Time and environmental conditions for heat stress recovery based on human physiological responses: Developing a predictive model

Breaks can protect workers exposed to high temperatures from heat stress and other health risks. However, the most suitable recovery conditions and how the body physiologically responds to them remain uncertain. The aim of this study was to provide scientific evidence of the human physiological response to step changes in environmental parameters of recovery stage through climate chamber experiments and to develop a predictive model. Volunteer subjects experienced 60 min of walking exercise in air temperatures of 32 and 36 degrees C, RH 60%, and an air velocity of 0.2 m/s to form two heat stress levels, and then moved into a resting space under designated environmental conditions, such as a standard effective temperature (SET) range of 15.6-26.0 degrees C. The results showed that the recovery time for physiological parameters decreased with decreasing SET, accompanied by a simultaneous increase in thermal discomfort rate. Correlation analysis suggested that recovery time was related to the physiological stress index at the beginning of the recovery phase (PSI0; r = 0.86) and the SET (r = 0.75) of the recovery environment. A predictive model of heat stress recovery time was developed based on PSI0 and SET, with a determination coefficient of 0.9. According to the model, a SET of 18.8-24.9 degrees C was suitable for people with high heat stress requiring full recovery in 15-30 min. The research findings contribute to the regulation of health and safety in high-temperature working environments and the operation of restroom environmental conditions.