One of the dangers of boiling water in the microwave is the chance of that water becoming "super-heated" and possibly explode in your face. Here's Alton Brown's solution to prevent this from happening.
Photo by selena marie.
The English Tea Store blog recounts an episode of "Good Eats" in which Brown explained the phenomenon. Basically, the problem is the way microwaves affect the water molecules when heating them rapidly:
The first thing to note is that water will form a film where the top layer of molecules in a cup or other container, or even in a drop or puddle where there is no motion, will cling together rather strongly, needing a bit of extra effort to break through. When heating water in the microwave, the molecules are heated within their center under that film. The molecules can reach boiling temperature (212° F or 100° C at lower elevations) without breaking the film and roiling (where bubbles burst up through the film in rapid succession). The best prevention, according to Brown, is a stick set in the cup. It breaks the film and allows the roiling to take place when it should, that is, when the water has reached boiling temperature, not much later when it has super-heated to a higher temperature.
The chances of this happening are low, but it could happen at least a few times around the world, according to Mythbusters, as more of us are using microwaves to cook food and make cups of tea. While making tea in a microwave isn't ideal because you can't control the temperature, you can stick a chopstick, dowel or other stick in the cup just in case.
Super-heated Water and Tea Flavour [The English Tea Store]