One factor in this whole deal is that auto safety glass utilizes a stressed surface to cause "crumbing" rather than "sharding" when it breaks. In manufacturing, as the glass begins cooling, they lightly stress the surface and allow it to cool. The result is that just about anything which relieves the surface tension locally (a scratch, ding, or abrasion) can suddenly cause the surface tension to be relieved for the whole glass, ie, a complete shattering. Be vewy, vewy careful (Elmer Fudd) when handling a scratch or you can zap your whole windshield. It's quite dramatic to watch!
"Go not to the elves for counsel for they will say both no and yes." JRR Tolkien