CHAPTER 14 Surface Supplied Mixed Gas Diving Procedures
Change A 14-11
corrected. The divers original schedule called for 32 minutes of oxygen at 30 fsw
and 58 minutes of oxygen at 20 fsw.
Seventeen minutes of oxygen time (32 - 15) remain at 30 fsw. Fifty-eight minutes
remain at 20 fsw. The diver should spend an additional 34 minutes (17 x 2) at 30
fsw on the 50/50 mixture, followed by 116 minutes (58 x 2) at 20 fsw. Surface the
diver on completing the 20 fsw stop.
Loss of Oxygen Supply in the Chamber During Surface Decompression. If the
oxygen supply in the chamber is lost during surface decompression, have the diver
breathe chamber air.
Temporary Loss. Return the diver to oxygen breathing. Consider any time on
air as dead time.
Permanent Loss. Multiply the remaining oxygen time by three to obtain the
equivalent chamber decompression time on air. If 50% helium 50% oxygen is
available, multiply the remaining oxygen time by two to obtain the equivalent
chamber decompression time on 50/50. If the loss occurred at 50 or 40 fsw,
allocate 10% of the equivalent air or helium oxygen time to the 40 fsw stop,
20% to the 30 fsw stop, and 70% to the 20 fsw stop. If the diver is at 50 fsw,
ascend to 40 fsw to begin the stop time. If the loss occurred at 30 fsw, allocate
30% of the equivalent air or helium oxygen time to the 30 fsw stop and 70% to
the 20 fsw stop. Round the stop times up to the next whole minute. Surface
upon completion of the 20 fsw stop.
The oxygen supply to the chamber is lost 10 minutes into the first 30 minute
period on oxygen. Helium oxygen is not available. The original surface decom-
pression schedule called for three 30 min oxygen breathing periods (total of 90
minutes of oxygen). The diver is at 50 fsw.
The remaining oxygen time is 80 minutes (90-10). The equivalent chamber
decompression time on air is 240 minutes (3 x 80). The 240 minutes of air stop
time should be allocated as follows: Twenty-four minutes at 40 fsw (240 x 0.1), 48
minutes at 30 fsw (240 x 0.2), and 168 minutes at 20 fsw (240 x 0.7). As addressed
above, the diver should ascend from 50 to 40 fsw and begin the 24 minute stop
time at 40 fsw.
Decompression Gas Supply Contamination. If the decompression gas supply be-
comes contaminated with the bottom mixture, 50/50 mix, air, or oxygen:
1. Find the source of the contamination and correct the problem. Probable