Playing it cool: how the body copes during heatwaves

What's the best way to keep cool in extreme temperatures?


With few signs that greenhouse gases are being sufficiently reined in, adapting to higher temperatures is now more necessary and urgent. The little known field of thermoregulatory physiology is developing lifesaving strategies.


The hottest place on the planet on 4 January 2020 was in Australia. But it wasn’t Alice Springs or Coober Pedy. It was Penrith, an outer suburb of Sydney nestled at the foot of the Blue Mountains.


The people, plants, animals and plastic fittings of Penrith wilted under the ovenblast of an unheard of 48.9C in the shade and about 65C in the sun. Other parts of Sydney and indeed Australia, also sizzled. And like any hellscape, there were flames, with bushfires raging around the nation and disaster emergencies being declared.


So how will we live in an Australia where climate change has made such unexpectedly high temperatures a more regular occurrence? Finding the answers, is Associate Professor Ollie Jay, who works in the increasingly important field of Human Thermoregulatory Physiology.


“Basically, I study how people are affected by, and can best deal with, extreme temperatures; both hot and cold,” this said with his naturally enthusiastic energy and an accent that he brought to Australia from the tiny North Wales village where he was born, via Canada where he worked in his chosen field for a number of years.


A killer heat

At the centre of Jay’s work is a powerful motivator: every year in Australia, heat waves kill more people than all other natural disasters combined and are estimated to cost the Australian economy $6.1 billion.


Extreme heat affects the lives of people in agriculture, construction, mining, factory work, warehousing, pregnant women (heat is implicated in premature and still births), young children, seniors and people who don’t have access to air conditioning; being those on low incomes and in developing countries.


Yet for all the human and environmental implications of extreme heat, it is a surprisingly ill-defined area. “Even what authorities tell people to do during heatwaves is rarely informed by any physiological evidence,” Jay says with a note of frustration. “It’s basically a bunch of old wives' tales.”


He cites the World Health Organisation’s advice not to use fans during very high temperatures because it’s like a fan-forced oven pushing hot air round a roast. The action of a fan is less straight forward than it seems.


When not to use a fan

When the air is hotter than the skin, which is 35C, blowing air on the skin actually adds some heat to the body. At the same time, the extra air flow makes sweat evaporate faster, creating coolness irrespective of the temperature. There is a limit to this benefit though. On a day above 43C, with low humidity, sweat evaporates without needing the fan, so the extra heat is still added to the body but without the evaporative cooling effect. So the fan can have a heating effect.


“We’ve simulated very hot/dry heatwaves (47˚C, 10% relative humidity) where fans worsen body heating, dehydration and cardiovascular strain,” says Jay. “But in cooler, more humid heatwave conditions (40˚C, 50% relative humidity) fans worked a treat.”


There’s air conditioning, but for Jay, it has serious flaws, “It’s expensive, which excludes many of the most vulnerable people from using it. It also uses lots of electricity, often from coal-fired power plants producing CO2 that contributes to climate change. It’s a classic vicious circle. So we’ve been looking at low cost cooling strategies and sustainable alternatives to air-conditioning.”


The answer could be a hybrid system where air conditioned environments incorporate moving air, with the motion giving the sense the air is cooler than it is. In effect, you get the same cooling effect but with the air conditioner set at a higher, less energy-hungry temperature. This is being investigated in collaboration with the School of Physics and the School of Architecture with the possibility this new approach could reduce greenhouse gas emissions.


This gives us the physiological evidence so we can say ‘if you do this, it will keep you cooler. But if you do this, it won’t work'.

Associate Professor Ollie Jay


Recreating extreme conditions

To investigate these ideas and others, Jay uses the toy that every thermal physiologist must dream of; a climate chamber. It resides at the Thermal Ergonomics Laboratory, where Jay is Director, and is part of the Sydney School of Health Sciences, Faculty of Medicine and Health. By using the chamber, Jay and his team can exactly recreate the conditions of any day at any location on Earth.


“Recently we mimicked the Chicago heatwave of 1995, which had massive health impacts,” he says. “Then we had some human participants come in.”


Wired up with physiological measuring systems, the participants were carefully exposed to the climate features of that day, tracking core temperature, dehydration, the work their hearts had to do, heat perception and comfort level. With those results recorded, various cooling strategies were introduced and likewise, the effects and benefits were measured.


“This gives us the physiological evidence so we can say ‘if you do this, it will keep you cooler. But if you do this, it won’t work.”


Too hot for tennis

Not all of Jay’s work is done from the relative safety of the lab. During the previously mentioned heatwave year of 2014, temperatures during the Australian Open tennis in Melbourne ranged from 41.5C to 43.9C in the shade, with water bottles and shoes melting, a ball boy fainting, nearly a thousand fans needing treatment for heat exhaustion and a number of the players withdrawing.


Tennis Australia knew of Jay’s work in developing successful heat policies for the National Rugby League (NRL) and Cricket Australia and they asked if he could help them protect fans and players from future severe heat events.


In the following years, and working with Tennis Australia’s Chief Medical Officer, Dr Carolyn Broderick, Jay and his team went courtside at the Australian Open. They measured the environmental factors that can contribute to heat exhaustion with its symptoms including, dizziness, vomiting, weak pulse, muscle cramps and fainting.


Key to this process was John Eisenhuth, a leading senior technical officer at the University. He and Jay created a bespoke device called an EMU (Environmental Measurement Unit) to measure temperature, radiation, humidity and wind. It was deployed around the Australian Open complex with information being sampled live at Jay’s computer, then fed into a specially designed algorithm to generate what’s now called the Australian Open Heat Stress Scale, giving conditions a one to five rating.


“I was worried the players would be saying ‘What’s the temperature?” says Jay. “Instead they’d say, ‘I just want to know the number. What’s the number?’ That was really satisfying because we’d hit on a clear and easy way of communicating the conditions.”


Of course, with a one-to-five Heat Stress Scale, with five meaning ‘stop play’, stopping play was always on the cards, and in 2019, it happened.


“It was kind of dramatic because it was in the middle of the women’s semi-final,” Jay remembers. “But the scale reached five so play was stopped and the roof closed. I think the people most happy about that decision were the fans. As the roof closed, there was a massive roar.”


4 December 2020.