How far can you push the human body before it fails? The New Scientist posed that question a few years ago, listing out a few “ultimate limits” for the human body: how fast can we run, how long can we concentrate, how long can we survive without sleep and so on. The one question they did not ask, and that’s increasingly bothering us, is: how much heat can we tolerate before we perish?

It’s just May. And we are already battling an intense heat wave. Last year, NASA experts predicted that in 2015, planet Earth will face an unprecedented heat wave. The three decades from 1983 to 2012 have been the warmest in the last 1,400 years. And summer of 2015 will be excruciatingly hot in several parts of the world. Clearly, India is one of those.

What’s excruciatingly hot for us? Remember 2010, when temperature hit a 50-year-high with Jalgaon in Maharashtra crossing 49 degrees? No. India has seen more: the highest so far has been 50.6 degrees at Alwar, Rajasthan, in May 1956.

Apparently, that’s not enough to make us one of the most spectacular hotspots in the world. At least, we haven’t seen temperature going up to 71 degrees, as it did at the salt deserts of Dasht-e Lut, Iran, in 2005. Or 69.3 degrees as in Queensland, Australia, in 2003. Or even neighbour Pakistan’s 2010 record, when temperature soared to 53.7 degrees at Mohenjo-daro — one of the warmest temperatures ever recorded in the world.

So how much heat can you tolerate? As much as your genes allow. Heat tolerance is coded in your genes. The mechanism goes back to human evolution over 1.7 million years, when humans started coming out of forested areas into open grassy lands. To survive the heat and to keep cool, our ancestors started losing body hair. A genetic adaptation for survival — just as bipedalism, a prominent nose, a large brain, and the ability to speak are. There’s more: people who are tall, slim and slender tolerate heat better. They have more skin to perspire. Woe be unto those who are fat: they have less skin surface for their weight.

Generally, the range between 18 degrees and 24 degrees is best for the body, says the World Health Organisation (WHO). But when temperature nears 40 degrees, the body finds it difficult to cool down — with or without humidity — leading to heat cramps, exhaustion, breathing difficulty and increased heart rate. If mercury soars well above 40 degrees, the heat can cause permanent damage to vital organs. As we all know, heat can be a killer.

Well, there’s a caveat from WHO: Your heat tolerance is linked to what you are used to. So Dilliwalas would fare better, than say Londoners, if the mercury goes beyond reasonable limits. Simply because we are used to it.

Some consolation that.



The writer is deputy editor, India Today and reports from hospitals.

6 Replies

  • I would like to add,not only how much but also HOW LONG.

  • Our Air conditioner are design for out side temp.max 55 degree centigrade.

    During high temp of above 60 Deg.any one can have idea?

    If pl.give in that so that any one can survive.

  • this 55 degrees is limit for small air conditioners i think.

    large ac with cooling tower and water spray

    has to work far above this 55.

    am i correct?

  • Extreme heat conditions are defined as regional temperatures that remain 10 degrees or more over the normal highs for a period of several weeks. Most air conditioning units are manufactured to function in outside temperatures up to 100 degrees Fahrenheit and to keep your home about 20 degrees cooler inside than the outside temperature. After that maximum outside temperature has been reached, the cooling system begins to fail, increased amounts of energy are consumed as the system attempts to cool the building, and the mechanical parts of the unit begin to malfunction.

    If the outside thermometer is showing temperatures of 95 or higher, your air conditioner is running at maximum capacity. The coolest temperature you can expect the interior of your home to reach is about 78 to 80 degrees Fahrenheit. Lowering your thermostat will not help the air conditioner function better. Instead, the unit will continually run with little to no change in interior temperatures. The older the air conditioning unit, the harder the system has to work, and the poorer the cooling results.

  • that is true about small room conditioners.

    but in large ac with water spray and pumped air cooling [cooling tower]

    the cooled water can obtain temperature low enough

    to operate the central ac system.

    because the latent heat of vaporization of water is so high that normal atmospheric air temp rise will not hinder the process.

    this is not the case with a fan,which

    cooling the grid of the expanded gas as in household small ac.where cooling is purely by the flow of heat from the expanded gas to the air from the fan .

    if both are equal,

    no transfer takes place.that is why we say- it has reached its designed maximum level of cooling.

    thanks for response.

    good luck

  • sorry,

    addition .

    the expanded gas goes to compressor and it is the compressed gas or liquid we try to cool with a fan.

    [or cold water from a cooling tower or any cold source]

    the expanded gas is generally very cool.on compression it gets heated.

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