CHAPTER 14 Surface Supplied Mixed Gas Diving Procedures
Change A 14-3
as it offers a decompression advantage to the diver. For operational planning, the
range of possible depths should be established and a mixture selected that will
meet the maximum/minimum specification across the depth range.
Selecting the Decompression Schedule. To select a proper decompression table
and schedule, measure the deepest depth reached by the diver and enter the table at
the exact or next greater depth. When using a pneumofathometer to measure
depth, correct the observed depth reading as shown in Table 14-1. Ensure the
pneumofathometer is located at mid-chest level.
The diver's pneumofathometer reads 250 fsw. In the depth range of 201-300 fsw,
the pneumofathometer underestimates the diver's depth by 4 fsw. To determine a
divers depth, add 4 fsw to the pneumofathometer reading giving the divers depth
as 254 fsw.
Bottom time is measured as the time from leaving the surface to leaving the
bottom, rounded up to the next whole minute, except as noted in paragraph 14-3.5.
Enter the table at the exact or next greater bottom time.
Travel Rates. The descent rate is not critical, but it should not exceed 75 fsw/min.
Ascent to the first stop, between stops, and during final ascent to the surface is at a
constant rate of 30 fsw/min except as outlined in paragraph 14-3.11. For all but the
first stop the ascent time between stops is included in the time of the subsequent
stop. For all but the first stop, stop time begins when the diver leaves the previous
Decompression Breathing Gases. Decompress on bottom mixture to 90 fsw,
then shift the diver to a 50% helium 50% oxygen mixture. Upon arrival at the 30
fsw stop, shift the diver to 100% oxygen.
For all dives, surface decompression may be used after completing the 40 fsw
water stop as described in paragraph 14-3.11. During surface decompression, the
diver surfaces while breathing 50% helium 50% oxygen.
Special Procedures for Descent with Less than 16 Percent Oxygen. To prevent
hypoxia, a special descent procedure is required when the bottom mixture contains
less than 16% oxygen:
Table 14-1. Pneumofathometer Correction Factors