Today thermal comfort is defined as »that condition of mind that expresses satisfaction with thermal environment«. Air temperature, radiant temperature, air velocity, humidity, clothing insulation, and metabolic rate are the six basic factors of thermal comfort. All of these factors should be taken into account, as each one is not a sufficiently accurate indicator of thermal comfort. In this paper, I will present the WBGT, PMV and PPD measurements of heat stress. WBGT parameter is used for large heat loads, and for its calculation we need dry bulb temperature, natural wet bulb temperature and globe temperature. WBGT is used together with metabolic rate to determine the limit for sustained work. PMV is an index that indicates the expected mean value of heat sensation and is presented on a seven-point scale. The index PPD indicates the expected percentage of people who are not satisfied with the thermal environment and is calculated from the PMV index. When the work environment is not comfortable, heat stress can occur, which in turn can lead to various occupational illnesses such as heat stroke, heat exhaustion, heat cramps, heat syncope, heat rash and, rhabdomyolysis. To prevent this, precautions such as temperature control, limiting work pace and duration of exposure, prevention of dehydration, worker training, and health surveillance must be taken.
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