Effects on heat stress of a flame-retardant ensemble for aluminum smelters.

A common belief is that a flame-retardant clothing ensemble will increase the level of heat stress over ordinary cotton work clothes. This is supported by bench tests on fabrics that indicate higher insulation and vapor resistance values for flame-retardant clothing. This research compared a flame-retardant clothing ensemble for an aluminum smelter (Zirpo wool shirt and FR8 denim pants) with typical cotton work clothing. Four young men walked on a treadmill at two work levels inside a climatic chamber under controlled conditions of heat stress. During each test, heart rate, core temperature, and skin temperatures were continuously monitored and recorded every 5 min. After a physiological steady state was achieved, temperature and humidity were slowly increased to maintain a relative humidity of 50%. The critical condition was the time when thermal regulatory control was lost (called the inflection point, marked by a steady increase in core temperature). The climatic conditions at the inflection point were used to assign a critical wet-bulb globe temperature (WBGT). A three-way analysis of variance examined the effects on critical WBGT of clothing, work level, subjects, and the interaction between clothing and work level. There were no significant findings. Therefore, there should be no difference in the level of heat stress between the two clothing ensembles under the same environmental and work conditions.