WORKER INSTALLING ANCHOR BOLT FOR THIMBLE HOUSING. WORKER ON OUTSIDE OF STRUCTURE BUMPED TRIGGER OF IMPACT WRENCH CAUSING NUT ON INSIDE TO SPIN AND RESULTING IN A LACERATION TO L INDEX FINGER. PROCEDURE CHANGE: RADIOS ORDERED TO FACILITATE COMMUNICATION BETWEEN WORKERS DURING THIS PROCEDURE. WORKER USING IMPACT WRENCH TO KEEP FINGER OFF OF TRIGGER UNTIL WORKER INSIDE COMMUNICATES H