Chapter 5- Decompression and Recompression Decompression and Recompression 159 interval required before a Group “H” diver may make a 30 minute dive to a depth of 18 m (60 ft) is 2 hrs and 24 mins. 4. Correctly calculate the maximum depth allowable for a repetitive dive of a given duration. For example, determine that a Group “F” diver who wants to make a 20 minute dive may not exceed a depth of 15 m (50 ft). Sample Dive Table Problems 1. A NAUI Master Scuba Diver dives to 30 m (99 ft) for 20 minutes, surfaces, remains at the surface for an hour and 25 minutes, then dives to a depth of 15 m (50 ft) for 35 minutes. What is the diver’s repetitive group designation following the second dive (figure 5-11)? Solution: 30 m (99 ft) for 20 min. = Group F. Surface Interval Time (SIT) of 1:25 = Group E. Residual Nitrogen Time for group E to 15 m (50 ft) = 38 min + Actual Dive Time (ADT) of 35 min = Total Nitrogen Time (TNT) of 73 min = 15 m (50 ft) for 73 min = Group J. 2. What is the AMDT for the second dive in question #l? Solution: AMDT for group E to 15 m (50 ft) = 42 minutes 3. If the diver in question #1 wanted to make the second dive to a depth of 21 m (70 ft) for 25 minutes, what is the minimum surface interval required to make the second dive a no-decompression dive? Solution: 21 m (70 ft) for at least 25 min. requires Group D. SIT to attain Group D from Group F = 1:30. 4. If the diver in question #1 wanted to make the second dive one hour after the first dive, what is the maximum depth allowed with a no-required stop dive time of 30 minutes? Solution: Group F with l:OO SIT = Group E. First AMDT for Group E equal to or exceeding 30 minutes is 15 m (50 ft). If you had any difficulty working the sample problems, please refer to The NAUI Scuba Diver course textbook for a review of NAUI Dive Table procedures. SPECIAL DIVE TABLE PROCEDURES Certain situations require special procedures for correct dive table calculations. The following list identifies the situations and the proper procedures. Cold or Strenuous Dives If a dive is particularly cold or strenuous, use the next greater dive time to determine your repetitive group. For example, if you are cold during a dive to 27 m (90 ft) for 20 minutes, consider the dive schedule as 27 m (90 ft) for 25 minutes. New research also indicates that there may be a danger associated with breath-hold diving (“free diving”) after scuba diving. Ascent Rate Variations Any delays in ascent during a no-decompression dive are simply added to the time of the dive (in minutes). Precautionary stop time can be considered part of dive time to add a margin of safety, but it is not required. NAUI considers dive time to be from the time you descend until the time you surface from a dive (except for safety stops). When using the dive tables, ascent times slower than the recommended 9 m/min (30 ft/ min) add little benefit compared to a precautionary stop, and may even add to the diver’s nitrogen load, making table calculations invalid. When using a dive computer, it is essential to follow the ascent time required by the computer. 1:25 ? 99'/30 m 50'/15 m Depth Time :20 :35 FIGURE 5-11. PROFILE OF THE ABOVE PROBLEM
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