WAS STRUCK IN THE LOWER RIGHT LEG BY A PIECE OF 3' BY 20' METAL FLOOR GRATING THAT WAS SUSPENDED BY A CENTER WELL HOIST. WHILE USING A 1 TON RATCHET CHAIN TO BRING THE GRATING ONTO THE SECOND FLOOR. THE GRATING BECAME FOULED ON A HAND RAIL THE HAND RAIL BROKE SUDDENLY, ALLOWING THE GRATING TO STRIKE THE INJURED.