Bottom Time Partial Pressure

ppO2 = Oxygen partial pressure in ata

% O2 = Oxygen percentage in the mixture

D = Diver's depth in fsw

Example. A diver is at 250 fsw breathing a 17.0 percent oxygen mixture. The oxygen partial pressure is:

To dive in accordance with this section:

1. Determine the bottom time that will be required to complete the task.

2. From Table 14-4, select the oxygen partial pressure that corresponds to this bottom time. If the bottom time is not exactly equal to the times listed in the table, round to the next longer bottom time.

3. Determine the deepest depth that will be attained by the diver during the dive.

4. Calculate the maximum oxygen percentage that can be used by rearranging the oxygen partial pressure equation to solve for the maximum oxygen percentage that can be used:

ppO2 x 33

Sample Problem. A dive to a maximum depth of 270 fsw will require 35 minutes of bottom time. Determine the maximum oxygen percentage that can be used for this dive.

1. Round the 35-minute bottom time to 40 minutes, the next longer bottom time given in Table 14-7.

2. The maximum allowable oxygen partial pressure for this bottom time is 1.50 ata.

3. Calculate the maximum oxygen percentage:

14-3.11.2 Gas Mixtures. Any gas mixture between the calculated maximum and minimum values shown in the decompression table may be used to make the dive under the provisions of this section.

14-3.11.3 Charting Surface-Supplied Helium-Oxygen Dives. Figure 14-7 provides the proper format for charting surface-supplied helium-oxygen dives.

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