FENCING AS AN ELEMENT OF A COMPLEX OF TECHNICAL MEANS FOR PROTECTING THE PERIMETER OF A FACILITY

LARIN Alexander Ivanovich, Candidate of Technical Sciences
ZVEZHINSKY Stanislav Sigismundovich, Candidate of Technical Sciences

FENCE — AS AN ELEMENT OF A COMPLEX OF TECHNICAL MEANS FOR PROTECTING THE PERIMETER OF A FACILITY

A fence as part of a complex of technical security means (TSM) acts as an obstacle that changes the conditions of movement of an intruder towards the protected facility.

All perimeter detection means (detectors) installed near or on the fence can be divided into 3 categories:

1. Carrying out signal blocking directly of the barrier, which is subject to mechanical deformations during the invasion;
2. Carrying out signal blocking of a certain zone of space (detection zone) near the fence;
3. Reacting both to deformations of the fence and to changes in the physical field near it caused by the intruder.

In the first case, it is required that the intruder's overcoming of it be accompanied by the emergence of some useful signals in the barrier structures, which would be reliably discriminated against interference caused by various natural, climatic and industrial factors, which also directly affect the barrier.

In the second case, it is necessary that the barrier change the parameters of the intruder's movement (for example, reduce the speed or change the direction of movement in the desired direction) so that its detection is reliable against the background of interference.

In the third case, both of these requirements are imposed on the barrier.

A fence is a physical barrier — a type of fencing that prevents an intruder from freely entering the territory of the facility.

As we see it, at present, attempts to build an effective KTSO perimeter of any facility without installing a fence are doomed to failure for several reasons:

• high (not decreasing) level of criminalization of the population;
• low legal level of property relations, lack of the right to own and use weapons when encroaching on property, including land;
• on the one hand, the fence “cuts off” most of the animals, which are a significant interference factor, as well as random passers-by, etc., on the other hand, it does not allow playing children or pets to get lost;
• the fence is a significant psychological factor for a potential intruder;
• the fence prevents the intruder from quickly leaving.

All barriers, depending on their purpose, can be divided into 4 types: signaling, signaling-electric (electric shock), construction (technical) and construction-signaling.

The first ones form conductive metal structures that are a sensitive element of the perimeter detection device, which is called a barrier.

For example, in the domestic alarm system “S-175M”, which has long been the basic one for protecting the state border, the fence (height ~ 210 cm) is formed by alternating lines of barbed wire (fixed to wooden or concrete posts), included in two active loops, sensitive to breaks and short circuits of adjacent lines, which are caused by a “normal” intruder.

In the modern electromechanical barrier DTR-2000 (Magal, Israel), the physical barrier (up to 4 m high) is formed by tightly stretched steel wires (taut wire sensor), fixed to metal posts using point tension sensors sensitive to deformations of the barrier caused by the intruder.

The electrified barrier is a system of current-carrying wires (insulated from the supports), along which high-voltage impulses (3…10 kV) are distributed, causing pain shock in the intruder upon contact.

Current international electrical safety standards regulate the energy of the impulses, which is not lethal in normal mode.

Having appeared on the world market more than 20 years ago, electrified barriers have now acquired the signaling qualities of an intrusion detector, allowing you to monitor not only their integrity and structure (break, short circuit of adjacent conductors, grounding), but also to localize (with an accuracy of several tens of meters) the place of intrusion.

Such “active” barriers include the Elecro-Fence system (APS, UK), Elecro-Guard 5000 (DeTikon, USA) and others.

The G.M. system based on ESB275 controllers (G.M. Advanced & Fencing Security Technologies, Israel) has proven itself in Russia.

Construction barriers are very diverse, their classification is given in Fig. 1.

It is interesting to consider them from the point of view of security and alarm qualities and ergonomics. A special type is formed by various combinations of construction and alarm barriers.

Fig. 1. Classification of construction barriers

Visibility through a barrier is determined by the design chosen by the customer in accordance with his understanding of safety and aesthetics.

In Russia, traditionally, the most common are solid (opaque) barriers.

The advantages of such barriers include:

• the ability to covertly move people around the facility, especially near the barrier from the inside (for example, the guard's response to an alarm signal);
• the covertness of the installation of detection equipment (DI) in the inner part of the perimeter;
• difficulty in visually collecting information about the nature of the facility's production activities, the composition and tactics of the security unit.

The disadvantages of the fence are the high cost and labor intensity of construction, as well as reverse opacity — for observing from the inside the movements or actions of people on the outside of the perimeter.

However, for an object with a perimeter of more than 300 … 500 m, when the observation range (to the border of the site) exceeds 50 m, the last disadvantage is common and can be eliminated by using a television surveillance and lighting system (or IR illumination).

Transparent barriers (for example, mesh, lattice) are relatively cheaper, the labor intensity of their construction is significantly lower, but they do not provide the above-described secrecy.

At the same time, when considering a barrier as an element of a complex of technical security means, the following considerations must be taken into account.

According to experts from a number of perimeter security manufacturers, including Galdor-Secotec Security Technologies Ltd. (Israel), the most effective barriers are the so-called “soft” fences made of various metal meshes, wire or reinforced barbed tape.

Any impact on such a fence for the purpose of overcoming (climbing, destruction of the fence fabric, digging) inevitably leads to vibrations of the fence fabric.

Currently, there is a whole arsenal of cable triboelectric and vibroacoustic detectors capable of converting these vibrations into an alarm signal (Godograph-SMV, Dolphin-MP, Gyurza-035, Multisensor, Guardwire, etc.).

As for reinforced concrete or brick fences, this type of barrier is most convenient for overcoming by climbing, especially with the use of various auxiliary means (ladders, stepladders, etc.).

For monitoring the canvas of a monolithic (reinforced concrete, brick) barrier from climbing, the choice of signaling means is extremely limited.

We can mention the domestic detector “Godograph-1” (NIKIRET), which works on a parasitic non-standard tribo-effect in a non-specialized cable, and the cable vibroacoustic device “Defensor” (Geoquip, Great Britain), however, they do not work on all types of monolithic fences, and the question of the possibility of their use must be decided in each specific case.

Therefore, in most cases, it is necessary to additionally equip monolithic (“hard”) fences with various canopies in the form of the same “soft” fences.

Thus, the most interesting properties are possessed by the so-called “translucent” barriers, the design of which:

• consists of opaque elements (for example, a brick base ~ 1.8…2 m high) and transparent ones (for example, a net at the top), providing relative invisibility from the outside of the perimeter (from below, from human height) and visibility from the inside (for example, from the roof or attic of a house, a hillock);
• consists of alternating “oblique” elements that allow only certain parts of the object to be seen from the outside, while when guards move along and inside the perimeter, it is possible to observe the actions of people from the outside (like blinds).

These and other possible composite designs can provide a reasonable compromise between cost, secrecy and technical aesthetics.

The height of the fence is an important parameter that determines its passability (by climbing over), the time it takes to overcome it, and the danger of falling that the intruder at the top is exposed to.

In principle, the higher it is, the better – for this reason, fences less than 1.5 m high, which can be overcome by jumping, are not recommended.

On the other hand, fences higher than 4 m (there are examples up to 6 m high), practically adding nothing in terms of security qualities, look unaesthetic, and require additional structural reinforcement due to the increased windage.

In general, the height of the fence should be determined by a reasonable compromise between the security function and aesthetics.

The cost of the fence (materials, work) is approximately proportional to its height, while the cost of signal blocking the boundary depends on its height (within the limits under consideration) to a weak degree.

A low fence up to 2 m high allows viewing part of the object's territory (for example, from a small elevation), using accessible and portable means to facilitate intrusion, for example, a stepladder that does not exert a «useful» mechanical impact on the fence when it is overcome.

Such a fence provokes the intruder to climb over «on the fly», which can be used when choosing and installing a perimeter security system on top of it.

Fences 2…3 m high are the most common due to their compromise security and aesthetic properties.

Overcoming by climbing is possible with the help of improvised means, however, if the structure is reinforced from above with an additional “barbed” volumetric or flat (preferably sloping outward) structure, for example, a spiral of reinforced barbed tape (RBT), it becomes unlikely.

A barrier 3…4 m high is difficult to overcome by climbing (even with the help of improvised means), and it becomes more likely to be undermined or destroyed.

Such a fence, due to its great height and subject to wind load (and the calculation should be based on gusts of up to 30 m/s), requires additional reinforcement of the foundation and the lower part of the structure, which is also desirable to resist destruction.

The foundation (primarily strip, along the entire perimeter) is a practically mandatory part of the fence, since:

• ensures less mobility of the barrier when exposed to strong wind, which is a significant interference factor for all (without exception) perimeter fire alarms installed on or near the barrier;
• at a depth of over 50…80 cm, it provides sufficiently reliable anti-undermining protection against intruders;
• promotes greater durability of the entire barrier.

If it is impossible to install a strip foundation, a “point” foundation is provided for the barrier supports (usually every 2.5…3 m), which bear the main load.

Experience shows that the “life” of a fence without a foundation, which is part of a sewage treatment plant, is no more than 3 years, after which either major repairs or installation of a new one is necessary, with the corresponding reworking of the signaling part.

In addition, a fence without a foundation (for example, in the form of a wire fence on wooden supports dug into the ground) sharply limits the types of possible CO for use, since interference associated with the impact of wind loads is the most difficult to compensate for.

Therefore, in the long term, it is absolutely impractical and can only be used as a temporary measure to improve the security of the facility.

The choice of the fence canvas and supports is usually determined by the aesthetic taste of the customer, taking into account the cost, construction load and design, and, to a greater extent, the security function performed:

• monolithic — «closed» type barriers are designed to ensure maximum secrecy of the object and its inhabitants, have the greatest resistance to destruction (especially welded metal ones), are aesthetically average (create a feeling of isolation from nature); their cost, as a rule, is maximum, and their resistance to overcoming «on the fly» by climbing over is minimal;
• «Open» type fences (mesh, lattice) are intended for the perimeter fencing of the object's territory, are practically transparent for end-to-end observation, have low resistance to destruction and subsequent overcoming (cutting 5…8 wires, sawing off one lattice post), are technically aesthetic and modern (according to Western European standards), and are best suited for control by means of perimeter security alarms;
• barriers made of standard and mass-produced sets of reinforced barbed tape (RBT), the overcoming of which is extremely difficult both by climbing over and by destroying the barrier (the technology for producing certified RBT ensures the resistance of the fence elements from destruction using conventional tools: pliers, nippers, etc.);
• wooden barriers, which are the most vulnerable structures to overcoming (including by dismantling, arson), which are, as a rule, only a beautiful frame for the territory — the most difficult from the point of view of signal blocking;
• combined barriers, in which the fabric is a composition of two or more types of barriers, which have the greatest potential for compromise between aesthetic and security functions.

The main obstacle to choosing barriers from ACL kits is often considerations such as “unaesthetic appearance, associated in our country with a concentration camp”, some experts even define this as a “disadvantage”.

Of course, the aesthetics of barriers are the most controversial issues, but we present the appearance of the standard “Burdock” barrier to the readers’ judgment (photo 1).

Photo 1. The appearance of the “Burdock” barrier (height 2.8 m)

The construction barriers discussed above can be divided into two groups:

1. The fabric of which can be destroyed by an intruder (in order to penetrate the facility) quite easily, for example, with a metalworking tool, and quickly (no more than 10…20 minutes) — mesh, lattice, wire (excluding AKL), wooden;
2. The fabric of which is difficult and takes a long time to destroy (monolithic and AKL barriers).

The main technical ideas that should be incorporated into the design of the barrier as part of the KTSO follow from ensuring maximum efficiency of the “link” of the barrier — SO, and consist of:

• for the 1st group
• make it as difficult as possible to overcome the obstacle by climbing over it, making the risk of injury real (for example, by using protective canopies made of flexible supports or flexible supports), and “force” the intruder to destroy the roadbed, the integrity of which must be strictly controlled; if the climb does occur, it must be accompanied by large mechanical deformations of the barrier and, accordingly, large useful signals comparable in magnitude to the signals from the destruction of the roadbed (an example of implementation is photo 2);
• for the 2nd group, make it as difficult as possible to overcome the obstacle by breaking through the roadbed and digging, “forcing” the intruder to climb over it, which must be reliably blocked with the help of the security system at the top; if the roadbed is destroyed, it must be accompanied by large useful signals and detected by the “upper” security system;
• for both groups, provide a compromise between the rigidity and flexibility of the barrier so that, on the one hand, it “sensitively” reacts to the overcoming of a human intruder, and on the other hand, it withstands the effects of wind, rain, snowfall, wild animals, birds and other significant sources of interference with perimeter security systems, discussed below.

Photo 2. An example of a combined barrier: climbing is difficult due to the canopy made of AKL,
the mesh fabric of the fence is controlled
cable triboelectric detector.

Thus, the consideration of construction barriers, in accordance with the classification (Fig. 1), allowed us to identify, in our opinion, the most suitable for use in the complex of technical means for protecting the perimeter of an object, such as:

1. Combined and barriers made of ACL;
2. Having a strip foundation along the perimeter with a depth of more than 50 cm;
3. “Translucent” with a height of about 3 m.

A suitable example would be a composite fence structure, the lower part of which (about 2 m high) is made of brick (it is difficult to destroy, wild animals outside are not able to shake it), and the upper part (at least 1 m high) is made of ACL or flexible welded mesh of the SSCP type: it is difficult to cut through it at a height, and climbing over it threatens the intruder with a fall from a height and injury.

Other types of fence combinations are also possible, successful in the sense of connections with the installed CO, allowing to ensure high tactical and technical characteristics of the KTSO as a whole.

This leads to the need to ensure technical compliance with the design of the barrier and the physical parameters of the perimeter CO, which applies to an even greater extent to construction and signaling barriers, in which the upper part is usually the sensitive element of the detection means.

Without such compliance, situations are possible when a good barrier and a reliable signaling system (in general) together give an unsatisfactory result.

For example, a monolithic metal barrier can so deform the detection zone of a radio-technical (radio wave) security system installed on it that zones of reduced sensitivity (“dead” zones) will arise, and the probability of detecting an intruder as a whole will be significantly reduced.

Another example is related to the use of an active IR beam CO installed on top of a fence (for example, a brick fence), the profile of the upper part of which is not straight (for example, the posts rise above the canvas), or the relief of the ground surface at the place of installation of the fence has a noticeable slope.

In such a case, it is not difficult for a specialist to determine the places where there are likely “holes” through which it becomes possible to overcome the fence by climbing over without issuing a detection signal.

From the above it follows that the design and manufacture of a fence erected on the perimeter of a protected facility must take place with the participation and under the supervision of specialists in the field of perimeter security.

At the end of the article, we draw attention to an important circumstance, often ignored when constructing a KTSO — a strip of soil up to 3 m wide, adjacent to the fence on the inner side of the perimeter of the facility, which we will call the exclusion zone.

It is intended for possible installation of a perimeter fire alarm (including in the ground) and the formation of a detection zone (DZ), which imposes restrictions on the planting of trees, bushes, and the movement of people in this zone.

It is necessary because:

1. Trees and bushes in the immediate vicinity of the fence have a significant interference effect on any perimeter fire alarm (during wind, rain, snowfall, uncontrolled growth of branches);
2. Large trees provide an additional opportunity for an intruder to cross the line (along the trunk);
3. “Opaque” trees and bushes make many types of fire alarms inoperative (for example, radio-technical, active IR);
4. Movement of people and dogs near the fence can cause false alarms, which leads to the need to turn off perimeter fire alarms during the daytime, which an intruder can take advantage of.

If the alienation strip cannot be formed for some reason, and trees grow along the fence from the inside, then, as practice shows, this leads to the impossibility of effective perimeter protection from the intrusion of trained intruders.

Only signal blocking of the fence from certain types of overcoming by a “normal” intruder becomes possible with some reduction in the potential characteristics of the detection means.

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