Central Nervous System Oxygen Toxicity in Closed-Circuit Scuba Divers

The U.S. Navy is currently interested in expanding its closed-circuit oxygen diving capabilities. Previous dive series at NEDU in 1982 and 1983 resulted in significant extensions of the oxygen exposure limits and the development of the transitexcursion concept in which a single excursion below 20 FSW is allowed during a four hour exposure providing the rest of the the dive is spent at 20 FSW or shallower. This series was conducted in NovemberDecember 1985 and was designed to explore the possibility of doing multiple downward excursion on a closed-circuit oxygen dive. One hundred fifty three experimental oxygen exposures of up to four hours were conducted in the Ocean Simulation Facility. Conclusions from this study were Increasing the time at 20 FSW between downward excursions from 30 minutes to 60 minutes reduced the incidence of serious toxicity episodes from 14 to 5. An initial excursion to 40 FSW for 15 minutes rendered divers susceptible to subsequent oxygen toxicity at 20 FSW. The U.S. Navy standard Oxygen Tolerance Test was not sensitive enough to produce symptoms in the three oxygen-susceptible divers identified in this dive series. Minor symptoms of pulmonary oxygen toxicity were noted after some of the four hour dives.