THE PLANT WAS SHUT DOWN TO PERFORM A MAINTENANCE REPAIR ON SCREEN #11, 6' X 12' PIONEER 3-DECK SIZING SCREEN. THE REPAIR INVOLVED DISASSEMBLY OF THE POWER BEARING HOUSING. AFTER THE EQUIPMENT WAS LOCKED OUT, HE ACCESSED THE INTERNAL SCREEN FRAME THROUGH AN ACCESS OPENING IN THE PORDUCT CHUTES. DURING THIS ACCESSING, HE STRAINED HIS RIGHT ARM/SHOULDER WHILE PULLING HIMSELF INTO POSI