Must have been scratched at some point. Then the internal tension of the tempering coupled with a temperature differential would have done that. I once worked in a skyscraper in the CBD where this happened to the external glass cladding. Turned out that the clamps that held the glass in place had scratched the glass in one corner when they were installed. On the morning of a very hot day after a cold night (like last night) the glass went boom crash opera all over the pavement outside as soon as the sun hit it. The security guards thought it was a bullet but turned out to be nothing so dramatic. Just fizzics and poor installation technique.
Must have been scratched at some point. Then the internal tension of the tempering coupled with a temperature differential would have done that. I once worked in a skyscraper in the CBD where this happened to the external glass cladding. Turned out that the clamps that held the glass in place had scratched the glass in one corner when they were installed. On the morning of a very hot day after a cold night (like last night) the glass went boom crash opera all over the pavement outside as soon as the sun hit it. The security guards thought it was a bullet but turned out to be nothing so dramatic. Just fizzics and poor installation technique.