Reheated Boiled Egg Injures Girl, 9

May 12, 2004 -- A microwave is the ultimate culinary convenience — but most people don't realize that it can go from being helpful to harmful.

In London recently, a 9-year-old girl attempting to re-heat a boiled egg in the microwave received a serious eye injury. The girl placed the egg in the microwave for 40 seconds at full power, then removed it and put it in a bowl. About 30 seconds later, the egg exploded, sending parts of the shell shooting into her right eye — causing serious damage to her eye, according to a letter of warning sent by British ophthalmologists to the British Medical Journal.

At first, the girl could only see hand movements with her right eye, but her vision was restored after a series of operations and the insertion of a plastic lens in her cornea.

Microwave manufacturers warn against heating eggs with a shell, and recommend multiple piercings before cooking or heating eggs in general. Advocates, including the British ophthalmologists, say such warnings should be displayed on the microwave itself.

But it's not just eggs. Several years ago, an Illinois woman scalded her face and her corneas after a bowl of water she heated in the microwave exploded in her face.

No Visible Bubbles

Professor Louis Bloomfield, a University of Virginia physicist, says there's a simple scientific explanation for how these explosions can happen.

"You're used to having water or liquid boil when you heat it above a certain temperature, but there are occasions, and they're more frequent than you'd expect, in a microwave oven when the water goes to or above boiling without any bubbles forming," Bloomfield said. "And that's a phenomenon known as superheating."

Water that has gone beyond boiling is very dangerous, he said.

"Well, it's almost like a bomb once you've got it superheated adequately, because anything that triggers the boiling, once you've reached that temperature, will cause catastrophic, very sudden flash boiling," Bloomfield said.