NAUI Master Scuba Diver 162 Decompression and Recompression dives per day or multiple days of diving, or 24 hours following any dive with required decompression. • Shorter, deeper dives rather than long, shallow dives are preferred when flying is planned. Short, deep dives are limited by the “fast” tissue halftimes. These tissues also offgas quickly, so your residual nitrogen is less when you fly than it would be for “slow” tissues which offgas slowly. Dive Computer Theory and Application Dive computers differ from most traditional dive tables in that they track multi-level dives, rather than the squarewave profile required by tables. Most recreational dives are multi-level, so significant increases in available underwater time can be obtained by using a computer. Dive computers utilize either a table-based or model-based program. There are computers based on the U.S. Navy tables, the Spencer No-D limits, the Swiss model, the Reduced Gradient Bubble model, and others. The wide variety of dive computers on the market can give a large range of decompression data for similar dive profiles. It is up to the individual diver to decide which is best for their purposes. The actual design and features of dive computers is covered in the Equipment section of this text. The use of a dive computer as a tool in dive planning, and as a decompression aid, requires skill and practice. While many of the dive computer’s features make it easier to conduct a dive, it can also add extra levels of complexity to dive planning with various dive buddies. Some general guidelines for the use of dive computers have been developed by the American Academy of Underwater Sciences (AAUS) and are presented here in slightly modified form. AAUS Dive Computer Guidelines • Each diver relying on a dive computer to plan dives and indicate or determine decompression status must have his or her own unit. • On any given dive, both divers in the buddy pair must follow the most conservative dive computer. • If the dive computer fails at any time during the dive, the dive must be terminated and appropriate surfacing procedures should be immediately initiated. • A diver should not dive for 18 hours (or as long as 24 hours with some newer computers) before activating a dive computer to use it to control his or her diving. • Once the dive computer is in use, it must not be switched off until it indicates complete offgassing has occurred or 18 hours have elapsed, whichever comes first. • When using a dive computer, non emergency ascents are to be at the rate specified for the make and model of dive computer being used. • Ascent rates shall not exceed 9 msw/min (30 fsw/ min) in the last 18 msw (60 fsw). • Whenever practical, divers using a dive computer should make a stop between 3 and 9 m (10 and 30 ft) (5 m or 15 ft for NAUI tables) for 5 min, especially for dives below 18 msw (60 fsw). • Only one dive on the dive computer in which the NDL of the tables or dive computer has been exceeded may be made in any 18 hour period. • Repetitive and multi-level diving procedures should start the dive, or series of dives, at the maximum planned depth, followed by subsequent dives of shallower exposures. • Multiple deep dives require special consideration. There are many NAUI training opportunities that will help you with learning the complexities of decompression management. Nitrox Diving The no-stop time limits for various depths can be extended by using a gas mixture containing a higher than normal percentage of oxygen and a lower percentage of nitrogen than air. Because nitrogen partial pressure is lower, less is absorbed. Such diving is referred to as Nitrox, oxygen enriched air, or enriched air nitrox (EANx) diving, and is commonly used in science and in the military. In the late 1980’s and early 1990’s, divers engaged in “technical diving” began to use nitrox on a regular basis. EANx diving has become so common place it is no longer considered technical. Special tables or computers, equipment, compressors, and training are required for nitrox diving.
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