Ergonomics of heat and cold.

The biophysical, physiological and some of the psychological aspects of work under unfavorable man-made ambient conditions are presented in light of the need to prevent excessive strain. Work is treated in two ways: 1) in terms of the muscles O2 demand as a fraction of maximal aerobic capacity; and 2) in terms of metabolic heat source. Since maximal aerobic capacity depends on factors such as physical fitness, age and sex, these factors require consideration in estimating strain due to work. The absolute metabolic heat (M) produced during work is needed in the consideration of the total heat balance. Radiation (r), convection (C), and, under some circumstances, evaporation (Eev) are the main avenues of heat exchange between man and his immediate environment. Eev is primarily a function of the ambient potential for evaporation (Emax). Since the relation of the sum M+R+C to Emax determines heat balance when man in under a heat load, evaluation of the avenues of heat exchange, the sources of heat load, and the stressing effect of all these on the physiological responses are treated in some detail. Psychrometrically defined limits of exposure are also discussed. Subjective sensation and mental performance are discussed in light of their correlation with physiological responses to heat. Cold is treated mainly from the point of view of safety and protective clothing.