The misconception that humidity accounts for 70% of WBGT

Abstract

WBGT (wet bulb globe temperature) is used in Japan as an index to alert people in general about the risk of heat stroke, although it was originally developed as a measure of the heat stress for people performing strenuous activities, such as outdoor works and athletic activities. In an effort to raise public awareness of WBGT as a part of heat stroke prevention measures, an illustration that attempted to explain natural wet bulb temperature, which is used to obtain WBGT, as an indicator of humidity has been widely quoted and spread. This illustration has led to the misconception that humidity accounts for 70% of the WBGT while air temperature accounts for only 10%. Needless to say, it is extremely dangerous to focus only on humidity and disregard temperature in formulating heat stroke countermeasures, and if inappropriate actions are taken based on the misconception, the risk of heat stroke may actually increase. Therefore, it is vital to clarify the widespread incorrect explanation of WBGT and to provide the public with correct knowledge on how temperature and humidity together affect the body’s ability to release heat and cause heat stroke.