This is an all too common example of what can happen. A man decided to have a cup of instant coffee, so he heated a cup of water in the microwave. When the timer went off, he removed the cup from the microwave and noticed that the water had not boiled.
Just then, the water literally “blew up” in his face. His whole face was blistered with first and second degree burns, which left some permanent scarring and damage to his left eye. While at the hospital, the doctor attending him stated that his is a fairly common occurrence. Water (alone) should never be heated in a microwave oven.
Why? This phenomenon is known as superheating. It can occur anytime water is heated – especially if the cup or bowl is new. What happens is that the water heats faster than the vapor bubbles can form. If the cup is very new, then it is unlikely to have small surface scratches in it that provide a place for the bubbles to form (called nucleation sites).
Without bubbles, the water cannot release the heat that has built up, the liquid does not boil, and it continues to heat up past its boiling point. If the water is bumped or jarred, it’s enough of a shock to cause the bubbles to rapidly form and the result is an exploding liquid that is scalding hot. One solution is to place a wooden stir stick or something non-metallic in the water to help diffuse the energy as it is heating in the microwave.
Dr. Gordon Lindberg, MD, PhD, and director of the burn unit at University of Colorado Health Sciences Center, agrees that the phenomenon of superheated liquids is a real problem. According to Dr. Lindberg, the American Burn Association (ABA) has identified scald burns from superheated liquids in microwaves as a target for a new public awareness campaign.
“These burns are dramatic and traumatic because they often affect the face and hands of the burn victim. Fortunately, these burns rarely need grafting; however, they are extremely painful and in children these burns often lead to hospitalization for wound care and pain control.
The best way to avoid these burns is to place a wooden coffee stirrer in the liquid when heating it and also to let all heated liquids cool for a few minutes inside the microwave before removing them.”
If you receive one of these burns, and especially if it covers the face or hands, seek a burn care specialist for care. Initial treatment for the burn can be performed in an ED or at a doctor’s office, but a burn specialist should see the burn within 24-48 hours after the injury, especially if the face is involved. If the eyes are involved, an ophthalmologist should be consulted immediately.