SolutionS-oriented Sydney heat lab tests ‘the limits of human survival’
By Laurie Goering
For years, parents taking their infants out in baby carriages or prams in Australia’s hot weather have tried to keep them cool by draping a light piece of shade fabric over the top.
But that popular technique, by limiting air flow, can increase the temperature the baby is exposed to by up to 3.7 degrees Celsius (6.7 degrees Fahrenheit) above outside temperatures - a potentially lethal difference on a hot day, scientists at a University of Sydney heat laboratory found.
After testing various alternatives, lab researchers said parents should instead soak the cover cloth in water to keep it moist and add a small clip-on fan to the pram - a combination of changes that can help keep babies up to 4.7 degrees Celsius cooler than outside temperatures on a hot day.
“We’re working with public health authorities to make sure what we’re telling people to do is informed by evidence,” said Ollie Jay, a professor of heat and health who runs the Heat and Health Research Centre at the University of Sydney. It aims to “identify the limits of human survival, comfort, and work performance in extreme climates.”
As climate change brings longer, more intense and more frequent heatwaves - with even hotter conditions predicted for decades to come - deaths and illness from extreme heat are quickly rising.
Worsening heat is also hitting worker productivity, with 470 billion hours of work lost to extreme heat in 2021, or an average of 139 hours per person affected, according to a 2022 report in the medical journal The Lancet.
Women, who often work in the informal economy, earn less than men, carry a heavy workload of domestic jobs and in some cases face cultural restrictions on their clothing or movement, suffer disproportionately from heat, researchers say.
And figuring out how to protect people - particularly the most vulnerable - is becoming increasingly urgent, health experts emphasize, with extreme heat exposure now linked to everything from worsening sleep and suicidal thoughts to miscarriages, stillbirths and premature births.
AIR CONDITIONING ALTERNATIVES
At Jay’s “thermal ergonomics laboratory," in a tall glass building on the University of Sydney campus, researchers and volunteers aim to do just that, testing the limits of human comfort and survivability in current, and predicted future, extreme heat conditions.
The lab, outfitted with temperature controls, humidity generators, sun-mimicking red heat lamps, fans, water taps and a range of monitors, aims to precisely replicate real-world extreme heat and help researchers understand what works best to keep people safe from it.
Scientists recently, for instance, copied the conditions inside Bangladeshi garment factories, with women sewing and men ironing fabric while wearing traditional clothing, testing what combinations of fan use, water access and reflective roof effects kept them coolest.
The answers aren’t always obvious. Fan use, on its own, for instance, did little to help workers, but giving them free access to water - something factory owners can be reluctant to do, fearing too many bathroom breaks - boosted productivity in hot conditions, Jay’s team found.
“If you give workers water they stop briefly to drink it but you’re clawing back that loss and more because of the cooling effect,” said the Wales-born scientist, who first developed an interest in heat impacts while studying at Britain’s Loughborough University.
Many of the Sydney lab’s efforts aim to find cooling solutions that don’t rely heavily on air conditioning - a technology that is too expensive for many people, worsens urban outdoor heat as air conditioners dump excess heat outside, and can drive further climate change if run on fossil fuels.
“We can’t just think about air conditioning all the time. It’s impossible to give everyone air conditioning and it takes electricity. When it’s hot and you have all these people using air conditioning you can have rolling blackouts,” noted Jay, wearing a light pink-checked shirt and tan shorts for an interview on a hot day in Sydney.
With most air conditioning use driving even more global warming, “we need to find novel and innovative ways to break that cycle,” Jay said.
One piece of the lab’s research, for instance, found that setting air conditioners to a higher 27 degrees Celsius (80 degrees Fahrenheit) rather than the normal 22 degrees Celsius (71 Fahrenheit) but adding a fan pointed at people to move the cool air gave them the same level of comfort with far less energy use.
“People say, ‘I can’t be comfortable at that temperature’ but if I blindfolded you and you focused on how comfortable you felt you wouldn’t be able to tell the difference between 22C and 27C with the fan moving,” he said.
Such changes can curb climate change, reduce energy bills, protect overtaxed grids and “you feel the same - you’re not sacrificing anything,” Jay said.
The 2022 study, in fact, found that if every Australian made the change, it would reduce electricity consumption from air conditioners by 70-75 percent and greenhouse gas emissions from air conditioners by 75 percent.
testing heat limits
The University of Sydney lab’s work - using volunteers who can withdraw from a test any time they feel unwell or unhappy, or are removed if their vital signs near a dangerous mark - has produced some worrying discoveries.
While fans work well to help cool people in many conditions, running fans alone indoors in conditions of very high heat and very low humidity can kill older people, creating a convection oven effect that makes the heart work three times harder and doubles the rate at which core body temperature ramps up, researchers found.
Dousing a person’s clothing and body in water, by comparison, is “by far and away the best way” to cool someone without air conditioning, a measure that is “never detrimental, always beneficial," Jay said.
The lab’s work has also brought into question a widely accepted assumption that the limit of human heat survivability is a 35 degree Celsius “wet bulb” temperature - a measure that combines heat and humidity.
While the 35C “web bulb” mark isn’t far off when humidity levels are high and temperatures lower, it “dramatically underestimates the risks” when heat is very high and humidity levels very low, the study found, especially for older people.
In a three-hour study of heat tolerance at 54 degrees Celsius (129 degrees Fahrenheit) and low 26 percent humidity - equivalent to a 35C web bulb temperature - 19 of 21 participants had to drop out because their core temperature got too high or they felt sick, he said.
Accurately understanding where the safe heat limits actually lie will be crucial to protecting lives as accelerating climate change drives ever greater temperature extremes, Jay said, noting that without such knowledge “we’re sleepwalking into a future scenario we think will be okay, and it will not be okay.”
Extreme heat “now is affecting the periphery of society but soon it will be affecting everyone,” he warned. “What worries me is we won’t take it seriously until we’re there, and when we’re there it will be too late.”
From lab to policy
Much of the lab’s most crucial work happens after its volunteers go home, Jay said, through efforts to move what’s learned inside the heat chamber into public policy, public knowledge and useful tools to combat heat.
“The translation piece into policy is what it’s all about,” said Jay, who has worked with organizations from Australian Open tennis to the state of Victoria's health department to try to cut heat risks. “It’s why we do what we do, and if it doesn’t happen it’s a real problem.”
His team, for instance, has developed an online HeatWatch app that allows individuals to input their postcode or location and their individual risk factors (such as age, health concerns, and medications) and pull up personalised heat protection advice for that day or week in parts of Australia.
The app, also designed for use by governments, has been deployed to determine when and where to erect trial pop-up cooling tents aimed at helping people who are homeless in Sydney cope with the worsening heat, Jay said.
“We don’t just want to reduce mortality events. We want to reduce suffering as well,” he noted.
Recognising that not everyone can afford a phone or data, his team is also developing low-tech protections, such as a cheap card that can be mailed out and that, tacked up on a home’s wall or in a child’s crib, shows the indoor temperature, which can sometimes be higher than outside temperatures.
Such measures are being developed with input from vulnerable groups including families with young children and low-income adults in social housing, as well as Vietnamese, Cantonese and Arabic-speaking families in Sydney, Jay said.
With heat now the leading cause globally of deaths from natural disasters, the already busy lab is ramping up its work, aiming to improve understanding on everything from how heat affects pregnancy in India and Bangladesh to whether bed nets - which protect families from malarial mosquitos but also slow air flow, making sleep hotter - can be modified to ensure people will continue to use them even as night-time temperatures soar.
“We’re really focused on solutions - understanding the mechanism of the problem then testing candidate solutions to find the best one,” Jay said.
One particular gap in heat research, he said, is a lack of data on how heat is affecting women, largely because too many studies still focus heavily on men. His lab hopes to correct that, he said, noting “we think we should always have an equal sample of men and women.”
With global average temperatures setting records year after year, and heat extremes worsening in many parts of the world, the data will be crucial to developing effective and cost-effective strategies to keep families safer, scientists say.
“We are looking at the limits of human survivability, at which regions will become uninhabitable at least part of the year,” Jay said. “With the chamber we can create the heatwaves of the future now, so we know what to avoid.”