this post was submitted on 05 Jul 2023
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I've seen the term misused a lot recently, so I'll state that a wet-bulb is a part of a measurement instrument. Wet-bulb temperature is a measured quantity (along with dry-bulb temperature, pressure etc.) and an Extreme wet-bulb temperature event is what actually kills people.
Used for humidity measuring instruments primarily, like a psychrometer.
Basically using a wick or wet material and forcing air over the sensor will evaporate the water and lower the temperature reading. Compared to a dry thermometer you can work out humidity.
A very high wet bulb temperature would mean very high humidity, which is dangerous for people as sweating is less effective.
Correct for the most part. You can still have very high relative humidity with a low WBT if the dry-bulb temperature is equally low.
When the WBT gets above 35°C, it's not only dangerous, but positively lethal when sustained for even the healthiest person as sweating (or any other form of evaporative cooling for that matter) can no longer keep the body at a suitable temperature.
WBT is also not to be confused with wet-bulb globe temperature (WBGT), which is an index for heat stress that also takes into account the effect of sunshine among other things. It's much more situational and best suited to judge the heat stress of athletic outdoor activity in sunshine.