IE was drilling with a jackleg to install bolts, a rock slab (24""x18""x9"") loosened from the rib and became donut-like on the 6' jackleg steel. IE & co-worker removed the drill and attempted to break the slab but were unsuccessful. IE slid the rock slab off the chuck end of the jackleg steel, the steel then sprung up towards IE's face, striking and fracturing nose.