ABSTRACT
Humans, like all mammals and birds, have physiological mechanisms designed to maintain a constant body temperature. When surroundings become hotter or colder, must have corresponding regulatory mechanisms to control our internal temperatures. Harm, termed heat stress, results from too great an increase in body temperature. Some jobs involve working at high surrounding temperatures, and so have the potential to cause such harm. Working under conditions of heat stress leads to a higher heart rate, so heart rate is used as a measure of heat stress. A person in good physical condition requires a smaller increase in heart rate to respond effectively to a given increase in core temperature. Heat loss due to evaporation of sweat depends not on temperature differences, but on the relative humidity of the surrounding air. Most workers exposed to extremely low temperatures are outdoor workers in northern winters or at high altitudes. Outdoors, the more significant measure of exposure is the wind chill.
