Habitability in nuclear-powered submarines during prolonged submergence, and the provision of an acceptable space cabin atmosphere pose considerable problems for environmental medicine. Until recently, the ranges of human adaptation to gaseous components were not defined, interaction of environmental stressors had not been investigated, and the threshold limit values for continuous exposure to toxic trace substances had not been reevaluated.
The September Archives of Environmental Health1 reviews environmental physiology as it relates to submarines and spacecraft. An experiment in which 21 subjects were exposed to 1.5% CO2 for 42 days established the tolerance limits to chronic CO2 exposure. The results showed no significant changes in performance or in basic physiological parameters such as body weight, temperature, and pulse rate. However, slow adaptive changes were observed in respiration, acid-base balance, and calcium phosphorus metabolism. It took 23 days for the subjects to acclimatize to 1.5% CO2 and about