This article aims to present the physical adaptation capabilities of a human, seen as a response to extreme hot and dry or hot and humid conditions. Adaptation capabilities are expressed as safe exposure time in two variants: at rest and during physical activity. The study shows the results of calculations of the variability over time of the core temperature and skin temperature as well as heat balance. Calculations were made according to Standard No. EN ISO 7933:2005 on the basis of assumed and actual meteorological data. The results of the calculations show that in these conditions a hot but dry environment enables a human (although to a limited extent) to stay and perform low physical activity, provided access to drinking water is ensured. In contrast, a hot but humid environment causes more serious problems, due to the inability to reduce skin temperature by evaporation of sweat from the skin surface.
Keywords: air humidity; heat balance; heat stress; hot environment; partial pressure of water vapor; predicted heat strain.