I have a Dovre Aurora 700 from 1993, and after about 14 years or so I noticed a split topple into the glass one night, but nothing happened-until the next morning when I looked at the glass and it had a good 4 inch crack in it! I ordered a replacement one from the shop and the owner said "that still shouldn't have broken like that", and the new piece was much better quality and newer technology because at that time Dovre was out of business and had been bought out by Quadri-fire, so I knew this was a better glass. Last night twice the same big "chunk" of Sycamore leaned into the window and I had "flashbacks" to the "accident" years ago, leapt out of my chair, said a few salty words, and moved him back, and just a little while ago I cleaned the glass off and the black marks came right off and I saw no cracks or anything so it should be good. I do remember someone telling me years ago that they have a metal ball on a rope and pull it back and let it smack into the glass, that's how they test them and how strong they are, but I don't know if that is fact or not. But I think this glass being from Quadri-fire should be very good for years to come. It just amazes me how strong and heat resistant they can make them!