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CHAPTER 12 — Surface-Supplied Mixed Gas Diving 12-7 Table 12‑2. Pneumofathometer Correction Factors. Pneumofathometer Depth Reading Correction Factor 0-100 fsw +1 fsw 101-200 fsw +2 fsw 201-300 fsw +4 fsw 301-400 fsw +7 fsw Example: 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 diver’s depth, add 4 fsw to the pneumofathometer reading giving the diver’s 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 12 - 4.5 . Enter the table at the exact or next greater bottom time. 12-4.3 Travel Rates and Stop Times. The descent rate is not critical, but in general should not exceed 75 fsw/min. The ascent rate from the bottom to the first decompression stop, between decompression stops, and from the last decompression stop to the surface is 30 fsw/min. Minor variations in the rate of ascent between 20 and 40 fsw/min are acceptable. For surface decompression, the ascent rate from the 40 fsw water stop to the surface is 40 fsw/min. The time at the first decompression stop begins when the diver arrives at the stop and ends when he leaves the stop. For all subsequent stops, the stop time begins when the diver leaves the previous stop and ends when he leaves the stop. In other words, ascent time between stops is included in the subsequent stop time. The single exception is the first oxygen stop at 30 fsw. The 30-fsw oxygen stop begins when the divers are confirmed to be on oxygen at 30 fsw and ends when the divers leave 30 fsw. The ascent time from the 30- to the 20-fsw oxygen stop is included in the 20-fsw oxygen stop time. 12-4.4 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 12 - 4.11 . During surface decompression, the diver surfaces while breathing 50% helium 50% oxygen. 12-4.5 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: 1. Place the diver on air on the surface.

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