REPAIRMAN WAS INSTALLING A NEW BELT SCRAPER ON THE #1 COOLER DISCH. CONVEYOR DURING SHUTDOWN ON 4/18/05. AT APPROX. 12:40PM WHILE USING A CUTTING TORCH TO TRIM OFF SOME ANGLE IRON TO MOUNT BRACKETS, MOLTEN SLAG DROPPED UNDETECTED & AS HE PULLED TORCH HOSES FORWARD THE SLAG MELTED THROUGH THE OXYGEN LINE CAUSING AN IGNITION. WHILE GETTING AWAY HE SUSTAINED A 2ND DEG BURN.