I have been very careful handling 100s of pieces of playfield glass and backglasses and always thought when someone breaks one it had to be at least some carelessness on their part.
However when I carefully picked up a piece of playfield glass I had in the garage that was leaning against the wall sitting on a piece of cardboard about a month ago and it just exploded in my hands I learned otherwise. It was tempered and not damaged around the edges, but an older piece.