Water in a microwave can be dangerous-Truth!

Water Heated a Microwave Can Violently Erupt and Cause Injury-Truth!

Summary of eRumor:
The writer of the email says his or her 26 year old son was scalded by water that erupted from a container after being heated in a microwave. The son experienced severe burns. The writer warns that water should never be heated by itself in a microwave and quotes a science teacher who says the eruption was because the water was heated in a new container that lacked scratches on the sides to allow bubbles to accumulate and be released. The email also quotes a doctor who treated the injured son as saying that theses incidents are fairly common.

The Truth:
This has been a complex one to try to track down and we've consulted a number of different sources. Here is our best understanding of the truth:
...As the millions of people who heat water in the microwave for coffee and tea can attest, this is not a common occurrence and we could find no record of injuries from it, although that doesn't mean none has happened.
...When water is heated on a stove and reaches the boiling point, there are usually the characteristic bubbles that emerge from the bottom of the heated pan. It would be easy, then, to think that all water boils like that when reaching the boiling point. The problem is, that's not always the case.
...It is possible to sometimes heat water beyond the boiling point but without the bubbles.   Why are there no bubbles? When water reaches the boiling point, the water molecules need to start joining arms with other water molecules in order to create the bubble of vapor that we see as boiling. In order to do that, some molecules need to all meet together at the same place and at the same time at what is called a "nucleation site."   A nucleation site can be a tiny impurity, another air bubble, even a scratch on the surface of the container.
...So, here's the scenario: Some water is heated in the microwave and both the water and the container are clean enough that there are no nucleation sites. The water temperature goes higher than the boiling point, but without "boiling." Not only that, but because of the way microwaves work, not all of the water in the cup is the same temperature. The water lining the sides of the cup becomes heated, while some of the water toward the interior of the cup is cooler.

A real example of the story as it has been circulated:

IMPORTANT!!! THIS IS NOT A JOKE!!

Please read the following important information.

Subject: Fwd: Heating Water in a Microwave

I feel that the following is information that any one who uses a microwave oven to heat water should be made aware of.

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 for 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 had flew out into 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. It is however a much safer choice to boil the water in a tea kettle.

Please pass this information on to friends and family.

Here is what our Science teacher has 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. 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.

Please pass this on to everyone you know, it could save a lot of injury.