Development history and verification of the WBGT estimation chart for indoors published in the "Guideline of heat disorders prevention in daily life" by Japanese Society of Biometeorology

Abstract

The WBGT estimation chart can estimate WBGT values using two thermal parameters of air temperature and relative humidity, and has been published in the "Guidelines of heat disorders prevention in daily life" issued by the Japanese Society of Biometeorology. It was pointed out, however, that the old version of the chart tends to underestimate in an environment with solar radiation and overestimate indoors without solar radiation. Therefore, in the revision of the heat disorders prevention guideline Ver.3.1, a revised version of the WBGT estimation chart that can be applied only to indoors without solar radiation was developed based on the heat balance theory. To verify this estimation chart, WBGT, air temperature, and relative humidity were measured using several WBGT measuring instruments with a globe thermometer in actual indoor spaces. The measurements clarified that the revised WBGT estimation chart was able to estimate WBGT values very close to the measured values in indoor spaces without solar radiation. Therefore, we concluded that the revised WBGT estimation chart is applicable in indoor spaces without solar radiation. Meanwhile, we emphasized the importance of using WBGT measuring instruments with a globe thermometer to appropriately assess the risk of heat disorders outdoors or in an environment with solar radiation.