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.
Figure 8.2. MK 20 MOD 0 UBA.
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Safety
considerations and working procedures
are covered in Chapter 6. NAVSEA
SS600-AK-MMO-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.
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.
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 (minimum 64.7 cubic feet) with either a K- or Jvalve,
charged to a minimum of 1,800 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.
-
An approved submersible pressure gauge.
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.
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).
