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Qs on science and my replies to them - Part 259 - heat strokes
Heat stroke occurs when the body becomes unable to control its temperature: the body's temperature rises rapidly, the sweating mechanism fails, and the body is unable to cool down. Body temperature may rise to 106°F or higher within 10 to 15 minutes.
This can cause altered mental state or behaviour. Confusion, agitation, slurred speech, irritability, delirium, seizures and coma can all result from heatstroke.
Heat emergencies have three stages: heat cramps, heat exhaustion, and heatstroke. All three stages of heat emergency are serious.
Compared to hot and dry climates, the human body cannot withstand hot and humid climates nearly as well. That's because at 100 percent humidity, our sweat cannot dissipate as easily to cool our bodies down.
In an absolutely dry environment, the human threshold for survival is probably around 50 °C. But for a completely humid environment, the research results suggest temperatures need only reach 31 °C before our bodies go into heat stroke.
With prolonged exposure to such conditions, death is inevitable.
As climate change drives excessive global warming and water evaporation, increasing the heat and moisture of our atmosphere, the threat of exceeding wet-bulb temperature thresholds becomes ever more likely. Especially in the tropics like south Asia.
Footnotes:
1. https://journals.physiology.org/doi/epdf/10.1152/japplphysiol.00738...
Q: Why are mud houses cooler in the summer and warmer in the winter?
Krishna: Mud is a bad conductor of heat as compared to bricks and concrete. Conductors are materials, which allow the flow of heat energy, while insulators are materials which resist the flow of heat energy. Then we can conclude that mud is a bad conductor and thus resists the flow of heat energy through it.
Earth and clay, in and of themselves, are not insulating materials. They have thermal mass, which means they store heat (or cold), but don't reduce the transmission of heat energy from inside to outside (or vice-versa)
Clay absorbs heat but does not conduct it. It absorbs the sun's radiation, trapping it in the center rather than letting it pass through.
The first thing you need to worry about is not the walls, it’s the roof. That’s where 60% of your heat goes. The air trapped in a thatched (or straw) roof too is a bad conductor of heat.
Thatched roofs provide excellent insulation, so your home will stay warm when it's cold outside and cool during the hot summer months. In addition, this superb insulation enables you to save on electricity for heating and cooling. Durability. Thatched roofs are typically last longer and are very durable.
So in summer, though the outside temperature is more, the heat from outside doesn't flow in. So we feel cooler in a mud house with thatched roofs when compared to the outside provided all the doors and windows are closed.
In winter the heat from inside doesn't flow out. So we feel warm inside a mud house.
Q: Can heat exhaustion occur immediately or come on hours later?
Q: Can heat stroke occur in the morning and evening?
Krishna: Do you know heat stroke isn’t something that only happens outdoors?
Indoor heat stroke is a heat-related illness that is caused when the body overheats by going over a core temperature of 40 degrees Celsius and is unable to cool itself down.
The condition can occur in homes that don’t have air conditioning, inside a hot vehicle or anywhere that doesn’t have a central cooling system, in the morning or evening if the atmospheric temperature is very high. Heat exhaustion or heatstroke can develop quickly over a few minutes, or gradually over several hours or days.
Also other factors too contribute (1).
Heat stress is mostly caused by temperature, but other weather-related factors such as humidity, radiation and wind are also important.
Our bodies gain heat from the air around us, from the sun, or from our own internal processes such as digestion and exercise. In response to this, our bodies must lose some heat. Some of this we lose directly to the air around us and some through breathing. But most heat is lost through sweating, as when the sweat on the surface of our skin evaporates it takes in energy from our skin and the air around us in the form of latent heat.
Underlying health conditions and other personal circumstances can lead to some people being more vulnerable to heat stress. Yet heat stress can reach a limit above which all humans, even those who are not obviously vulnerable to heat risk – that is, people who are fit, healthy and well acclimatised – simply cannot survive even at a moderate level of exertion.
One way to assess heat stress is the so-called Wet Bulb Globe Temperature. In full sun conditions, that is approximately equivalent to 39°C in temperature combined with 50% relative humidity. This limit will be exceeded in some places .
In less humid places far from the tropics, the humidity and thus the wet bulb temperature and danger will be much lower.
In reality, most people are already vulnerable well below the survivability thresholds, which is why we can see large death tolls in significantly cooler heat waves. Furthermore, these global analyses often do not capture some very localised extremes caused by microclimate processes. For example a certain neighbourhood in a city might trap heat more efficiently than its surroundings, or might be ventilated by a cool sea breeze, or be in the “rain shadow” of a local hill, making it less humid.
The tropics typically have less variable temperatures. For example, Singapore sits almost on the equator and its daily maximum is about 32°C year round, while a typical maximum in London in mid summer is just 24°C. Yet London has a higher record temperature (40°C vs 37°C in Singapore).
Given that regions such as south-east Asia consistently have high heat stress already, perhaps that suggests that people will be well acclimatised to deal with heat. Initial reporting suggests the intense heat stress of the recent heatwave lead to surprisingly few direct deaths .
Footnotes:
1. why-40-c-is-bearable-in-a-desert-but-lethal-in-the-tropics
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