OPEN-CIRCUIT
SYSTEMS
In the open-circuit system, air is breathed from
a supply tank and exhausted directly into the surrounding
water. The supply tank(s) can be worn on the
diver (SCUBA) or he may breathe from SDV air tanks,
if he is in an SDV. SDV personnel may use SDV-supplied
air for long offshore transits and switch to a closed-circuit
system in danger areas. Open-circuit systems
are limited in duration by the capacity of the air
supply, depth, dive work rate, and with decreased
water temperature. Long duration deep dives
may require diver decompression following U.S. Navy
Standard Air Decompression Table.
CLOSED-CIRCUIT
OXYGEN UBA
The LAR V Draeger is a self-contained closed-circuit,
100 percent oxygen, underwater breathing apparatus,
designed for clandestine operations in shallow water.
The LAR V is worn on the diver's chest. With
this closed-circuit system, the diver breathes 100
percent oxygen and his exhaled breath is re-circulated
in the diving apparatus. The divers exhaled
breath passes through a chemical filter which removes
carbon dioxide, replenishing the oxygen that is consumed.
Depth, water temperature and oxygen consumption rate
all affect the duration of the LAR V Draeger.
CLOSED
CIRCUIT MIXED GAS UBA
The Mk 15 is a self-contained, closed circuit mixed-gas,
underwater breathing apparatus. The breathing
gas is completely retained within the apparatus except
during ascent when excess pressure is vented.
In the MK 15, oxygen is mixed with a diluent gas (normally
air) to maintain a present partial pressure of oxygen
(PPO2) level. The constantly preset PP02 level
increases the depth and duration capability as compared
to a 100 percent oxygen system. The duration
of the MK 15 is limited by the carbon dioxide scrubber
canister. Long duration, deep dives may require
diver decompression following U.S. Navy MK 15 Decompression
Tables.
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