Every tempered glass window I have punched broke into a jilliion little pieces and fell out, altho I have seen them shatter from "natural causes," and stay in place. Once, when not wearing gloves, I got a nice cut on one finger when my hand went thru. If you punch near the corner you can support your punching hand and maybe not go thru. The pieces have sharp edges, but are not slivers or shards like plate glass. The primary purpose for covering a victim when punching a window is to keep the glass out of their eyes or any open wounds (glass does not show up on x-rays and is hard to see. Having a chunk stay inside of a laceration after it is sutured is less than fun)