Once the wet-bulb temperature, which considers both temperature and humidity, reaches 35 degrees Celsius, we can’t release heat as the sweat does not evaporate. This is why the wet-bulb temperature of 35 degrees Celsius is called the maximum survival temperature. According to a research team at the California Institute of Technology, the Indus River basin in Asia, the coastal Red Sea in the Persian Gulf of the Middle East, and the Southeastern coast of North America have already recorded the wet-bulb temperatures of 35 or higher.
The wet-bulb temperature may be a new concept to most people, but there is one more type of temperature worth our attention – the black globe temperature, which is related to radiant heat. Even at the same temperature and humidity, the body feels different levels of heat stress depending on radiant heat. The wet-bulb temperature is related to the autonomous control of the body while the black globe temperature is deeply associated with the damage to the body.
Therefore, to understand the heat to which the body is exposed, data about both temperature types is necessary. This is where the wet-bulb globe temperature (WBGT) considering the temperature, radiant heat, and humidity comes in. Developed by the U.S. Department of Defense to reduce the impact of stressful thermal conditions on the army training outdoors, it is currently published by the meteorological offices of Japan and Australia.
In South Korea, the Seoul Metropolitan Government uses WBGT the most. It has installed IoT city-data sensors in over 850 locations last year to use WBGT as an important indicator of the city’s environment. In particular, black globe thermometers have been installed to 18 city data sensors in Yangcheon to measure WBGT. The collected data reveals that WBGT varies between 25.7 to 29.1 depending on locations, even within the same district. It is okay to work out for less than 30 minutes drinking enough water in places with the lowest WBGTs, however, any strenuous workout should be avoided in places with the highest WBGTs.
So far, we have been dependent on the number on a mercury thermometer to gauge the level of heat. However, it should be taken into consideration that such a figure is different from the heat felt by the body while coming up with his or her own ways to deal with the heat. Furthermore, guidelines in consideration of WBGT should be put forward by schools and jobs that require working outdoors. We may hope that everyone in the country can understand heat stress and overcome it smartly.