OPERATOR WAS DISCONNECTING MOTOR FROM GEAR BOX ON CONVEYOR APPROX. 5 FT OFF GROUND. HE UNHOOKED SAFETY LANIARD AND STARTED TO CLIMB DOWN. HE SLIPPED AND FELL ON HIS ARM AND BACK SIDE. IT WAS D ETERMINED WITH A DR VISIT THAT HIS LEFT WRIST WAS BROKEN, AND POSSIBLE BACK INJURY.