Development and use of a simplified WBGT estimation chart for indoor environments

Abstract

Wet Bulb Globe Temperature (WBGT) is widely used in fields of labor, sports, school education, and general living environments as an informative parameter for preventing heat disorder. A WBGT measuring device is required to obtain this value. In general, in living environments where heat disorder often occurs, WBGT measuring devices are almost unavailable. In 2008, the Japanese Society of Biometeorology developed and released a “Simplified WBGT estimation chart for indoor environments” as a tool for estimating WBGT based on air temperature and relative humidity. This estimation chart has been widely used, but it underestimates WBGT in environments with sunlight and overestimates this value in indoor environments without sunlight. A risk of misuse has also been found in that the range of applicability of the simplified estimation chart is not clearly stated. A revised estimation chart, which can only be applied to indoor environments without sunlight, has thus been developed based on heat balance theory and released in 2022. This revised estimation chart was able to make very accurate estimations in indoor environments without sunlight as assessed by comparing it with actual WBGT measurements. The revised version of the estimation chart is extremely useful for countermeasures against heat disorder in indoor environments where heat disorder is common.