Objective. The purpose of the study was to determine the influence of initial conditions of a microclimate on volunteers' permissible exposure limits to a hot and humid environment. Materials and methods. Eighteen experimental studies with the participation of three volunteers were performed under controlled microclimate conditions (two climate chambers). The skin temperature and body core temperature were measured after they had stabilized in the following microclimate conditions: temperature of 17, 21 and 23 °C, relative humidity of 50% and hot microclimate conditions, i.e., temperature of 35 and 42 °C, humidity of 80% and physical work load at 30 W. The time needed to reach a body core temperature of 38 °C was determined under hot conditions. Heat accumulation was calculated. Results. Lowering volunteers' skin temperature under conditions of stabilized physiological parameters prolongs the time necessary for the body core temperature to reach 38 °C during physical work in a hot and humid environment. Conclusions. Appropriate acclimatization before exposure may prolong the time of safe work in a hot environment, e.g., during activities of rescue services.
Keywords: heat accumulation; heat load; pre-cooling; skin and body temperature; time of safe exposure to heat.