Dive_Man_ChangeA

CHAPTER 8 — Surface-Supplied Air Diving Operations Change A 8-23 Sample calculations for dive duration, based on bank air supply, are presented in Sample Problem 1 in paragraph 8-2.2.3 for the MK 21 MOD 1. The sample prob- lems in this chapter do not take the secondary air system requirements into account. The secondary air system must be able to provide air in the event of failure of the primary system per U.S. Navy Diving and Manned Hyperbaric Systems Safety Certification Manual, SS521-AA-MAN-010. In the MK 21 sample problem (Sample Problem 2), this would mean decompressing three divers with a 30-minute bottom time using 1.4 acfm per diver. An additional requirement must be considered if the same air system is to support a recompression chamber. Refer to Chapter 22 for information on the additional capacity required to support a recompression chamber. 8-7.2.4 Shipboard Air Systems. Many Navy ships have permanently installed shipboard air supply systems that provide either LP or HP air. These systems are used in support of diving operations provided they meet the fundamental requirements of purity, capacity, and pressure. In operation, a volume source (such as a diesel or electrically driven compressor) pumps air into a volume tank. The compressor automatically keeps the tank full as long as the amount of air being used by the diver does not exceed the capacity of the compressor. The ability of a given unit to support a diving operation may be determined from the capacity of the system. 8-8 DIVER COMMUNICATIONS The surface-supplied diver has two means of communicating with the surface, depending on the type of equipment used. If the diver is using the MK 21 MOD 1, or the MK 20 MOD 0, both voice communications and line-pull signals are avail- able. Voice communications are used as the primary means of communication. Line-pull signals are used only as a backup. Diver-to-diver communications are available through topside intercom, diver-to-diver hand signals or slate boards. 8-8.1 Diver Intercommunication Systems. The major components of the intercommu- nication system include the diver’s earphones and microphone, the communication cable to each diver, the surface control unit, and the tender’s speaker and microphone. The system is equipped with an external power cord and can accept 115 VAC or 12 VDC. The internal battery is used for backup power requirements. It should not be used as the primary power source unless an external power source is not available. The intercom system is operated by a designated phone talker at the diving station. The phone talker monitors voice communications and keeps an accurate log of significant messages. All persons using the intercom system should lower the pitch of their voices and speak slowly and distinctly. The conversation should be kept brief and simple, using standard diving terminology. Divers must repeat verbatim all directions and orders received from topside.