EE was working in R325 overhaul yard on a kiln end plate. He was installing a gasket to fit around the outside edge of the plate. He was trimming the width of the gasket using a utility knife in a clenched fist & pulling down & across it. When the knife came to the end of the gasket, it slipped down & struck him in the rt leg above the knee. Laceration was closed w/sutures.