Too Hot to Handle: How to Survive Extreme Heat and Humidity


A few summers ago, Gordon Giesbrecht was doing some work on a lakeside dock when he started feeling “a little funny.” Minutes later, he was vomiting – a symptom he immediately recognized as heat exhaustion.

As an expert on how extreme temperatures affect the human body, Giesbrecht is the first to admit he should have seen the warning signs.

“After I finished throwing up, I said, ‘That’s it for the dock’… I went and got a lawn chair and stuck it in the shallows, and sat in the lake …and I got cold,” said Giesbrecht, professor of thermophysiology at the University of Manitoba.

Amid heat wave warnings Across much of Canada this week, Giesbrecht’s experience reminds us of how summer heat can affect our bodies without us realizing it – and the need to watch out for life-threatening symptoms.

In Europe, more than 1,100 people have died from the heat in Spain and Portugal in recent days. There are also fears for people elsewhere in Europe and the UK – places where few have air conditioning to cope with temperatures well over 30C.

WATCH | Climate change is driving extreme weather events, says a climatologist:

A Canadian climatologist on the link between climate change and extreme weather events

Dave Phillips, a senior climate scientist with Environment Canada, says “the evidence is compelling” that climate change is the root cause of the upward trend in extreme weather and weather-related disasters.

Adding humidity to that heat makes it harder for us to cool down by sweating – and humans can literally be cooked alive.

“Our body can actually survive a core temperature decrease of 10 or even 20 degrees, but our body can only survive a core temperature increase of five degrees. [to] seven degrees – and then you can be in big, big trouble,” Giesbrecht said.

The hotter and more humid it is, the greater the risk of heat exhaustion. Symptoms include headache, heavy sweating, clammy skin, dizziness or confusion, cramps, rapid breathing, nausea and vomiting, among othersaccording to Health Canada.

It’s not (just) the heat, it’s the humidity

The point at which a combination of heat and humidity becomes particularly dangerous, even deadly, is explained by scientists as the “wet bulb temperature” – the lowest temperature to which an object can cool due to evaporation. humidity.

Imagine a thermometer wrapped in a damp cloth: water will continue to evaporate from the cloth up to a certain level of humidity, when the air contains too much moisture for evaporation to continue. Due to the evaporation effect, the temperature of the thermometer will be lower than that of the air around it, that is, until the evaporation stops.

This graph shows how air temperature and humidity combine for a wet bulb temperature, which explains the points at which it becomes difficult or impossible for water or sweat to evaporate. This causes an increase in the core temperature of the human body. (Radio-Canada News)

Our bodies work the same way: at a wet bulb temperature of 35°C (for example when it is 40°C outside with 70% humidity), sweat no longer evaporates from our body, and scientists believe that a human being can only survive about six hours under these conditions.

“No matter how much water you have, it won’t help you because you can’t maintain a body temperature to survive,” said Tapio Schneider, a climatologist and professor at the California Institute of Technology in Pasadena.

As your core temperature rises, your organs — including your heart, kidneys, and brain — begin to suffer damage and the proteins in your cells break down. A person with heat stroke can convulse, fall into a coma, and die.

Lower wet bulb temperatures can also be deadly, especially for the elderly, young children, and people with medical conditions. For example, during the European heat wave of 2003, which killed more than 20,000 people, wet bulb temperatures remained below 28 C.

People cool off in the Dreisam River in Freiburg im Breisgau, Germany, on Tuesday. Few European households have air conditioning, leaving their occupants stifled by the current heat wave. (Arnd Wiegmann/Reuters)

Even at this level of wet bulb reading, it can be dangerous to do anything that could further raise your body’s core temperature, such as exercise or the type of manual labor that Giesbrecht did when he suffered from heat exhaustion.

“If you’re an outdoor worker, or if you work in agriculture or construction in hot, humid weather…you’re at risk for heat stroke, heart stress, etc.,” Schneider said. “The heat can be deadly long before you reach that absolute limit of survivability.”

Stay cool and stay aware

With more hot, humid days to come this summer – and many more to come as the planet warms up – experts say people should limit the time they spend outdoors in the heat and use air conditioning to keep the living areas cool.

People relax on a beach in Ottawa on Tuesday as the temperature soared above 31°C. Experts say people shouldn’t spend too much time in the sun, especially when it’s humid, to avoid heat-related illnesses. (Francis Ferland/CBC/Radio-Canada)

Fans only help if the air temperature is below your skin temperature of 33°C; if the air is warmer, the fan will only raise the temperature further, Giesbrecht said.

Staying hydrated will help you sweat, while spraying water on your body or clothes also has a cooling effect on your skin as the water evaporates.

If someone is suffering from heat stroke, call 9-1-1 and move them immediately to a cool place, ideally an air-conditioned building or vehicle. Symptoms include high body temperature, confusion and lack of coordination, dizziness or fainting, lack of sweating and very hot and red skin.

Instead of taking off someone’s shirt to cool them down, Giesbrecht advises pouring water on their clothes: remember the wet bulb effect?

People rest in the shade on the bank of the River Thames during a heatwave in London on Tuesday (Henry Nicholls/Reuters)

“The water in the shirt evaporates and cools the skin. If you don’t have a shirt on any part of their skin, that water will just roll off the floor,” Giesbrecht said.

“I’m going to take a liter [of water] and pour it over that person, and wait for it to start drying, and then I’ll put some more on it, so I can continue to use that cooling effect of evaporation.”