An environmental stress index (ESI) as a substitute for the wet bulb globe temperature (WBGT)

The purpose of this study was to develop a new environmental stress index (ESI) based on different parameters relating to heat stress. Meteorological measurements were taken in three climatic zones (hot/wet, hot/dry, and extremely hot/dry) for 60 days, and a new stress index based on these databases was developed as follows: ESI = 0.63T_a - 0.03RH + 0.002SR + 0.0054(T_a·RH) - 0.073(0.1 + SR)^-1. where T_a is the ambient temperature (°C), RH the relative humidity (%), and SR the solar radiation (W·m^-1). The correlation coefficients between ESI and wet bulb globe temperature (WBGT) were very high (R²>0.981). Therefore, we conclude that ESI, based on fast response and the more commonly used accurate climatic microsensors (T_a, RH, SR) which can be combined in a small portable device, has the potential to be a practical alternative to the WBGT.