EE WAS ROOF BOLTING AT THE FACE IN C.M. SECTION. THE SUCTION FOR HIS DUST COLLECTOR BECAME CLOGGED AND TOP OF 2 PIECE DRILL STEEL STUCK IN ROOF. HE BEGAN CLEANING THE DRILL HEAD. THE TOP SECTI ON OF DRILL STEEL FELL OUT OF ROOF AND HIT EE'S RIGHT THUMB, AGAINST DRILL HEAD.