[abstract] UPWARD EXCURSION LIMITS FROM NITROX SATURATION.

Abstract

As part of the work designed to study upward excursion limits which could be used in a submarine rescue scenario, research dives were conducted using the nitrox equivalent of standard air at 5 ATA (132 FSWG) in order to reduce the problems of pulmonary oxygen toxicity (POT). Using a partial pressure of oxygen (p02) of 0.4, the depth equivalent to 5 ATA is 4.4 ATA (111 FSWG). Ten chamber dives were carried out. On the upward excursion from 4.4 to 3.1 ATA (111 to 70 FSWG), with six subjects, no symptoms of decompression sickness (DCS) were reported, nor were any venous gas emboli (VGE) using doppler techniques. The following two dives, with six subjects, used an upward excursion to 2.8 ATA (60 FSWG), again with no DCS reported. The next dive with an excursion to 2.7 ATA (55 FSWG) resulted in three of four divers reporting symptoms of DCS, the fourth diver reporting only pruritus prior to all divers being recompressed for treatment. Making the assumption that the 2.8 ATA depth was a viable excursion, two additional dives were carried out with the upward excursion from 4.4 ATA to that depth. with eight divers, three reported DCS and were treated. Three additional dives were conducted with the upward excursion from 4.4 to 3.0 ATA with nine divers. No DCS was reported. The conclusion was reached, therefore, that the air equivalent of this upward excursion limit could be recommended for further fleet testing. During all dives VGE were monitored both at rest and exercise. The results indicate that bubble formation is greatest, and is sustained longest, the greater the pull from 4.4 ATA. Review of the data shows that bubbling, even at significant levels, is neither necessary nor sufficient to predict the occurrence of DCS. certain divers with high bubble grades did not develop DCS, while at least one diver with no evidence of VGE did develop DCS.