EMPLOYEE WAS WALKING FROM THE BELT ENTRY TO THE ENTRY OF A LONGWALL SECTION BEING SET UP FOR FUTURE MINING. HE STEPPED INTO A HOLE IN THE MINE FLOOR AND FELT PAIN IN HIS BACK. THERE WAS NO DAM AGE OR IMPAIRMENT TO THE OPERATION OR ANY EQUIPMENT. AWARENESS OF CONDITION OF TRAVELING WAS THE CAUSE. NO OTHER FACTORS WERE INVOLVED.