TODAY IN PART 2, WE CONTINUE TIDBITS gleaned from Warren Cornwall’s AAAS SCIENCE “When is it Too Hot to Use a Fan?” It turns out it’s more than just the heat….
The NEJM Methodology. “To test these recommendations in high-risk groups,” Cornwall describes, “Jay and colleagues recruited people over age 65, some of whom had heart conditions. As people age they perspire less, so they get less cooling from evaporating sweat. And cardiac problems such as heart attacks are one of the biggest dangers.”
He continues, “The researchers tested 58 people inside special climate-controlled chambers that created two different climates: a humid one resembling places like Mumbai, India, at 38°C (106ºF) and 60% humidity, and a desertlike setting at 45°C (120ºF) and 15% humidity.”
Mumbai-like. Jay et al. described, “When exposed to the moist heat for 3 hours, even older people with coronary artery disease showed a 31% reduction in cardiac stress—based on heart rate and blood pressure—while sitting in front of a fan, compared with a separate test with no fan…. Under the hot humid conditions, we show definitely that fans are protective at a temperature above the threshold used by the CDC. That is because by circulating the air, the fans enable more moisture on the skin to evaporate than if air close to the body remains static.”
A man in Iraq seeks relief from electric fans during a heat wave. Image from Science.
Phoenix-like. “By contrast,” Cornwall recounts, “results in dry conditions starkly illustrated the dangers of misusing fans. The scientists stopped the experiments after testing just 14 people because their cardiac stress went through the roof as the fan blew hot air on them. Nearly half the participants couldn’t stay in the test room for 3 hours. The reason for that dramatic response: The air was so dry that any sweat quickly evaporated, resulting in little additional cooling as the fan bathed participants in extremely hot air, Jay says.”
A Competing Experiment. At the University of Ottawa, thermal physiologists performed similar experiments. Cornwall observes, “The key point: Above 35ºC (100ºF), humidity matters a lot. In very dry conditions, a fan could be counterproductive, whereas in very humid ones it could continue to help at much higher temperatures.”
The CDC Keeps its 32.2 Threshold. Cornwall writes, “For now it seems likely to remain confusing. Jay says WHO’s 40°C (110ºF) limit is safe, based on lab experiments, modeling, and historical weather data from around the world. CDC, meanwhile, continues to defend the 32.2°C (90ºF) limit. ‘We don’t have studies, done in the real world, that show that these higher thresholds are safe for people who are less able to cope with heat,’ the agency said in a statement.”
Dueling Conclusions. Cornwall cites Kristie Ebi, a heat epidemiologist at the University of Washington: “The dueling conclusions underscore the tricky balance facing public health agencies. The message needs to be simple”… but not too simple.
After all these years, it’s comforting to learn that the hand-wielded fan still seems a non-productive idea. ds
© Dennis Simanaitis, SimanaitisSays.com, 2024