| High temperature weather conditions occur frequently due to the global warming,the over heating risks of human body in hot working environments have aroused widespread concerns.Hot weather in the summer has been constantly refreshed the records in recent years throughout China,with increasing occupational injuries in hot working environment.Heat stress is a risk factor derived from the natural environment,which not only affects human health,work status,productivity,but also easily lead to accidents.Excessive exposure to heat can directly lead to a variety of thermal diseases and even death.Furthermore,due to the working intensity of modern industries,the over heating risk is likely to increase.In the majority of cases,people cannot avoid the direct exposure in a hot environment,heat injours have penetrated into many aspects in their daily life,including industry,agriculture,tourism,military activities,sports science and other fields.How to evaluate the effects of hot environment on the physiological parameters of the human body has become,and will continue to be the focus of future studies in heat stress.On the other hand,the process of urbanization in China has been increasing with the emergence of a large number of aging workers.China has formed more than 800 million manual workers by 2015,which is currently the world's largest manual labor population.The population has been engaged in in long-term outdoor or semi-outdoor environment with high-intensity physical labor,which is quite vulnerable to hot environments.However,at present,there is still a big gap between China and the developed countries on hot environment management level in industry in legislation in regard to the hot working environment.There is need to ensure the safety of labours and the implementation of related laws,regulations and standards.It is urgent to carry out basic research on the heat strain for the Chinese population in its specific working environments.In order to research into the characteristics of physiological responses of the Chinese working population under hot environments and put forward an effective heat stress prediction model,this study firstly carried out a field study of the heat stress environment on a construction site in Chongqing.Field study revealed that,in practical working sites,the workers' sleep quality,drinking habits and smoking habits and other non-quantitative factors directly affected their heat responses,workers are difficult to guarantee the ideal healthy states in working conditions.According to the continuous monitoring on heart rate of the workers on the construction site,the heart rate of the workers had been in a state of continuous fluctuation between 50 bpm and 150 bpm,indicating an unsteady working metabolic rate.Ten normal workers with average age of 41 years were selected for the experimental study on human body physiological responses in the artificial climate chamber.Their rectal temperature,skin temperature,heart rate and sweating rate were continuously monitored.The concept of mean difference,coefficient of variation and SKEW were introduced to study the control ability and logic of each physiological parameter of subjects in the hot working environment.The result from such experiments in the artificial climate chamber has verified the existence of individual differences and provided the quantitative analysis on the effect of individual differences in the heat stress.The linear relationship between rectal temperature and skin temperature was found through the combination of theoretical derivation and experimental verification.Combined with the the measured physiological parameters and statistical analysis on its average difference,coefficient of variation and skewnees,the comprehensive deviation coefficient(CDC)model was proposed,which can comprehensively indicate the human heat stress risk.At the same time,the time-based fluctuation trend of each physiological index of human heat responses has been analyzed based on the human experimental study carried out in the artificial climate chamber.It is found that the predicted sweat rate of the PHS model in the 90 sub-working conditions is generally smaller than the measured value.Based on the experimental results and the human body heat balance equation,the dynamic prediction model of human heat stress in a hot working environment has been established.In the process of developing the model establishment,firstly,the human metabolic rate prediction method based on heart rate was put forward and its accuracy was compared with the prediction of human metabolic rate based on oxygen consumption.Secondly,according to the results of field study on the construction site,the control items of the human body heat balance equation were redefined.Finally,the time iteration term ti to ti + 1 in the PHS model was eliminated and the concept of the time-dependent element ??tx(x = 1,2,3...i)was introduced instead,and opened the computing process.This open loop not only realizes the dynamic monitoring and input of environment parameters and personal parameters,but also established the intact mathematical expression of Required Evaporation Heat(Ereq)as the objective function for the direct prediction of human heat stress level.The new model covers the six basic elements introduced in the classic heat stress research,and achieves the human heat stress prediction under the condition of both dynamic thermal environments and working conditions.The objective function Ereq in the model can perform the quantitative analysis on its single variable and the coupling variables by partial derivative analysis,and make it possible to design,evaluate and improvement the hot working environment based on human body heat stress protection.According to the characteristics and inputs parameters of the developed model of human heat stress prediction,the dynamic thermal experience experiment was carried out for model validation.The experiment has explored the fluctuation characteristics of human physiological parameters and thermal sensation in the dynamic heat process and continuous environment change.The results show that human thermal sensation changed prior to the thermal physiological indicators,providing support for the best working-resting plan.The verification of the model has two approaches of ISO case verification and dynamic thermal process experiment verification.Comparing the PHS model with the developed model based on the prediction performance of cases in ISO 7933,the results show that the predicted skin temperature of the developed model is in good agreement with the ISO 7933 standard(+0.16°C).The experiment results show that the difference between predicted skin temperature(Tsk)and measured Tsk in male and female subjects is 0.0931 ± 0.8750? and 0.4861±0.7484? respectively,and the model shows better prediction performance compared with the PHS model.Finally,the study on the application of the developed model was carried out.Taking Ereq as the objective function,the dynamic process of human heat stress under the influence of single factor and multi-factor was quantitatively analyzed based on the fluctuation of Tsk and Tre(rectal temperature)over time,including time,air temperature,radiation temperature,pressure,airflow velocity,heart rate,clothing heat insolation,coupled air temperature & velocity effect,coupled temperature & humidity effect,coupled time factor & heart rate effect.The application of the model can provide guidance for the design,operation,evaluation and improvement of hot working environments,and the best work-rest schedule for workers and working managers who are engaed in the work in hot environments with its boundary conditions.A total of 69 field workers and laboratory subjects were selected in the study for the heat stress study in summer on a construction site besides a total of 274 times of artificial climate chamber testing,this thesis developed the CDC coefficient as the index for the identification of overheating risk,the physiological response characters of Chinese working population,and finally the dynamic prediction model of human heat strain under hot working environments.The new model develops the traditional PHS model with the combination of ISO7999 and ISO8996 in the framework of the human body heat balance equation,and transforms the time iteration term into the time element summation term to form a new individual dynamic prediction model.Compared with the traditional PHS model,the new model solves the problem that the human heat stress is difficult to predict under the changing working environment and working intensity.With the combination of Tcr and Tsk transformation,the model achieves heat stress prediction at any time point of the whole working process.Based on the experimental results,the prediction efficiency of the new model on Chinese population is better than that of the PHS model,and the closed calculation loop of PHS model is opened for the design of hot working environment,representing practical significance to improve the human heat stress study in China,and also help to provide theoretical support for Chinese high-temperature labor protection standards in the future. |
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