Public health guidelines that recommend turning off fans when temperatures exceed 35 degrees are likely flawed and may unnecessarily expose vulnerable people to health effects during heatwaves, researchers at the University of Sydney say.
Ollie Jay, director of the university's Thermal Ergonomics Laboratory that simulates a range of heat extremes and how humans respond, said advice in many jurisdictions for coping with heatwaves was "not really based on a lot of scientific evidence".
By adjusting the laboratory's special heat room - originally set up three decades ago by the late Professor Martin Thompson to help athletes on hot days - the researchers have been able to study how people handle precise heatwave conditions.
These include mimicking a 2009 Adelaide heatwave when the mercury climbed to 48 degrees with humidity of just 5-6 per cent, and a 2015 "heat dome" over the Pakistani city of Karachi when residents endured 45 degrees at about 50 per cent humidity.
The aim is to develop strategies for the public to cope, such as with or without a fan and applying water, for a range of ages and medical conditions.
Planetary health
The work comes as a heatwave continues to bake eastern Australia, with much of Sydney expected to exceed 40 degrees on Thursday. Adelaide and Melbourne both clocked mid to high-30s on Wednesday.
Sydney University will also launch its new Planetary Health Platform on Thursday aimed at bringing together disciplines - from public health and religion, to architecture and economics - to build knowledge and capacity for societies to cope with intensifying threats such as from climate change.
Research challenging advice on electric fan use during heatwaves was raised in earlier papers by Associate Professor Jay and other scientists, such as in 2014.
They noted authorities often relied on data showing that increased air movement above about 35 degrees added to skin temperature from convection.
However, as people tend to perspire, fans help to accelerate evaporation of sweat, providing cooling.
"Young, healthy people who are able to sweat quite freely experience less strain at 42 degrees with a fan than at 36 degrees without a fan," Professor Jay said. "The benefits in terms of extra sweat that evaporates far outweighs the extra heat that is loaded on the body [from convection]."
Debate over fan use is also important because often the most vulnerable in the community can't afford airconditioning or struggle to pay for the electricity to run it. Fans can be run as a fiftieth the cost of airconditioning.
Tailoring the message to fit the audience is not without complications. The elderly are typically less able to lose heat by perspiring than younger people - although application of wet towels or other means could help.
Likewise, if humidity is very low, the body may already be losing heat through evaporation of perspiration as fast as it can.
Even so, the 2014 research found fans would apparently still provide marginal benefits at air temperatures as high as s 51.1 degrees at 10 per cent relative humidity for young adults, and 48.1 degrees at similar humidity levers for the elderly.
Professor Jay's team hopes a $1.1 million grant over five years from the National Health and Medical Research Council announced this week will help it refine knowledge of the best strategies to deal with heatwaves.
NSW Health, meanwhile, said it was aware of the research on fans, and welcomed it.
"During excessive heat events, NSW Health recognises the use of electric fans as an effective source of relief," a spokesperson said.
"We also advise people to try to spend time in airconditioned places like a shopping centre, library or cinema if they do not have access to their own cooling source."
'Lost the plot'
Tony Capon, the university's Professor of Planetary Health, said the research could have flow-on effects for other areas.
Housing, for instance, had increasingly been built assuming airconditioning would be the main coolant.
As a result, ceilings were too low for safe use of overhead fans, while homes also lacked eaves and space for vegetation to provide shade, and were not oriented to account for sunshine exposure.
"It's absolute madness," Professor Capon said. "We need to reclaim some of our knowledge of how to stay cool without airconditioning. We've kind of lost the plot."
Richer societies had increasingly lost touch with nature, and as a result were suffering the consequences.
"We are animals, we're part of nature, and our future health entirely depends on the health of natural systems," he said.
