Back in 1968 while working at Pacific Clay Products in Santa Fe Springs, Calif. - (Worlds largest manufacturer of vitrified clay sewer pipe) - I was working on the ground level of our new, experimental, 11 story tall Iso-Press Tower when a co-worker accidently dropped a 12 inch Crescent wrench from the 7th floor. The wrench hit squarely across the top of my Alumilite hard-hat, knocking me unconscious. I don't know how long I was out, but when I came to, there were about a dozen people around me including a bunch of BIG bosses from the front office. They took me by ambulance to be checked out, Doctor said I had a concussion. When I returned to work several days later, they had my hard-hat & the wrench mounted on the wall in the front office, with the wrench in the crease it made in my hard-hat - that crease was a measured 1 1/2 inches deep. To the best of my knowledge, that hard-hat & wrench still hang on the wall in the front office as a reminder to everyone to wear their hard-hats.