unwieldy contraption through the kelp

forest located a resting otter then pushed the trap under the animal. Approximately 80-90 sea otters

were captured using this method but it obviously took a great deal of effort. In addition many capture

attempts failed when sea otters swam away after seeing hearing or even smelling the bubbles

produced by the approaching divers.

Figure 2. Diver with Wilson Trap and underwater vehicle.


nternational Pacifica Scientific

Diving

The third method uses divers to sneak

up

under otters resting on the surface, usually in a kelp

bed. This method is somewhat more selective and is discussed in more detail below.

In Califomia, sea otters are generally associated with kelp forest

Macrocystis

and Nereocystis

communities. Aside from foraging, interacting with other otters, and grooming, otters wil l spend

significant periods of time

resting. Often. resting sea otters will wrap themselves in a kelp bed canopy

and sleep. Divers may take advantage of this behavior to sneak up under an otter and capture it.

Captures of sea otters using divers was pioneered by the California Department of Fish and

Game. Early attempts used a metal basket-shaped framework that supported a net that could be

pursed closed to trap an otter. This device was later refined with the basic design intact and is today

called the Wilson trap Figure 2 . named after its inventor, Ken Wilson, a Department of Fish and Game

biologist. The first dives were made using two divers using standard air scuba. A long pole was

attached to the Wilson trap. The divers pushed and pulled this unwieldy contraption through the kelp

forest, located a resting otter, then pushed the trap under the animal. Approximately 80·90 sea otters

were captured using this method, but it obviously took a great deal of effort. In addition, many capture

attempts failed when sea otters swam away after seeing, hearing,

or

even smelling the bubbles

produced by the approaching divers.

Figure Diver with Wilson Trap and underwater vehicle.



Sanders

&

Wendell Closed circuit Oxygen Apparatus

A significant improvement was made by using

an

underwater vehicle to push the trap and pull

the diver. The underwater vehicle allowed each member

a dive team

to

carry a trap. This increased

the odds of one diver capturing

an

otter and allowed for the possibility of two otters being captured in

one dive. The vehicles also enabled the divers to travel faster. Bubbles produced by the diver

surfaced slightly behind the actual position of the diver, and the quantity of the bubbles was

somewhat reduced since the diver did not need to work as hard. A compass was mounted on the

vehicle to assist in navigation. Although efficiency was improved, the bubbles still provided clues to

resting otters that divers were present.

In 1988, the California Department of Fish and Game began to use closed-circuit oxygen

scuba in conjunction with the underwater vehicles and Wilson traps for sea otter captures. The U.S.

Fish and Wildlife Service followed suit with their own dive program also using closed-circuit apparatus.

The rebreathing apparatus increased the effectiveness of the diving technique dramatically. There

were no bubbles to alert a resting otter or give away the divers' position. Divers were allowed to take

more time to locate and position their traps as well as select a specific target animal. Recapture of

otters was also enhanced because there were few clues for an otter to key on when a diver

approached. This improved efficiency came with added risks associated with oxygen diving.

Adequate training was essential for minimizing these risks.

PRINCIPLES OF CLOSED-CIRCUIT OXYGEN DIVING

Conventional open-circuit scuba divers utilize air as a breathing medium, and exhaled gases

are released directly into the water. Air contains approximately 80 nitrogen and 20 oxygen. The

nitrogen is considered inert and

is

not consumed during respiration. Each time

an

open-circuit diver

takes a breath, only a small percentage of the available oxygen is used; the rest is lost when the

diver exhales. The open-circuit diver's air consumption is directly related to the respiration rate a

function of work load, emotional, and environmental factors) and the ambient pressure (depth) at

which the diver is working. As the diver's depth increases, there is a proportional increase in air

consumption. Higher ambient pressures do not increase the physiological need for oxygen; the diver

is simply breathing denser a ir at depth and loses more oxygen with each exhalation. As a

consequence, the open-circuit diver must carry a relatively large gas supply to compensate for loss of

oxygen in the exhaled gas.

In closed-circuit scuba, the diver's exhaled gas is kept within the apparatus, scrubbed of

carbon dioxide

by

chemical absorbent, and is returned to be rebreathed by the diver.

No

gas is

released into the water

no

bubbles). This allows the diver to utilize his/her gas supply with little or

no

waste. Gas consumption is related only to the physiological consumption

oxygen as a function of

workload and is independent of depth. Only a small amount of oxygen

is

required for extended dives.

There are both oxygen and mixed-gas closed-circuit systems available. Only oxygen systems

will be discussed here. Although oxygen rebreathers have severe physiological limitations (see

Medical Aspects, below), they are simple in design, easy to use and maintain, and are cost-effective

for shallow water operations (less than 7.5 m .

The typical closed-circuit oxygen diving apparatus consists of

an

oxygen cylinder. chemical

absorbent canister, flexible breathing chamber or bag, and a mouthpiece with both inhalation and

exhalation hoses.

Oxygen is fed directly into the breathing chamber/bag, either by a demand regulator,

manually, or

at

a constant rate.

If

a demand regulator is used, oxygen is automatically added when

the

volume of gas in the breathing chamber/bag is reduced. Rebreathers that use manual controls

require the diver to open and close a valve when the volume of the breathing chamber/bag is

reduced. Generally, an apparatus with a demand regulator will also have a manual override in the

event the regulator fails. A constant flow system adds oxygen at a predetermined rate based on an

average oxygen consumption rate.

In most systems, the diver breathes oxygen directly from the breathing chamber/bag.

Exhaled gas passes through a separate hose to a chemical absorbent canister. Check valves near the

91


Sanders & Wendell Closed circuit Oxygen Apparatus

A significant improvement was made by using an underwater vehicle to push the trap and pull

the diver. The underwater vehicle allowed each memberof a dive team to carry a trap. This increased

the odds of one diver capturing

an

otter and allowed for the possibility of two otters being captured in

one dive. The vehicles also enabled the divers to travel faster. Bubbles produced by the diver

surfaced slightly behind the actual position of the diver, and the quantity of the bubbles was

somewhat reduced since the diver did not need to work as hard. A compass was mounted on the

vehicle to assist in navigation. Although efficiency was improved, the bubbles still provided clues to

resting otters that divers were present.

In 1988, the California Department of Fish and Game began to use closed-circuit oxygen

scuba in conjunction with the underwater vehicles and Wilson traps for sea otter captures. The U.S.

Fish and Wildlife Service followed suit with their own dive program also using closed-circuit apparatus.

The rebreathing apparatus increased the effectiveness of the diving technique dramatically. There

were no bubbles to alert a resting otter

give away the divers' position. Divers were allowed to take

more time to locate and position their traps as well

as

select a specific target animal. Recapture of

otters was also enhanced because there were few clues for an otter to key on when a diver

approached. This improved efficiency came with added risks associated with oxygen diving.

Adequate training was essential for minimizing these risks.

PRINCIPLES OF CLOSED-CIRCUIT OXYGEN DIVING

Conventional open-circuit scuba divers utilize air as a breathing medium, and exhaled gases

are released directly into the water. Air contains approximately 80 nitrogen and 20 oxygen. The

nitrogen is considered inert and is not consumed during respiration. Each time an open-circuit diver

takes a breath, only a small percentage of the available oxygen is used; the rest is lost when the

diver exhales. The open-circuit diver's air consumption is directly related to the respiration rate

a

function of work load, emotional. and environmental factors)

and

the ambient pressure (depth) at

which the diver is working. As the diver's depth increases, there is a proportional increase in air

consumption. Higher ambient pressures do not increase the physiological need for oxygen; the diver

is simply breathing denser air at depth and loses more oxygen with each exhalation. As a

consequence. the open-circuit diver must carry a relatively large gas supply to compensate for loss of

oxygen in the exhaled gas.

In closed-circuit scuba, the diver's exhaled gas is kept within the apparatus, scrubbed of

carbon dioxide by chemical absorbent, and is returned to be rebreathed by the diver. No gas is

released into the water (no bubbles). This allows the diver to utilize his/her gas supply with little or

no

waste. Gas consumption

is

related only to the physiological consumption of oxygen as a function of

workload and is independent of depth. Only a small amount of oxygen is required for extended dives.

There are both oxygen and mixed-gas closed-circuit systems available. Only oxygen systems

will be discussed here. Although oxygen rebreathers have severe physiological limitations (see

Medical Aspects, below), they are simple in design. easy to use and maintain, and are cost-effective

for shallowwater operations (less than 7.5

m .

The typical closed-circuit oxygen diving apparatus consists of an oxygen cylinder, chemical

absorbent canister, flexible breathing chamber or bag, and a mouthpiece with both inhalation

and

exhalation hoses.

Oxygen is fed directly into the breathing chamberlbag, either by a demand regulator,

manually, or

at

a constant rate.

If

a demand regUlator

is

used, oxygen is automatically added when the

volume of gas in the breathing chamber/bag is reduced. Rebreathers that use manual controls

require the diver to open and close a valve when the volume of the breathing chamber/bag is

reduced. Generally, an apparatus with a demand regulator will also have a manual override in the

event the regulator fails. A constant flow system adds oxygen at a predetermined rate based on

an

average oxygen consumption rate.

In most systems, the diver breathes oxygen directly from the breathing chamber/bag.

Exhaled gas passes through a separate hose to a chemical absorbent canister. Check valves near the

91



nternational Pacifica Scientific iving 99

mouthpiece ensure that gas passes in only one direction, thus preventing rebreathing of carbon

dioxide-contaminated gas. Placement of the check valves near the mouthpiece also limits dead

space in the system that may allow carbon dioxide build-up see Figs. 3 and 4 .

CO

2

SCRUBBER

-

t

=

MOUTHPIEce

SHUT-OFF

ADDITION VALVE

BY PASa

VALVE

Figure 3 Flow diagram for Biomarine CCR-25.

Mouthpiece

Bottle

Valve

Flexible

Breathing

Bag

Demand

Valve

Supply

Hose

Oxygen

~ ~ ~ ~ ~ ~ ~ ~ ~ = ~

O r

Regulator

Oxygen

Cylinder

Exhaust

Hose

C02

Scrubber

Conis1er

Figure

4:

Flow diagram for Draeger Lar V

92


nternational Pacifica Scientific iving 99

mouthpiece ensure that gas passes in only one direction, thus preventing rebreathing of carbon

dioxide-contaminated gas. Placement of the check valves near the mouthpiece also limits dead

space in the system that may allow carbon dioxide build-up see Rgs. 3 and 4).

CO

2

SCRUBBER

-

t

~

MOUTHPIECE

SHUT-OFF

ADDmON

V Lve

BY-PASS V Lve

Rgure Flow diagram for Biomarine CCR-25.

Mouthpiece

Bottle

Valve

Flexible

Breathing

BaQ

Demand

Valve

Supply

Hose

Oxygen

~ ~ ? ~ ~ ~ ~ ~ ~ ~ ~

O r

Regulator

Oxygen

Cylinder

C

Scrubber

Canister

Figure

4:

Flow diagram for Draeger Lar

9



Sanders

&


Upon ~ t ~ n .the chemical absorbent canister, exhaled gas passes through a chemical bed

where carbon dioxide IS removed or scrubbed. The chemical reactionfo r a typical carbon dioxide

absorbent, SODASORB HP, manufactured by W. Grace

&

Co., is diagrammed below:

C 2 + H2 - - -> H ~

2H2C03 + 2NaOH + 2KOH - - -> N a ~ + K ~ + 4H2

Na2COs

+

K2

C

3

+

2Ca(OH)2 - - -> a ~

+

2NaOH

+

2KOH

SODASORB HP has a high moisture content (10-19 ), and normal respiration of the diver

also adds small amounts of water. Note that water is required for this react ion to proceed. On the

other hand,

if

the chemical absorbent canister is f looded, by equipment or operator failure, the

chemical reaction may be compromised and a caustic slurry could form. The diver could suffer serious

burns i f caust ic solution reaches the mouthpiece. This situat ion is somet imes ca lled a Caustic

Cocktail.

Gas leaving the chemical bed enters the breathing chamber/bag, and is returned to the diver.

The

cycle continues unt il

the

d ive is terminated, the

oxygen

cylinder

is

spent, or the chemical

absorbent reaches capacity. The Draeger Lar V and the Biomarine CCR-25 oxygen rebreathers were

designed to support a diver for about hours, using approximately 6.2 m

3

11 ft3

of oxygen and 2.2

kg (5

Ib

of chemical absorbent.

MEDICAL ASPECTS OF CLOSED·CIRCUIT OXYGEN DIVING

Certain medical aspects associated with conventional air diving also apply to oxygen diving.

Oxygen divers must equalize pressure in their inner ear as ambient pressure changes during a dive,

they must maintain an open airway during ascent to reduce the possibil ity of gas embolism, and they

must be concerned with immersion in the aquatic environment (Le., ear infection, hypothermia, etc. .

There is, however, a very important dif ference between div ing with oxygen and div ing with air. The

oxygen diver has no accumulation of inert gas (nitrogen) during a dive. Dive tables, computers, and

ascent rates developed

for

air diving do not apply. The oxygen diver cannot develop decompression

sickness and may fly without risk immediate upon completion of a dive. Oxygen diving is not care-free,

however.

This section covers the medical aspects of closed-circuit oxygen diving.

Most

concerns are

related to breathing of oxygen at higher than normal partial pressures, but there are mechanical and

hygienic aspects unique to closed-circuit diving operations that must also be considered.

Oxygen Toxicity

Breathing oxygen at high part ia l pressures can lead to two types of oxygen toxici ty: central

nervous system

or

pulmonary oxygen poisoning. The onset of symptoms is related to the pressure

and duration of the oxygen exposure (Thorn and Clark 1990). As a result, oxygen toxicity limits both

the depth and t ime a d iver can work safely. Divers using oxygen as a breathing medium must have

knowledge of the effects of breathing oxygen at high part ial pressures and learn to recognize and

react to symptoms of oxygen toxicity.

In 1878, Paul

Bert

published

La

Pression Barometrique. In this paper, he showed

that

oxygen could be lethal when breathed at high pressures. Larks (small birds) exposed to ordinary air at

15 - 20 ATA developed convulsions. This same effect was observed when larks were exposed to

pure oxygen at 5 ATA. Clearly there

was

some type of central nervous system impairment

when

oxygen was breathed at high partial pressures. Today central nervous system oxygen toxicity is

sometimes referred to as the Paul Bert Effect.

The mechanisms for central nervous system oxygen toxicity are not clearly understood. It

is

thought that breathing of oxygen at high pressures increases the production of oxygen free radicals,

which in turn d isrupt normal cel l funct ions. Current studies are focusing on the biochemistry of

oxygen free radicals and cellular antioxidant defenses.


anders

& Wendell Closed circuit OxygenApparatus

Upon ~ t ~ n .the chemical absorbent canister, exhaled gas passes through a chemical bed

where carbon diOXide S removed or scrubbed. The chemical reaction for a typical carbon dioxide

absorbent, SODASORB HP, manufactured by W. R Grace

&

Co., is diagrammed below:

C02 + H2

0

• -

->

H2C

O

2H2COS + 2NaOH + 2KOH - -

->

Na2CO:3 + K2CO:3 + 4H20

Na2C03 + K2

+2Ca(OH}2 - - ->

2CaC0:3

+ 2NaOH + 2KOH

SODASORB HP has a high moisture content (10-19 ), and normal respiration of the diver

also adds small amounts of water. Note that water is required for this reaction to proceed. On the

other hand, if the chemical absorbent canister is flooded, by equipment or operator failure, the

chemical reaction

may

be compromised and a caustic slurry could form. The diver could suffer serious

burns if caustic solution reaches the mouthpiece. This situation is sometimes cal led a Caustic

Cocktail.

Gas leaving the chemical bed enters the breathing chamber/bag, and is returned to the diver.

The cycle continues unti l the dive is terminated, the

oxygen

cylinder is spent, or the chemical

absorbent reaches capacity. The Draeger Lar V and the Biomarine CCR-25 oxygen rebreathers were

designed to support a diver for about 3 hours, using approximately 6.2 m

3

11

ft3)

of

oxygen

and 2.2

kg (5

Ib

of chemical absorbent.

MEDICAL ASPECTS OF CLOSED·CIRCUIT OXYGEN DIVING

Certain medical aspects associated with conventional air diving also apply to oxygen diving.

Oxygen divers must equalize pressure in their inner ear as ambient pressure changes during a dive,

they must maintain

an

open

airway

during ascent

to

reduce the possibility of gas embolism, and they

must be concerned with immersion in the aquatic environment Le., ear infection, hypothermia.

etc. .

There is. however, a very important difference between diving with oxygen and diving with air. The

oxygen diver has no accumulation of inert gas (nitrogen) during a dive. Dive tables, computers. and

ascent rates developed for air diving do not apply. The oxygen diver cannot develop decompression

sickness and may fly without risk immediate upon completion of a dive. Oxygen diving is not care-free,

however.

This section covers the medical aspects of closed-circuit oxygen diving. Most concerns are

related to breathing of

oxygen

at higher than normal partial pressures, but there are mechanical and

hygienic aspects unique to closed-circuit diving operations that must also

be

considered.

Oxygen Toxicity

Breathing oxygen at high partial pressures can lead to two types of oxygen toxicity: central

nervous system or pUlmonary

oxygen

poisoning. The onset of symptoms is related to the pressure

and duration of the oxygen exposure (Thom and Clark 1990). As a result, oxygen toxicity limits both

the depth and time a diver can work safely. Divers using oxygen as a breathing medium must have

knowledge of the effects of breathing oxygen at high partial pressures and learn to recognize and

react to symptoms of oxygen toxicity.

In 1878, Paul Bert published La Pression Barometrique.

In

this paper, he showed that

oxygen could be lethal when breathed

at

high pressures. Larks (small birds) exposed to ordinary air at

15 - 20 ATA developed convulsions. This same effect was observed when larks were exposed to

pure oxygen at 5 ATA. Clearly there was some type of central nervous system impairment when

oxygen was breathed at high partial pressures. Today central nervous system oxygen toxici ty is

sometimes referred to

as

the Paul Bert Effect.

The mechanisms for central nervous system oxygen toxicity are not clearly understood. It is

thought that breathing of oxygen at high pressures increases the production of oxygen free radicals.

which in turn disrupt normal cell funct ions. Current studies are focusing

on

the biochemistry of

oxygen free radicals and cellular antioxidant defenses.



International Pacifica Scientific Diving

99

Symptoms most commonly associated with central nervous system oxygen toxicity include

nausea, muscle twitching especially in the facial muscles), vertigo, tinnitus, visual

~ i s t u r n c e s

including tunnel vision), respiratory disturbances, changes in mental status. and convulSions.

Visual Symptoms

Ear Symptoms

Nausea

Twitching

Irritability

Dizziness

v -

E

N -

T

I

D

The U.S. Navy created the mnemonic device VENTID to assist their divers in recalling

common symptoms of central nervous system oxygen toxicity:

Symptoms

mayor

may not precede a convulsive episode of the classic grand mal, tonic-clonic

type. When minor symptoms do occur,

an

oxygen convulsion may follow with little

or

no warning.

Oxygen convulsions may result in vertebral fractures. laceration of the tongue, or vomiting. An

unattended diver convulsing underwater may drown or suffer a gas embolism.

The U.S. Navy has conducted research into safe depths and durations for oxygen diving

Butler 1985, 1986; Butler and Thalmann 1984, 1986). They have concluded that there is very little

risk of central nervous system oxygen toxicity for divers who dive at depths less than 6 m 20 fsw [1.6

ATA]), and that an increase in depth to 7.5 m 25 fsw [1.8 ATA]) increases this risk only slightly.

In

some cases, deeper excursions may be allowed.

Table 1 was published in the

U S Navy Diving Manual

Volume 2, October 1987. The

excursion and exposure limits in this table were specifically developed for closed-eircuit 100 oxygen

diving. The military diver has a specialized mission. The Navy tables and corresponding oxygen

diving limits were developed with this mission in mind. There may be times when a military diver would

be forced to make a deeper excursion to evade detect ion systems, place explosive devices,

or

escape from a hazardous situation. In general, using a maximum depth of 7.5 m for closed-circuit

100 oxygen diving will minimize the risk of developing central nervous system oxygen toxicity.

Table Oxygen diving, excursion and exposure limits U.S. Navy Diving Manual, Volume 2, 1987).

Excursion Limits Single Depth Oxygen

Exposure

limits

Depth Maximum time Depth Maximum Oxygen Time

2. Only one excursion is taken during the dive

3. The diver returns to 20 fsw or shallower

before the end of the prescribed time.

A diver who has maintained a depth of 20 fsw

or shallower may make one brief downward

excursion using the table above if:

1. The maximum total dive time does not

exceed 240 minutes.

Exposure times are determined by the time

the diver goes on oxygen to the time the

diver goes off oxygen.

The maximum depth attained during the

dive is used to determine the allowable

exposure time. No excursions are

allowed when using these limits.

21·41 fsw

41·50 fsw

15 minutes

5 minutes

5fsw

3 fsw

35 fsw

4 fsw

5 fsw

For the table above:

240 minutes

80 minutes

25 minutes

15 minutes

10 minutes

4. The excursion t ime limit is

determined by the maximum depth

attained during the excursion.

94


International Pacifica Scientific Diving 1991

Symptoms most commonly associated with central nervous system oxygen toxicity include

nausea, muscle twitching especially in the facial muscles), vertigo, tinnitus, visual disturbances

including tunnel vision), respiratory disturbances, changes in mental status, and convulsions.

Visual Symptoms

Ear Symptoms

Nausea

Twitching

Irritability

Dizziness

v

E

N

T

I

D -

The U.S. Navy created the mnemonic device VENTID to assist their divers in recalling

common symptoms of central nervous system oxygen toxicity:

Symptoms mayormay not precede a convulsive episode of the classic grand mal, tonic-clonic

type. When minor symptoms do occur, an oxygen convulsion may follow with little or no warning.

Oxygen convulsions may result in vertebral fractures, laceration of the tongue, or vomiting.

n

unattended diver convulsing underwater may drown or suffer a gas embolism.

The U.S. Navy has conducted research into safe depths and durations for oxygen diving

Butler

1985, 1986:

Butler and Thalmann

1984, 1986 .

They have concluded that there is very little

risk of central nervous system oxygen toxicity for divers who dive at depths less than 6 m 20 fsw

[1.6

ATA]), and that an increase in depth to 7.5 m 25 fsw [1.8 ATA)) increases this risk only slightly.

n

some cases, deeper excursions may be allowed.

Table

1

was published in the U S

vy

Diving Manual Volume

2,

October

1987.

The

excursion and exposure limits in this table were specifically developed for closed-eircuit 100 oxygen

diving. The military diver has a specialized mission. The Navy tables and corresponding oxygen

diving limits were developed with this mission in mind. There may be times when a military diver would

be forced to make a deeper excursion to evade detect ion systems, place explosive devices, or

escape from a hazardous situation. In general, using a maximum depth of

7.5

m for closed-circuit

100 oxygen diving will minimize the risk of developing central nervous system oxygen toxicity.

Table 1. Oxygen diving, excursion and exposure limits U.S. Navy Diving Manual, Volume 2,1987 .

Excursion Limits Single Depth Oxygen

Exposure

limits

Depth Maximum time Depth

Maximum Oxygen Time

A diver who has maintained a depth of 20 fsw

or

shallower

may

make one brief downward

excursion using the table above

if:

1. The maximum total dive time does not

exceed 240 minutes.

2. Only one excursion is taken during the dive

3. The diver returns to 20 fsw or shallower

before the end of the prescribed time.

4. The excursion t ime limit is

determined by the maximum depth

attained during the excursion.

Exposure times are determined by the time

the diver goes on oxygen to the time the

diver goes off oxygen.

The maximum depth attained during the

dive is used to determine the allowable

exposure time. No excursions are

allowed when using these limits.

21·41 fsw

41·50 fsw

15 minutes

5 minutes

5fsw

30 fsw

35fsw

4 fsw

5 fsw

For the table above:

240 minutes

80 minutes

25 minutes

15 minutes

10 minutes



Sanders Wendell Closed circuit Oxygen Apparatus

. Central nervous system oxygen to.xicity is directly related to the partial pressure of oxygen

bemg breath.ed. However, oxygen convulsions may be accelerated by immersion in water, exercise,

cold stress, mcreased time of exposure, or carbon dioxide build-up (hypercapnia). In addition, there

may be substantial individual variability in oxygen tolerance.

Certain individuals may be less tolerant of oxygen than others. The Navy developed a

standard o ~ y n tolerance test t? .screen its divers. The diver to be tested is placed in a dry

recompression chamber and administered 100 oxygen

at

a pressure equivalent to 60 fsw for 30

minutes. A diver is disqualified if any symptoms of oxygen toxicity appear.

From January 1972 to December 1981, the U.S. Navy conducted 1347 oxygen tolerance

tests. Twenty-six episodes of oxygen toxicity were noted, for a derived failure rate of 1.9 (Butler and

Knafelc 1986). During the same period, the Navy experienced 3 episodes of non-convulsive oxygen

toxicity during closed-circuit oxygen dives. Although this test is not sensitive enough to detect all

divers that may be relatively susceptible to oxygen toxicity, i t does appear to screen for those

individuals who are extremely intolerant of oxygen.

Up to this point, only central nervous system oxygen toxicity has been discussed. Pulmonary

oxygen toxicity becomes a factor during prolonged exposures to oxygen at high partial pressures.

Extended exposure to high partial pressures of oxygen may lead to substernal irritation, coughing,

and painful breathing. Continued breathing of high pressure oxygen may result in reduced

pulmonary function.

n

most cases, any loss

in

pulmonary function is completely reversible within a

few days under normoxic conditions.

Pulmonary oxygen toxicity is not likely to be a factor for most diving operations. The oxygen

diver must be exposed to hyperbaric oxygen for many hours before symptoms occur. The U.S. Navy

permits a maximum of four hours of oxygen time within a 24-hour period. This limit is considered

relatively conservative. Pulmonary oxygen toxicity is more prevalent during aggressive hyperbaric

oxygen treatment of decompression sickness.

Chemical Burns

Current designs of closed-circuit oxygen apparatus use chemicals to remove carbon dioxide

from the breathing loop. Although there are slight differences between manufacturers, the chemical

used is a granular form of soda lime. When dry, this chemical can be handled easily, using simple

precautions. However, introducing water to the dry chemical could result in the formation of a caustic

solution, causing severe burns.

During normal diving operations, the chemical scrubber bed remains dry at all times.

f

the

apparatus were to flood, through equipment failure or operator error, the chemical scrubber bed could

become wet and caustic solution may migrate to the diver's mouth via the inhalation hose. Generally,

the diver has time to abort the dive before caustic solution reaches his mouth.

Caustic solutions react slowly and are difficult to remove. Divers may experience a slippery

feeling at the site of contact prior to any burning sensation. The eyes are particularly susceptible to

caustic burns, and may be contaminated by careless handling of either dry

wet chemicals.

Hypoxia

Closed-circuit oxygen rebreathers generally have

no

sensors to determine oxygen levels

being delivered to the diver. They instead rely on change in the volume of the gas in the apparatus.

s oxygen is metabolized, the volume of gas is reduced and fresh oxygen is added.

Oxygen divers must purge air out of their lungs and the apparatus prior to making a dive. The

diver may assume that his gas mixture is very close to 100 after completing a proper purge

procedure. During the course of the dive, this gas mixture may change slightly as nitrogen leaches

from body tissues.


Sanders Wendell Closed circuit xygen pparatus

. Central nervous system oxygen to.xicity is directly related to the part ial pressure of oxygen

bemg breath.ed. o w e ~ e r oxygen convulsions may be accelerated by immersion in water, exercise,

cold stress, Increased time of exposure,

or

carbon dioxide bUild-up (hypercapnia). In addition, there

may be substantial individual variability in oxygen tolerance.

Certain individuals may be less tolerant of oxygen than others. The Navy developed a

standard

o ~ y g e n

tolerance test t? .screen its divers. The diver to be tested is placed in a dry

recompression chamber and administered 100 oxygen

t

a pressure equivalent to 60 fsw for 30

minutes. A diver is disqualified if any symptoms of oxygen toxicity appear.

From January 1972

to

December 1981, the U.S. Navy conducted 1347 oxygen tolerance

tests. Twenty-six episodes of oxygen toxicity were noted, for a derived failure rate of 1.9 (Butler and

Knafelc 1986). During the same period, the Navy experienced 3 episodes of non-eonvulsive oxygen

toxicity during closed-circuit oxygen dives. Although this test is not sensitive enough to detect all

divers that may be relatively susceptible to oxygen toxicity, i t does appear to screen for those

individuals who are extremely intolerant of oxygen.

Up

to this point, only central nervous system oxygen toxicity has been discussed. Pulmonary

oxygen toxicity becomes a factor during prolonged exposures to oxygen at high partial pressures.

Extended exposure to high partial pressures of oxygen may lead to substernal irritation, coughing,

and painful breathing. Continued breathing of high pressure oxygen may result in reduced

pulmonary function. In most cases, any loss in pulmonary function is completely reversible within a

few days under normoxic conditions.

Pulmonary oxygen toxicity is not likely to be a factor for most diving operations. The oxygen

diver must be exposed to hyperbaric oxygen for many hours before symptoms occur. The U.S. Navy

permits a maximum of four hours

of

oxygen time within a 24-hour period. This limit is considered

relatively conservative. Pulmonary oxygen toxicity is more prevalent during aggressive hyperbaric

oxygen treatment of decompression sickness.

Chemical Burns

Current designs of closed-circuit oxygen apparatus use chemicals to remove carbon dioxide

from the breathing loop. Although there are slight differences between manufacturers, the chemical

used is a granular form of soda lime. When dry, this chemical can be handled easily, using simple

precautions. However, introducing water to the dry chemical could result

in

the formation

of

a caustic

solution, causing severe burns.

During normal diving operations, the chemical scrubber bed remains dry at all times. f the

apparatus were to flood, through equipment failure or operator error, the chemical scrubber bed could

become wet and caustic solution may migrate to the diver's mouth via the inhalation hose. Generally,

the diver has time to abort the dive before caustic solution reaches his mouth.

Caustic solutions react slowly and are difficult to remove. Divers may experience a slippery

feeling at the site of contact prior to any burning sensation. The eyes are particularly susceptible to

caustic burns, and may be contaminated by careless handling of either dry

or

wet chemicals.

Hypoxia

Closed-circuit oxygen rebreathers generally have no sensors

to

determine oxygen levels

being delivered to the diver. They instead rely on change in the volume of the gas in the apparatus.

As oxygen is metabolized, the volume of gas is reduced and fresh oxygen is added.

Oxygen divers must purge air out of their lungs and the apparatus prior to making a dive. The

diver may assume that his gas mixture is very close

to

1 after complet ing a proper purge

procedure. During the course of the dive. this gas mixture may change slightly as nitrogen leaches

from body tissues.




The diver risks hypoxia if a proper purge

p r o e d u ~ e

is

no t p e r f o r , ~ d : m p r o p ~ r

purging

leaves a substantial amount of air in the apparatus. The nitrogen m the air IS mert and Its volume

remains constant throughout the dive. Too much nitrogen will lead to inadequate addition of oxygen

to the breathing chamber/bag, resulting in hypoxia.

The closed-circuit oxygen diver suffering from hypoxia may become unconscious without

warning. The brain (hypothalamus) regulates respiration by monitoring levels of carbon dioxide rather

than oxygen. Low levels of oxygen cannot be detected, and all carbon dioxide exhaled by the diver is

effectively removed from the breathing loop.

Hypercapnia

Hypercapnia, excessive carbon dioxide, can result from a number of different situations.

These include failure of the check valves in the breathing hoses, improper packing of the chemical

bed (channeling), and use of inactive or exhausted chemical absorbents. All of these situations are

easily preventable.

Symptoms of hypercapnia include increased respiratory rate, impaired mental function, and

loss of consciousness. The diver generally has time to abort the dive before loss of consciousness

occurs. Hypercapnia may also hasten the onset of symptoms assodated with oxygen toxicity.

Arterial Gas Embolism

The closed-circuit oxygen diver has the same risk of arterial gas embolism as the conventional

air diver. There is a minor difference, however. The oxygen diver operates a closed system. When

the diver ascends, gas in the apparatus expands, forcing gas into the diver s mouth. Some gas must

eventually be vented. The diver must consciously vent gas through his nose and not his mouth. For

the inexperienced diver, the sensation of gas being forced into the mouth can be quite

uncomfortable and could lead to inadequate ventilation during ascent.

Hygiene

The closed-circuit diving apparatus requires more attention to hygiene. The breathing hoses

and breathing chamber/bag provide an ideal breeding area for bacteria. Sharing of an apparatus could

facilitate the transfer of pathogens. Each apparatus must be carefully disassembled, sterilized, and

dried at the end of each diving day.

EaUIPMENT SELECTION AND INITIAL TRAINING

The U.S. Fish and Wildlife Service (USFWS) and the California Department of Fish and Game

(CDFG) use different types of closed-circuit oxygen apparatus. CDFG divers use the Draeger LAR V

a German-made, front-mounted unit commonly used by the U.S. Navy divers. USFWS divers use the

CCR-25, originally manufactured by Biomarine, Inc. (Figure 5). The CCR-25 is a back-mounted system

with relatively new design features. The rights to this design have been sold recently to Carleton

Technologies. Carleton plans to redesign certain features of the CCR-25 and market the unit under

the new name COBRA (Closed-Circuit Oxygen Breathing Apparatus). The specifications for both

units are found in Figure

6

The LAR

has a fairly extensive track record with the U.S. Navy. In 1982, the Navy

conducted unmanned evaluations of six different closed-circuit oxygen apparatus (Middleton 1982).

The LAR

V

was chosen to replace the Navy s Emerson Apparatus as a result of these tests. The

Modified BioPak 240, the precursor to the CCR-25, compared favorably in the 1982 tests but had

design features the Navy considered incompatible with underwater work. Biomarine. Inc. responded

to the Navy s concerns and developed the CCR-25. Unmanned evaluation of the CCR-25 was

conducted at Duke University (Porter, l 1986). The Navy has continued to use the Draeger LAR

however. The CCR-25 has been used and exhibited by divers at Epcott Center (ToaI1989). More

rigorous open water work has been performed by USFWS divers. A number of improvements to the



The diver risks hypoxia if a proper purge

p r o c e d u ~ e

is no

p e r f o r ~ ~ d m p r o p ~ r

purging

leaves a substantial amount of air in the apparatus. The mtrogen

In

the air IS mert and ItS volume

remains constant throughout the dive. Too much nitrogen will lead to inadequate addition of oxygen

to the breathing chamberlbag, resulting in hypoxia.

The closed-circuit oxygen diver suffering from hypoxia may become unconscious without

warning. The brain (hypothalamus) regulates respiration by monitoring levels of carbon dioxide rather

than oxygen. Low levels of oxygen cannot

be

detected, and all carbon dioxide exhaled by the diver is

effectively removed from the breathing loop.

Hypercapnia

Hypercapnia, excessive carbon dioxide, can result from a number of different situations.

These include failure of the check valves in the breathing hoses, improper packing of the chemical

bed (channeling), and use of inactive or exhausted chemical absorbents. All

of

these situations are

easily preventable.

Symptoms of hypercapnia include increased respiratory rate, impaired mental function, and

loss of consciousness. The diver generally has time to abort the dive before loss of consciousness

occurs. Hypercapnia may also hasten the onset of symptoms associated with oxygen toxicity.

Arterial Gas Embolism

The closed-circuit oxygen diver has the same risk of arterial gas embolism as the conventional

air diver. There is a minor difference, however. The oxygen diver operates a closed system. When

the diver ascends, gas in the apparatus expands, forcing gas into the diver's mouth. Some gas must

eventually be vented. The diver must consciously vent gas through his nose and not his mouth. For

the inexperienced diver, the sensation of gas being forced into the mouth can be quite

uncomfortable and could lead to inadequate ventilation during ascent.

Hygiene

The closed-circuit diving apparatus requires more attention to hygiene. The breathing hoses

and breathing chamber/bag provide an ideal breeding area for bacteria. Sharing of an apparatus could

facilitate the transfer of pathogens. Each apparatus must be carefully disassembled, sterilized, and

dried at the end of each diving day.

EQUIPMENT SELECTION AND INITIAL TRAINING

The U.S. Fish and Wildlife Service (USFWS) and the California Department of Fish and Game

(CDFG) use different types of closed-circuit oxygen apparatus. CDFG divers use the Draeger LAR V,

a German-made. front·mounted unit commonly used by the U.S. Navy divers. USFWS divers use the

CCR·25. originally manufactured by Biomarine, Inc. (Figure 5). The CCR·25 is a back-mounted system

with relatively new design features. The rights to this design have been sold recently to Carleton

Technologies. Carleton plans to redesign certain features of the CCR-25 and market the unit under

the new name COBRA (Closed·Circuit Oxygen Breathing Apparatus). The specifications for both

units are found in Figure

The LAR

V

has a fairly extensive track record with the U.S. Navy. In 1982, the Navy

conducted unmanned evaluations of six different closed-circuit oxygen apparatus (Middleton 1982).

The LAR V was chosen to replace the Navy's Emerson Apparatus as a result of these tests. The

Modified BioPak 240. the precursor to the CCR-25. compared favorably in the 1982 tests but had

design features the Navy considered incompatible with underwater work. Biomarine, Inc. responded

to the Navy's concerns and developed the CCR-25. Unmanned evaluation of the CCR-25 was

conducted at Duke University (Porter, l 1986). The Navy has continued to use the Draeger LAR

however. The CCR-25 has been used and exhibited by divers

at

Epeott Center (ToaI1989). More

rigorous open water work has been performed by USFWS divers. A number of improvements to the



Sanders

Wendell Closed circuit Oxygen Apparatus

CCR-25 have been suggested to the manufacturer by USFWS. The current redesign effort is based

on a number of these suggestions. The LAR V units have worked well for CDFG divers.

Figure Fish and Wildlife Service diver using the CCR-25 closed-circuit underwater breathing

apparatus.

Initial training for CDFG divers was done through the U.S. Navy. The training was geared

towards the military diver, and used the closed-circuit diving section of the U.S. Navy Diving Manual

as

a guideline. Initial training for the USFWS was conducted by a representative of Biomarine, Inc. Both

agencies conducted additional follow-up training specific to sea otter capture activities before

proceeding to actual sea otter captures. Currently, each agency is conducting in-house training

of

new divers.

IN·HOUSE TRAINING OF DIVERS FOR CLOSED·

CIRCUIT OXYGEN OPERATIONS

Diving with closed-circuit oxygen apparatus requires additional training and expertise. The

USFWS and CDFG diving programs have approached closed-circuit oxygen apparatus with caution. A

clear operational need for this equipment was established before training and operational procedures

were developed.

Only experienced divers authorized to dive for each agency

are

allowed to train in closed

circuit apparatus. The skills required for sea otter captures (e.g., underwater navigation with

underwater vehicles and Wilson traps) are developed using conventional air scuba prior to training in



CCR-25 have been suggested to the manufacturer y USFWS. The current redesign effort is based

on a number of these suggestions. The LAR V units have worked well for CDFG divers.

Figure

Fish and Wildli fe Service iver using

the

CCR-25 closed-circuit underwater breathing

apparatus.

Init ial training for CDFG divers was done through the U.S. Navy. The training was geared

towards the military diver, and used the closed-circuit diving section of the U.S. Navy Diving Manual as

a guideline. Initial training for the USFWS was conducted by a representative

of

Biomarine, Inc. Both

agencies conducted addit ional fol low-up training speci fic to sea otter capture act iv it ies before

proceeding to actual sea otter captures. Currently, each agency is conducting in-house training of

new divers.

IN·HOUSE TRAINING OF DIVERS FOR CLOSED·

CIRCUIT OXYGEN OPERATIONS

Diving with closed-circuit oxygen apparatus requires additional training and expertise. The

USFWS and CDFG diving programs have approached closed-circuit oxygen apparatus with caution. A

clear operational need for this equipment was established before training and operational procedures

were developed.

Only experienced divers authorized to dive for each agency are allowed to train in closed

circuit apparatus. The skills required for sea otter captures (e.g., underwater navigat ion with

underwater vehicles and Wilson traps) are developed using conventional air scuba prior to training in




closed-circuit. Candidates

for

oxygen diving are required to pass a standard oxygen tolerance test

administered at a qualified hyperbaric facility. Introduction to the design of the equipment, diving

procedures, medical aspects of oxygen diving, and pool exercises are included in initial training. After

a diver becomes comfortable with assembly/disassembly of equipment and use of the equipment in a

pool, he/she may proceed to open-water training.

Biomarine CCR-25 Draeger Lar V

Length

19.3 in

16.9 in

Width

14.0 in

11.8 in

Height

7.0 in

6.7 in

Weight in air

33.01b

24.21b

Weight in water

neutral

neutral

C

Scrubber

capacity

4.21b

5.51b

Oxygen bottle

volume 11.9

ft3

10.5 ft

3

3000 psi

2900 psi

206 bar)

200 bar)

Unit is worn on

Unit is worn on

diver s back

front of diver

Biomarine CCR-25

Draeger Lar

V

Figure : Specifications of the Biomarine CCR-25 vs. Draeger LAR

V

98


International Pacifica Scientific iving 99

closed-circuit. Candidates for oxygen diving are required to pass a standard oxygen tolerance test

administered at a qualified hyperbaric facili ty. Introduction to the design of the equipment, diving

procedures, medical aspects of oxygen diving, and pool exercises are included in initial training. After

a diver becomes comfortable with assembly/disassembly of equipment and use of the equipment in a

pool, he/she may proceed to open-water training.

Biomarine CCR-25 Draeger Lar V

length 19.3 in

16.9 in

Width 14.0 in

11.8 in

Height

7.0 in

6.7 i n

Weight in air

33.01b

24.21b

Weight in water

neutral

neutral

C Scrubber

capacity

4.21b

5.51b

Oxygen bottle

volume 11.9

ft

10.5 ft

@

@

3000 psi

2900 psi

206 bar)

200 bar)

Unit is worn on

Unit is worn on

diver s back

front of diver

Biomarine CCR-25

Draeger Lar V

Figure 6: Specifications of the Biomarine CCR·25 vs. Draeger LAR V




The USFWS diving program requires a minimum of 15 open-water rebreather dives under

carefully controlled conditions, before a diver can move on to sea otter capture operations. Training

s i ~ ~ s : T l u s t

meet three conditions:

1

The bottom must be

no

greater than 7.5 m (25

ft)

depth;

2

VIsibility must be 4.5 m

15 ft)

or greater;

and

3) The dive conditions must approximate those in which

th.e diver expected to work. No more than two such training dives are conducted in each day.

Divers trammg for sea otter captures are allowed to dive only with the closed-circuit unit for the first

i v ~ s More complex tasks, such as underwater vehicle use or Wilson trap work, are added gradually.

A diver that has completed the required

15

dives will need to build additional experience in -no

bottom environments (areas where the bottom is not within sight of the diver because of depth and

visibi li ty restrictions) before he/she is ready to attempt sea otter captures with closed-circuit

equipment.

The CDFG program requires a combination of 30 pool and open-water dives, working from

simple to more complex tasks in a staged progression similar to what has been described above.

In

either program, the number of required dives is a minimum. Divers must feel comfortable with each

task before progressing further in the program.

The training dives serve a dual purpose. Not only do they allow the diver to become familiar

with the apparatus

in

the water, but they also allow the divers to assemble and disassemble their

equipment many times. Each diver is required to assemble and disassemble his/her own apparatus.

In a closed-circuit system, proper assembly is critical. All pieces must be in their proper positions, the

check valves in the mouthpiece must be physically checked, and the chemical absorbent canister

must be filled and sealed. A checklist system has been adopted to ensure that each step the

assembly process is performed.

In

addition, the dive partners check each other's equipment to

be

sure that nothing has been forgotten or missed. After the apparatus has been assembled, it is -dip

tested by immersing the entire rig underwater and checking for any gas leaks. If a leak is found, the

apparatus is disassembled, fixed, and retested.

As

mentioned earlier, USFWS and CDFG divers use

different types of equipment. Design differences require pre-dive procedures to be somewhat

different as well. USFWS and CDFG divers must be familiar with procedures for both types of

apparatus if they are

to

dive together.

The closed-circuit oxygen diver must purge air from his/her apparatus and lungs prior to

beginning a dive. Failure to perform a proper purge procedure could result in hypoxia (see Medical

Aspects, above). Air is sucked out of the apparatus prior to adding oxygen. The diver exhales, places

the mouthpiece into his/her mouth, inhales oxygen from the apparatus, and exhales again through

his/her nose. The cycle is repeated three times. Once on oxygen, the diver may

no

longer remove

the mouthpiece. Pre-dive planning that requires verbal communication must be done before purging.

If

the diver goes off oxygen, the entire purge procedure is repeated. Strict adherence to the purge

procedure is critical.

During the training dives, special attention

is

paid to buoyancy

and

depth control. Divers must

be

properly weighted for the dive. Most buoyancy compensation devices (BC's) cannot be used to

change buoyancy during the dive. This is because most BC's require a power inflator hose to

be

attached to the diver's breathing cylinder. The closed-circuit diver has a very limited gas supply and

cannot afford to use gas for buoyancy control. Of course, oral inflation is an option, but would not

be

practical. The diver trying to orally inflate a

BC

would need to close the mouthpiece, exhale into the

BC, and open the mouthpiece. This operation is difficult at best, risks flooding of the unit, and once

again ''wastes'' the limited gas supply for buoyancy. USFWS divers have had success using a front

mounted Fenzy-style BC with its own small air bottle attached; otherwise, proper weighting

and

training effectively eliminates the need for buoyancy compensation.

Depth control is extremely important. The diver must learn to be conscious of his/her depth

at

all times. Most divers

are

brought

up

to

be

benthic creatures. These divers must leam to orient to

the

surface rather than the bottom. A kelp bed canopy often proves to be a useful reference for the sea

otter diver. Navigation with underwater vehicles

at

a depth of 3.3 m

10 ft

is practiced. In blue water

conditions, where

no

bottom or top references are available, depth control can be difficuh.

The closed-circuit diver must have a well-fitted mask. Once again, the available gas supply is



The USFWS diving program requires a minimum of 15 open-water rebreather dives under

carefully controlled conditions, before a diver can ov on to sea otter capture operations. Training

s i ~ ~ s r n u s t meet three conditions: 1 The bottom m u ~ t be no greater than 7.5 m (25 ft) in depth; 2)

VISibIlIty must be 4.5 m (15

ft)

or greater;

and

3) The dIve conditions must approximate those in which

th.e diver expected to work. No more than two such training dives are conducted in each day.

Divers trainIng for sea otter captures are allowed to dive only with the closed-circuit unit for the first

i v ~ s More complex tasks, such as underwater vehicle use or Wilson trap work, are added gradually.

A diver that has completed the required

15

dives will need to build additional experience in no

bottom environments (areas where the bottom is not within sight

o

the diver because of depth and

visibi li ty restrictions) before he/she is ready to attempt sea otter captures with closed-circuit

equipment.

The CDFG program requires a combination

of

30 pool and open-water dives, working from

simple to more complex tasks in a staged progression similar to what has been described above. In

either program, the number of required dives is a minimum. Divers must feel comfortable with each

task before progressing further in the program.

The training dives serve a dual purpose. Not only do they allow the diver to become familiar

with the apparatus in the water, but they also allow the divers to assemble and disassemble their

equipment many times. Each diver is required

to

assemble and disassemble his/her own apparatus.

In a closed-circuit system, proper assembly is critical. All pieces must be in their proper positions,

the

check valves in the mouthpiece must be physically checked, and the chemical absorbent canister

must be filled and sealed. A checklist system has been adopted to ensure that each step

n

the

assembly process is performed. In addition, the dive partners check each other's equipment to

be

sure that nothing has been forgotten or missed. After the apparatus has been assembled, it is dip

tested by immersing the entire

rig

underwater and checking for any gas leaks.

If

a leak is found, the

apparatus is disassembled, fixed, and retested. As mentioned

ear1ier

USFWS and CDFG divers use

different types of equipment. Design differences require pre-dive procedures to be somewhat

different as well . USFWS and CDFG divers must be familiar with procedures for both types of

apparatus if they are to dive together.

The closed-circuit oxygen diver must purge air from his/her apparatus and lungs prior to

beginning a dive. Failure to perform a proper purge procedure could result in hypoxia (see Medical

Aspects, above). Air is sucked out of the apparatus prior to adding oxygen. The diver exhales, places

the mouthpiece into his/her mouth, inhales oxygen from the apparatus, and exhales again through

his/her nose. The cycle is repeated three times. Once on oxygen, the diver may no longer remove

the mouthpiece. Pre-dive planning that requires verbal communication must be done before purging.

If the diver goes off oxygen, the entire purge procedure is repeated. Strict adherence to the purge

procedure is critical.

During the training dives. special attention is paid to buoyancy and depth control. Divers must

be properly weighted for the dive. Most buoyancy compensation devices (BC's) cannot be used to

change buoyancy during the dive. This is because most BC's require a power inflator hose to be

attached to the diver's breathing cylinder. The closed-circuit diver has a very limited gas supply and

cannot afford to use gas for buoyancy control. Of course. oral inflation is an option, but would not be

practical. The diver trying to orally inflate a BC would need to close the mouthpiece, exhale into the

BC, and open the mouthpiece. This operation is difficult at best, risks flooding

o

the unit, and once

again ''wastes'' the limited gas supply for buoyancy. USFWS divers have had success using a front

mounted Fenzy-style BC with its own small air bottle attached; otherwise. proper weighting and

training effectively eliminates the need for buoyancy compensation.

Depth control is extremely important. The diver must learn to

be

conscious of his/her depth at

all times. Most divers are brought up to be benthic creatures. These divers must learn to orient to the

surface rather than the bottom. A kelp bed canopy often proves to be a useful reference for the sea

otter diver. Navigation with underwater vehicles at a depth of 3.3 m (10 ft) is practiced. In blue water

conditions, where no bottom ortop references are available, depth control can be difficult.

The closed-circuit diver must have a well-fitted mask. Once again, the available gas supply is



International Pacifica Scientific iving

l imited, and frequent clearing of a mask could significantly reduce the l n ~ h o f the dive. In d d i t ~ o n

the mouthpiece is only removed from the mouth after is has been closed. If It IS left open and the diver

is in the water, the apparatus will flood. Flooding of a unit requires the diver to abort the dive

immediately.

Divers being trained in closed-circuit equipment will experience a number of new sensations.

The unit is bubble-free, so the only sound heard is the occasional hissing of oxygen being to

the unit. The inhaled gas is usually warm and humid. Most important of all, when an ascent

IS

made,

gas expands in the apparatus. If the new volume of the gas exceeds the capacity of the apparatus,

gas is forced into the diver s mouth. Divers must learn

to work at minimum operational depths (1.3

3.3 m as they approach a sea otter, and to make slow, gradual ascents. This will reduce or eliminate

the need for venting of gas. In the event gas must be vented, the diver must learn to expel gas

through the nose rather than the mouth.

After a diver has become comfortable with the closed-circuit oxygen apparatus and navigation

with the underwater vehicle and Wilson trap, he/she may proceed to actual operational dives.

SEA OTTER CAPTURE:

OPERATIONAL

REQUIREMENTS

A sea otter capture team is composed of a minimum of three persons: two divers, and one

boat-operator/safety diver. A complete set of conventional air scuba is kept on the capture boat. The

air scuba may be used in the event of a diving accident. The safety diver may be able to effect a

rescue/recovery of a downed diver in depth exceeding the safe limits for closed-circuit oxygen

equipment. The air scuba also proves to be useful if an important piece

of

equipment is dropped

overboard.

Af ter a sea ot ter is sighted. the capture boat anchors downwind and the divers enter the

water. The safety diver hands additional capture equipment to the divers. Once the divers have

descended. they are virtually impossible to detect on the surface. The capture boat flies a Diver

Down flag,

and

the safety diver must

be

especially vigilant for other boats operating in the area. Since

the divers are not producing bubbles

to

mark their location, other boaters must not be allowed in the

area

Divers must follow all procedures discussed in the training section above. They are limited to

a maximum depth of 7.5

m

but usually work about 3.3 - 4.5 m from the surface. Deeper excursions

are not allowed except in life-threatening situations and then only to the extent allowed by the U.S.

Navy tables. If an excursion below 7.5 m is made. whether it be operator error

or

medical emergency,

all

closed-circuit dive operations are canceled for the day. A review of the incident may bewarranted.

Upon completion of a dive. the divers signal the boat

to

pick them up. The boat operator wil l always

wait until signaled to approach the divers.

Dives are typically from 10-20 min in length. with a minimum of one hour between dives. Two

to six dives may

be

made each day.

SUMMARY

Closed-circuit oxygen apparatus has been used since 1879. Open-circuit scuba became

popular in the 1950·s. Closed-circuit oxygen apparatus has since fallen into disuse for all but very

specialized diving operations.

The California Department of Fish and Game and the U.S. Fish and Wildlife Service have used

closed-circuit oxygen apparatus for sea otter captures. They have documented a significant increase

in the efficiency of their diving operations. This increase is attributed to the bubble-free operation of

closed-circuit apparatus.

The use of closed-circuit oxygen apparatus poses additional risks to divers. Oxygen toxicity.


International Pacifica Scientific iving

1991

l imited, and frequent clearing of a mask could significantly reduce the

l n ~ h o f

the dive. In d d i t ~ o n

the mouthpiece is only removed from the mouth after is has been closed. If It IS left open and the dlyer

is in the water, the apparatus will flood. Flooding of a unit requires the diver to abort the dIve

immediately.

Divers being trained in closed-circuit equipment will experience a number of new sensations.

The unit is bubble-free, so the only sound heard is the occasional hissing of oxygen being added to

the unit. The inhaled gas is usually warm and humid. Most important of all, when an ascent is made,

gas expands in the apparatus. If the new volume of the gas exceeds the capacity of the apparatus,

gas is forced into the diver s mouth. Divers must learn to work at minimum operational depths

1.3 -

3.3

m as they approach a sea otter, and to make slow, gradual ascents. This will reduce or eliminate

the need for venting of gas. In the event gas must be vented, the diver must learn to expel gas

through the nose rather than the mouth.

After a diver has become comfortable with the closed-circuit oxygen apparatus and navigation

with the underwater vehicle and Wilson trap, he/she may proceed to actual operational dives.

SEA

OTTER CAPTURE: OPERATIONAL REQUIREMENTS

A sea otter capture team is composed of a minimum of three persons: two divers, and one

boat-operator/safety diver. A complete set of conventional air scuba is kept on the capture boat. The

air scuba may be used in the event of a diving accident. The safety diver may be able to effect a

rescue/recovery of a downed diver in depth exceeding the safe limits

for

closed-circuit oxygen

equipment. The air scuba also proves to be useful if an important piece of equipment is dropped

overboard.

Af ter a sea otter is sighted. the capture boat anchors downwind and the divers enter the

water. The safety diver hands additional capture equipment to the divers. Once the divers have

descended, they are virtually impossible to detect on the surface. The capture boat flies a Diver

Down flag, and the safety diver must be especially vigilant for other boats operating in the area. Since

the divers are not producing bubbles to mark their location, other boaters must not be allowed in the

area.

Divers must follow all procedures discussed in the training section above. They are limited to

a maximum depth of 7.5

m

but usually work about 3.3 4.5 m from the surface. Deeper excursions

are not allowed except in life-threatening situations and then only to the extent allowed by the U.S.

Navy tables. If an excursion below 7.5 m is made, whether it be operator error

or

medical emergency,

all closed-circuit dive operations are canceled for the day. A review of the incident may be warranted.

Upon completion of a dive, the divers signal the boat

to

pick them up. The boat operator wil l always

wait until signaled to approach the divers.

Dives are typically from 10-20 min in length, with a minimum of one hour between dives. Two

to

six

dives may made each day.

SUMMARY

Closed-circuit oxygen apparatus has been used since 1879. Open-circuit scuba became

popular in the 1950 s. Closed-circuit oxygen apparatus has since fallen into disuse for all but very

specialized diving operations.

The California Department of Fish and Game and the U.S. Fish and Wildlife Service have used

closed-circuit oxygen apparatus for sea otter captures. They have documented a significant increase

in the efficiency of their diving operations. This increase is attributed to the bubble-free operation of

closed-circuit apparatus.

The use of closed-circuit oxygen apparatus poses additional risks to divers. Oxygen

tOXicity



Sanders

Wendell: Closed-circuit Oxygen Apparatus

caustic burns, hypOXia, hypercapnia, arterial gas embolism,

and

hygiene are al l concerns. Proper

education, training, and practical experience are critical to safe diving operations regardless of the

type of equipment being used.

Projects that are considering closed-circuit oxygen apparatus should carefully evaluate the

need for such equipment before developing a closed-circuit program. Closed-circuit oxygen diving

should be l imited to a maximum depth of 25 fsw. Specialized training, strict adherence to basic safety

procedures, and dedication to maintaining proficiency are required.

LITER TURE ITED

Butler, F. K 1985. Closed-circuit oxygen diving. Panama City, FL. Navy Experimental Diving Unit,

Report No. 7-85.

Butler, F.

K

1986. Central nervous system oxygen toxicity in closed-circuit scuba divers. III. Panama

City,

FL

Navy Experimental Diving Unit, Report No. 5-86.

Butler, F. K. and M. E Knafe lc 1986. Screening

for oxygen

intolerance in U.S.

Navy

divers.

Undersea Biomedical Research, 13(2): 91-98.

Butler, F.

K

and

E

D Thalmann. 1984. CNS oxygen toxicity

in

closed-circuit scuba divers. pp. 15

30. In:

Proceedings of the Eighth Symposium on Underwater Physiology.

J. Backrach and

M.

M

Matzen (eds.). Bethesda, MD, Undersea Medical Society.

Butler, F. K. and E

D

Thalmann. 1986. Central nervous system oxygen toxicity in closed-circuit

scuba divers. II Undersea Biomedical Research, 13(2): 193-223.

Cousteau, J. Y 1950. The Silent World pp. 15-20. Harper Brothers, New York, NY.

Doukan, G. 1957. The World Beneath the Waves, pp. 147-155. American Book Stratford Press, New

York, NY.

Dugan, J. 1965. Man Under The Sea, pp. 31-33, pp. 271-281. Collier Books,

New

York, NY.

Hass, H. 1975. Men Beneath the

ea

pp. 15-26. St. Martin s Press,

New

York, NY.

Middleton, J

R

1982. Unmanned evaluation

of

six closed-circuit oxygen rebreathers. Panama City,

, FL, Navy Experimental Diving Unit, Report No. 3-82.

Porter, S. V., M. J. Natol i, and R D Vann. 1986. Unmanned evaluation

of

the Rexnord CCR-25 and

Limepak carbon dioxide absorbent. F G. Hall Laboratory, Duke University, Durham.

Riedman, M. L. and J.

Estes. 1990. The sea otter Enhydra lutris : behavior, ecology, and natural

history. U.S. Rsh and Wildlife Service, Biological Report 90(14).

Sweeny, J. 1955. Skin Diving nd Exploring Underwater, pp 72 73 McGraw-Hili Book Co., New

York, NY.

Thorn, S. R and J. M. Clark. 1990. The toxicity of oxygen, carbon monoxide, and carbon dioxide. pp.

82-94. In:

Diving Medicine.

A. Bove and J. C. Davis (eds.). Philadelphia, PA. W B.

Saunders Co.

Toal, F. J. 1989. Closed-circuit

oxygen

Rebreathers - a

new

approach pp. 321-324. In:

Proceedings

of

the AAUS Ninth nnu l Scientific Diving Symposium. M. A. Lang and

W

C.

Jaap (eds.). Woods Hole, MA.

U.S. Navy 1987. Closed-circuit oxygen div ing. pp. 1-21. In: U.S. Navy Diving Manual, Volume 2,

Section 16.

101


Sanders

Wendell: Closed-circuit Oxygen Apparatus

caustic burns, hypoxia, hypercapnia, arterial gas embolism, and hygiene are all concerns. Proper

education, training, and practical experience are critical to safe diving operations regardless of the

type of equipment being used.

Projects that are considering closed-circuit oxygen apparatus should carefully evaluate the

need for such equipment before developing a closed-circuit program. Closed-circuit oxygen diving

should be limited to a maximum depth of 25 fsw. Specialized training. strict adherence to basic safety

procedures. and dedication to maintaining proficiency are required.

LITER TURE ITED

Butler,

F K

1985. Closed-circuit oxygen diving. Panama City, FL Navy Experimental Diving Unit,

Report No. 7-85.

Butler, F K 1986. Central nervous system oxygen toxicity in closed-circuit scuba divers. III. Panama

City, FL Navy Experimental Diving Unit, Report No 5-86.

Butler, F K and M

E

Knafelc 1986. Screening for oxygen intolerance in U.S. avy divers.

Undersea Biomedical Research, 13(2): 91-98.

Butler, F

K

and E D Thalmann. 1984. CNS oxygen toxicity in closed-circuit scuba divers. pp 15-

30. In: Proceedings

of

the Eighth Symposium on Underwater Physiology.

A

J Backrach and

M M Matzen (eds.). Bethesda, MD, Undersea Medical Society.

Butler, F. K and E

D

Thalmann. 1986. Central nervous system oxygen toxicity in closed-circuit

scuba divers. II Undersea Biomedical Research, 13(2): 193-223.

Cousteau, J Y 1950.

The Silent World,

pp. 15-20. Harper

Brothers, New York, NY.

Doukan, G 1957. The World Beneath the Waves, pp. 147-155. American Book Stratford Press, New

York NY.

Dugan, J 1965. Man Under The Sea, pp 31-33, pp 271-281. Collier Books, New York, NY.

Hass, H. 1975. Men Beneath the Sea, pp. 15-26. St. Martin s Press, NewYork, NY.

Middleton, J R 1982. Unmanned evaluation of six closed-circuit oxygen rebreathers. Panama City,

. FL, Navy Experimental Diving Unit, Report

No

3-82.

Porter, S V M. J Natoli, and

R

D Vann. 1986. Unmanned evaluation of the Rexnord CCR-25 and

Umepak carbon dioxide absorbent. F

G

Hall Laboratory, Duke University, Durham.

Riedman, M. L. and J

A

Estes. 1990. The sea otter Enhydra lutris : behavior, ecology, and natural

history. U.S. Fish and Wildlife Service, Biological Report 90(14).

Sweeny, J 1955.

Skin Diving

and

Exploring Underwater, pp 72 73

McGraw-Hili Book Co., New

York

NY.

Thom, S. R and J M Clark. 1990. The toxicity of oxygen, carbon monoxide, and carbon dioxide. pp.

82-94. In: Diving Medicine. A A Bove and J C Davis (eds.). Philadelphia, PA. W

B

Saunders Co

Toal, F J 1989. Closed-circuit oxygen Rebreathers - a new approach. pp. 321-324. In:

Proceedings

of the

US Ninth nnual Scientific Diving Symposium. M. A Lang and

W C

Jaap (eds.). Woods Hole, MA

U.S. Navy 1987. Closed-circuit oxygen diVing. pp 1-21. In:

U.S. avy Diving Manual,

Volume 2,

Section 16.

101

Rebreathers: Minimizing Risks O2-CCRB

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Transcript of Rebreathers: Minimizing Risks O2-CCRB