Exploring on the prediction model of human skin temperature and rectal temperature under heat stress

Hot environments cast direct influence on people's well-beings and health besides working productivity during the accelerating global warming. The systematic mechanism is not entirely clear due to the complex human physiological response which also handled human heat strain protection. This study carries out mathematical derivation on the rectal temperature and skin temperature under human heat strain based on the PHS model of ISO 7933 standard. The experimental validation was conducted in a climate chamber with continuously monitoring the typical physiological parameters of 10 subjects in 9 hot working environments. Physiological parameters of subjects were analyzed on average difference (AV), coefficient of variation (CV) and skewness (SKEW) to explore their mutual linkages. Both experimental and theoretical result shows that certain relationship existed between the rectal temperature and skin temperature. The Poisson's ratio on their average value, coefficient of variation, average difference and skew were 0.957, 0.991, 0.990 and 0.941 respectively. Linear relation with coefficient of 0.73 was found between rectal temperature and skin temperature coupling with the constant of 12.09. Comparison on the dynamic changes of rectal temperature and skin temperature was carried out and verified under PHS model. The results showed that rectal temperature was adjusted earlier and more forcefully than skin temperature indicating that human core temperature was better protected under heat stress. The findings contribute to a convenient method of human heat strain prediction when taking rectal temperature as the best physiological threshold with fast human skin temperature and environment parameters monitoring in complex high temperature working environments.