[PBARC] Microwaving Water!

[E Glenn Wolf Jr]

Wow, how many of us do that?
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).

General Electric's Response:

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 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 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.'

If you pass this on you could very well save someone from a lot of pain 
and suffering.