I LEARNED AN IMPORTANT LESSON in pre-air-conditioned, pre-climate-change Sowinski Elementary School, Cleveland, Ohio, when our teacher taught us not to bother fanning ourselves on a hot day: The exertion of fanning generated more body heat than its increased air flow dissipated. A net loss.
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Pre-electric fanning: The Viceroy of Kush Amenhotep called Huy holding the long fan with the single feather indicating his rank as fan-bearer. Image from Wikipedia.
But what about electric fans?
Warren Cornwall addresses this in “When is it Too Hot to Use a Fan?, AAAS Science magazine, November 6, 2024. Briefly, it depends: Cornwall writes, “Climate chamber experiments in older people offer conflicting answers.”
This, of course, prompts me to glean tidbits from his article, presented here in Parts 1 and 2 today and tommorow.
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A Temperature Threshold, But Where? “During a heat wave,” Cornwall describes, “many people seek relief by sitting in front of a fan. But public health agencies warn that if it’s too hot, the blowing air can actually make things worse by acting like a convection oven—and they differ on that threshold.”
He continues, “The U.S. Centers for Disease Control and Prevention (CDC) recommends not using a fan at temperatures above 32.2°C (90ºF). Others, including the city of Phoenix, give higher thresholds, and the World Health Organization (WHO) puts the limit at 40°C (104ºF).”
Cº to Fº Conversions. The parenthetical Celsius/Fahrenheit conversions are mine. Apart from 0ºC = 32ºF and the range 20º-30ºC = 68º-86ºF, I haven’t any equivalents memorized. And the conversion formula ºF = ºC x (9/5) + 32 is a pain compared to a handy Cº/Fº app.
What’s more, the Metric Conversions website offers an estimate sufficient in discussions of weather: “Double C + 30.” Let’s use this from here on.
Differing Views. Cornwall gets specific: “New research from two different groups of thermal physiologists favors the higher temperature limits, especially in humid weather. But the groups don’t agree on a single temperature threshold. One study, published on 6 November in The New England Journal of Medicine (NEJM), reports that fans can relieve stress on the heart in elderly people in humid conditions at 38°C (106ºF). The other, published on 17 October in JAMA, concluded there was little additional benefit from using a fan above 35°C (100ºF).”
Previous Thinking. “In the past,” Cornwall recounts, “many health advisories converged around 35°C (100ºF) as the temperature limit for fans, because that’s the typical temperature of human skin. Above this level, the thinking went, a fan would exacerbate overheating by displacing the layer of air that has cooled to equilibrium with adjacent skin temperature, much like a convection oven that speeds cooking by circulating hot air.”
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More Recent Experiments. Cornwall cites Ollie Jay, a thermal physiologist at University of Sydney and co-author of the new NEJM paper: “Over the past decade, Jay has conducted a series of experiments and done computer modeling that suggest the temperature limit might be much higher than 35°C (100ºF)…. His results helped persuade WHO to adopt its 40°C (110ºF) limit in May and informed a Phoenix educational campaign that in 2023 recommended a cutoff between 37°C (94ºF) and 39°C (98ºF) depending on a person’s age and health.”
Tomorrow in Part 2, we’ll learn more of the NEJM methodology as well as the importance of humidity. (It’s more complicated than “It ain’t the heat, it’s…..”). ds
© Dennis Simanaitis SimanaitisSays.com 2024