Validation of Environmental Stress Index by Measuring Infrared Radiation as a Substitute for Solar Radiation in Indoor Workplaces

Abstract

Background: The exposure of individuals to heat at different jobs warrants the use of heat stress evaluation indices. Objectives: The aim of this study was to validate environmental stress index using an infrared radiation (IR) measurement instrument as a substitute for pyranometer in indoor workplaces. Methods: This study was conducted on 2303 indoor workstations in different industries in Isfahan, Iran, during July, August, and September in 2012. The intensity of the Infrared Radiation (IR) (w/m2) was measured at five-centimeter distances in six different directions, above, opposite, right, left, behind and below the globe thermometer. Then, the dry globe temperature (Ta), wet globe temperature (Tnw), globe temperature (Tg) and relative humidity (RH) were also simultaneously measured. The data were analyzed using correlation and regression by the SPSS18 software. Results: The study results indicate that a high correlation (r = 0.96) exists between the environmental stress index (ESI) and the values of wet bulb globe temperature (P < 0.01). According to the following equation, WBGT = 1.086 × ESI - 1.846, the environmental stress index is able to explain 91% (R2 = 0.91) of the WBGT index variations (P < 0.01). Conclusions: Based on the results, to study heat stress in indoor workplaces when the WBGT measurement instrument is not available and also in short-term exposures (shorter than 30 minutes) when measuring the wet bulb globe temperature shows a considerable error, it is possible to calculate the environmental stress index and accordingly to the WBGT index, by measuring the parameters of dry bulb temperature (Ta), relative humidity (RH), and infrared radiation intensity that can be easily measured in a short time.