Study On The Thermophysiological Responses And Heat Strain Prediction And Evaluation Of Workers In Hot Coal Mines

With the increase of mining depth and the improvement of mining mechanization,heat hazard in deep coal mines has been getting more serious,which has become another major mining disaster following the disasters of geological disaster,mining gas,coal fire,inrush water,and coal dust explosion.Heat hazard not only greatly reduces the production efficiency,but also does harm to the physical and mental health of coal mine workers.In recent years,scholars and engineers have paid more and more attention to the research on the prevention and control of head hazard in hot coal mines.Taking advantage of the thermal comfort assessment methods,thermal stress evaluation indicators,experiments,and on-site monitoring methods,a large amount of work has been done on the evaluation of thermal comfort and thermal stress in underground coal mines.In general,in the study on evaluating thermophysiological responses of miners in hot mines,domestic and foreign scholars have only placed emphasis on steady-state and certain high temperatures in the laboratory.The research work employing the thermal stress index or thermal comfort evaluation models has been also mainly focused on the analysis of the thermal response of the workers at steady-state constant temperature,which is inconsistent with the changing temperature conditions of along the working face.At present,domestic and foreign scholars have achieved a lot on the evaluation of human body heat stress under hot working condition,and established many human thermophysiological responses and heat strain evaluation models,whereas they seldom work on the evaluation of workers'heat stress in hot coal mines.In view of the problems in the study of heat safety assessment of workers in hot coal mines mentioned above,this paper thoroughly measures and analyzes the thermal performance(thermal insulation)and moisture transmission performance of coal mine working ensembles in China using the thermal manikin and artificial environment chamber.On this basis,this paper further established a thermal strain prediction and evaluation model for mining workers in steady-state and transient thermal environments.In addition,in this paper,the thermal responses and heat strain of the miners at certain temperature locations and temperature-changing working face are simulated and analyzed.This research is of scientific significance and of great application value for making reasonable working strategies in hot coal mines.The main research work carried out in this thesis and the research results obtained are concluded as follows:a)In view of the lack of accurate reference value for the thermal insulation of coal mine overalls in the thermal safety analysis of high-temperature coal mines,this paper thoroughly measures and analyzes the thermal performance(thermal insulation)and moisture transmission performance of coal mine working ensembles in China using the thermal manikin and artificial environment chamber,and the dynamic thermal insulation and evaporative resistance under the influence of body movement and wind speed were corrected.Firstly,the thermal insulation and evaporative resistance of the coal mine ensemble under the standard thermal conditions recommended by the international standards were measured and analyzed.The results show that the local thermal insulations and evaporative resistances of coal mine ensemble vary a lot,and the thermal insulation of hand and foot ends are small,and the thermal insulation at thighs,abdomen,buttocks,and shoulders are high.The evaporative resistance of at abdomen,buttocks and feet are greater.The thermal resistances of old and new coal mine ensemble do not change a lot,but the evaporative resistance decreases by 13.5%after one year use.Secondly,considering the high-temperature and high-humidity environment conditions in hot coal mines,this paper also analyzes the effect of temperature and humidity changes on the thermal insulation and evaporative resistance of coal mine suits by thermal manikin experiment,and the results show that:when the relative humidity exceeds 70%,the thermal resistance of coal mine working overall is significantly reduced,and when the relative humidity is increased form 50%to 80%,the thermal resistance will be reduced by nearly 20%and then maintained at a stable level.However,the thermal resistance of coal working overall varies little under different ambient temperature conditions;the evaporative of coal working overalls varies significantly under different humidity conditions.When the relative humidity increases from 55%to 70%,the evaporative of coal working overalls reduced by about25%.When the relative humidity increased again,the reduction in the evaporative of the coal working overalls became smaller.However,under different ambient temperature conditions,the local evaporative resistance of the coal mine overalls varies significantly and is different from that at the upper arm,the foot and the buttocks.b)When the human body moves or the air speed is relatively high,the coal mine clothing openings(collars,cuffs,etc.)will have a“pumping effect”,resulting in thermal convection between the air at the skin surface and the external environment air flow increase,which will reduce the thermal insulation of coal mine clothes.This paper introduces a more accurate heat and moisture resistance correction formula proposed by Havenith based on massive experimental data,and then calculates and corrects the dynamic thermal insulation and evaporative resistance of coal mine suits.The results show that when the walking speed of underground coal miners is 0.5 m/s and the air velocity is 2 m/s,the total thermal resistance of the coal mine working clothes is reduced from 0.202 m~2?K/W at static state to 0.114 m~2?K/W.When air speed in the coal mine increase from 2 m/s to 3 m/s,the decrease extent of the thermal insulation of coal mine working clothes declines compared with the increase of the air speed in the coal mine from 1 m/s to 2 m/s.c)In this paper,the Predicted Heat Stain(PHS)model was improved by adding the measured and corrected thermal insulation and evaporative resistance of working ensemble for hot coal mines and also by introducing a metabolic rate formula for evaluating mining activity.Based on the improved PHS model,the heat strain of workers at certain spots in hot coal mines was calculated and analyzed.The results show that under the hot environment conditions of high temperature coal mine with relative humidity lower than 90%and air temperature lower than 28°C,increasing the air flow velocity at the working site of high temperature coal mine can effectively prolong the acceptable exposed working time for workers.However,when the wind speed at this site is higher than 2 m/s,the longest acceptable exposed working time for coal mine workers will change less.Secondly,when the relative humidity of air in hot coal mines is higher than 80%and the air temperature is higher than 30°C,the sweating rate of workers increases.In this case,by increasing the speed of the air flow at hot coal mine working site,it will not significantly affect the sweating rate and the amount of sweating of mining workers.Finally,the established model was used to analyze the thermal and physiological response of workers at constant temperature locations in high-temperature coal mines wearing normal mine overall,normal shorts,and short-sleeved with protection against heat radiation,especially under conditions of high-temperature heat radiation.The results show that under the high-temperature heat radiation environment,the short-fitting shorts with heat radiation effect can effectively relieve the thermal stress and prolong the acceptable longest working time for the miners.This working time is three times bigger than that of normal mining clothes in the same high temperature,high humidity and heat radiation environment,and 1.5times bigger than that of ordinary shorts.d)In order to apply the PHS model to the prediction and calculation of human thermal stress under transient thermal condition,this paper further improves the steady-state PHS model.The PHS calculation flow was modified,and C++programming technique was employed to customize the calculation initialization structure“DefnParams”.At the same time,a function named“SetEnvi”is introduced for accomplishing a variable temperature environment and human factors.Firstly,the working environment,human factor parameters,and other calculation parameters are initialized by DefnParams,and then,as the working time passes,a custom heat and humidity environment condition is dynamically input to the PHS calculation module using the loop structure.In this case,the change of the hot and humid environment at any time interval is realized so as to calculate the amount of human body heat stress response under variable thermal condition.e)In this paper,a multi-segment thermophysiological model with an improvement in heat and moisture transfer through clothing was used to evaluate heat stress at the working face in hot coal mines.The improved thermophysiological model was demonstrated with miners'thermal response data collected by field measurements.Based on the above model,the thermal responses and thermal sensation of the workers under transient working face were simulated.Parametric simulations were done to evaluate the physiological influences of the relative humidity and the unsteady(cool-hot changing)air temperature along the working face.It is found that the cool-hot changing thermal environments significantly affect miners'physiological responses and thermal sensations,especially the air temperature changes around 24?~26?,and the heat stress can be relieved if a proper work-rest organization in a hot working face is addressed.f)In order to facilitate engineers to quickly analyze the impact of high temperature mining environment on thermal responses of workers and then effectively perform the thermal strain prediction and evaluation of workers in hot coal mines,this paper employs C++and Qt programming language to develop a software for heat strain prediction and evaluation of workers in hot coal mines.Good main interface,parameter input interface and result displaying interface were designed,and the application of the software was demonstrated with a case study.The software has the following main functions:calculating the metabolic rate according to the worker's labor intensity;calculating the thermophysiological responses such as perspiration rate,sweat rate,body core temperature under certain working hours and certain work intensity;determining the longest acceptable exposed working time for miners according to human body sweating rate and the core temperature.The main innovative work of this thesis at theoretical and application levels is concluded as follows:a)This paper measures and analyzes the thermal performance(thermal insulation)and moisture transmission performance of coal mine working ensembles in China using the thermal manikin and artificial environment chamber,and the dynamic thermal insulation and evaporative resistance under the influence of body movement and wind speed were corrected.At the same time,taking into account the high-temperature and high-humidity environmental conditions in hot coal mines,the influence of environmental temperature and humidity changes on the thermal insulation and evaporative resistance of coal mine suits was analyzed.b)Thermophysiological responses prediction and heat strain evaluation models for both steady-state and transient thermal environments in coal mines have been developed,and then the thermal responses of workers at certain hot spots and variable temperature-changing working face have been analyzed.c)Based on the proposed thermophysiological responses prediction and heat strain evaluation models for certain hot spots and variable temperature-changing working face in hot coal mines,this paper this paper employs C++and Qt programming language to develop a software with friendly and convenient main interface,parameter input interface and result displaying interface for heat strain prediction and evaluation of workers in hot coal mines.