A Warning About Microwaving Water
Most of you that know me are aware I rarely, if ever, pass on generic warnings received in e-mails from friends. However, this one was different. I had a similar thing happen to me and this story explained the phenomena very well. It also points out that it is not an isolated event. Apparently it happens fairly frequently. I don't know the players in this drama, but please read on.....
Subj: Helpful information all should read
People should be aware of the following information in case they use a microwave oven to heat water.
Here is what he said:
About five days ago my 26 year old son decided to have a cup of instant 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; but he told me 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 instantly 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 flew out onto his face due to the buildup 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 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.
Explanation:
At sea level, water boils at 212 degrees Fahrenheit. While boiling, the liquid remains at 212, and the released vapor is hotter than 212. A catalyst is required to start water boiling. A kettle usually has enough imperfections to start the water boiling when the temperature reaches 212 degrees. Water can be superheated under the right conditions; the liquid can be heated above 212 degrees without starting to boil. When using a perfectly smooth container, water can be heated to 215 degrees or more without achieving the typical bubbling action. But, the moment when a container of superheated water is jarred, or when an impurity is thrown in, the water will rapidly "flash" from liquid to vapor.
For example: water can be superheated in a ceramic mug. A granule of instant coffee thrown into the mug can initiate a violent conversion from liquid to vapor. A wooden stick in the mug ensures that the water will not superheat; instead, it will begin bubbling at 212 degrees.
I didn't know the exact physics but assumed all the water heated evenly and boiled at the exact same instant. In reality, it was past boiling and waiting for something to trigger the conversion from water to steam.
I figure another way to avoid this problem is not to boil water in a microwave. I still heat it up but never attempt to achieve a boil.
The real story here is to be aware of the risk and use your head.