My microwave tried to kill me
February 23, 2008 10:31 AM   Subscribe

Why did my microwave "explode"?

Due to an unfortunate incident with microwave popcorn, I filled a small corning ware bowl with half water and half vinegar and set it to microwave for 3 minutes. After the cycle was done, I wiped the inside of the microwave clean, then tested the temperature of the vinegar / water mix with my finger. It was quite warm, but not hot. Perhaps 5 minutes had elapsed from the first microwave cycle. I set it for another 3 minutes then fortunately walked away. Two minutes later, I heard a big bang. The microwave door had been blown open and the bowl was in pieces across the kitchen. The filter at the bottom of the microwave had also been blown off (over-stove type of microwave with air filter in bottom). So, what happened. A build-up of steam? Flawed corning ware?
posted by TorontoSandy to Science & Nature (17 answers total) 2 users marked this as a favorite
Probably due to superheating
posted by gadha at 10:41 AM on February 23, 2008

Flawed corningware is possible, certainly. A scratch could potentially do this as well, although the thermal-expansion properties of (correctly-made) pyrex-type glasses would discourage this. Vinegar isn't explosive, nor anything it outgasses. It releases hydrogen in contact with some bases, but even that would cause an implosion, not the explosion you reported.

Sorry I'm not providing much help here. If you're into it, you might write a letter to Corning (and put the pieces in a box, JIC). You might get a new microwave out of it.
posted by IAmBroom at 10:46 AM on February 23, 2008

gadha, I considered superheating too, but I've never seen it nor heard of it with that strong an effect. Glass' conductivity (which is high, especially in pyrex-type "glasses") would mean the superheating would be especially unlikely within the container walls.
posted by IAmBroom at 10:55 AM on February 23, 2008

Seconding gadha's response. Boiling hot water needs somewhere for bubbles to form, and sometimes in a smooth container it can superheat. Then as soon as the liquid is disturbed, it can suddenly explode in a rush of steam.

The worst thing you can do is heat water in a microwave twice, because the first heating will clear out any tiny bubbles, meaning the second time through will be more likely to superheat it.
posted by lucidium at 10:57 AM on February 23, 2008

It is not due to super heating. That would mean the liquid would erupt not the container explode. There were probably air bubbles in the pyrex. See here...

The issue with glass that is not microwave safe is that micro-air bubbles may be present in the glass and as the glass heats in the microwave oven, the bubbles may expand to the point where the glass breaks or shatters. (Obviously, you shouldn't eat food where it's glass container has broken.) Pyrex glassware is an excellent example of microwave safe, heat resistant glass that can also be baked. Even Pyrex glass cannot withstand the intensity of direct heat, such as a range or a broiler, for long, so don't use glassware with such heating methods.

Go get your money back. Does your microwave still work?
posted by bkeene12 at 11:00 AM on February 23, 2008

Someone I work with had a pyrex casserole dish spontaneously explode at thanksgiving. It was sitting on a stove top but hadn't been heated on the stove, a guest had brought the dish with a pre-baked item in it. My coworker then googled about it and was astonished to see thousands of similar incidents. My only guess is that glass wasn't annealed properly when it was cast. If it is brought down in temp. too fast, it creates little flaws in the glass. These flaws can generate their own stresses over time and it builds up like a fault line does before an earthquake. This isn't something you caused and it wasn't caused by your normal use-- if it was due to inproper annealing, it would have happened when the dish was made. It wouldn't be a flaw visible to you.
posted by 45moore45 at 11:22 AM on February 23, 2008

I have had my microwave door blown open by what could only be superheated water. Perhaps your pyrex bowl was damaged by impact after being flung from the microwave, and was not the cause of the explosion.

In my case, the pyrex measuring cup was not damaged at all--in fact, it was sitting in the microwave where I left it, basically empty. Water was dripping from everywhere in the microwave and across the kitchen where the water had "exploded" to.

Since my microwave just has a "pull to open, no particular latching involved" door, there was no permanent damage.
posted by IvyMike at 11:24 AM on February 23, 2008

Thermal shock.

Pyrex exploding due to thermal shock.
(I realize yours is Corningware, not Pyrex.)

Corningware explosion happening to somebody else. See also #7 in that thread, and then #14 which says Mythbusters has looked into the superheating theory. (Not found in the Mythbusters wiki, however. Paging Adam Savage).
posted by beagle at 11:34 AM on February 23, 2008

Some old Corningware is not microwave safe (because of its electrical conductivity, I think). The stuff that is safe has a little symbol like a static version of the clock on the gray screen when you start up your Mac.

If bubbles were the issue, wouldn't the dish be equally likely to break if you put it dry into a conventional oven?

But it's been a long time since that kind of Corningware has been manufactured, and I doubt it would explode on failure like this anyway. However, contemporary Corelle dishware, on the rare occasion when it does break, explodes like tempered glass only more so, and for similar reasons (its surface layers are under compression) and yet I've always heard it's microwave safe. A flaw or a bad scratch is a strong possibility, but I'm wondering if a metal streak on the Corelle from contact with aluminum or silver might not be able to produce strong enough local heating in a microwave (somewhat like the aluminum film on Corningware bacon cookers and pizza-crispers) to cause it to shatter as explosively as this.
posted by jamjam at 11:54 AM on February 23, 2008

"...The microwave door had been blown open..."

Not to your question but, make sure the door still closes and seals properly so that there is no radiation leak. Might be worth getting a radiation testing strip - not expensive if I remember correctly from many years ago.
posted by Kevin S at 12:03 PM on February 23, 2008

Note that both CorningWare and Pyrex aren't the old stuff anymore (thermal shock resistance). Beagle pasted one link, and there are more that I had commented here.

In any case, I had never heard of microwave superheating, but we use a separate water kettle or water boiler (I'll be sure to keep this in mind). I'm more inclined to believe a flaw in the container, like bkeene12, because the container itself was destroyed, not merely the liquid inside "exploded."

jamjam may also have a point about really old vintage CorningWare not being microwave-safe, but you may be using the term generically rather than the brand.
posted by Ky at 12:49 PM on February 23, 2008

I have absolutely no scientific knowledge of microwaves or radiation or what have you, but something did catch me eye: "...then tested the temperature of the vinegar / water mix with my finger." Is it possible that this has something to do with oils on his finger? Again, I'm just talking out of my butt here, but maybe it's a possibility? Someone who's actually smart should weigh in on this.
posted by joshrholloway at 12:50 PM on February 23, 2008

....something to do with oils on his finger?... Someone who's actually smart should weigh in on this.

Ok. No, the oils had nothing to do with it.
posted by fatllama at 2:17 PM on February 23, 2008

Response by poster: My husband and I tried to dissect the crime scene. We realized that there were no shards in the microwave, only across the kitchen. As well, it looks like the dish was ejected at a 45 degree angle, probably due to the angle of the door when it opened was blown open.
posted by TorontoSandy at 3:20 PM on February 23, 2008

Good work, TorontoSandy, that changes everything.

No shards in the microwave means the dish did not break inside the microwave. It must have broken when it hit after being blown out of the microwave.

So now the mystery is how it got blown out of the microwave. I would say the vinegar mix boiled over, and ran under the dish. The solution under the dish then boiled and flung the dish against the door, forcing it open, and when the dish bounced off the door its trajectory changed to a 45 degree angle with respect to the microwave.
posted by jamjam at 8:56 AM on February 24, 2008


I was wrong: acetic acid fumes ARE flammable!

My new guess is that the fumes exploded, blew the bowl out of the microwave, and then the bowl broke on landing.
posted by IAmBroom at 10:42 AM on February 24, 2008

I think you could well be right, IAmBroom.
posted by jamjam at 5:03 PM on February 24, 2008

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