Micro waving Water
http://www.our21.com
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). It is however a
much safer choice to boil the water in a tea kettle.
General Electric's response:
Thanks for contacting us, I will be happy to assist
you. The email that you received is correct. Micro waved water and other liquids
do not always bubble when they reach the 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 our local 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
anytime 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 vapor 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."