8-2 Change A
U.S. Navy Diving Manual—Volume 2
8-2.2.1
Emergency Gas Supply Requirements. The emergency breathing supply valve
provides an air supply path parallel to the nonreturn valve and permits attachment
of the EGS whip. The EGS system consists of an adequately charged ANU
approved scuba cylinder with either a K- or J- valve and a first stage regulator set
at manufacturer’s recommended pressure, but not lower than 135 psig. A relief
valve set at 180
5 psig over bottom pressure must be installed on the first stage
regulator to prevent rupture of the low pressure hose should the first stage regu-
lator fail. The flexible low pressure hose from the first stage regulator attaches to
the emergency supply valve on the helmet sideblock. A submersible pressure
gauge is also required on the first stage regulator.
An adequately charged scuba cylinder is defined as the pressure that provides
sufficient air to bring the diver to his first decompression stop or the surface for
no-decompression dives. It is assumed that this will give topside personnel enough
time to perform required emergency procedures to restore umbilical air to the
diver.
For enclosed space diving an extended EGS whip 50 to 150 feet in length may be
used. If the diving scenario requires the EGS topside, adjust the first stage regu-
lator to 150 psig.
NOTE
For open water dives 60 fsw and shallower, the diving supervisor may
use an ANU approved cylinder designated for MK-21 as an emergency
air source.
Sample Problem 1. Determine the minimum EGS cylinder pressure required for a
MK-21 MOD 1 dive to 190 fsw for five minutes.
1. To calculate the EGS cylinder pressure, you must first determine the amount of
gas required to get the diver back to the stage and leave bottom plus the gas
required for ascent to the first decompression stop. The formula for calculating gas
required is:
Where:
Vr
=
Capacity required (scf)
D
=
Depth (fsw)
1.4
=
Consumption rate in acfm per diver from Table 8-2
T
=
Time (minutes)
Air required while on the bottom: For this example, if the time to get the diver to
the stage and leave bottom is 3 minutes, then:
Vr
D
33
+
33
----------------
1.4
T
=
Bottom Vr
190
33
+
33
---------------------
1.4
3
=
