January 27, 2011
Helpful Hints from joeeze: Water can "explode" in your microwave
Here is the back story, related in an enlightening "On The House" column by James and Morris Carey.
Danger lurks in the microwave
A man placed a cup of cold water into his microwave to bring it to a boil. He had done this on numerous occasions. We do not know what length of time was set on the microwave. When it stopped, the man removed the cup, looked into it and noticed the water was not boiling.
Suddenly the water in the cup "exploded." While the cup remained intact, the hot water splashed onto his face, giving him first- and second-degree burns to his entire face and neck.
While at the hospital, the attending physician told the man that the circumstances surrounding his injuries were fairly common. How would you like to be told that such a common event could produce such serious injuries — on a regular basis?
What we found is that water (alone) should never be heated in a microwave oven. When water is heated in a microwave, something should be placed in the cup to diffuse the energy — such as a wooden stir stick or even a tea bag. Obviously, nothing metal should be used.
Here is how a major appliance manufacturer responded to the above event:
"Thanks for contacting us. The information that you received is correct. Microwaved water and other liquids do not always bubble when they reach their boiling point. They can actually become superheated and not bubble at all. The superheated liquid will bubble up out of the cup when it is moved or when something like a spoon or tea bag is placed therein."
Here is what one expert had to say: "I have seen this happen before. It is caused by a phenomenon known as "super heating." It can occur anytime water is heated and will particularly occur if the vessel that the water is heated in is new, or when heating a small amount (less than half a cup).
"What happens is that the water heats faster than vapor bubbles can form. If the cup is very new, 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 it continues to heat up well past its boiling point.
"Bumping or jarring the container can cause 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."
To prevent water from exploding in a microwave:
• Do not heat any liquid for more than two minutes per cup.
• After heating, let the cup stand in the microwave for 30 seconds before attempting to remove it or add anything to it.
• Use a container whose interior surface is at least a little scratched.
• 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.
• Keep your face well away from the open oven door and from the container.
All of these precautions should reduce the chance or extent of superheating and resultant injury. Nevertheless, very hot water is always dangerous and one should always treat it with caution.
January 27, 2011 at 10:01 AM | Permalink
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Personally, I would amend this to "water (alone) should never be heated in a microwave" if you're an incorrigible ninny who isn't overly familiar with how long water takes to get hot in a microwave or an absent-minded person who frequently confuses thirty minutes with three.
In a similar vein, sharp knives should never be given to jokers who have a propensity to spontaneously juggle anything you put into their hands.
Also, never eat lit matches.
Posted by: Mike Harney | Jan 28, 2011 5:08:58 PM
If you are trying to get it to explode (we homeschool, and have two boys) it's not too hard. It also is fun when the microwave needs cleaning too.
First, remove any agitation from the microwave - turntable, etc.
Fill your glass (pyrex) with water and boil it for a minute.
let it cool for a minute after it stops boiling, then boil it again.
It's ready to explode when it has been heated significantly longer than before without boiling.
Tap the front of the microwave, and it will explode, spraying superheated water all over inside.
It works by exhausting the available cavitation points, eventually leading to water that is above the boiling point.
You can also do the same thing with freezing, but it is much more difficult.
Posted by: Randy | Jan 27, 2011 2:31:44 PM
I've lost all mine.
Posted by: bookofjoe | Jan 27, 2011 10:35:46 AM
I use a marble or two as a boiling chip.
Posted by: jim` | Jan 27, 2011 10:34:16 AM
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