A study conducted by the University of Sydney shows that using a fan to cool off when the air is dry can be counterproductive by increasing our heat stress.
During the two recent heat waves that struck the hexagon, many of us used an electric fan to try to refresh us or, at least, to circulate the air in our interiors.
But maybe that was not such a good idea.
This is demonstrated by a recent study published by the University of Sydney and published in Annals of Internal Medicine. According to its authors, the safety and efficiency of fans in hot weather would be correlated with meteorological measurements, such as the humidity level in the air. When the air is too dry, it would be useless, even dangerous for the health to turn on a fan.
The fan is not recommended in case of dry heat
This work puts into question World Health Organization (WHO) guidelines, which state that fans above 35 ° C would have no beneficial effect.
To reach this conclusion, the authors of this new study simulated heatwaves to examine the effect of ventilator use on body temperature, cardiovascular tension, dehydration risk, and blood pressure levels. comfort.
12 healthy male volunteers were exposed for two hours to two types of heatwaves: one very hot and dry, reproducing the peak conditions of the July 2018 heat wave, and the other wetter, similar to heat waves in Chicago in July 1995 and Shanghai in July 2017.
Comparing the data collected, the researchers then found that in hot, humid conditions with a heat index of 56 ° C (a meteorological measurement expressing both air temperature and relative humidity, and which helps to measure a person's feeling of warmth), ventilators lower body temperature and cardiovascular tension, and improve thermal comfort.
On the contrary, fans appear to have negative effects on all measurements under very hot and dry conditions, despite a lower heat index of 46 ° C.
Official recommendations to review
"Our results suggest that under environmental conditions that represent the vast majority of peak heat waves in the United States and Europe, fans should be recommended and guidelines issued by most public health authorities are unnecessarily conservative", says Ollie Jay, Senior Associate Professor, Faculty of Health Sciences and Charles Perkins Center. "Only when the air temperature is very high and the humidity very low that the fans are harmful, can be seen in arid conditions like Phoenix or Las Vegas in the United States, or Adelaide in South Australia. "
According to the researcher, current research suggests that neither the temperature nor the ceilings of the thermal index are the best basis for public health advice on the use of fans. However, further research on a larger scale is needed to confirm the results, he conceded.