With summer
temperatures reaching 100 degrees Fahrenheit (38 degrees
Celsius) in many cities, heat stroke is becoming a big problem.
Heat stroke can be fatal in many cases because it happens so
quickly -- there is not much time to react.
Let's say that it
really is 100 degrees F outside. The human body wants to stay at 98.6
degrees F. The only way to stay at 98.6 is to sweat. By
putting moisture on the skin and letting it evaporate, your body
can cool itself very effectively and keep its temperature in the
proper range.
Sweat works really
well as long as there is plenty of water in your body -- it
takes water to manufacture sweat. If you run out of water, sweat
stops and your body rapidly overheats. It turns out that it is
extremely easy to run out of water -- your body can produce 0.5
gallons (2 liters) of sweat every hour in a hot environment.
Unless you are drinking water at the same rate, you will dehydrate
and then stop sweating. Your internal thirst meter often is
not sensitive enough when you need that much water (and it has
been said that by the time you feel thirsty, you're already
dehydrated), so you have to keep drinking regardless of how
thirsty you feel.
The other thing
that can lead to heat stroke is very high humidity, which
keeps sweat from evaporating.
In either case --
be it the lack of sweat or the inability to evaporate it -- the
core body temperature can rise very quickly if it is hot outside.
Once the core gets to 106 degrees F, it is a serious
problem. Symptoms include red, hot, dry skin (the body dilates
skin blood vessels to try to release heat, making the skin red,
and the dryness comes from lack of sweat), rapid heart rate,
dizziness and confusion. The dizziness and confusion come from the
high body temperature, which affects the brain.
For children
and pets, one way for heat stroke to happen suddenly and
unexpectedly involves a hot car or a hot room in a house. Cars are
especially dangerous. We did the following experiment for this:
-
We turned on
the air conditioner in a car at 3:30 p.m. on a sunny, hot
summer afternoon in Raleigh, NC.
-
We waited until
the interior of the car cooled to a comfortable 75 degrees F.
-
We turned the
engine off.
Within 15 minutes,
the interior temperature of the car was 110 degrees F. This
temperature is quickly fatal.
The reason the
temperature rises so high and so fast is because the interior of a
car is an excellent solar oven that uses the greenhouse effect
to trap heat. Sunlight heats the sheet metal of the car, and it
streams in through the windows to heat the interior. It turns out
that glass is completely transparent to visible light but opaque
to infrared light -- and infrared light is the heat that is trying
to radiate back out of the interior. So the temperature rises
rapidly, to the point where you often cannot touch the steering
wheel without getting singed. Leaving the window cracked is not
going to help -- it is never safe to leave a child or pet in a
parked car for any length of time.
The only solution
for heat stroke is to cool the person down. You can:
-
Try to get the
person to drink water if the person is conscious.
-
Soak
the person's entire body in cool water.
-
Sponge
cool water onto the person's body.
-
Apply ice
packs to the head, neck, armpits and groin.
If not treated,
heat stroke can be fatal in less than an hour.
