The establishment of a secure perimeter is possibly the most foundational concept in the security industry. Whether the task is to apply Crime Prevention Through Environmental Design (CPTED) principles to a new campus environment or to protect Class A national assets, the secure perimeter identifies that point at which the security program is initiated.
The technological tools that are applied at the perimeter can vary according to a number of factors, such as the specific purpose of the perimeter, the characteristics of the site and the nature of the asset.
Three Categories of Perimeter Security
It may be helpful to think about perimeter types in three categories. First, security perimeters define a line of demarcation from a public to a non-public area. Once the perimeter is crossed, new rules are in force as promulgated by the property owner or the authority having jurisdiction. In some instances, this is the only defined perimeter for a facility — college campuses generally fall into this category. As an individual turns off the public street and onto the campus, signage is normally used to inform the individual that they are now on university property, to obey posted speed limits, etc. In CPTED terms, the university is establishing territoriality. Everything else on campus is largely open to the visitor.
A second type of perimeter also establishes a line of demarcation but with an ability to detect those that violate that line. Reliable perimeter intrusion detection has been and is an essential component of security systems for the protection of assets. These perimeters provide for authorized passage through access control portals for both personnel and vehicles; however, an unauthorized penetration initiates an alarm, which signals the malevolent intent of the intruder and simultaneously initiates response activities. Depending on the facility, the response could range from notification of the local law enforcement agency to activation of an armed response team.
A third type of perimeter is defined and designed to physically deny unauthorized access. Almost exclusively focused on vehicle-borne threats, this approach arose out of the vehicle bomb attacks on U.S. Department of State (DOS) and Department of Defense (DoD) facilities beginning in the mid-1980s. The importance of this type of protection has been reemphasized with events such as the Khobar Towers bombing in the mid-1990s and, of course, recent events in Iraq. These perimeters are typically characterized by systems that can absorb the kinetic energy of a fully loaded truck traveling at high speeds; and intrusion detection systems are typically not deployed (or needed) in these circumstances.
It logically follows that different technological solutions are employed to achieve the different goals implied by the second and third perimeter types discussed above.
Types of Sensors
Perimeter intrusion detection is a well-developed and, in some ways, mature technological offering. These types of sensors typically fall into three categories.
The first and possibly the most common type of sensor is fastened to and thus supported by the fence (normally chain link), defining the secure boundary. Current fence sensor offerings have overcome some of the limitations of previously available sensors, such as:
• Disturbance Location: Current fence sensor products such as the Southwest Microwave Intrepid can locate the source of the intrusion-indicating disturbance to within approximately three meters. From an overall system design standpoint, this is a significant improvement over the 100-meter zone differentiation of a few years ago. This capability also affects the functional requirements of the associated CCTV assessment system. Instead of the traditional fixed CCTV camera viewing an entire 100-meter zone, the improved signal discrimination capabilities opens up the option of using pan-tilt-zoom (PTZ) with pre-set views or tracking software for alarm assessment and adversary tracking.
• Zone Configuration: Zones are constructed based on software definition and not physical cable construction. This allows cost effective tailoring of the zones to the specific site configuration.
• Integrated Power Distribution: Many sensors of this type distribute power to the distributed processing electronics through the sensor cable, eliminating the expense of a separate power distribution system.
• Reduced Nuisance Alarm Rate: The digital processing and segmented calibration of the sensor cable has reduced the nuisance alarm rate associated with these types of sensors.
Free-standing sensors do not rely on a fence for support. These products range from single-technology microwave sensors (bistatic and monostatic) offered by firms such as Southwest Microwave; to the G-Line II and the veteran taut wire system offered by Magal Senstar. In broad terms, these sensor systems have also benefited from digital signal processing resulting in reduced nuisance alarm rates.
Buried sensors allow for high probability of detection in undulating terrain, a bane to most perimeter intrusion detection systems. Similar to the fence-mounted sensors, digital processing has allowed target location discrimination to well below three meters, as well as meter-by-meter sensitivity adjustments through the signal processing software. The performance of current buried sensor products is less dependent on soil type and burial depth than offerings of just a few years ago. These features are characteristic of products offered by both Southwest Microwave (MicroTrack) and Magal Senstar (OmniTrax).
There is no doubt that current intrusion detection products can provide a high probability of detection with a low nuisance alarm rate when properly installed, calibrated and maintained. However, perimeter intrusion detection systems should be augmented by a CCTV assessment system in order to ascertain and verify the source of the alarm and to initiate and coordinate response activities. The next level in perimeter IDS will be to replace the intrusion detection sensors with video analytic-equipped cameras, thus combining two necessary and supporting systems into one. This technology is currently in use with mixed results. This is the exclusive topic of an article in next month’s issue.
Vehicular Threats
Industry veterans are familiar with the wedge-type, pop-up barriers developed by a variety of manufacturers beginning in the mid-1980s. Delta Scientific continues to provide the broadest selection of barriers evaluated to Department of State (DOS) requirements as defined in “SD-STD-02.01, Vehicle Crash Testing of Perimeter Barriers and Gates, March 2003,” however, other manufacturers such as Nasakta, Robotic Security Systems Inc., B&B ARMR, and Boon Edam Tomsed Inc., are also listed on the DOS list of certified barriers. While the basic principles and design of these types of barriers have remained somewhat constant, significant improvements have been made in deployment times and power efficiency. For example, RSSI and Norshield are currently marketing a K12-rated, pop-up-type barrier that deploys using a set of internal springs. Upon loss of prime power, this particular model can operate for approximately 200 cycles on the internal battery backup module provided with the barrier system. These types of engineering innovations and efficiencies allow for enhanced cost-effectiveness in the deployment of these barriers.
One of the concerns surrounding the development of these types of barriers is the potential for accidental or otherwise inappropriate barrier activation and the danger this poses to normal, non-threatening vehicular traffic. This has spawned a significant amount of effort to define effective strategies to heighten the safety of automated vehicle barrier (AVB) installations. These safety schemes can involve the complete range of signs, warning lights, and vehicle presence detection devices. Specific guidance on the use of AVBs in the DoD environment can be found in the Unified Facility Guide Specification UFGS 34 41 26.00 10 and in Entry Control Facilities/Access Control Points, UFC 4-022-01.
Partially in response to these safety concerns, an energy-absorbing technology is being marketed by Universal Safety Response Inc. (USR) — the GRAB-sp barrier. The barrier’s patented energy absorbing pistons reduce the vehicle speed, injury to vehicle occupants, and structural damage to the vehicle with zero penetration. With 70 real-world impacts under its belt with no injuries, the barrier has been tested and certified by the DOS, rated at K8 and K12.
The ongoing U.S. Army Access Control Point (ACP) Program represents an interesting approach to denying unauthorized vehicle access to Army installations. As shown in Figure 1 (above), vehicular approaches to an Army installation are divided into three segments: the approach zone, the identification credential check and verification zone, and the response zone. One or more automated crash rated vehicle barriers (AVB) are located at the end of the response zone. Activities in the ID/credential check area validate the authorization of an individual (and associated vehicle) to enter a given site at the specific location, day and time the credential is presented. In a properly designed access control point, those individuals/vehicles not possessing the proper credentials are directed to leave the site via a designated turnaround (U-turn) area; conversely, those with the proper credentials are granted site access.
One of the threat scenarios considered by the ACP Program is a vehicle proceeding normally to the turnaround area and then immediately accelerating in an attempt to enter the site. Upon detection of this action by the security forces in the ID/credential check area, their responsibility is to initiate AVB deployment. Due to safety features designed into the AVB logic circuit, there is a three to four second delay between the time the button is pushed and the barrier raises. In addition to this barrier deployment time, there is a certain amount of time needed for the security officer to identify the malevolent action (accelerating into the site instead of turning around), determine the proper response (need to push the button to deploy the barrier), and initiate barrier deployment (push the button); this total response time is the time the adversary has to drive from the turnaround area to the location of the AVB.
During the design phase, the location of the AVB is determined based on certain assumptions regarding incoming speed of the threat vehicle, its maximum rate of acceleration, the response time of the security offices, and the barrier deployment time.
A second scenario assumes the threat vehicle enters the ID/credential check area at a high rate of speed and continues on toward the AVB in an attempt to clear the AVB before it can be deployed. As before, the location of the AVB is determined based on certain assumptions about the maximum speed at which a vehicle can successfully pass through the ID/credential check area, and the maximum rate of acceleration of the vehicle once clear of the ID/credential check area, the response time of the security officers, and the barrier deployment time.
Finally, the bulk of the perimeter of a fixed site often needs to be designed to prevent unauthorized vehicular penetration. Tests have clearly shown that chain link fences present no impediment to a vehicle. To address this category of perimeter security issues, various fence designs have been developed and subjected to DOS testing. The pioneer in this area is Ameristar Fence Company whose Impasse product satisfies the DOS K12 requirements using a tensioned cable and post design. As an added bonus, the Impasse design is considered to be less aesthetically intrusive than other fence designs.
Define Your Purpose
Establishment of a secure perimeter requires a clear conceptual framework defining the purpose of the perimeter as well as the physical and technological tools to achieve the desired functional performance. While much progress has been made in developing active vehicle denial barriers, the current challenge is implementing them safely and cost efficiently at existing sites. Securing the remainder of the perimeter against a variety of threats is also a reality with the DOS-listed fencing products. Finally, the available intrusion detection sensors offer cost effective and reliable detection in realistic exterior environments.
Randall R. Nason, PE, CPP is a corporate vice president and manager of the Security Consulting Group at C.H. Guernsey and Co. His experience spans a broad spectrum of the security profession including threat assessment, vulnerability analysis and master plan development through complete system design, construction management and design-led build projects. He has also designed and conducted full-scale emergency response exercises for a federal agency.
