PHYSIOLOGICALLY EQUIVALENT CONDITIONS OF AIR TEMPERATURE AND HUMIDITY

Abstract

212 expts. of 2 to 6 hours'' duration were performed on men in an air-conditioned room with dry bulb temps. ranging from 23 to 50[degree] C. in combination with various relative humidities. The effect of the environment in each exposure was expressed as "index of physiological effect," by weighting equally the elevation of the subject''s heart rate, rectal temp., skin temp., and rate of sweating from the base values of these functions detd. in a cool environment on each subject in each activity. The indices were plotted in relation to dry bulb and wet bulb temps. and relative humidity. Expts. were run to determine the most severe environmental conditions in which men could maintain thermal equilibrium after the 2d hr. of 6-hr. exposures. The men walking in shorts maintained thermal equilibrium from the 2d through the 6th hrs. of exposures at 34[degree]C. with 91% relative humidity and at 50[degree]C. with 21% humid- ity when their metabolic rates were 188 Cal.mVhr. With metabolic rates of 130 Cal./m2/hr. they maintained equilibrium at 35[degree]C. with 96% humidity and at 50[degree]C. with 32% humidity. With resting metabolic rates of 46 Cal./m2/hr. the men in shorts could maintain equilibrium at 36[degree] C. with 98% humidity and at 50[degree]C. with 34% relative humidity. Clothed men maintained thermal equilibrium at the respective metabolic rates only in environments distinctly less severe than those listed above for the men in shorts.