13-4 Change A
U.S. Navy Diving ManualVolume 3
duration of gas supply and carbon dioxide absorbent material, oxygen tolerance,
and the possibility of nitrogen narcosis when using emergency gas (air). Divers
must be prepared to work at low temperatures and for long periods of time.
Operations deeper than 300 fsw usually require Deep Diving Systems (DDSs).
The decompression obligation upon the diver is of such length that in-water
decompression is impractical. Using a personnel transfer capsule (PTC) to trans-
port divers to a deck decompression chamber (DDC) increases the margin of diver
safety and support-ship flexibility.
Bottom Time Requirements. The nature of the operation may influence the
bottom time requirements of the diver. An underwater search may be best under-
taken by using multiple divers with short bottom times or by conducting a single
bounce dive simply to identify a submerged object. Other tasks, such as under-
water construction work, may require numerous dives with long bottom times
requiring surface supplied or saturation diving techniques. Although primarily
intended to support deep diving operations, saturation diving systems may be ideal
to support missions as shallow as 150 fsw where the nature of the work is best
accomplished using several dives with extended bottom times. Under these condi-
tions, time is saved by eliminating in-water decompression obligations for each
diver and by reducing the number of dive team changes, thus compensating for the
increased logistical complexity such operations entail.
Environment. Environmental conditions play an important role in planning mixed
gas diving operations. Environmental factors, such as those addressed in Chapter
6, should be considered when planning such operations. Mixed gas diving opera-
tions often involve prolonged dives requiring lengthy decompression and travels
that carry divers great distances from a safe haven. Special attention should there-
fore be given to preventing diver hypothermia. Mixed gas diving apparatus are
designed to minimize thermal stress, but the deepest, longest helium-oxygen dives
place the greatest stress on the diver. Exposure to extreme surface conditions prior
to the dive may leave the diver in a thermally compromised state. A diver who has
been exposed to adverse environmental conditions should not be considered for
Table 13-2. Equipment Operational Characteristics.
Normal Working Limit
MK 21 MOD 1 UBA
EXO BR MS UBA
MK 21 MOD 0 UBA
MK 22 MOD 0 UBA
Part of system
(7 per watch)
Depth limits are based on considerations of working time, decompression obligation, oxygen tolerance and nitrogen
An on-station chamber is defined as a certified and ready chamber at the dive site.