CHAPTER 17 — Closed-Circuit Mixed-Gas UBA Diving
Change A 17-11
17-4.1.1
Oxygen Flask Endurance. Ine calculating the endurance of the MK 16, only the
oxygen flask is considered. The endurance of the oxygen flask is dependent upon
the following:
Flask floodable volume
Initial predive pressure
Required reserve pressure
Oxygen consumption by the diver
Effect of cold water immersion on flask pressure
17-4.1.1.1
Flask Floodable Volume. The oxygen flask floodable volume (fv) is 0.1 cubic
foot (2.9 liters).
17-4.1.1.2
Initial Predive Pressure. The initial pressure is the pressure of the oxygen flask at
ambient temperature when it has cooled following charging. A reserve pressure of
500 psig is required to drive the reducer. Calculation of initial pressure must also
account for gas loss resulting from UBA predive calibration. Oxygen consumption
by the diver is computed as 0.049 scfm (1.4 lpm). This is a conservative value for
a diver swimming at 0.85 knot (Chapter 3, Figure 3-6). Refer to Table 17-3 for
information on the average breathing gas consumption rates and CO2 absorbent
usage.
17-4.1.1.3
Effect of Cold Water Immersion on Flask Pressure. Immersion in cold water will
reduce the flask pressure and actual cubic feet (acf) of gas available for the diver,
in accordance with Charles’/Gay-Lussac’s gas law. Based upon direct measure-
ment, available data, or experience, the coldest temperature expected during the
dive is used.
17-4.1.1.4
Calculating Gas Endurance. Combining these factors produces the formula for
MK 16 gas endurance:
Table 17-3. Average Breathing Gas Consumption Rates and CO2 Absorbent Usage.
CO2 Absorbent
Diving
Equipment
Overbottom
Pressure (Minimum)
Gas Consumption
(Normal)
Gas Consumption
(Heavy Work)
Capacity
(lbs.)
Duration 40°F
(Note 1)
Duration 70°F
(Note 1)
MK 16 UBA
(Mixed-gas)
Variable with bottle
pressure
12-15
psi/min
15-17
psi/min
7.75-8.0
5h
6h 40m
Note:
1.
CO2 absorbent duration is based upon a comfortable work rate (0.8-knot swimming speed).
