MINER/DRILLER ON THE LOWER WORK DECK WAS STANDING ON THE FLIPPED UP DECK LEANING OVER THE H.R. CABLE TIGHTENING A BOLT IN THE FORM DOOR. THE SOCKET SLIPPED OFF OF THE BOLT HEAD & M/D FELL FORW ARD OVER H.R. CABLE, CO-WORKER GRABBED M/D BY THE BELT BUT COULD NOT HOLD ON AND M/D FELL 6-7'TOTHE GROUND. THE MINER/DRILLER HAS 2 HERNIATED DISC'S, CO-WORKER PULLED MUSCLES.