Delhi, and several other parts of North India, are reeling under severe heatwave since mid-May. In some areas of the national capital, the temperature was recorded over 48-49 degree Celsius, while in Rajasthan the mercury touched 50 degree Celsius in some places. Deaths due to heatstroke and related ailments were reported in several areas in the north, which brings us to the question how much heat can a human body tolerate.
Experts mention humidity and the ‘wet bulb’ temperature to understand how much heat a human body can sustain. The wet bulb temperature is a meteorological term used to describe the lowest temperature that can be reached by evaporating water into the air at constant pressure. This temperature helps measure humidity and understand how much water can evaporate into the air, affecting things like comfort, farming and weather patterns.
According to a Delhi-based think tank, Centre for Science Environment (CSE), the body works best within a narrow range of body temperature – 36 degree Celsius to 37.5 degree Celsius. Once 40 degree Celsius is reached, it can be dangerous even with low humidity levels. With temperature touching 50 degree Celsius, the situation is critical.
When the air temperature is 46.1 degrees Celsius with a relative humidity of 30%, the wet bulb temperature is 30.5 degrees Celsius. But when the air temperature is 38.9 C and the relative humidity is 77%, the wet bulb temperature is about 35 degree Celsius.
Humidity aggravates heat conditions, making it harder for a body to process hot temperatures. With more water in the air, it harder for sweat to evaporate off the body.
According to Sagnik Dey, an Associate Professor at the Centre for Atmospheric Studies in IIT Delhi, when a body is exposed to heat, it tries to maintain its core temperature. Depending on the environmental and physiological conditions, the body’s core temperature starts building and humans start to feel fatigue.
What Happens To Body When It Is Too Hot
People tend to start breathing more heavily, and their heart rates can go up, say medical experts. Once a person’s body can no longer get rid of excess heat — a condition known as “heat stress” — the core temperature rises. That can result in confusion, nausea, dizziness, headache or fainting.
Continued exposure to 48-50 degree Celsius and beyond leads to a severe breakdown of muscle and even death.
According to Dr Sanjeev Bagai of Nephron Clinic, discomfort can be felt at any temperature beyond 40 degrees Celsius. “Headache, vomiting and dehydration are experienced at temperatures beyond 40-42 degrees. At 45 degrees delirium, palpitations and drop in blood pressure become common,” he said.
A human body is equipped to acclimating to heat, up to a point. But once the body can longer process the heat, it will denature proteins and cause irreparable brain damage. This change happens over a period of time and is not an immediate effect.
Once the body temperature rises, the brain can struggle to process information, there could a drop in cognitive function, which can affect judgment and put people at risk of falling. In extreme cases, high heat can even cause dangerous brain inflammation.
Not just the brain, the human heart also gets affected. Stephen Cheung, a senior research fellow at Brock University in St. Catharines, Ontario, said, as quoted by CBC News, that’s because more blood is trapped out in the skin as your body tries to cool itself. “What happens is that it places greater strain on your heart because now it has less blood coming back, and it has to work harder to pump that blood out to the rest of the body,” he said.
Extreme heat also is found to affect the kidneys and the lungs.
Highest Recorded Temperatures at Which Human Survived
The Furnace Creek Ranch in California recorded 56.7-degree Celsius or 134-degree Fahrenheit on July 10, 2021. The place was earlier called the Greenland Ranch.
Furnace Creek Ranch officially became the hottest place on the earth after the World Meteorological Organisation (WMO) rejected the claim of 58 degree Celsius recorded at El Azizia in Libya in 1922 in a review during 2010-12.
Phalodi in Rajasthan recorded the temperature of 51-degree Celsius or 123.8-degree Fahrenheit on May 19, 2021.
In Churu (Rajasthan), the temperature touched 50.8 degree Celsius or 122.4-degree Fahrenheit in August 2019.
Delhi’s two weather stations — Mungeshpur and Narela—observed the highest temperature touching 49.9 degrees Celsius on May 29, 2024. The previous highest maximum logged at a Delhi station was 49.2°C at Mungeshpur on May 15, 2022, officials of the weather department said.
How To Protect Yourself
According to the UNICEF, keep these steps in mind when facing severe heat conditions.
• Know how hot and humid it is going to get today, this week and this month to help plan outside activities.
• Keep an emergency kit at home that contains oral rehydration salt (ORS) packets, a thermometer, water bottles, towels or cloths to wet for cooling, a handheld fan or mister with batteries, and a checklist to identify and treat symptoms of heat stress.
• Know how to get help. Note down the contact information for the nearest health care provider or ambulance/transport services.
• When possible, close the curtains during the hottest parts of the day and open windows at night time to cool down the house.
• Drink water at regular intervals before you are thirsty. Carry a water bottle and a small towel, so you can hydrate and cool down by placing a wet towel on your neck.
• Wear light and loose clothes. Cotton is ideal during hot days to help reduce heat rashes and absorb sweating.
• When outside, wear sunscreen and try to stay in the shade or use hats and umbrellas for protection.
How Many Indians Have Died of Heatwave?
Across the country, 32 people have died due to heatstroke, and another 28 deaths are suspected to be caused by heatstroke. Government data also revealed that on May 22 alone, two people in Andhra Pradesh and Rajasthan’s Kota died of suspected heatstroke.
Since March 1, there have been 16,344 suspected heat stroke cases, with 486 cases reported on May 22 alone.
Dileep Mavalankar, head of the Indian Institute of Public Health (IIPH) in Gandhinagar, said, as quoted by Business Standard, “There are two types of heatwave deaths – exertional, caused by exertion in direct sunlight leading to an inability to cool down by sweating, accounting for only 10% of heatwave deaths. Non-exertional deaths occur among the vulnerable – the elderly, the sick, and infants who cannot cool down even at night. Their kidneys and heart start failing following dehydration. These people may not have access to cooling at home and can die anywhere, even at home, as it’s not related to exertion. These are not categorised as heat strokes and are hence, possibly not counted as heat deaths at all”.
In Europe, high temperatures in 2022 may be responsible for 70,000 excess deaths, according to a new study by Barcelona Institute for Global Health.