posted January 02, 2007 05:36 AM         

A 26-year old man decided to have a cup of coffee. He took a cup of water and put it in the microwave to heat it up (something that he had done numerous times before). I am not sure how long he set the timer for, but he wanted to bring the water to a boil. When the timer shut the oven off, he removed the cup from the oven. As he looked into the cup, he noted that the water was not boiling, but suddenly the water in the cup "blew up" into his face. The cup remained intact until he threw it out of his hand, but all the water had flown out into his face due to the build up of energy. His whole face is blistered and he has 1st and 2nd degree burns to his face which may leave scarring.

He also may have lost partial sight in his left eye. While at the hospital, the doctor who was attending to him stated that this is a fairly common occurrence and water (alone) should never be heated in a microwave oven. If water is heated in this manner, something should be placed in the cup to diffuse the energy such as a wooden stir stick, tea bag, etc., (nothing metal).

It is however a much safer choice to boil the water in a tea kettle.

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Water superheated in a microwave oven can indeed "blow-up" under certain conditions. That is, the superheated liquid can be explosively ejected from its container and potentially cause injury to a person in close proximity.

a specific set of circumstances is necessary to cause microwaved water to explode in this manner. In an article about superheating and microwave ovens, Professor Joe Wolfe of the University of New South Wales notes that such events can take place when the following conditions are present..

1. Using a container with a very smooth surface, such as an unscratched glass or glazed container.
2. Heating for too long.
3. Quickly adding a powder, such as instant coffee (or sometimes even an object to stir it).

Superheating occurs when the liquid is heated to a temperature greater than its normal boiling point. Wolfe explains that the "superheated state is unstable, and it can very rapidly turn into liquid at the boiling point, plus a substantial quantity of vapour." Thankfully, some simple precautions can minimize the chance of injury due to superheating. Professor Wolfe suggests the following strategy for avoiding superheating related injuries...

1. Before putting the water into the oven, insert a non-metal object with a surface that is not smooth. (e.g. a wooden stirrer. A wooden skewer or icecream stick will do.)

2. Use a container whose surface is at least a little scratched.

3. Do not heat for longer than the recommended time for the quantity of water used.

4. Tap the outside of the container a few times with a solid object while it is still in the oven. Use a long object so that your hand remains outside the oven. Alternatively, and still keeping your hand outside the oven, insert a stirrer while the container is still in the oven. (Thus, if vigorous boiling occurs, most of the boiling water will strike the inside of the oven.)

The FDA has received reports of serious skin burns or scalding injuries around people's hands and faces as a result of hot water erupting out of a cup after it had been over-heated in a microwave oven. Over-heating of water in a cup can result in superheated water (past its boiling temperature) without appearing to boil.

This type of phenomena occurs if water is heated in a clean cup. If foreign materials such as instant coffee or sugar are added before heating, the risk is greatly reduced. If superheating has occurred, a slight disturbance or movement such as picking up the cup, or pouring in a spoon full of instant coffee, may result in a violent eruption with the boiling water exploding out of the cup.

What Can Consumers Do to Avoid Super-Heated Water?

Follow the precautions and recommendations found in the microwave oven instruction manuals, specifically the heating time.
Do not use excessive amounts of time when heating water or liquids in the microwave oven.
Determine the best time setting to heat the water just to the desired temperature and use that time setting regularly.

Keep your face well away from the open oven door and from the container.

So be careful everyone!

AL