• PM_Your_Nudes_Please@lemmy.world
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    6 months ago

    Yeah, some parts of the US recently experienced something called a wet bulb event. Basically, that’s a phenomenon where the heat and humidity are both so high that your body’s natural cooling mechanism (sweating) stops working entirely and people will overheat simply by being outside. No amount of shade or cool drinks will help, because your body’s primary cooling mechanism has been defeated.

    Basically, sweat works by evaporating. When water evaporates, it takes heat with it. This allows sweat to cool you down as it dries. To be able to accurately determine what the temperature feels like, you can’t just use a regular dry thermometer. You need to use something called a wet bulb thermometer. This is basically a thermometer with some wet cotton wrapped around it, to simulate sweat. As the wet cotton dries, it creates a more accurate gauge of what the ambient temperature feels like, the same way sweat cools you.

    But a wet bulb event is when the wet bulb thermometer reads above 95°F. At that point, it means the cotton isn’t drying fast enough to cool a person down. At this point, the temperatures are dangerous even to fit and healthy individuals in the shade with fans and cool drinks. Because a breeze won’t even cool you down when it’s that hot outside; A fan will actually heat you up even faster, because the air is adding heat faster than evaporative cooling can remove it.

      • PM_Your_Nudes_Please@lemmy.world
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        6 months ago

        Nah, true wet bulb events are pretty rare. With a wet bulb event, you overheat even while sitting still in the shade with a breeze. Because again, you’ve reached the point where a breeze is actually warming you up instead of cooling you down. They’re becoming more common nowadays due to global warming, but they still only happen occasionally. Again, a wet bulb thermometer will typically read significantly lower than the ambient temperature, because it’s being cooled by evaporation.

        At wet bulb temps in the 90’s, construction crews start delaying, school athletics aren’t allowed to practice outdoors, cities start setting up pop-up cooling centers for the homeless, etc… Even the army limits outdoor work to 10 minutes per hour, because the risk of heat stroke is too high. Wet bulb temps above ~87 are rare, so when it reaches the 90’s emergency management crews go into full blown crisis mode as people start getting heat exhaustion just from walking around the block.