Studies say it’s too hot when....

Plenty of walkers and runners braving the heat

I’ve blogged before about the heat and the humidity, known as the Heat Index--those Feels Like temps--and a new study shows that not only does the humidity play a role, it’s hugely significant.

Professors from Penn State set out to answer a simple question: “When will it get too hot for normal daily activity as we know it, even for young, healthy adults?” The study set out to determine the dangers at different temperatures and humidity doing fairly easy tasks, like cooking or eating. Known as the Pennsylvania State University H.E.A.T. project, young adults swallowed a telemetry pill which is basically an oral thermometer. Then they were monitored in an environment chamber moving just enough as if doing simple tasks. In hundreds of separate experiments, the scientists raised either the temperature or the humidity and monitored the subject’s core body temperature and heart rates.

The idea is to determine the “critical environmental limit”, or basically how hot is too hot before that core body temperature begins to rise continuously and is no longer stable.

The reasoning is pretty direct: When the body overheats, the heart has to work harder to pump blood flow to the skin to dissipate the heat, and when you’re also sweating, that decreases body fluids. In the direst case, prolonged exposure can result in heat stroke, a life-threatening problem that requires immediate and rapid cooling and medical treatment.

Interestingly, the studies showed that the limit occurred at even lower temperature/humidity combinations than expected: 87° at 100% humidity or 100° at 60% humidity. This is for young, healthy adults. Given that the majority of heat stroke victims are older than 65, the group is turning next to that age group to determine where those limits are.

You can see the entire range of temperatures and humidity in a chart created right here. The yellow zone is when we need to start being careful of the heat! The study was highlighted recently in The Conversation magazine.

Bottom line: on hot, humid days staying cool and hydrated is as much a matter of safety as comfort! And it doesn’t take a lot of heat to cause problems.

Find the shade and the hydration!

We have another two weeks of brutally hot temperatures every afternoon (100s almost every day). Take the heat seriously and don’t push yourself!


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About the Author:

KPRC 2's chief meteorologist with four decades of experience forecasting Houston's weather.