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
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.
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.
Diver Intercommunication Systems. The major components of the intercommu-
nication system include the divers earphones and microphone, the
communication cable to each diver, the surface control unit, and the tenders
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.