NAUI Master Scuba Diver 160 Decompression and Recompression Surface Interval Less Than Ten Minutes If the time between dives is less than 10 minutes, the two dives are considered to be a single dive with a schedule consisting of the deepest depth of either dive and the combined dive times of the two dives. The surface interval is ignored. An example is a dive to 18 m (60 ft) for 30 minutes followed by a dive to 15 m (50 ft) for 25 minutes. The dive schedule for these dives is 18 m (60 ft) for 55 minutes (figure 5-13). Multi-level Diving The U.S. Navy Dive Tables are based on the concept of spending the entire time of a dive at a single depth, but recreational divers seldom remain at a constant depth while diving. You are charged with more nitrogen than you actually absorb when diving at multiple levels (figure 5-12). Procedures have been developed to manually calculate multi-level dives (a dive with varying depths) using the Navy dive tables, but these techniques are not recommended because they are complicated and errors are easily made. Those who wish to avoid the “maximum time-at-maximum-depth” penalty when diving at varying depths are encouraged to consider the use of a dive computer which continuously calculates the exact depth and time spent there, thus allowing longer dive times without decompression stops. Omitted Decompression The former U.S. Navy procedure for omitted decompression, which involved recompressing the diver in water, has been updated based on conclusions reached by noted physicians and physiologists. The old procedure has been replaced with the following: Divers who have missed decompression stops are to remain out of the water, rest, breathe 100% oxygen if adequate supplies exist to handle an emergency as well, drink fluids, be monitored for signs and symptoms of decompression sickness, and be transported to a hyperbaric facility if symptoms of bends are suspected. No exposure to altitude should be allowed for 24 hours. The rationale for the new procedure is that bubbles form in the system very quickly upon surfacing. In addition, there are air supply and thermal considerations. In-water recompression breathing air does not eliminate bubbles after they have formed, and decompression sickness can actually result or be aggravated by in-water recompression. Breathing oxygen on the surface is more beneficial than the in-water procedure on air. A diver who has omitted required decompression is to refrain from further diving for at least 24 hours even if no symptoms of decompression sickness are evident. Additional Dive Table Problems 1. Two hours after surfacing from a cold dive of 30 minutes duration to a depth of 24 m (80 ft), you plan a dive to a depth of 21 m (70 ft). What is your maximum dive time with no required decompression? Solution: 24 m (80 ft) for 30 min = 24 m (80 ft) for 35 min for a cold dive = Group H. 2:00 SIT = Group E. AMDT for Group E at 21 m (70 ft) = 19 min. :05 60' 50' :30 :25 FIGURE 5-13. LESS THAN TEN MINUTE SIT. 2. You spend the first 10 minutes of your first dive of the day at a depth of 33 m (110 ft), then spend another 20 minutes at a depth of 15 m (50 ft). What is your total ascent time for the dive and your repetitive group designation at the end of the FIGURE 5-12. PENALTY FOR A SQUARE-PROFILE DIVE dive (figure 5-14)?
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