What Are 'Wet-Bulb' Temperatures
The 1st chart has temperatures on top in C. and Humidity on Left. The intersection of both shows the applicable wet-bulb temperature.
The second chart shows how to interpret the colours of the wet-bulb temperature squares in the first chart. Concern really begins at Red and then Black squares.
When the wet-bulb temp is in Red, one should not work for more than 30 min at a time (followed by rest for 30 min), and one should be having one litre of water for every such work hour. Even these guidelines are for fit hikers, and the rest of us ordinary folks should work even less I suppose.
When the wet-bulb square is black, one is not suppose to work at all outside of airconditioning.
What Did This Imply in say Delhi, in June, 2018 ?
What Did This Imply in say Delhi, in June, 2018 ?
What does this imply for Delhi wet-bulb temperatures, say in June ? The science says, no work should be done in day light hours, at all outside of airconditioning in June ! Here are four sample June days where i studied the hourly temperatures :
# On June 1st, 2018, for example, one could have done restricted work from midnight-7.30 AM, and 8 PM to midnight ! but no work in day time as it would fall into black wet-bulb squares.
# On 8th Jun, one could have done unrestricted worked midnight to 6 AM. No work till midnight after that !
# On 15th June, no work outside of airconditioning over 24 hours !
# On 22nd June, only midnight to 6 AM was within safe wet bulb temperature. All the rest of the hours were in black, that is no one was supposed to do any work outside of airconditioning !
Health Impacts of Great Heat and Humidity
A healthy internal body temperature falls within a narrow window. The average person has a baseline temperature between 98°F (37°C) and 100°F (37.8°C). If your body temperature rises as high as 107.6°F (42 °C), you can suffer brain damage or even death.
Just 5 degrees C deviation of temperature from the usual can have severe health consequences in the human body.
If your body needs to cool down, these mechanisms include:
# Sweating: Your sweat glands release sweat, which cools your skin as it evaporates. This helps lower your internal temperature.
# Vasodilatation: The blood vessels under your skin get wider. This increases blood flow to your skin where it is cooler — away from your warm inner body. This lets your body release heat through heat radiation.
This makes the heart beat faster and pump harder. On a hot day, it may circulate two to four times as much blood each minute as it does on a cool day.
Sweat pulls more than heat from the body—it also pulls out sodium, potassium, and other minerals needed for muscle contractions, nerve transmissions, and water balance. Most healthy people tolerate these changes without missing a beat. People with damaged or weakened hearts, have a much harder time, and may succumb to heat stroke.
Here is a detailed study on what high wet-bulb temperatures do to the human body :
Distance runners were asked to run at speed for 60 min at 31 C temperature at 5 levels of humidity : 23, 43, 52, 61 and 71% (on separate days for each varying level of humidity I presume).
Immediately thereafter, participants continued running at the same velocity while the treadmill gradient was elevated by 2% every 2 min until volitional exhaustion.
There was a non-linear increase in core temperature and skin temperature during the exercise taken when humidity was at 61 % and at 71 %.
Evaporation of sweat from the skin halved as humidity levels increased from 23 to 71 %.
The study showed that evaporative heat loss plays a vital role as the main avenue for heat dissipation during exercise in the a heat-stress environment.
Heat Stress Imposes a Robust Upper Limit to Adaptation by Humans
A pioneering study published in 2010 had shown that heat stress imposes a robust upper limit to adaptation by humans to gloabl warming.
Peak heat stress, quantified by the wet-bulb temperature TW, is surprisingly similar across diverse climates today (the reference is to 2010). TW never exceeds 31 °C. Any exceedence of 35 °C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with higher levels of global warming.
Humans maintain a core body temperature near 37 °C that varies slightly among individuals but does not adapt to local climate. Human skin temperature is strongly regulated at 35 °C or below under normal conditions, because the skin must be cooler than body core in order for metabolic heat to be conducted to the skin.
Sustained skin temperatures above 35 °C imply elevated core body temperatures (hyperthermia), which reach lethal values (42–43 °C) for skin temperatures of 37–38 °C even for acclimated and fit individuals.
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