By Girish Linganna

Bengaluru, Sep 9: As climate change leads to rising temperatures worldwide, extreme heat is increasingly becoming a serious health risk.

The human body is strong, but it has its limits. So, what is the highest temperature a person can tolerate?

The answer is simple: a wet-bulb temperature of 95 degrees Fahrenheit (35 degrees Celsius), as found in a 2020 study published in the journal Science Advances.

Wet-bulb temperature is different from the regular air temperature you see reported by your local weather forecast or app.

A wet-bulb temperature is measured using a thermometer wrapped in a damp cloth (or water-soaked cloth), which considers both heat and humidity. This is important because higher humidity makes it harder for sweat to evaporate, preventing the body from cooling down a person effectively.

Colin Raymond, a postdoctoral researcher at NASA's Jet Propulsion Laboratory who studies extreme heat, explained to LiveScience that if either the humidity is low or the temperature is high (but not both), the wet-bulb temperature likely won't reach the point where it becomes dangerous for the human body.

However, when both humidity and temperature are very high, the wet-bulb temperature can rise to dangerous levels.

For example, if the air temperature is 115°F (46.1°C) and the humidity is 30%, the wet-bulb temperature would be around 87°F (30.5°C). This value is calculated by factoring in both the heat and the moisture in the air, showing how the humidity affects how we experience the temperature.

When the air temperature is 102°F (38.9°C) and the humidity is 77%, the wet-bulb temperature reaches around 95°F (35°C). This shows how high humidity and heat together can push the temperature to dangerous levels for the body.

People can't survive in extreme heat and humidity because their bodies can't regulate temperature properly. According to Raymond, who spoke to Live Science, "if the wet-bulb temperature goes above the body's temperature, you may still sweat, but your body won't be able to cool down enough to function normally."

At this stage, the body overheats, reaching temperatures above 104°F (40°C). This can cause signs like a fast heartbeat, confusion, no sweating, dizziness, and even coma, according to the National Institutes of Health.

A wet-bulb temperature of 95°F (35°C) doesn’t lead to immediate death. However, according to Raymond, it would likely take around three hours for that level of heat to become fatal.He mentioned that it's impossible to determine the exact time for certain. However, studies have attempted to estimate it by placing participants in hot water tanks and pulling them out when their body temperatures started to rise uncontrollably.

There's no definite way to prove that 95°F (35°C) is the exact wet-bulb temperature that’s fatal. Raymond suggested that the actual range could be between 93.2°F and 97.7°F (34°C to 36.5°C).

While a wet-bulb temperature above 95°F (35°C) is fatal, even lower temperatures can be dangerous. Physical activity and direct sunlight can cause the body to overheat more quickly.

Older adults, people with health conditions like obesity, and those taking antipsychotic medications have a harder time controlling their body temperature, making them more vulnerable to heat-related death.

This is why some people can die from heat even when the wet-bulb temperature is below 95°F (35°C).

Fortunately, air conditioning can protect people from extreme heat conditions.However, not everyone has access to air conditioning, and in areas where many do, the electrical grid can still be unreliable, Raymond explained.

According to a study in Science Advances, only a few places in recorded history have reached a wet-bulb temperature of 95°F (35°C). Since the late 1980s and 1990s, the hotspots have been the Indus River Valley in central and northern Pakistan, along with the southern coast of the Persian Gulf.

Raymond mentioned that some places are already experiencing these conditions for an hour or two. He added that with global warming, such events will happen more often.He added that areas likely to face these temperatures in the next 30 to 50 years include northwest Mexico, northern India, Southeast Asia, and West Africa.

(The author of this article is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach him at: girishlinganna@gmail.com)