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Where:

Fy = Floodable volume of flask in cubic feet Pi = Initial Pressure in psia PR = Reserve Pressure in psia

Rankine conversion factor:

All pressure and temperature units must be absolute.

17-4.1.1.5 Example. The endurance of a MK 16 MOD 0 UBA charged to 2,500 psig for a dive in 50° F water when the ambient air temperature is 65° F would be computed as follows:

A/rx,1R , ni [(2, 514.7 x 510/525) - 514.7] 492 MK 16 gas endurance = (U x -A-0.049 x 14.7-X 4410

= 258 minutes

This duration assumes no gas loss from the UBA during the dive and only considers metabolic consumption of oxygen by the diver. Divers must be trained to minimize gas loss by avoiding leaks and unnecessary depth changes. Clearing a flooded face mask is a common cause of gas loss from the UBA. When a full face mask (FFM) is used, gas can pass from the UBA breathing loop into the FFM and escape into the surrounding seawater due to a poor face seal. Leaks that continue unchecked can deplete UBA gas supply rapidly. Additionally, during diver ascent, the dump valve opens to discharge breathing gas into the surrounding water, thereby preventing overinflation of the breathing diaphragm. Depth changes should be avoided as much as possible to minimize this gas loss.

17-4.1.2 Diluent Flask Endurance. Under normal conditions the anticipated duration of the MK 16 diluent flask will exceed that of the oxygen flask. The MK 16 diluent bottle holds approximately 21 standard cubic feet (595 liters) of gas at a stored pressure of 3,000 psig. Diluent gas is used to maintain the required gas volume in the breathing loop and is not depleted by metabolic consumption. As the diver descends, diluent is added to maintain the total pressure within the recirculation system at ambient water pressure. Loss of UBA gas due to offgassing at depth requires the addition of diluent gas to the breathing loop either automatically through the diluent add valve or manually through the diluent bypass valve to make up lost volume. Excessive gas loss caused by face mask leaks, frequent depth changes, or improper UBA assembly will deplete the diluent gas supply rapidly.

17-4.1.3 Canister Duration. Canister duration is estimated by using a working diver scenario. This allows an adequate safety margin for the diver in any situation. Table 17-4 shows the canister duration limits and approved absorbents for the MK 16 UBA.

Canister Duration with HeO2

Temperature (°F)

Depth (fsw)

Time (minutes)

40 and above

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