Fence and Sensibility
In Cole Porter’s 1940s classic song, Bing Crosby implores his audience, “Give me land, lots of land, and the starry skies above. Don’t fence me in!” With America entering World War II and the government rationing everything from sugar to tire rubber, it was no wonder that listeners shared that idealistic vision. As in the 1940s, today’s dream of unrestricted space and unencumbered freedom is limited by an insecure and hazardous reality.
To help address these hazards, many companies and federal agencies have installed sensored fencing, which can act as both a physical barrier and a detection device. This technology can be effective if properly installed and maintained. Companies considering this approach need to address several factors including the risk to the facility, placement, fence type, calibration, and testing.
Risk assessment. The first step in any fencing project is to establish the risks to the site. The risk assessment should address the level of vulnerability in a given site, and contractors should design a perimeter detection system that takes into account these risks.
For companies and agencies with current risk assessments, a separate evaluation is not needed. Companies without such documentation, however, should consider hiring a contractor to conduct the assessment.
The contractor evaluating the site should identify the likely targets for criminal activity. For instance, a chemical company might have toxic product that would offer an attractive target for terrorists, while a manufacturing company might be more concerned about theft of its valuable machinery.
Once the likely targets have been established, the contractor should determine the best method for securing them.
For example, I conducted a threat assessment of a dam, which was responsible for creating power for the surrounding area. In a worst-case scenario, criminals could release the dam, causing flooding and disrupting power.
The methods a criminal could use to release the water were determined. Detonation of a bomb near the dam was one such threat. Another threat was a criminal infiltrating the facility and using the operating equipment to release the water. To mitigate these threats, sensored fences were strategically placed to detect intruders. If a criminal breaches the secured perimeter, the sensors in the fence will alert security.
In other cases, a facility may already have a chain-link or ornamental fence, but the security manager would like to add sensors. The contractor must determine whether the fence can withstand the strenuous requirements associated with properly installing a sensor, which can include increased tensioning of the fence fabric. In addition, large anchors and line posts are often required to withstand the increased tensioning.
Another consideration is that most fences, particularly chain-link fences, deteriorate over time, due to corrosion, vegetation overgrowth, or misuse. The cost of repairing an existing fence is often comparable to simply replacing the fence, and contractors must determine the most effective course of action before adding sensors.
Placement. Placement of the fence is critical. The contractor should, therefore, be asked to evaluate the site for the sensored fence before designing the project. Among the issues to be considered are proximity to facilities, climbing aids, disruptive landscaping, character of the neighboring areas, and placement of entryways.
Proximity. The fence should be placed as far away as possible from the structure it is protecting to allow for optimum warning time. If, however, the perimeter is so large that it becomes cost prohibitive to enclose the entire space, it is advisable to fence only the most vulnerable assets.
Climbing aids. Climbing aids include structures such as telephone poles that an adversary might use to get over the fence without triggering the sensors. It may be possible to eliminate some climbing aids, such as large trees, but it will not be possible to remove others, such as telephone and light poles.
If there is a structure near to the intended fence path that might help an adversary breach the perimeter, either the structure must be removed or the plans for the fence location must be altered appropriately.
A general rule of thumb is to keep all climbing aids at least 10 feet away from the fence. When that is not possible, additional motion sensors can be added inside the secured perimeter to supplement the sensored fence. These additional sensors will help reduce the risk that an intruder will go undetected after successfully using a climbing aid.
Disruptive landscape. When surveying the prospective fence site, the contractor and the company should pay particular attention to low-lying areas, like drainage ditches, which could allow intruders access. Additionally, drainage areas can also cause erosion, allowing further access to intruders.
The standard limit for an opening is 96 square inches. If, for instance, the drainage area exceeds 96 square inches, the opening may need to be protected by some means, such as microwave sensors. Another possibility is to create more frequent drainage culverts that are smaller than 96 square inches.
Environs. The character of the neighborhood surrounding the fence must also be taken into account before placement. If, for instance, the protected perimeter is located adjacent to a public area, pedestrians may inadvertently disturb the fence, causing it to alarm.
These types of nuisance alarms can be avoided by placing a nonsensored fence outside the sensored area. This method is also helpful when a perimeter is located near wooded or other areas where animals are likely to come in contact with the fence.
Entryway. Another factor to consider is how the entryways will be configured and how emergency or other large vehicles will access the property. When installing fence gates, it is important to design the gate for the largest vehicle, even if these vehicles do not frequently access the perimeter. It may make sense to install both a maintenance gate and a pedestrian gate that can accommodate foot traffic and vehicles of every size. While the maintenance gate is typically used much less frequently than the pedestrian gate, it ensures that later modifications will not be needed to accommodate unforeseen large vehicles.
Fence type. There are two basic fence types: ornamental and chain link. Sensors can be used with either or a combination of the two.
Ornamental. Ornamental fencing is designed to be both functional and pleasing to the eye. These types of barriers can be made of various materials ranging from powder-coated steel and aluminum to wrought iron. They offer curb appeal and, because they are made from more durable materials, require less maintenance than traditional chain-link fences. They are well-suited to sensors. But they can cost between $80 and $200 a foot, compared to only $30 to $40 per foot for a chain-link fence.
Several manufacturers have created ornamental fence products specifically designed for the application of sensors. Some fences include features such as an integral channel within which the sensor cable can be installed.
Additionally, ornamental fences are made from rigid materials that give them stability and reduce swaying. They are, therefore, less likely to produce false alarms.
In selecting the design of the ornamental fence, planners should consider the aesthetics of the facility. When a durable fence is needed, but an unobstructed view is also desired, wrought iron or other ornamental fencing should be considered. For instance, the fence surrounding the White House manages to remain secure without hampering the view.
Chain link. When aesthetics is not a major consideration, chain-link fences can be extremely useful and cost effective. As previously mentioned, however, placing a sensor on a chain-link fence requires additional tensioning of the fence to reduce movement caused by wind and other elements. While chain-link fences are often less formidable than ornamental fencing, they can be enhanced by adding security features such as razor or barbed wire.
Combinations. A practical approach to reducing costs is a combination of ornamental and chain-link perimeter fencing, with the ornamental fencing in areas most visible to visitors or the general public. For example, one client site served as both an industrial and tourist site. The areas frequented by tourists, including the visitor’s center, were encompassed by attractive ornamental fencing. A sensored chain-link fence was placed around all industrial areas.
The client saved money by using the expensive fencing only where it would be most seen by the public. An added benefit was that the chain-link fence helped differentiate between public and private areas.
Calibration and testing. All sensored fences must be calibrated to detect vibrations associated with climbing or cutting. Adjustments in the fence’s sensitivity must be made to prevent false alarms.
The type of fence dictates the amount of sensitivity applied. Chain-link fences are more prone to movement than are ornamental fences. For this reason, sensors installed on chain-link fences are configured differently in terms of their level of sensitivity. Because sensitivities vary for each type of fence, if two different types of fence are located along the same line, separate processors or zones may be required to allow for the different vibrations created by each material.
In addition, the environment and weather must be taken into consideration when determining the sensitivity level to which the sensors will be set. For instance, areas prone to high winds will be subject to more fence movement, which could result in more false or nuisance alarms if the sensitivity level is not set properly.
Each sensor system will come with specific installation requirements. These must be met to ensure optimal performance and minimal false alarms.
Inexperienced installers will often install sensors and make them hypersensitive because it makes the customer feel better to know the fence will detect everything. This tactic often produces a high number of false alarms, leading operators to ignore alarms, which ultimately reduces the fence’s effectiveness.
Testing. The company should witness a test of the integrated system to ensure that the final product works as promised. In this phase, companies should be vigilant in making sure that tests are conducted fairly so that results are valid.
Unfortunately, a dishonest contractor may skew the test to show favorable results. One tactic used by such contractors is to calibrate the fence sensor so that it will detect minor attempts to breach the perimeter during the test. After the test, the contractor lowers the sensitivity to eliminate false alarms. This trick is often used to hide a defective installation.
To reduce this risk, it is important that each facility review the contractor’s testing procedures or hire an outside contractor to review the tests. The owner or end user should understand the system and be involved in the test.
It is not particularly useful to test for unique, unlikely “what if” situations such as employees with little knowledge of the system attempting to subvert its weaknesses. It is likely that the sensor will detect this attempt, and testing for unique situations could damage the fence or the sensor.
It is helpful to conduct an endurance or burn-in test to detect performance problems that might not surface in a one-time test. This test is conducted after installation and requires that the contractor remain at the facility to monitor fence performance for several days under real-life conditions.
The owner should not accept responsibility for the fence until the test is complete. Essentially, the contractor is ensuring that everything works properly before certifying the work. The goal is not necessarily zero false alarms, however, although normal false-alarm rates are typically less than one per 30 days.
It is also important to understand that the tension of some fences, particularly chain-link fences, can change seasonally or lessen with time, causing problems. It is, therefore, necessary to test the fence for reliability on a periodic basis, with the frequency depending on the security level of the facility.
Controlling sensitivity levels. Frequent testing to keep false and nuisance alarms to a minimum can reduce the likelihood of a maintenance or security person lowering the sensitivity levels below the recommended level simply to reduce excessive alarms. To further guard against an unauthorized reduction in the sensitivity level, any calibration or repair of the system should be documented by the contractor and closely monitored by the owner.
The sensitivity on some sensor systems can be remotely controlled by computers networked to the fence. These systems are typically password protected, thus making it difficult for unregistered users to change the sensitivity.
For other systems, sensitivity is controlled through processors attached to the fence. These processors typically come with or can be equipped with tamper switches and high-security locks.
There is no one solution to a sensored fencing project. Working with reputable engineers and contractors throughout all phases of the project will help guarantee an effective and reliable system. The best advice for facilities interested in installing sensored fences is to stay involved, ask questions, and get a second opinion if doubts arise.
Roddy Traxler is the director of security for Adesta, LLC, and a member of ASIS.