Hard-boiled eggs are a dish served cold.
When it is quickly reheated in a microwave oven and then pierced, the picnic food can explode with a loud bang in a hot, elastic shrapnel shower. But this explosion is much more likely to cause a disaster that harms your hearing, according to an investigation presented Dec. 6 at the Acoustic Society of America meeting in New Orleans.
That distinction is not as strange as it might seem. In one lawsuit, a man claimed to have suffered burns and hearing damage after an egg cooked in the microwave exploded in a restaurant. Researchers at Charles M. Salter Associates, Inc. in San Francisco asked that expert witnesses could not find scientific articles that support the claim that an egg could explode with enough vigor to cause hearing loss, just many YouTube videos documenting egg spills. 19659002] So the researchers cooked hard-boiled eggs peeled in water at high power for three minutes.
The eggs were "uncooperative," said study co-author Anthony Nash at a news conference. Some exploded in the microwave, while others would not explode at all. But out of almost 100 tested eggs, 28 exploded out of the microwave after being hit with a meat thermometer. At 30 centimeters distance, the sound pressure of these explosions varied from 86 to 133 decibels.
The recorded average sound pressure level, 108 decibels, is approximately the same as that of an average rock concert. Continuous exposure to that level of noise could damage the hair cells within the ears that respond to the sound. The National Occupational Safety and Health Institute sets the recommended exposure limits for acoustic pressures above 85 decibels, says William Murphy, a NIOSH researcher who was not part of the study. But those limits are based on daily exposure over the years, he says.
The burst of an egg burst, on the other hand, lasts only milliseconds, not long enough to cause much damage. "The probability of hearing damage from a single egg in explosion was very low," Nash said.
The lawsuit was settled out of court before Nash and his colleagues conducted the second phase of the study, considering how the sound hits your ears when it's coming from inside your mouth. An explosion in your mouth could send a little more of sound pressure to the ears, says Nash, but it probably is not enough to cause lasting damage like a one-time accident.
A peeled egg probably explodes when pockets of water trapped in the yolk overheat – warmer than the boiling temperature of the water without actually bubbling, Nash suggested. When they break, say with a fork or a tooth, the pockets of water boil spontaneously, burst through the egg white and blow up pieces. (It is the same phenomenon that can occasionally cause heated coffee to come out of the cup on clean work clothes)
A greater risk than noise could be heat. Nash and his colleagues measured the temperature of the yolks in eggs that did not burst. Those temperatures were, on average, 12 degrees Celsius above the surrounding water bath, which was often close to boiling.