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

[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 (T_a), 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 (T_a), relative humidity (RH), and infrared radiation intensity that can be easily measured in a short time.