Study On Thermal Safety Evaluation Of Construction Workers Under High Temperature Environment In Guangzhou

With the progress of social civilization,more and more people pay attention to the health problems of outdoor workers.Extreme thermal environment directly endangers outdoor workers’health,poses a threat to work safety and reduces workers’productivity.The changes of human physiological indexes and heat exposure time are the main factors to evaluate thermal safety in extreme thermal environment.Therefore,it is necessary to determine the relationship between human physiological indexes,cognitive ability and thermal parameters in order to accurately predict and evaluate human thermal safety in extreme thermal environment.In the summer of 2019,we conducted field investigations including thermal parameter measurements at construction sites in the Guangzhou area.Two kinds of questionnaires,namely the thermal comfort survey and the cognitive ability survey,were obtained,with 1063valid questionnaires respectively.We analyze the relationship between health risks and thermal parameters(outdoor ambient temperature,mean radiation temperature,wind speed,relative humidity).The adaptability and sensitivity of the workers to thermal parameters,physiological indicators(heart rate,ear canal temperature),as well as the changes in the cognitive ability of the workers are analyzed.Firstly,based on the analysis of workers’thermal sensation vote and satisfaction with outdoor environmental factors,some suggestions are put forward based on the comparison of thermal indexes.The results showed that 40%of the employees felt unwell,and the main symptoms were fast heartbeat and sweating,accounting for 30%and 40%respectively.When T_a≥34°C,it is necessary to reduce the work intensity of workers on the construction site.When the temperature is lower than 33°C,increasing the wind speed(V_a)has a positive effect on improving human thermal comfort.When the wind speed is greater than 1.3m/s,the satisfaction rate of workers is relatively high(more than 80%).When the relative humidity(RH)is between 45%and 70%,people’s satisfaction with relative humidity is higher.Second,the analysis found that physiological indexes and cognitive ability had significant effects on the physical and mental state of workers.Heart rate(HR)and ear canal temperature(ACT)increased with the increase of working hours,while cognitive ability decreased with the increase of thermal parameters.To avoid discomfort,it is recommended to keep the heart rate around 94 beats/minute.With the increase of thermal environment parameters,the efficiency decreases by about 8%.By comparing the average efficiency of different age groups,it is found that the efficiency value of each age group is 5%different.Finally,this paper modifies the adaptability of Physiological Equivalent Temperature(PET),Universal Thermal Climate Index(UTCI),Tropical Summer Index(TSI)and The Wet Bulb Globe Temperature(WBGT).When the thermal index is used to evaluate the thermal comfort of outdoor workers,it needs to be modified according to the local climate and working environment to avoid excessive exposure to hot outdoor environment.According to the MTSV regression model,the interval division of thermal indexes(PET,UTCI,TSI and WBGT)and the classification of thermal stress were modified.The maximum acceptable levels for PET,UTCI,TSI and WBGT were 22.6°C,25.3°C,30.7°C and 28°C,respectively.PET exceeds 47.0°C,UTCI exceeds 46.7°C,TSI exceeds 41.0°C,or WBGT exceeds 34.6°C,the thermal environment is in an intolerably high temperature state,which may pose a risk to human health,and the operation is recommended to be stopped.The results of this study have a guiding significance for the construction workers in Guangzhou to work in hot environment,regulate the labor intensity of workers in different hot environment,reduce the thermal hazards,protect the health of workers,and have a certain reference value for the establishment of relevant safety standards on construction sites.