As heat records fall, how hot is too hot for the human body? | Health & Fitness

Extreme heat has been breaking records across Europe, Asia and North America, with millions of people sweltering in heat and humidity well above “normal” for days on end.

Death Valley hit 128 degrees Fahrenheit (53.3 degrees Celsius) on July 16, 2023 – not quite the world’s hottest day on record, but close. Phoenix broke a record heat streak with 19 straight days with temperatures above 110 F (43.3 C), accompanied by a long string of nights that never got below 90 F (32.2 C), leaving little opportunity for people without air conditioning to cool down. Globally, Earth likely had its hottest week on modern record in early July.

Heat waves are becoming supercharged as the climate changes – lasting longer, becoming more frequent and getting just plain hotter.

One question a lot of people are asking is: “When will it get too hot for normal daily activity as we know it, even for young, healthy adults?”

The answer goes beyond the temperature you see on the thermometer. It’s also about humidity. Our research is designed to come up with the combination of the two, measured as “wet-bulb temperature.” Together, heat and humidity put people at greatly increased risk, and the combination gets dangerous at lower levels than scientists previously believed.

Scientists and other observers have become alarmed about the increasing frequency of extreme heat paired with high humidity.

In the Middle East, Asaluyeh, Iran, recorded an extremely dangerous maximum wet-bulb temperature of 92.7 F (33.7 C) on July 16, 2023 – above our measured upper limit of human adaptability to humid heat. India and Pakistan have both come close, as well.

People often point to a study published in 2010 that theorized that a wet-bulb temperature of 95 F (35 C) – equal to a temperature of 95 F at 100% humidity, or 115 F at 50% humidity – would be the upper limit of safety, beyond which the human body can no longer cool itself by evaporating sweat from the surface of the body to maintain a stable body core temperature.

It was not until recently that this limit was tested on humans in laboratory settings. The results of these tests show an even greater cause for concern.

To answer the question of “how hot is too hot?” we brought young, healthy men and women into the Noll Laboratory at Penn State University to experience heat stress in a controlled environmental chamber.

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Extreme heat has been breaking records across Europe, Asia and North America, with millions of people sweltering in heat and humidity well above “normal” for days on end.

Death Valley hit 128 degrees Fahrenheit (53.3 degrees Celsius) on July 16, 2023 – not quite the world’s hottest day on record, but close. Phoenix broke a record heat streak with 19 straight days with temperatures above 110 F (43.3 C), accompanied by a long string of nights that never got below 90 F (32.2 C), leaving little opportunity for people without air conditioning to cool down. Globally, Earth likely had its hottest week on modern record in early July.

Heat waves are becoming supercharged as the climate changes – lasting longer, becoming more frequent and getting just plain hotter.

One question a lot of people are asking is: “When will it get too hot for normal daily activity as we know it, even for young, healthy adults?”

The answer goes beyond the temperature you see on the thermometer. It’s also about humidity. Our research is designed to come up with the combination of the two, measured as “wet-bulb temperature.” Together, heat and humidity put people at greatly increased risk, and the combination gets dangerous at lower levels than scientists previously believed.

Scientists and other observers have become alarmed about the increasing frequency of extreme heat paired with high humidity.

In the Middle East, Asaluyeh, Iran, recorded an extremely dangerous maximum wet-bulb temperature of 92.7 F (33.7 C) on July 16, 2023 – above our measured upper limit of human adaptability to humid heat. India and Pakistan have both come close, as well.

People often point to a study published in 2010 that theorized that a wet-bulb temperature of 95 F (35 C) – equal to a temperature of 95 F at 100% humidity, or 115 F at 50% humidity – would be the upper limit of safety, beyond which the human body can no longer cool itself by evaporating sweat from the surface of the body to maintain a stable body core temperature.

It was not until recently that this limit was tested on humans in laboratory settings. The results of these tests show an even greater cause for concern.

To answer the question of “how hot is too hot?” we brought young, healthy men and women into the Noll Laboratory at Penn State University to experience heat stress in a controlled environmental chamber.

…continued

swipe to next page