The various companies who make crock-pot or slow cookers have gravitated toward clear glass lids, some with locks, some without. The lids are made specifically to stand up to the kind of heat exposure expected of slow cookers on setting from “warm” all the way up to “high”.
I had set up a dish the night before in a pot with a locking lid, without the locks engaged, turned it on, and headed for bed. After checking the dish again first thing in the morning, I lowered the heat and allowed it to continue to simmer. When I came back in an hour or so later, I found this.
The lid shattered into pieces that maintained their position and shape until I experimentally tried to lift the lid by the handle.The handle popped up with bits of glass clinging to it.
I was utterly flabbergasted. I understand that glass is a non-porous amorphous solid, that it will “run” over time, that it is an extremely useful material in our daily lives, and that any single piece of glass will have a stress-point that can cause it to shatter like my crock lid.
I’m not inclined to think the slow cooker itself is defective. More that the glass of the lid found it’s weak point and gave in.
Other kitchen witches out there have encountered lids that shattered explosively, as well as a few who have had a similar experience to my own. A popping sound is often reported with this sort of incident, though I do not recall hearing anything when my lid cracked.
Fortunately, a replacement lid was available online for a relatively small price, and the crock-pot was back in use before too many days had passed with no repeat of our little adventure.
As with any appliance in the kitchen, please be sure to read the instructions and take good care of your equipment. Things like this will happen and it’s best to be prepared.