Electric fans help in extreme heat, humidity

2015-02-17 23:02

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Sydney - Electric fans can help keep core body temperatures and heart rates from going up in extreme heat and humidity, according to a small new study from Australia.

Public health organizations recommend against using fans in extreme heat, because it may warm people up rather than cool them down. The new study suggests fans keep people cool by helping sweat evaporate off their bodies, said Ollie Jay, the study's senior author from the University of Sydney.

For the new study, eight healthy young men completed four high-temperature trials lasting two and a half hours each. The trials were separated by two days of break time. They wore shorts and t-shirts and sat in a chamber kept at either 36°C or 42°C.

The World Health Organization and the Centres for Disease Control and Prevention recommend against using fans in heat that exceeds 32°C.

For one session, there was no fan in the room, and in a second session at the same temperature they had an 45cm electric fan blowing on them from about one metre away. The researchers gradually increased the relative humidity.

They also monitored the participants' heart rates and core temperatures.

"People often perish in heat waves not because they had a critically high body temperature but because the elevated heart rate that arose from the heat stress exposed some underlying cardiovascular problem, which results in some kind of cardiac event," Jay told Reuters Health by email.

According to the results, core body temperatures and heart rates reached a critical point at a higher relative humidity when the fan was running at both 36°C and 42°C.

At 36°C, the metrics sharply increased at an average of 83% humidity with a fan compared to 62% humidity without a fan. At 42°C, the same thing happened at 47% humidity with a fan and 38% without a fan.

"Elevated body temperature is associated with heat stress, heat exhaustion, and heat stroke [which can be fatal]," said Dr. Jonathan Patz, who is director of the Global Health Institute at the University of Wisconsin in Madison.

Air conditioning

Deaths and hospitalisations during heat waves are a serious problem, Jay noted, citing a 2009 heat wave in Australia. Fans could actually have large protective benefits, based on the new results.

In fact, he said the participants experienced less stress at the higher temperature with a fan than at the lower temperature without a fan.

"With respect to other measures, ideally one should seek air conditioning if possible," Jay said. "However, some people, particularly those found to be at elevated risk during heat waves, do not necessarily have access to air conditioning."

"Other options include putting some cold water in a bath tub and immersing yourself in it to cool you down," Jay said.

Hydration is one of the most important preventive measures during heat waves, said Patz, who was not involved in the new study.

On the citywide level, enhanced tree canopies and more reflective, less heat-absorbing surfaces, could reduce heat-related mortality by more than 40% in Atlanta, Philadelphia or Phoenix, he said.

The researchers write in their research letter in JAMA that the results don't apply to anyone other than young healthy men.

Additionally, Jay said sweat may evaporate without a fan under hot and dry conditions. Adding a fan would probably increase a person's temperature.

Read more on:    australia  |  research  |  health

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