Decompression tables and dive-outcome data: graphical analysis.
We compare outcomes of experimental air dives with prescriptions for ascent given by various air decompression tables. Among experimental dives compiled in the U.S. Navy Decompression Database, many profiles that resulted in decompression sickness (DCS) have longer total decompression times (TDTs, defined as times spent at decompression stops plus time to travel from depth to the surface) than profiles prescribed by the U.S. Navy table; thus, the divers developed DCS despite spending more time at stops than the table requires. The same is true to a lesser extent for the table used by the Canadian forces. A few DCS cases occurred in profiles having longer TDTs than those of the VVal-18 table and a table prepared at the University of Pennsylvania. The TDTs for 2.2% risk according to the probabilistic NMRI'98 Model are often far longer than TDTs of experimental dives that resulted in DCS. This analysis dramatizes the large differences among alternative decompression instructions and illustrates how the U.S. Navy table provides too little time at stops when bottom times are long.
Van Liew
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Navy Experimental Diving Unit, Panama City, FL 32407, USA.
Flynn
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D003664:Decompression / Q000009:adverse effects / Q000592:standards*; D003665:Decompression Sickness / Q000209:etiology* / Q000517:prevention & control; D004242:Diving / Q000009:adverse effects / Q000592:standards*; D017408:Guidelines as Topic; D006801:Humans; D012016:Reference Values; D013997:Time Factors