The MK 20 MOD 0 is a surface-supplied UBA consisting of a full face mask, diver communications components, equipment harness, and an umbilical assembly (Figure 8-2). One of its primary uses is in enclosed spaces, such as submarine ballast tanks. The MK 20 MOD 0 is authorized for use to a depth of 60 fsw with surface-supplied air and must have an Emergency Gas Supply when used for enclosed space diving.
Operation and Maintenance. Safety considerations and working procedures are covered in Chapter 6. NAVSEA SS600-AK-MM0-010 Technical Manual, Operations and Maintenance Instruction Manual is the technical manual for the MK 20 MOD 0. To ensure safe and reliable service, the MK 20 MOD 0 system must be maintained and repaired in accordance with PMS procedures and the MK 20 MOD 0 operation and maintenance manual.
8-3.2 Air Supply. Air for the MK 20 MOD 0 system is supplied from the surface by either an air compressor or a bank of high-pressure flasks as described in paragraph 8-6.2.3.
8-3.2.1 EGS Requirements for MK 20 MOD 0 Enclosed-Space Diving. In order to ensure a positive emergency air supply to the diver when working in a ballast tank, mud tank, or confined space, an Emergency Gas Supply (EGS) assembly must be used. As a minimum, the EGS assembly consists of:
■ Single scuba cylinder steel 72 with either a K- or J-valve, charged to a minimum of 1,800 psi or aluminum 80 charged to 1,900 psi.
■ An approved scuba regulator set at manufacturer's recommended pressure, but not lower than 135 psi, with an extended EGS whip 50 to 150 feet in length. If the diving scenario dictates leaving the EGS topside, adjust the first-stage regulator to 150 psig.
The scuba cylinder may be left on the surface and the EGS whip may be married to the diver's umbilical, or it may be secured at the opening of the enclosed space being entered. The diver may then enter the work space with the extended EGS whip trailing. The second-stage regulator of the EGS is securely attached to the diver's harness before entering the work space so that the diver has immediate access to the EGS regulator in an emergency.
8-3.2.2 EGS Requirements for MK 20 MOD 0 Open Water Diving. When conducting open water dives, the diving supervisor may use a MK 20 designated ANU approved cylinder with the DSI sideback assembly as an emergency air source.
8-3.2.3 Flow Requirements. The MK 20 MOD 0 requires a breathing gas flow of 1.4 acfm and an overbottom pressure of 90 psig. Flow and pressure requirement calculations are identical to those for the MK 21 MOD 1 (see paragraph 8-2.2.3).
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