Thermal influence of sunshine and clothing on men walking in humid heat

¹ Applied Physiology Branch, U.S. Army Chemical Research and Development Laboratories, Army Chemical Center, Maryland

For two men walking on a treadmill and wearing two layers of permeable clothing, the same physiological strain measured by the rate of increase in mean body temperature could be produced a) next to a building outdoors in the sunshine with an average air temperature of 85 F and humidity of 20 mm Hg and b) indoors with the same humidity and an air temperature 10 F higher. Under these conditions, the underwear was mainly wet with sweat and the outer layer was mainly dry. In comparable indoor tests on a third subject, the temperature of the underwear approached equilibrium 1 or 2 F lower than the temperature of the skin at air temperatures of 85 and 115 F. The error in calculating clothing insulation introduced by assuming the clothing to be dry is determined by the size and direction of the temperature gradient between skin and air. Adding 10 F to the indoor air temperature does not duplicate all the effects of sunshine.