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.