Jun 30, 2022 16:00:00

It turns out that the limit heat that humans can tolerate is the wet-bulb temperature '31 degrees'

In June 2022, the

temperature was unthinkably high during this period, and the media is calling for measures against heat stroke. In addition, a study published in March 2022 examining the central temperature of a subject's body showed that the temperature and humidity that humans can tolerate are lower than conventional wisdom.

Evaluating the 35 ° C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT Project) | Journal of Applied Physiology
https://journals.physiology.org/doi/full/10.1152/japplphysiol.00738.2021

Humans can't endure temperatures and humidities as high as previously thought | Penn State University
https://www.psu.edu/news/research/story/humans-cant-endure-temperatures-and-humidities-high-previously-thought/

According to a research team at the University Park of the University of Pennsylvania, it has been the established theory that the maximum temperature at which humans can adequately regulate body temperature is the wet- bulb temperature of 35 degrees Celsius. Wet-bulb temperature is the temperature at which the heat taken away when water evaporates and the heat replenished from the surroundings by the amount of the decrease are equal. When the wet-bulb temperature of 35 degrees is converted to the general dry-bulb temperature , the humidity is 100%, that is, 35 degrees if the sweat does not evaporate from the skin, and about 46 degrees if the humidity is 50%.

This wet-bulb temperature of 35 degrees was theoretically calculated based on physiology, but it has never been verified with empirical data. Therefore, the research team conducted an experiment in which 24 participants aged 18 to 24 were invited to exercise while measuring their body temperature. The recruitment of young and healthy subjects is in the hope that the limits of temperature that humans can tolerate will be investigated.

In the experiment, we asked participants to drink a wireless measuring device in a small capsule so that they could see the temperature inside the body. Each participant then went into a special room where temperature and humidity could be controlled, where they did some light exercise, such as lightly riding a fitness bike or walking slowly on a treadmill.

by Patrick Mansell / PennState

When the research team asked the participants to exercise while gradually increasing the temperature and humidity in the room and analyzed the body temperature data measured in it, the 'marginal wet-bulb temperature' that can maintain a constant body temperature was 35. The number of participants was zero. The 'marginal wet-bulb temperature' was 25 to 28 degrees in a hot and dry environment and 30 to 31 degrees in a warm and humid environment, both of which were significantly lower than 35 degrees.

'Our findings show that young and healthy people must be worried when wet-bulb temperatures rise above 31 degrees Celsius in the humidest parts of the world,' said Larry Kenney, who headed the research team. We will continue to study what happens in older people, but it will probably be even lower. '

According to the research team, 'The heat that humans can adapt to depends on the humidity, so there is a high possibility that the' maximum value 'that humans can tolerate in all environments on the earth is not one.'