I still vividly recall my experience of 40 years ago. I was a student in a room with a tiny "cupboard" kitchen. My parents visited, and while washing up, my mum stacked 3 pyrex plates on the electric ring. Somehow - possibly during wiping down the cooker - the ring got switched on (on low). Some time later, we realised what had happened, and turned the ring off very carefully.
We then left the plates there to cool, and they stayed there overnight. Next morning, everything seemed fine - the plates appeared no worse for wear, and I picked them up to put them away.
BANG.