Research On Human Heat Tolerance Under Extreme Heat Environment

With the social development and civilization progress, workers' operation environment attains more and more attention. Health harm to workers and latent threat to operation security by extreme heat environment need urgent solution. The variation tendency of human physiological parameters, exposure limit duration and corresponding limit physiological values are the main factors for evaluating heat stress under heat exposure. A simple, accurate and easily calculated evaluation method to assess heat stress always is the research direction scholars pursue. Through the large-scale subjective experiments, exploration research on human heat tolerance abilities and evaluation method for heat stress assessment under extreme heat environment was performed.The chamber with the adjustable environment of high temperature and humidity was constructed. The dry bulb temperature in it can vary from 30 to 42℃and relative humidity can be controlled from 40% to 80%. 192 university students were chosen as the experimental subjects, who performed the physical activities with different intensities when exposed in some heat environment. Heat tolerance abilities of human bodies under the conditions of extreme heat environment were evaluated according to subjective and objective methods. The variation tendency of physiological parameters during the process was obtained. The utmost heat tolerance duration and physiological limit values of human bodies at heat exposure limit were achieved. The influence of heat environment parameters to heat tolerance of human body was analyzed.The relative curves between heat exposure limit duration and WBGT, and corresponding mathematical models were established in the combination with different working intensities and thermal parameters. They both can be applied to predict the maximal duration of human body's heat tolerance. At heat exposure limit, the limit values of oral temperature, the maximum values of sweating rate and the relation between oral temperature and heart rate of male subjects were all analyzed and summarized. How the difference between oral temperature and skin temperature impacted the human ability of heat exposure was obtained. The gender difference of heat tolerance ability was analyzed.A new subjective evaluation system different from ASHRAE's heat comfort evaluation system is proposed. Score in new system can reflect human body heat tolerance ability. The principle of heat-humidity exchange between human body and extreme heat environment was analyzed. The factors influencing body heat regulation were determined. Contrasted with different heat evaluation index, each adaptation condition and advantage were analyzed. The physiological stress index developed from D.S. Moran was revised instead of rectal temperature by oral temperature and applied to evaluate heat exposure limit and healthy heat exposure, which can definitely reflect body heat exposure condition. Also, recommended warning duration and recommended limit duration in the course of heat exposure in different WBGT were given, which can provide reliable data support to instruct safety working standard under heat environment.