Special Procedures for Descent with Less than 16 percent Oxygen

14-3.2.1 Descent Procedure. To prevent hypoxia, a special descent procedure is required when the bottom mixture contains less than 16 percent oxygen:

1. Place the diver on the surface on air.

2. Make the appropriate predive checks.

3. Have the diver descend to 20 fsw.

4. At 20 fsw, shift the diver to the bottom mix and ventilate. The diver is allowed 10 minutes at 20 fsw to shift to the bottom mixture and perform equipment checks.

5. Confirm the diver is on bottom mix, then perform a final leak check.

6. Have the diver begin descent. On the diving chart, note the time from leaving the surface to leaving 20 fsw in case the dive must be aborted during descent.

7. Start counting bottom time:

■ If the diver spends 10 minutes or less at 20 fsw, bottom time starts when the diver leaves 20 fsw.

■ If the diver spends more than 10 minutes at 20 fsw, bottom time starts at the 10-minute mark.

14-3.2.2 Aborting the Dive. If it is necessary to bring the diver back to the surface from 20


1. Shift the diver from the bottom mixture to air.

3. Confirm the diver is on air.

4. Have the diver begin ascent.

5. When the diver reenters the water the 10-minute period begins again.

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