Study On Local Cold Stimuli Sensitivity Of Physical Workers In Summer

Manual labour workplaces such as factories generally do not have cooling facilities such as air conditioning.In summer,the natural ventilation and fans are usually used to regulate the thermal environment.Therefore,people working in workshops are often in a hot environment in summer.Considering the characteristics of physical work,workers need to complete operation,walking,moving,etc.,whose intensity are higher than that of light activities such as office works.And most of physical workers are generally required to wear uniforms due to the requirement of work,which restricts the regulation of clothing.Fans alone cannot guarantee the heat dissipation needs of physical workers,and excessive wind speeds will also interfere with their normal operation.The wearable cooling PCS（PCS,personal cooling system）can be combined with human clothes,and the heat dissipation of human body is greatly improved through contact heat transfer.And it is an effective equipment to improve the thermal comfort of human.In summer,the heat dissipation needs of physical workers are higher,in order to increase the heat dissipation of wearable cooling PCS,the cooling temperature can be further reduced.However,the cooling effect of lower cooling temperature is good,but it will easily cause discomfort of cold stimuli.Existing research shows that there are great differences in the sensitivity of various body parts to cold stimuli when sitting.Are the differences will be changed when engaging in physical works?And how does the sensitivity of each body parts change?All of these questions should to be taken into account when applying the wearable cooling PCS device for physical workers.Therefore,this paper carries out related researches on physical workers.Based on the fact that taking the wearable cooling PCS to improve the thermal comfort of physical workers in the summer workshop,this paper carries out an experimental study on the cold stimuli sensitivity of different body parts of physical workers.By combining subjective questionnaires and physiological parameters,the differences in cold stimuli sensitivity of different body parts,regional differences,gender differences and the impact on local thermal sensation under sitting and physical working are investigated.In the experiment,20 college students（10 men and 10 women）dressing uniformly were recruited as subjects.Three cold stimuli temperatures were selected（22℃、24℃、26℃）,and eight body parts（chest,back,abdomen,forearm,upper arm,thigh,lower leg and ankle）were stimulated one by one both at sitting and physical working.Each body part was stimulated for 3 min.The overall thermal sensation,local thermal sensation,overall thermal comfort,and local thermal comfort vote were collected before and after cold stimuli of each body part.During cold stimuli,the cold stimuli sensation and cold acceptance were collected at the 10th s,1st min,2nd min and 3rd min.The mean skin temperature(T_sk)and the local skin temperature(T_lsk)of the stimulated site were continuously recorded.Through the analysis of experimental data,the main conclusions are as follows.1)During physical working,the cold stimuli sensitivity of subjects is reduced,and the acceptance of cold stimuli can be increased by 20%to 40%.During cold stimuli,the local thermal sensation decreased significantly,and the local thermal comfort has been significantly improved.The improvement of each body part during physical working is lower than that of sitting.2)During the cold stimuli,the T_lsk of most body parts are influenced significantly by activity levels,with significant difference between sitting and physical working.Except for the change rate of T_lsk on back,thigh and lower leg,there is no significant difference on the other body parts between the two states.3)Considering the difference of T_lsk,this study proposes the index of stimulus temperature difference(temperature difference between stimulus temperature and T_lsk).The analysis showed that the cold stimuli sensation during sitting and physical working increases with the increase of the stimulus temperature difference.Under the same stimulus temperature difference,the cold stimuli sensation during physical working is lower than that of sitting.When the stimulus time is≥2min,the cold stimuli sensation hardly changes with the stimulus temperature difference.4)Based on the cold stimuli sensitivity and the changes of local thermal sensation vote,the sensitivity level of the body parts is classified as three level groups both at sitting and physical working.The thigh and abdomen are more sensitive to cold stimuli when sitting,while the upper arm and abdomen are more sensitive when physical working.Based on the changes of local thermal sensation vote,cold stimuli to abdomen and chest are more effective to reduce the local thermal sensation during sitting,while cold stimuli to back and chest are more effective during physical working.5)Both during sitting and physical working,there is no significant gender difference in cold stimuli sensation,the reduction of local thermal sensation after cold stimuli,and the change rate of T_lsk.During cold stimuli,the T_lsk of each body parts has significant gender difference,and the T_lsk can be influenced by stimulus temperature.According to sensitivity,both men’s and women’s abdomen are strongly sensitive;and according to the local thermal sensation,during sitting,women’s abdomen and back and men’s upper arm and chest have strong effect;during physical working,both men’s and women’s back have a strong effect on reducing local thermal sensation.Through the experimental research in this paper,during physical working,the sensitivity to cold stimuli is lower than that of sitting,but there is no significant gender difference to cold stimuli sensitivity.Considering the reduced sensitivity of physical workers to local cold stimuli,the feasibility of lowering the cooling temperature can be further considered when applying the wearable cooling PCS on physical workers to meet the higher heat dissipation requirements in summer.Relevant results can further provide reference for the development of wearable cooling PCS.