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.

Introduction: This study aimed to investigate the effects of cooling vests on heat strain and reaction time while wearing protective clothing against chemical, biological, and radioactive contamination.

Materials and Methods: Twelve male students with the mean age of 25 ± 2 years and mean body mass index (BMI) of 23.0 ± 1.5 kg/m2 were recruited in this experiment. Each student was asked to run on a treadmill at a speed of 2.4 km/h for 20 minutes. The experiments were performed at 35 °C and 30% relative humidity. Physiological strain index score, oral temperature, heart rate, reaction time, and number of errors were measured at the end of the two phases. The findings were analyzed by SPSS.

Results: According to Wilcoxon test, exercising with and without the cooling vest resulted in significantly different physiological strain index scores (P = 0.02), oral temperature (P = 0.02), reaction time (P = 0.02), heart rate (P = 0.02), and errors (P = 0.03). The mean physiological strain index score was 4.038 ± 0.882 without the cooling vest and 1.42 ± 0.435 with the cooling vest. The mean reaction times with and without the cooling vest were 0.539 ± 0.977 and 0.769 ± 0.0972, respectively.

Conclusion: The results of this study showed that using a cooling vest reduced the physiological strain, reaction time, and error rates in workers.