After the first experiment, Jay explains to me what I just went
through.
“So whenever people think about hot weather, they always talk about
the temperature,” he says.
“There’s two issues with that. First of all, most people don’t
realise that the temperature is measured in the shade.
“So if you’re in direct solar radiation, the amount of heat stress
you’re exposed to is much greater as it will stress your body out a
lot more.”
That explains the heat lamps. And, according to Jay, the other
important variable is the humidity.
“Humidity is the amount of water vapour that’s in the air. And the
reason that’s important is that the only way in which your body can
physiologically keep cool is that you produce sweat.
“But it’s not production of sweat that cools you down. It’s the
evaporation of sweat and it’s the humidity in the air that prevents
that sweat from evaporating, even though the ambient temperature
might be the same.”
So when high humidity goes along with extreme temperatures, your
body can no longer cool itself down, and the heat becomes deadly.
This is why in the next experiment I’m going to experience
conditions at the same temperature as the first experiment, but with
a much higher humidity of 36%.
Professor Ollie Jay
Even though 36% relative humidity doesn’t sound high, at 43C that
means a lot of moisture because warmer air can hold more water. When
it’s this hot, sweating isn’t going to help me stay cool very much.
Another way to think about it is the “feels like” temperature that
weather forecasts sometimes tell us about. Under the conditions I am
experiencing, the “feels like” temperature is over 49C or 120F.