INJURED STATED THAT AS HE WAS CHECKING SUPPLIES ON THE BOLTER, HE THOUGHT HE HEARD THE ROOF POP & HE RAN INTO THE ROOF BOLTS ON THE BOLTER HITTING HIS LEFT RIB CAGE AREA CAUSING PAIN. HE WENT TO THE DR. & HAS A POSSIBLE HAIRLINE FRACTURE TO RIBS. INJURED RETURNED TO WORK HIS NEXT REGULAR SCHEDULED SHIFT.