Today's PSA - Microwave water?

[George K]

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).

General Electric's Response:

Thanks for contacting us; I will be happy to assist you. The e-mail that you received is correct. Microwaved water and other liquids do not always bubble when they reach boiling point. They can actually get 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 put into it.

To prevent this from happening and causing injury, do not heat any liquid for more than two minutes per cup. After heating, let the cup stand in the microwave for thirty seconds before moving it or adding anything into it.
Here is what a local high school science teacher had 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, or when heating a small amount of water (less than half a cup).

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.

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Looking around on the interwebz seems to confirm this, for the most part. One site said that this is more likely to occur with distilled (pure) water. Tap water has enough impurities that this might not be an issue.

Link to video

[Doctor Phibes]

I've actually seen that happen. The water went everywhere, but didn't burn me at least.

[Horace]

On the other end of the temperature scale I have seen demonstrations of super-cooled water which doesn't freeze until nudged. Same principle, I suppose.

I notice the type of advice you tend to see for these low probability dangers. "Spend the rest of your life carefully setting microwave water for two minutes ONLY and wait thirty seconds before moving it". Personally I'm comfortable not worrying about it, rather than remembering this one extra thing that I have to do that will make my day just slightly more tedious and annoying.

[Horace]

Presumably a spinning microwave table would prevent this as well. Which nearly all microwaves have.

[George K]

@Horace said in Today's PSA - Microwave water?:

I have seen demonstrations of super-cooled water

That's because you're super cool.

But we knew that.

[Horace]

@George-K said in Today's PSA - Microwave water?:

@Horace said in Today's PSA - Microwave water?:

I have seen demonstrations of super-cooled water

That's because you're super cool.

But we knew that.

Thanks George. It's true. I'm a super cool, big fat jerk. Also a libertarian.

[taiwan_girl]

I think it was on this forum board (did a quick search of the mildly interesting thread but could not find), someone posted a video of water freezing and boiling at the same time due to the correct temperature/pressure situation.

[Copper]

https://www.aopa.org/news-and-media/all-news/2019/january/07/training-tip

That melting process is unlikely in January, when temperatures may sit in a regrettably reduced range for days on end. Yet on those mornings, frost may diminish even if temperatures never rise above freezing—that is, the temperature at which the state of water changes from ice to a liquid. (And if an aircraft that is airborne on an instrument flight plan has begun icing up while flying in clouds, upon breaking out into clear air, the pilot may be happy to observe that the leading edges of wings, struts, and other surfaces have begun to lose their ice.)

The process called “sublimation” is the driver of such transitions. Think of it as eliminating the middleman of a liquid state for water between the icy state and the gaseous state, or vapor.

A formal definition of sublimation is a “process by which a solid is changed to a gas without going through the liquid state.”

The Pilot’s Handbook of Aeronautical Knowledge notes in Chapter 12 that water can exist in those three states within the atmosphere’s temperature range, and that “sublimation is the changing of ice directly to water vapor, completely bypassing the liquid stage.”

[Klaus]

Isn't the microwave water issue common knowledge? All my kids told me about how they learned about this at school.