Tolerance of hot, wet environments by resting men

¹ U. S. Army Natick Laboratories, Natick, Massachusetts

Studies were conducted on 10-man groups exposed at rest to 51 different hot, wet environmental conditions. "Tolerance times" of unacclimatized volunteers established objectively, as the time of occurrence of a rectal temperature of 102.5 F and/or a heart rate of 180 beat/min, were similar to reported values established on a subjective basis. The wet and dry bulb index (WD) of environment was the best predictor of tolerance time. Prior acclimatization to work in hot, dry conditions did not result in prolonged tolerance for resting men exposed to hot, wet environments; neither did it alter the rates of sweat production, the final skin temperatures, or the rates of increase in heart rate or rectal temperature during these resting, hot, wet environmental exposures. Finally, "passive" resting in hot, wet environments (up to 3 hr/day) did not prolong tolerance times or induce other manifestations of heat acclimatization during subsequent resting exposures to hot, wet environments for either unacclimatized or prior, hot, dry, acclimatized subjects.

Submitted on June 17, 1964