When you least expect it (near microwave disaster).

Another kitchen horror from my youth was the exploding pressure-cooker.

I recall a teacher in the 1980's being called out off class for an emergency, because his elderly mother's pressure cooker went ka-boom!

The next day we heard all about how they literally had to scrape the chicken off the ceiling.

Well, I learnt a lot so far, I didn't grow up with a microwave in the home (my family was very against it, seemingly for cultural rather than safety reasons) until recently when their hot-air oven finally gave up the ghost.