EMPLOYEE WAS PERFORMING MAINTENANCE WORK ON A BOLTING MACHINE.HE WAS USING CONTROLS TO MOVE THE BOOM OF THE BOLTER. A METAL BAR WAS UNDER THE BOOM AND IT FLEW UP. EMPLOYEE RAISED BODY UP TO KE EP BAR FROM HITTING HIM AND HIT HARD HAT ON TOP OF MINE ROOF. THERE WAS NO DAMAGE OR IMPAIRMENT TO THE MINING OPERATION OR EQUIPMENT. THE INJURY DID NOT INVOLVE ANY ASPECT OF COMPLIANCE, JOB