Don't Microwave Water

A few days ago I was cleaning the microwave by boiling some water in it. Steam makes scrubbing dirt off the walls easier.

This time, instead of boiling after a few minutes, the water seemed calm. I thought the power setting must be off and continued doing the dishes. Then the water exploded.

All of the water flew out of the cup in a burst of steam and boiling water, accompanied by a surprisingly loud bang.

It is fairly easy to superheat liquids in a microwave. The temperature of such liquid has risen above its boiling point, because there are no good nucleation sites for steam to start forming.

This metastable state is dangerous, because even a minor disturbance may be enough to trigger the violent conversion to steam. This can happen e.g. when grabbing the cup or lowering it to a table. Both may cause severe burns.

#post #protip