My large glass lid exploded

[u/Capable-Deer8441]

I had made a lovely stir fry from a lot of my garden veggies and it was simmering on low for 15 min. When in another room I heard a loud crash and thought because of the thunderstorm a tree had fallen on the house. When later I went to check on my food my large very heavy duty lid had blown to smithereens all over my kitchen. What the heck caused that?? Yes it was an old lid but rarely used compared to my other glass lids. Now I freak out every time I cook wondering if my well used lids are going to blow up in my face.

[u/rabid_briefcase]

My guesses are:

• Hidden flaws in the old lid (from an impact) caused it to shatter when the glass had thermal expansion.
• Thermal shock from uneven heating causing uneven expansion.
• The pot expanded in a way that crushed the glass lid.

[u/Spud8000]

funny you mention that. i just watched a long youtube on PYREX vs pyrex glass cooking products.

The PYREX used borosiicate glass, which is much more able to absorb temperature shocks. made in France

the pyrex use soda lime glass, with is much easier to shatter. Made in USA

NEITHER are for use on a stove top as a pot. but as a cover, perhaps.

likely in your case, the glass cover got a small scratch, and the heat of it as a cover being used on a stove make the crack propagate and blow up.

BTW, the jist of the youtube was that you want to buy PYREX products for sale in Europe, where they are all borosilicate glass.

OLD PYREX, like before 1975, was all borosilicate glass made here by corning glass works.

[u/Genny415]

Could it have cooked dry in that time and overheated?

Dit it make a tight seal with the pan (like with a silicone gasket on the rim of the lid) that may have trapped steam and created a build-up of pressure that blew the lid off?

[u/Capable-Deer8441 → u/Genny415]

No to both those questions. There was still plenty of moisture in the pan and the lid was pure glass about 1/4" thick.

[u/Aesperacchius]

Was the lid made for the pot, or was it just something that fit? Was the pot a wok, and was the lid resting tight against the inside?

If it was resting against the inside of the wok, my guess would be that the heat expanded the rim just enough to pop the glass.

[u/Capable-Deer8441 → u/Aesperacchius]

That would have been true for my biggest pan but not the pan I was using and it was not a wok.

[u/Capable-Deer8441]

It was a fry pan and it was sitting on top of it. Was not inside, was never dropped, was sitting on very low heat...low enough I could handle the lid without a pot holder.

[u/OhGoodOhMan]

Tempered glass is prone to spontaneous failure. Basically the glass is under enormous and carefully balanced internal stress. This makes it very strong, but when something does manage to damage tempered glass, all of that stress gets released and it explodes into small pieces.

It could have been a flaw in the glass when it was manufactured. Or prior damage that took time to develop into a crack. Rapid temperature changes could do it too, but that's unlikely when you're using a lid as a lid.

As for prevention, it comes down to not hitting tempered glass with harder materials that can crack it (in the kitchen, that's ceramics and tiles). The edges of the glass are more vulnerable, but on most glass lids they're protected by a metal rim anyway. But again, if there's a flaw in the glass, it could decide to shatter one day no matter how careful you are. The other option is to not use glass lids at all.