I was wearing safety glasses several years ago using a metal chop saw and the blade came apart. One piece of it hit square on the right lense hard enough to crack it. If I hadn't had them on I'm quite sure it would have taken my eye out. In hind sight, I should have also had a face shield on because the stuff that hit my skin didn't feel real good either not to mention it cut the **** out of me. I won't pick up a grinder, drill, saw, or any other power tool without them.