Application of Infrared Radiation Instead of Solar Radiation in the Environmental Stress Index Equation in Outdoor Weather Conditions

In many work environments, especially in the summer, heat stress assessment is necessary. The present research aimed to determine the feasibility of the application of infrared (IR) beams instead of the intensity of solar radiation in the environmental stress index (ESI) equation.
This cross-sectional study was performed from 8 am to 18 pm from June to October 2013 in the weather conditions of Isfahan, Iran. IR intensity was measured in 4 main directions and top and bottom of the globe thermometer. Moreover, wet bulb temperature, dry bulb temperature, and globe temperature were measured. The wet bulb globe temperature (WBGT) and environmental stress index (ESIIR) were calculated based on the IR intensity instead of solar radiation. Pearson correlation test and regression analysis were used to analyze the data.
Findings: The results showed that there is high correlation between WBGT and ESIIR in all 6 directions (P >0.01). The correlation coefficients between the two indices were 0.963 for all 6 directions. The estimate of WBGT of ESIIR, the predictor variable, was gained through the following equation, WBGT = 0.959ESIIR 1.427 (R2 = 0.94).
To evaluate heat stress in the outdoor work environment, ESIIR, calculated based on dry bulb temperature, relative humidity, and IR, is a good estimator for WBGT.