ASSISTING 3 OTHER EE IN HIGH AREA TO LEFT BELT STRUCTURE, LIFTED TOP STORED UP OVERHEAD, OPPOSITE SIDE OF STARTED SLIPPED OFF BED RAIL AND TOP STAND STRUCK HIM ON TOP OF HEAD. COMPLAINE WITH R ULES, REG NOT A FACTOR. PORTECTURE ITEM NOT A FACTOR PROFICENCY COMMUNICATION BETWEEN WORKERS COVED BE A FACTOR DID NOT MISS DAYS UNTIL 6-16-00.