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:
The first layer is the outside skin of the onion which translates to the site perimeter of the property. The building skin of the architecture is the next layer. Sensitive areas within a building are deeper layers requiring protection, and finally special persons,
information, or property may require point protection or the center of the onion. 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.


