EE WAS HANGING PIPE & SUSPENDED IT WITH A CHAIN ON A MAT. A ROCK 20"" X 10"" X 8"" SLID FROM BEHIND THE MAT & STRUCK THE BACK OF HIS RIGHT HAND. INITIAL X-RAY DID NOT SHOW A FRACTURE. REVIEW OF X -RAYS SHOWED HAIRLINE FRACTURE ON RIGHT METACARPAL. FIRST SHIFT MISSED 11/10/02.