EMPLOYEE REPORTED: HE & CO-WORKERS WERE HANGING HIGH VOLTAGE CABLE. AT THE ACCIDENT LOCATION THE MINE ROOF WAS APPROX. 8'HIGH. HE WAS STANDING ON TOP OF A SCOOP SO THAT HE COULD REACH THE ROOF BOLT PLATES WITH THE HANGER. HE SLIPPED, LOST HIS FOOTING & FELL TO THE MINE FLOOR INJURYING HIS RIB CAGE. STARTED MISSING SCHEDULED WORK DAYS 9/7/04.