Expansion of effective wet bulb globe temperature for vapor impermeable protective clothing

Abstract

The wet bulb globe temperature (WBGT) is an effective measure for risk screening to prevent heat dISOrders. However, a heat risk evaluation by WBGT requires adjustments depending on the clothing. In this study, we proposed a new effective WBGT (WBGTeff*) for general vapor permeable clothing ensembles and vapor impermeable protective clothing that is applicable to occupants engaged in moderate intensity work with a metabolic heat production value of around 174W/m2. WBGTeff* enables the conversion of heat stress into the scale experienced by the occupant dressed in the basic clothing ensemble (work clothes) based on the heat balances for a human body. We confirmed that WBGTeff* was effective for expressing the critical thermal environments for the prescriptive zones for occupants wearing vapor impermeable protective clothing. Based on WBGTeff*, we succeeded in clarifying how the weights for natural wet bulb, globe, and air temperatures and the intercept changed depending on clothing properties and the surrounding environmental factors when heat stress is expressed by the weighted sum of natural wet bulb, globe, and air temperatures and the intercept. The weight of environmental temperatures (globe and air temperatures) for WBGTeff* for vapor impermeable protective clothing increased compared with that for general vapor permeable clothing, whereas that of the natural wet bulb temperature decreased. For WBGTeff* in outdoor conditions with a solar load, the weighting ratio of globe temperature increased and that of air temperature decreased with air velocity. Approximation equations of WBGTeff* were proposed for both general vapor permeable clothing ensembles and for vapor impermeable protective clothing.