The task assignment in this project were principally concerned with the implementation of a CDC 3600 computer program for computing PF's of structures (PF-COMP) as well as with addition to the programs which would make it more useful to architects and engineers. The program was implemented by The Research Triangle Institute (RTI) through the Office of Civil Defense first in the performance of the Military Overseas Selter Survey (MOSS) and subsequently in the analysis of federal buildings designated by the Office of Civil Defence. Finally, implementation of the computer program as a sevice to qualified fallout shelter analysts was performed in the Shelter Analysis for New Design (SAND) program. A principal addition to the PF-COMP computer program which will render it more useful to architect and engineers consisted of an analytical routine for cost effectiveness modification of structures to improve basement shelter PF. Incorporated as a subroutine in this supplementary program is a technique which permits definition of shelter boundary as a funktion of percentage roof contribution and shelter location within a structure.