Printer Friendly

The facts on the fence.

PERIMETER BARRIERS ARE A FACILITY'S first line of defense. To put the value of the perimeter barrier into perspective, imagine the security nightmare you'd have without perimeter barriers to keep the general public from walking, biking, or driving their cars anywhere within the boundaries of your facility.

Perimeter barriers can be divided into two classes-natural and manufactured. Natural barriers include rivers, lakes, streams, cliffs, canyons, and other natural obstacles that are difficult to cross. Manufactured perimeter barriers include fences and walls. The most common include the following:

Brick or block walls are built as independent systems or as part of the facility. While they provide some increased protection against tunneling and may keep people from observing activities inside the grounds, the delay time they Provide against climbing is about the same as for any other perimeter barrier.

Stone walls are just as effective as brick and block walls, with the added benefit of being decorative. They are also the most expensive to install.

Reinforced concrete walls are stronger than brick or block walls and if designed correctly are effective as a vehicle barrier as well as a fence. Concrete is versatile and can be designed to blend in with almost any architectural style.

Landscaping such as hedges and thorny bushes (boxwood, quince, locust, bougainvillea, etc.) can provide security that is at least as good as most manufactured fences. The disadvantages of these barriers are maintenance, insects, and disease.

Fencing has been used for many years as a perimeter barrier for critical facilities. Although a variety of materials are available, such as barbed wire, wood, and plastic, the most Popular for security is chain link because of its cost and easy maintenance. Fences, as used in physical security, serve one or more of the following functions:

provide a legal boundary by defining the outermost limit of a facility

* assist in controlling and screening authorized entries into a secured area by deterring entry elsewhere along the boundary

* support detection, assessment, and other security functions by providing a zone for installing intrusion detection equipment and closed-circuit television (CCTV)

* deter casual intruders from penetrating a secured area by presenting a barrier that requires an overt action to cross

* cause an intruder to make an overt action that will demonstrate his or her intent

* briefly delay access to a secured area or facility under construction, thereby increasing the possibility of detection

The most cost-effective perimeter fence should be selected based on security and engineering requirements. Fences are primarily used to control vehicles and pedestrians and establish a buffer zone between areas with different security levels. Besides establishing the location, height, and configuration of the fence and gates, a decision must also be made on whether the fence should be open or opaque. This decision depends on the trade-off between the need to shield activities on the facility and the value of guard force observation of externa] threats.

Considering the range and number of security fencing installations around the world, it is doubtful that additional unique engineering factors will be identified. From an engineering viewpoint, soil conditions, erosion, wind and snow loads, and corrosion must all be considered when designing a fence.

Many different fences have been tested to obtain baseline penetration times. Trained intruder teams have demonstrated that an 8-ft. chain link fence topped with a barbed wire outrigger can be penetrated within three to eight seconds, without the use of climbing aids. Untrained individuals have been timed crossing the 12-ft. -high fence between California and Mexico in eight to 12 seconds. These same fences can be easily cut in less than 16 seconds using 18-in. bolt cutters (which are concealable) and can be breached underneath in less than five seconds using a steel pipe.

At present, the only fences tested and evaluated are those made of standard chain link fabric with various enhancements (see Exhibit 1). The recommendations made for the design and construction of a standard security fence are the most cost-effective based on the penetration times observed during testing. Therefore, enhanced fences should not be deployed with the expectation that they will significantly delay intruders.

The two types of fencing normally used for security are chain link and barbed wire. A standard security fence is made with chain links and is primarily used for protecting permanent security areas, while barbed wire is usually used for fences at temporary or remote facilities.

The construction of a security fence using the following recommendations meets most requirements for a balanced security system cost-effectively.

Standard chain link fencing including gates shall be 7 ft. high with one of the outrigger configurations shown in Exhibit 2. Mesh openings are a maximum of 2 in. on each side, twisted and barbed top and bottom, and the fabric wire is 9-gauge galvanized wire (polyvinyl coated if construction is at a location near the shore). Metal posts are set in concrete at 10-ft. intervals to give the fencing material necessary support, and the fabric is attached to each post with tie wires (top and bottom and at four equal intervals between).

The bottom of the fence fabric has a tension wire that extends to within 2 in. of stabilized ground or pavement or 2 in. below the ground in sandy or loose soil. Culverts or washes under the fence line are secured by using heavy steel bars to deter passage but allow normal drainage of water and associated debris.

Standard barbed wire fencing is twisted, double-strand, No. 12 gauge galvanized wire with four-point barbs spaced 4 in. apart. The fence is 7 ft. high, and the wire is stretched and tied to posts spaced 6 ft. apart. The spacing between strands is 6 in. and extends to within 2 in. of firm ground.

For more information on the design and construction of chain link and barbed wire fences, contact the Chain Link Manufacturers Institute (1776 Massachusetts Avenue, NW, Suite 500, Washington, DC 20036, 202/659-3537), the American Society for Testing and Materials (1916 Race Street, Philadelphia, PA 19103, 215/299-5400), or the International Fence Industry Association (5300 Memorial Drive, Suite 116, Stone Mountain, GA, 30083 800/8224342), which publish specifications and guidelines that establish standards for manufacturing and installing chain link and barbed wire fences.

A security fence should have an established clear zone of at least 20 ft. on both sides of the fence line to provide further deterrence and visual observation beyond the fence and to preclude the possibility of having trees or bushes close enough to the fence to provide a breaching aid.

Since fences alone don't deter intruders, attention has been focused on developing and testing enhanced fence configurations. Fence enhancements are typically limited to different configurations and combinations of barbed wire outriggers, barbed concertina wire, and General Purpose Barbed Tape Obstacle (GPBTO), developed by the Navy (see Exhibits 2 and 3). As in the case of conventional fences, hardening options and enhancements do not affect penetration times significantly, but they do increase the cost substantially.

The height of a fence has also proven to add little more than seconds to the penetration time. To make it more difficult to penetrate under a fence, fabric tie downs can be installed. Tie downs vary from steel wires holding the fabric firmly to anchor posts to encasing the fabric in a concrete sill. (Embedding the fence fabric in a concrete sill effectively precludes future retensioning of the fabric.) The use of tension wires along the lower portion of the fabric also hampers a penetration attempt under the fence.

A security fence is most effective when used along with other components of a security system. A security fence forms the basic building block for the rest of the system. It establishes an observation zone that can be illuminated, viewed using CCTV or staffed observation posts, sensored using intrusion detection systems, and reinforced against vehicle penetration to provide a reliable first line of defense for a critical facility. * About the Author ... Gary R. Cook is director of security engineering divisions for the Naval Civil Engineering Laboratory in Port Hueneme, CA. He is an ASIS member and a member of the Architect-Engineer Subcommittee of the ASIS Standing Committee on Physical Security. The Great Gate Opener

WHAT SHOULD YOU, A SECURITY Manager, look for in a gate opener? That may seem like a straightforward question, but you must consider many important factors before making such a potentially expensive decision. Based on 33 years' experience in security, I suggest you ask yourself the following questions about your business, your usage, and your business's physical location:

What kind of gate opener is best. a slide gate opener, barrier gate opener, swing gate opener, or vertical lift opener? The answer depends on the site. For example, if a gate is placed on an inclined driveway, make sure it has the latitude to swing up the incline.

Is the job site salty, dusty, or very hot or cold? Some gate openers are more fragile than others. Make sure the mechanism is housed in a way that protects the motor and components from the environment. Hydraulic systems, for example, are durable in adverse conditions.

What are the space limitations, security requirements, traffic volume, and width and weight of the gate? If it's in a high traffic area, make sure the gate opens and closes quickly and safely to prevent injuries, equipment damage, and traffic jams.

How will the gate be controlled, and what functions will be required? The types of controls vary with the level of security needed. Remote manual control by a guard, card access in and free passage out, card access in and out, and radio control are just a few possibilities.

What are the safety devices? The gate must be secured against uncontrolled closing. Common safety devices include ground loops, photo eyes, and safety edges. Decide whether to include such options in your installation.

Even after answering these questions, you must make the fundamental decision of whether to buy a chain-operated or hydraulic gate opener, the two most popular systems in use today. Understanding how a gate opener works and what to look for when purchasing one minimizes maintenance time and helps ensure lasting security.

Some users spend more than 40 hours a year adjusting, lubricating, and fixing their gate openers. Other users have gate openers that require 40 hours of maintenance a year but don't receive it. Those gate openers fall into disuse, and security is lost.

Price is important, but the cost of ownership is equally important. For example, a chain-operated gate opener may need more maintenance than a hydraulic one. In a chain-operated gate opener, the chain is powered by an electric motor that has a high speed and a low torque output. Since the desired output of a gate opener is low speed and high. torque, that type of opener must use a series of gears, sprockets, pulleys, chains, and belts to achieve the low torque. The number of parts makes the opener inefficient, and the parts cause metal-to-metal contact, which causes friction and wear, thus requiring more maintenance.

Any additional mechanical parts mean even more maintenance. For example, a chain that is attached to the ends of a gate panel and that runs over drive and idler sprockets must regularly be cleaned, checked for proper tension, and lightly oiled to perform as the manufacturer intended. If the chains are slightly out of alignment, the sprockets and chains wear excessively. If the gate panel is heavy or it cycles frequently, maintenance problems are magnified.

In addition to the power-transmission parts, a chain-driven gate opener requires brakes to lock the gate closed. They must be checked and adjusted regularly because poorly adjusted brakes result in a loss of security.

By contrast, a hydraulic system has few moving parts and a powerful hydraulic motor, reducing wear and tear on moving parts. The use of hydraulics enables power to be transmitted to the gate panel without the use of mechanical speed-reduction parts.

Hydraulically powered gate openers are also self-lubricating and self-locking, making them durable, easy to work on, fast, and cost-effective over the life of the gate. They also require only two hours of maintenance a year.

Obviously, buying a gate opener is not as easy as it seems. Price, weather, and maintenance all play a part in the purchasing decision. * About the Author . . . Philip Anderson is vice president of sales for D/A Technology of Needham, MA. The company designs and installs building security systems. He is a member of ASIS. The First Line of Defense

THE FIRST LINE OF SECURITY DEFENSE in protecting and safeguarding property is a physical barrier. You must evaluate what type of physical barrier will best complement the property. The majority of first line defense barriers are fences. It's management's responsibility to know what type of fence will be used in evaluating the criticality and vulnerability of the property. The term "target hardening" is associated with surveying a physical property. It means observing the area to be protected and surveyed as a whole. Fencing in conjunction with access control must reduce risk, secure the environment, and reduce security and liability costs. A properly installed fence may also reduce the target area and decrease the chances of intrusion. However, believing that a fence will eliminate all illegal access is foolish. A fence can only reduce or delay intrusion.

The next step is to find a suitable fence. A fence should reduce the opportunity for crime and make the property aesthetically pleasing.

Prior to installing a fence or chain links, check with your city's Department of Building Regulations to be sure the type, height, and gauge are allowed in your zoning district. In New York City, for example, fences may be erected to a maximum height of 10 ft., except in residential districts. In residential districts, the city zoning commission states that fences cannot be more than 6 ft. above the ground. The exception is fences used in conjunction with nonresidential buildings and public playgrounds, excluding accessory to dwellings that may be built to a height of 15 ft.

Fences can be raised to a greater height to enclose public playgrounds, school yards, and parks with the written approval of the zoning commissioner. In researching zoning variances and city ordinances, inquire with the Board of Standards and Appeals to find out about fencing restrictions. The chain link fence is the most widely used fence today. According to Jeff Grossman, president of Accurate Construction in Freehold, NJ, "the chain link design should be constructed of 9-gauge wire, with the mesh openings not larger than 2 sq. in. It is wise to lengthen the chain link to within 2 in. off the ground. However, if the ground is soft, such as soil or grass, the mesh should protrude below the surface." The fence mesh should be taut, affixed to rigid metal posts, and set in concrete. The fence should be a minimum of 8 ft. in height. Seven feet should be chain link mesh topped with I ft. of either three or six strands of barbed wire slanted outward.

The barbed wire topping can be replaced with coiled barbed tape or razor ribbon. Razor ribbon consists of a lone helical coil of barbed tape, approximately 18 in. in diameter, mounted on top of the fence. This is then attached to the top strand and is angled away from pedestrian traffic.

Openings in the periphery of the fence must be kept to a minimum. If it is necessary to have an opening, it should be protected or secured. If gates are installed they should be locked, but make sure the gates can be opened in case of emergency or connected to the fire system.

Signs should be posted every 30 ft. stating that the fenced-off area is private property and violators are subject to arrest. The signs might also note the area is protected by guard dogs, alarms, or closed-circuit television cameras.

Fencing is manufactured and designed in a variety of ways, but it accomplishes one important goal--to provide an effective physical barrier. Not only must the fabric and height of the fence be designed appropriately, but it also must meet the standards set by the International Fence Industry and The Chain Link Manufacturers Institute.

As a security director or property manager you can choose inexpensive fencing, such as chain link, or go to the other extreme and install a wrought iron fence. Many times, the iron grillwork is connected to masonry barriers. While this combination is costly, it is effective in preventing or delaying intrusion. In many residential homes, chain link fences are used for privacy. Privacy can be accomplished by placing solid strips of material in the chain link fence. The openings or "toe holes" in the fence should not enable people to climb the fence. Openings should be small enough to prevent intruders from placing their fingers and toes in the fence opening. A 2-in. toe hole opening is the most effective size. Once the physical perimeter is in place, it needs to be protected or monitored. Electronic equipment such as microwave, electrostatic, and ultrasonic devices as well as metal detectors are used in security fencing applications. The type of alarm or monitoring detector chosen depends on the location of the fence.

Microwave detectors are not recommended in areas with constant vehicular traffic since traffic can cause false alarms. Weather also may cause problems with an infrared system.

Properties are using fence disturbance sensors to detect intruders. While intruders can gain access by cutting through, climbing over, or tunneling under a fence, fence disturbance sensors monitor the fence and notify a central station when the fence is violated.

Design, economics, and planning are crucial when installing a fence. Explore all options prior to making any commitment to a fence manufacturer. The fence is usually the first line of defense against intrusion. If it is designed and used properly, intruders should be deterred and will conduct their criminal activity elsewhere. * About the Author . . . Kevin A. Cassidy is vice president and general manager of Access Controls International in Brooklyn, New York.
COPYRIGHT 1990 American Society for Industrial Security
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:includes articles on gate openers & fence materials; perimeter barriers
Author:Cook, Gary R.; Anderson, Philip; Cassidy, Kevin A.
Publication:Security Management
Date:Jun 1, 1990
Previous Article:The intrusion detection misconception.
Next Article:The Cuckoo's Egg: Tracking a Spy Through the Maze of Computer Espionage.

Related Articles
The first line of defense.
Sensing your way to security.
The big deal with barriers.
Taking the nuisance out of intrusion detection.
Security barriers: raising the ramparts.
Stone Walls Do Not a Prison Make.
US fencing products demand to reach $3.3 billion in 2007.
Deer deterrance ideas continued.
Horse-proof fencing.

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters