Integrating Physiological and Psychological Responses to Evaluate Human Heat Strain Under Equivalent Wbgt and Varying Physical Parameters Conditions

Abstract

The WBGT index is commonly used in heat stress evaluation, while how about its performance under varying environmental parameters and equivalent WBGT condition is underexplored. This study examined the protection efficiency of WBGT index under varying temperature, air velocity and thermal radiation, with controlled equivalent values of 26 ℃, 29 ℃ and 32 ℃. 16 subjects walked on the treadmill to simulate moderate metabolic rate (165 W/m2) and their physiological parameters and subjective evaluations were measured in 9 conditions. The results showed increasing WBGT led to remarkable differences in mean skin temperatures, tympanic membrane temperatures, and thermal sensation; significant differences were also found among different temperature, air velocity, thermal radiation conditions, regardless of the same WBGT level. A Heat Physiological and Perceptual Index (HPPI) was developed to reveal the differences caused by physical parameters. Three sensitive indicators of heart rate, tympanic membrane temperature and thermal sensation were adopted in HPPI method and the calculated weights were 0.232, 0.311 and 0.457 respectively, using the entropy weight-CRITIC method. The risk evaluation was provided in 10 classifications with different HPPI ranges. The recommended limits of WBGT for safety were thus refined based on HPPI scores for different thermal environments. The work reveals that the existing WBGT methods fails to predict human heat strain under equivalent WBGT and combined physical parameters. The developed HPPI method innovatively integrates physiological and psychological effects and quantifies accurately human heat strain, which contributes to the development of WBGT method and standards for better population protection, under global warming.

Keywords: WBGT, Human Heat Strain, Radiation, Air Velocity, Integrated Evaluation Index