Laboratory evaluation of permissible exposure limits for men in hot environments.

Forty-six industrial workers completed a total of 653 one-hour work bouts requiring an average of 122-235 kcal/M2/hr in an environmental chamber maintained at heat stress levels ranging from 8-37 degrees C wet bulb globe temperature (WBGT). Heart rates (HR) and rectal temperatures (Tre) were measured at the end of each work bout. Environmental heat stress levels were divided into two groups - those above and those below the permissible exposure limits (PEL). The PEL is the proposed maximum environmental thermal stress to which industrial workers can be exposed without endangering their health. The number of observations in each of these regions was further divided into those which were above the recommended limits of a World Health Organization study group (HR less than or equal to 110 bpm, Tre less than or equal to 38.0 degrees C) and those which were not. The number of "safe" (HR less than or equal to 110 bpm, Tre less than or equal to 38.0 degrees C) observations in environments with heat stress less than or equal to the PEL ranged from 100% to 2.4% depending on subject acclimatization and work rate. The degree of protection was always less in the winter than in the summer and was less for higher work rates. Men who normally worked in hot environments had fewer "excessive" HR's and Tre's than those who did not.