Iranian Journal of Ergonomics

Introduction: The incidence of heat stress is one of the most common problems in work environments as well as many different industries. The exposure of workers to heat results in heat strain. The purpose of the present study was to validate the Perceptual Strain Index through determining its relationship to the Physiological Strain Index and the Wet Bulb Globe Temperature Index under hot laboratory conditions.

Materials and Methods: The present cross-sectional study was conducted on 15 men in five different temperature conditions (21, 24, 27, 30 and 35ºC) in a climate chamber and on the treadmill with three different activity levels –light (2.4km/h), medium (4.8km/h) and heavy (6.3km/h). Participants' heart rate and oral temperature were measured in order to calculate the Physiological Strain Index, and their thermal sensation and the rate of perceived exerted activity were measured for calculating the Perceptual Strain Index. The correlations between the indices were then evaluated using Pearson's correlation test and the regression analysis.

Results: Pearson's correlation test showed a significant correlation between the Perceptual Strain Index and the Physiological Strain Index (P=0.001 and r=0.94). The Perceptual Strain Index was also found to have a significant correlation with oral temperature and heart rate (p=0.001 and r=0.78 (p=0.001 and r=0.90). In addition, a significant correlation was found between the Perceptual Strain Index and the Wet Bulb Globe Temperature Index (p=0.001 and r=0.71) however, no relationship was observed between the Perceptual Strain Index and the Body Mass Index (p=0.79 and r=0.0009).

Conclusion: The findings of the study showed that the Perceptual Strain Index can be used for evaluating heat strain in the absence of access to other methods of evaluating heat stress as it has an acceptable correlation with valid indices of heat stress.