8-18 Change A
U.S. Navy Diving ManualVolume 2
Water Vapor Control. A properly operated air supply system should never permit
the air supplied to the diver to reach its dewpoint. Controlling the amount of water
vapor (humidity) in the supplied air is normally accomplished by one or both of
the following methods:
Compression/Expansion. As high-pressure air expands across a pressure
reducing valve, the partial pressure of the water vapor in the air is decreased.
Since the expansion takes place at essentially a constant temperature (isother-
mal), the partial pressure of water vapor required to saturate the air remains
unchanged. Therefore, the relative humidity of the air is reduced.
Cooling. Cooling the air prior to expanding it raises its relative humidity, per-
mitting some of the water to condense. The condensed liquid may then be
drained from the system.
Standby Diver Air Requirements. Air supply requirements cannot be based solely
on the calculated continuing needs of the divers who are initially engaged in the
operation. There must be an adequate reserve to support a standby diver should
one be needed.
Primary and Secondary Air Supply. All surface-supplied diving systems must
include a primary and a secondary air supply in accordance with the U.S. Navy
Diving and Manned Hyperbaric Systems Safety Certification Manual, SS521-AA-
MAN-010. The primary supply must be able to support the air flow and pressure
requirements for the diving equipment designated (Table 8-2). The capacity of the
primary supply must meet the consumption rate of the designated number of
divers for the full duration of the dive (bottom time plus decompression time). The
maximum depth of the dive, the number of divers, and the equipment to be used
must be taken into account when sizing the supply. The secondary supply must be
sized to be able to support recovery of all divers using the equipment and dive
profile of the primary supply if the primary supply sustains a casualty at the worst-
case time (for example, immediately prior to completion of planned bottom time
of maximum dive depth, when decompression obligation is greatest). Primary and
secondary supplies may be either high-pressure (HP) bank-supplied or
Requirements for Operating Procedures and Emergency Procedures. Operat-
ing procedures (OPs) and emergency procedures (EPs) must be available to
support operation of the system and recovery from emergency situations. OPs and
EPs are required to be NAVSEA or NAVFAC approved in accordance with para-
graph 4-2.6.3. Should the surface-supplied diving system be integrated with a
recompression chamber, an air supply allowance for chamber requirements (Vol-
ume 5) must be made.
All valves and electrical switches that directly influence the air supply shall be
DIVER'S AIR SUPPLY - DO NOT TOUCH