Dive_Man_ChangeA

8-18 Change A U.S. Navy Diving Manual—Volume 2 8-7.1.4 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. 8-7.1.5 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. 8-7.2 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 compressor-supplied. 8-7.2.1 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 labeled: “DIVER'S AIR SUPPLY - DO NOT TOUCH”