Microwaved Water

Classification Status


Urban Legend

Chain Mail



Scam   Related to  
"Dim bulb" Rating (Click here for details)

This is an urban legend and a chain e-mail which has been circulating on the Internet for many years. As with some Urban Legends, there is  a grain of truth hidden somewhere in the concocted story. This UL follows the usual rules to make it timeless, no way to verify the facts, no names, no dates, no places mentioned, it is left for you to fill in the blanks and jump to the conclusion that it is 'all' true.

Yes, liquids can superheat in microwaves, yes, they can explode as described below, BUT, you have more chance of being burnt by your conventional oven/hob  than injured in this way in 'normal' responsible everyday use of a microwave (following the guidelines for heating that came with the microwave). This is unlikely to occur naturally, without over-heating liquids.

So, to sum it up, some of the information is correct, but the rest is just pure unfounded scare mongering. Hence, the tick in both the True and False status boxes above, and the single 'Dim bulb' rating.

I was very glad to get this email from a friend, because I have been guilty of heating water in a microwave many times. You'll be glad you read it.

I also suggest passing it along to friends and family. About five days ago, my 26-year-old son decided to have a cup of instant 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 told me 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. Then instantly 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 buildup of energy. His whole face is blistered and he has 1st and 2nd degree burns to his face, which may leave scarring. He may also 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 such as a wooden stir stick or a tea bag should be placed in the cup to diffuse the energy.

Here is what our science teacher has to say on the matter:

"Thanks for the microwave warning. I have seen this happen before. It is caused by a phenomenon known as super heating. It can occur any time water is heated and will particularly occur if the vessel that the water is heated in 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 inside it that provide a place for the bubbles to form. As the bubbles cannot form and release some of the heat that has built up, the liquid does not boil, and the liquid continues to heat up well past its boiling point.

What then usually happens is that the liquid is bumped or jarred, which is just enough of a shock to cause the bubbles to rapidly form and expel the hot liquid. The rapid formation of bubbles is also why a carbonated beverage spews when opened after having been shaken.

Here's a few simple suggestion to help minimise the risk of this happening even further:

  1. Don't overheat any liquid or food in a microwave.

  2. Follow the guidelines for heating which came with your Microwave.

  3. Don't use it to heat water, heat the complete beverage instead.

  4. Place a wooden or microwavable plastic spoon, stir stick, or other microwave safe utensil in the beverage when heating it.

  5. When removing heated liquids from microwaves, use oven gloves and hold the container at arms length, and place it on a heat resistant surface for at least a minute, preferably two.

  6. Stir all liquids before heating.

  7. Do not heat a liquid in a microwave for longer than two minutes, also take it out after a minute and stir it before continuing to heat again for the final amount of time.

  8. Use the supplied  turntable in the microwave, without one superheating is more likely to occur.

  9. Never heat liquids in Styrofoam cups in a microwave.

If you receive a message about this urban legend then please ignore it and don't pass it on as this only serves to propagate it.

Want to know more about microwave ovens? Try here: http://landau1.phys.virginia.edu/Education/Teaching/HowThingsWork/microwave%255Fovens.html

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