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Microwaving Water!
A 26-year old man decided to have a cup of coffee. He took a cup of water and put it in
the microwave to heat it up (something that he had done numerous
times before). I am not sure how long he set the timer for, but he
wanted to bring the water to a boil. When the timer shut the oven
off, he removed the cup from the oven. As he looked into the cup, he
noted that the water was not boiling, but suddenly the water in the
cup 'blew up' into his face. The cup remained intact until he threw
it out of his hand, but all the water had flown out into his face due
to the build-up of energy. His whole face is blistered and he has 1st
and 2nd degree burns to his face which may leave scarring.
He also may have lost partial sight in his left eye. While at the
hospital, the doctor who was attending to him stated that this is a
fairly common occurrence and water (alone) should never be heated in
a microwave
oven. If water is
heated in this manner, something should be placed in the cup to
diffuse the energy such as a wooden stir stick, tea bag, etc,
(nothing metal).
GeneralElectric'sResponse:
Thanks for contacting us; I will be happy to assist you. The e-mail
that you received is correct. Microwaved water and other liquids do
not always bubble when they reach boiling point. They can actually
get superheated and not bubble at all. The superheated liquid will
bubble up out of the cup when it is moved or when something like a
spoon or tea bag is put into it.
To prevent this from happening and causing injury, do not
heat any liquid for more than two minutes per cup.
After heating, let the cup stand in the microwave for thirty
seconds before moving it or adding anything into it.
Here is what a local high school science teacher had to say on the
matter: 'Thanks for the microwave warning. I have seen this happen
before. It is caused by a phenomenon known as super heating. It can
occur any time water is heated and will particularly occur if
the vessel that the water is heated in is new, or when heating a
small amount of water (less than half a cup).
What happens is that the water heats faster than the vapour bubbles
can form. If the cup is very new, then it is unlikely to have small
surface scratches inside it that provide a place for the bubbles to
form. As the bubbles cannot form and release some of the heat that
has built up, the liquid does not boil, and the liquid continues to
heat up well past its boiling point.
What then usually happens is that the liquid is bumped or jarred,
which is just enough of a
shock to cause the bubbles to rapidly form and expel the
hot liquid. The rapid formation of bubbles is also why a carbonated beverage spews when opened after having
been shaken.'
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