CHAPTER 17 — Closed-Circuit Mixed-Gas UBA DivingChange A 17-1117-4.1.1Oxygen Flask Endurance. Ine calculating the endurance of the MK 16, only theoxygen flask is considered. The endurance of the oxygen flask is dependent uponthe following:Flask floodable volumeInitial predive pressureRequired reserve pressureOxygen consumption by the diverEffect of cold water immersion on flask pressure17-4.1.1.1Flask Floodable Volume. The oxygen flask floodable volume (fv) is 0.1 cubicfoot (2.9 liters).17-4.1.1.2Initial Predive Pressure. The initial pressure is the pressure of the oxygen flask atambient temperature when it has cooled following charging. A reserve pressure of500 psig is required to drive the reducer. Calculation of initial pressure must alsoaccount for gas loss resulting from UBA predive calibration. Oxygen consumptionby the diver is computed as 0.049 scfm (1.4 lpm). This is a conservative value fora diver swimming at 0.85 knot (Chapter 3, Figure 3-6). Refer to Table 17-3 forinformation on the average breathing gas consumption rates and CO2 absorbentusage.17-4.1.1.3Effect of Cold Water Immersion on Flask Pressure. Immersion in cold water willreduce 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 thedive is used.17-4.1.1.4Calculating Gas Endurance. Combining these factors produces the formula forMK 16 gas endurance:Table 17-3. Average Breathing Gas Consumption Rates and CO2Absorbent Usage.CO2 AbsorbentDiving EquipmentOverbottom 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 pressure12-15psi/min15-17psi/min7.75-8.05h6h 40mNote:1.CO2 absorbent duration is based upon a comfortable work rate (0.8-knot swimming speed).
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