What is the principle of 'defense in depth' and how is it applied in facility security?

• A. It relies on a single powerful barrier.
• B. It uses multiple overlapping protective layers (perimeter, access control, surveillance, personnel) so a failure of one layer doesn't lead to breach.
• C. It delays response by isolating layers.
• D. It focuses solely on cybersecurity rather than physical security.

Answer: (B)

Defense in depth means layering security controls so that a failure or bypass of one layer does not automatically lead to a breach. In a facility, this is put into practice with several protective rings: an outer perimeter like fences and lighting; access controls such as badges, authentication, and visitor management; continuous surveillance and alarms; and trained security personnel and procedures inside. Each layer is designed to deter, detect, delay, and respond. If someone gets past the outer barrier, they still face locked doors, badge checks, turnstiles, cameras, and guards, which together buy time for a response and reduce the chance of a successful intrusion. This approach blends physical barriers, monitoring, and human processes to create a resilient security posture rather than relying on a single measure.