01 What is the Wet Bulb Temperature?

Wet-bulb temperature – Wikipedia

The cooling limit temperature, measured as the wet bulb temperature, is the lowest temperature that can be achieved by direct evaporative cooling in a given environment.

In human biometeorology, the cooling limit temperature is applied to indicate heat stress. It is either used directly or is incorporated into the calculation of indices that quantify sensed temperature and thermal stress, such as the wet bulb globe temperature (WBGT) index.

It is assumed that a healthy human at rest in the shade can survive cooling limit temperatures of about 35 °C for about six hours: The metabolism of a resting human generates about 100 W of heat that must be dissipated to the environment through the skin. To dissipate this heat to the skin while maintaining a core temperature close to 37 °C, the body must keep its temperature at 35 °C or below. The skin, in turn, dissipates the heat to the environment through convection and evaporation. Even with good ventilation, both are only possible if the cooling limit temperature is still below the skin temperature. Permanently higher temperatures lead to overheating (hyperthermia) even in healthy and acclimatized people, already at 37-38 °C skin temperature to deadly 42-43 °C inside the body.

I.e. the combination of high humidity and high temperature can lead to death under appropriate stress.

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