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May 21, 2020

Helpful Hints from joeeze: Water can "explode" in your microwave

Who knew?

Here's the back story, related in an enlightening 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.

May 21, 2020 at 04:01 PM | Permalink


Confirmed again last week when The Wife was not home and I made tea instead of coffee. Boiled the water for 3:30 and when I dropped in the bag, the water “exploded.”

Posted by: Paul Tempke | May 24, 2020 2:49:43 PM

I've had this happen while making Jello. Pyrex 2 cup measure, zap for 3 minutes and it's not boiling. Zap for another minute and still not boiling. Got it all the way to the counter top 5 feet away before it erupted. Scared the bejesus out of me but no injury.

Posted by: xoxoxoBruce | May 22, 2020 2:01:59 PM

The phenomenon is pretty much the opposite of the 'instant' freezing water whereby a the 'change of state does not occur at the usual point 100 degrees C or 0 degrees C in the case of the ice. (https://www.youtube.com/watch?v=kEHdyiBMgAg)

Posted by: hl | May 21, 2020 9:12:20 PM

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