Evaluation Of Heat Stress Index And Determination Of Safety Limits In A Hot Environment

Since the 20th century,more than 160 heat stress indices have been proposed for various environments,but the applicability of the index is still unclear.Most studies on heat stress index and the determination of safety limits are based on physiological parameters,while there are fewer studies on mental health and cognitive performance,and there is no"quantitative"description of cognitive performance.Therefore,this thesis evaluates the applicability of heat stress index in hot environments.In addition to commonly used physiological parameters,subjective sensation and cognitive performance are also considered.Based on the optimal indicators,safety limits are obtained.This thesis is based on a series of climate chamber experiments completed by the research group.The experiment is divided into 3 phases,10 working conditions are designed,that is,a combination of 5 temperature（26,30,33,37,and 39°C）and 2 relative humidity（50%,70%）.A total of104 healthy subjects participated in this series of experiments.The subjects were different in different phases of the experiment,and changes in physiological parameters were recorded during the experiment.Subjects maintained a sedentary state to complete a series of experimental tasks under light activity intensity（average metabolic rate was 58W/m²）.During the whole experiment,the physiological parameters of the subjects were measured by experimental instruments.At the same time,cognitive performance tests and subjective questionnaires were also required to be completed.The results are:（1）Most of the"empirical"heat stress indices were strongly linearly correlated with eardrum temperature,skin temperature and thermal sensation vote（r>0.8）.（2）Considering the correlation coefficient and goodness of fit comprehensively,DI,DI_Sohar,ESI,ET,RHDT,THI and WBDT can better reflect the changes of eardrum temperature,and ET,Humidex,RHDT,THI and WBDT can better to reflect changes in thermal sensation votes.（3）Based on the optimal index,the safety limits for reflecting physiology,thermal comfort and cognitive performance in a hot environment are obtained.By comparing with the original scale of the index,it is found that the DI,DI_Sohar,ET and THI all overestimate the heat stress on subjects in hot and humid areas.（4）Compared with temperature,humidity has a greater impact on the accuracy of cognitive performance,so a dynamic model of moisture content and cognitive accuracy is established.With the increase of moisture content,the accuracy of cognitive test gradually decreased,showing an"inverted U"trend.From the perspective of cognitive performance,31.5g/Kg（dry air）is recommended as the upper limit of safe working humidity for heat-adapted personnel in hot and humid areas.