In Site Security Planning and Design Criteria, security expert witness Randall Atlas Ph.D., AIA and Anthony DiGreggario of Atlas Safety & Security Design, Inc. write on security layering: the Onion Philosophy (part 2):
New developments in blast curtains, window films, and break resistant and bullet resistant glazing provide the designer with more choices for protection. Yet, a building that is resistant from an exterior bomb blast may be in conflict with the threat of an interior bomb blast and having no ability for decompression or blast out walls. Inside the building, zones or layers of security may be established with various types of access control devices reinforcing physical separations. Protected work stations are critical in many occupations, and safe rooms for CEO protection. Building design should also contribute to or ease implementation of operational security policies and procedures.
The site perimeter is the first, not last, line of defense. The State Department seeks setbacks of at least 100 feet for new buildings, and even that distance is difficult to obtain in most urban settings. While most perimeter fences and walls are designed to discourage intruders, they are of little use against a determined person or bomb vehicle. Designs are now available for vehicle-stopping capabilities. However, the bomb of the future may be delivered by a moped or pedestrian, thus rendering truck bombs unnecessary.