Experimental studies of the effects of enriched air nitrox dive on shortening of decompression time and reduction of risks of decompression sickness

Abstract

Enriched air nitrox diving has been conducted to shorten decompression time as well as to reduce risks of decompression sickness. Nine volunteer divers served as subjects for nitrox (-a: 60% N2 and 40% O2, and -b: 67.5% N2 and 32.5% O2) and air chamber dives of 20 m/60 min, 30 m/60 min and 40 m/60 min. Venous gas emboli (VGE) were examined after surfacing in a series of nitrox dives and of air dives to compare the risks of decompression sickness (DCS). Three divers as a group were compressed in a chamber for each dive. Decompression was carried out according to the Norwegian Navy nitrox decompression tables for the nitrox dives, and for the air dives the Japanese Ministry of Labor tables were used. Decompression time was much shorter in nitrox diving than in air dives for the same dive profiles. All of nitrox-a and air divers showed no VGE nor DCS symptoms after surfacing of 20 m dives. In case of 30 m dives, VGE appeared in one diver (33%) without DCS symptoms in nitrox-a dive but no VGE nor DCS in nitrox-b dive, whereas for the same air dives two subjects (66%) had VGE and DCS symptoms. When the depth was increased to 40 m in the nitrox dive, nitrox-b did not show both VGE and DCS, while the air dive showed one VGE and one DCS. These results suggest that the nitrox dive with suitable decompression schedule reduces the risks of DCS as well as shortening decompression obligation.