EE stated that he finished bolting #3 entry on #1 unit, as he went to hang a red ribbon at last bolt a piece of rock fell from between bolts and struck EE in the back of the head, knocking EE into the canopy of the bolter EE received 11 staples and a broken nose. ATRS was still set against the roof. Rock measured 2.8'x2.7'x1=3'