3 SOUTH SECTION, HE WAS WORKING ON EMICO ROOF BOLTER, TRYING TO REMOVE TO BOOM SWING JACK. THE BOLTER MAST WAS RESTING ON LOOSE MATERIAL ON THE BOTTOM, WHEN HE PULLED THE SWING JACK PIN OUT, T HE BOOM MAST SWUNG AND PINNED HIM BETWEEN THE BOLTER FRAME AND BOLTER MAST.