INJURED EMPLOYEE WAS WORKING ON HYDRAULIC SYSTEM ON 785 ROCK TRUCK. WHILE REMOVING A HOIST LINE (HOSE) THE '0' RING SUDDENLY BLEW WHICH CAUSED AN ENORMOUS AMOUNT OF PRESSURE TO BE RELEASED. TH E EMPLOYEE WAS STRUCK IN THE FACE BY THE HYDRAULIC FLUID AND KNOCKED HIS GLASSES OFF. APPARENTLY, SOME RUST WAS IN THE HYDRAULIC FLUID AND SOME GOT IN HIS EYE.