Developing a continuous graphical index to assess heat strain in extremely hot environments

Extremely hot environments are common in industrial buildings, which impose thermal risks on the homeostasis of the human body. Thermal protective clothing (TPC) also places physical and thermal burdens on workers. In order to ensure workers' health and work efficiency, a continuous graphical index is developed in this paper to assess heat strain in extremely hot environments, avoiding hard measurements of physiological parameters. To study human interaction with the indoor thermal environment, a climate chamber was constructed to simulate extremely hot environments. Twenty male sports majors were asked to perform intermittent treadmill exercise while wearing TPC. During the human trials, rectal temperature, heart rate, hand grip strength, ratings of perceived exertion, and ratings of thermal sensation were measured. The results of a two-way repeated analysis of variance revealed that the perceptual strain index (PeSI) can reflect influences of different work intensities and dry bulb temperatures on human heat tolerance. The results of a regression analysis revealed a strong correlation between the physiological strain index (PSI) and the PeSI. In addition, the results also revealed a strong correlation between the PSI and work efficiency. By fitting the continuous function, the proposed index defined the comfort limit, efficiency limit, and safety limit for manual labourers wearing TPC. Therefore, the proposed index derived from the findings can be used to assess heat strain and work efficiency of workers in extremely hot environments.