I don't know if this will help or not, but I once witnessed a large mirror getting broken by accident. It wasn't as big as the one in the picture, but it was pretty large. The person broke it by tripping and placing their palm and all their weight against the glass.
It splintered in a circular pattern with a ton of small dagger-shaped pieces in the middle that got larger the farther you went from the impact. The entire mirror was bolted to the wall, so the frame didn't budge. A bunch of glass fell immediately, but not all of it fell.
She didn't have a scratch on her hand, but a giant, triangular chunk of glass fell on the top of her sandaled foot, and she had to get stitches.
Also, some old mirrors were made with tin and mercury. I don't know much about mercury poisoning, but I know it's a nasty, deadly metal.