An unplanned roof fall was discovered 2/20/12.The loc. of the fall is #5 zone #36 blk in #3 entry in the intersct. There were no injuries, Eq. damage or escape ways blocked. The area around the fall has been supported by cribs & timbers and all approaches have been dangered off. The fall dimen. are 27' L. X 17' W. X 8' H. This area was dev. on 2/27/11 with approx. 180' of cover.