Circular 774
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Fences may be used to protect or divide property, to improve its appearance, to confine animals, or to exclude animals. Whatever its purpose, one should plan a fence carefully. This is especially important on farms where fences represent a large investment and their location and arrangement may affect production efficiency.
Permanent fences &#; those intended to last for many years with minimal repairs &#; should be well constructed and made of good materials. Temporary fences &#; those intended to stay in place only a short time &#; need not be so sturdily constructed and may be made of less expensive materials. Whether you select permanent or temporary fencing, careful consideration of uses and proper maintenance is necessary.
Fencing is a long term investment. Good fences should last from 25 to 50 years. Planning is the key to good fencing. This is true whether fencing an area for the first time or replacing old, worn-out fences. If present fences are in good shape you may want to develop plans around them. But look ahead to the day when these fences, too, may have to be replaced. It is not wise to construct new divider fences if boundary fences are in disrepair and failing.
The easiest way to prepare a sketch of your farm is to start with an aerial photograph. A good aerial photo shows details of the present farm layout, plus some indications of the lay of the land. Aerial photographs have been made of practically all farming areas. You can get one that includes your farm from the Farm Service Agency (formerly Agricultural Stabilization and Conservation Service) or your local tax office. You can also obtain one from any commercial aerial survey firm listed in the classified section of directories in major cities.
A land capability map will look something like this if prepared by the Natural Resources Conservation Service.
This step may already be complete if your land is in a Soil Conservation District. Land capability maps, available from the Natural Resources Conservation Service (formerly Soil Conservation Service), generally show types of land and spell out use and management plans for the farm (Figure 1).
Figure 2. Land capability layout.Land capability layout.
If an NRCS plan is not available for your farm, use the sketch of your land which you previously obtained. Divide your land into areas that are best suited for: (1) permanent pastures or hay production, (2) woodlands not to be pastured, (3) woodlands that can be pastured and (4) cultivated crop production (Figure 2). These land assignments are made based on uses that will return the greatest possible profit for each type of land.
Consider the following points when developing your plan. If possible, locate fences in terraced fields at terrace's crest and other natural water divides. Avoid running your fences down-slope across terraces. If your field needs to be cross-fenced, try to plan a contour fence parallel to a terraced ridge. If a fence must be located at the outlet end of a terrace, allow for a fence location that will not block the outlet water movement from channels. Pastures located at the end of terraced land provide good grass receiving areas for excess water flow. Wherever possible, plan for straight fences; they are cheaper and easier to build.
Locate permanent lanes to avoid erosion yet allow access to as many fields as possible.
Ideally, a lane should connect livestock buildings and working pens with every field that eventually may be pastured (Figure 3). Keep in mind that a permanent pasture located between other fields can be considered a lane itself.
Locate lanes in the driest areas possible, such as along a terrace or natural ridge; otherwise gullies may develop after repeated use. If a well-drained location is impossible, plan on movable lane fences which can be relocated after a year or two. If lanes are used frequently, it may be desirable to grade the area and install geotech fabric covered with 6 in. of compacted crusher-run gravel in the lane. Specifications for such "heavy use areas" can be found at your local NRCS office. They can be installed for about half the price of concrete.
Wherever possible, locate gates and passageways for livestock and equipment in the corner of each field closest to farm buildings. If you have fields on opposite sides of a road or highway, locate gates opposite each other so livestock can go directly across.
First, a permanent fence around the farm boundary is highly desirable. This will establish a fixed property line between you and your neighbor. It will also help confine your livestock to protect both them and the driving public from possible highway collisions. If a fence around the entire boundary is not affordable, then install the parts which are most helpful in your operations. Other boundary fences can be added at a later date.
Next, permanent pastures which will be used year after year also deserve high priority in fencing plans. Plan to fence ponds, also, to control livestock access. Since these fences are not apt to be moved, plan for well built, low-maintenance construction. If the plan includes a lane that gives livestock access to water, this fence should also have high priority. Livestock may enter and damage a well managed timber stand if there are gaps in surrounding fences. Such fences should have a high priority.
Also consider permanent fencing for cultivated fields used for pasture. If you follow the practice of "hogging" corn or peanuts, or of turning your livestock into a field for "grazing down" after it has been harvested, a permanent fence is highly desirable. With careful study, temporary or movable fences such as electric fences may do the job economically and effectively around cultivated fields. However, movable fences usually don't last more than 3 years and may not be economical replacements for permanent fences.
Temporary fences are intended for use over a period of a few weeks or months. After that they will be removed and used in some other location or stored until needed.
Movable fences cost less to build than permanent fences, but they are not as effective and will not last more than 1 to 3 years the way most of them are built. They do not take the place of permanent fences, but can be very beneficial in some instances.
Movable fences have a definite place in any livestock program. They can be used temporarily in place of permanent fences until you can afford permanent fencing. They can be relocated from year to year until you decide what field layout best fits your needs. They are easily moved to allow pastures to be rotated and are especially desirable for intensive rotational grazing programs. They can also help adjust the size of a temporary pasture to the amount of livestock being grazed.
Now that you have your fencing plan laid out, your next job will be to decide what kind of permanent or movable fence to select. The kinds of fences commonly used on farms include board, barbed wire, woven wire, cable, mesh, high-tensile, electric or a combination of any of these.
The type of fence that you will need depends on the livestock, crops, and other vegetation that border the fence. Horses will run through a fence or get tangled in it causing harm to themselves. Cattle will crawl over fences, sheep try to crawl under. Hogs, of course, try to root their way under a fence. Any livestock will put a fence to its greatest test when there is a lush green crop on the opposite side.
Rail fences are typically used as border fences around farm buildings or the home. They are also popular on horse farms where expensive show animals are confined. Today, many choices are available for building board fences including PVC plastic, vinyl coated wooden boards, treated wood, and painted wood. PVC plastic fences are not as strong as wood and cost more, but they are very attractive and do not require painting since they are the same color all through the material. White PVC boards may require periodic washing with mildew removing agents, especially in the humid South. Numerous heights of board fences are possible, but 4 to 5 ft are most common for livestock. The cost of lumber, nails, paint and other materials along with labor is generally higher for rail fences than for most other fences.
One type of fence that has the appearance of a rail fence, but is actually a wire fence is called a high-tensile polymer fence. The "rails" consist of vinyl plastic 4 to 6 in. wide with two to three high-tensile steel wires encased. It is less expensive than a rail fence, is very strong, and has a nice appearance and good visibility, but the wires must be tightened once or twice per year to maintain the proper tension. (This is true of any high-tensile fence.)
Common spacings of wire in barbed wire fences.
Barbed wire fences are generally classified in two categories: standard barbed wire fences and suspension barbed wire fences.
Standard barbed wire fences (Figure 4) usually have posts spaced 10 to 12 ft apart and use three to five strands of wire.
Figure 5. Typical barbed wire suspension fence.Typical barbed wire suspension fence.
Suspension barbed wire fences (Figure 5) consist of four to six strands of barbed wire. Each strand is stretched taut so there is no more than 3 in. sag between posts. The suspended barbed wires are held apart by twisted wire stays or short pieces of fiberglass posts spaced approximately 10 to 12 ft apart. Line posts are spaced from 50 to 60 ft apart. The suspension barbed wire fence sways back and forth in the wind or when animals hit it. The swaying motion helps keep animals away from the fence and discourages them from fighting through it. For this reason the lower end of the stays must not touch the ground or the effectiveness of the suspension fence will be reduced.
Some common woven wire designs. Standard design numbers describe the wire: 949-12-11, for instance, means the fence has 9 horizontal wires and is 49 in. high; has 12-in. spacing of stay (vertical) wires and 11-gauge stay and intermediate wires. (Top and bottom wires are usually two sizes larger.)
Woven wire fences consist of a number of horizontal lines of smooth wire held apart by vertical wires called stays. Spacing between horizontal line wires may vary from as close as 1.5 in. at the bottom for small animals to 9 in. at the top for large animals. Spacing of the wires generally gets wider as the fence gets higher.
Stay wires are spaced 6 in. apart for small animals and 12 in. for large animals. The height of most woven wire fencing materials ranges from 26 to 48 in. The height needed will depend on the size and jumping ability of the animals. Many combinations of wire sizes and spacing as well as a number of fence heights are available. Standard woven wire fence designs are shown in Figure 6.
These fences usually consist of 3/8-in. smooth, steel wire cables stretched from one anchor post to another (Figure 7). Each cable is normally made out of seven strands of wire twisted together. Heavy springs are placed at one end of each cable to absorb any shock on the wires. The other end is rigidly attached to the next anchor post. Cables are usually passed through holes in wooden posts. If other kinds of line posts are used, cables are attached to them with heavy wires. A fence may have as many cables as desired, however, a six cable fence is common. Spacing between wires depends upon the kind of animal to be confined. Cable wire fences are expensive, thus they are mostly used for confinement areas such as holding pens, feed lots or corrals.
Figure 7. Cable fence &#; one type of installation.Cable fence &#; one type of installation.
a) Detail of diamond-mesh fence; b)Stiff-stay, square-knot fence design.
Mesh wire fences are strong and provide great safety to animals. They are replacing wood board fencing in many areas, but are even more expensive than good woven wire. Because of the cost they are used primarily for confinement fencing such as that around corrals, feed lots, or small crop acreage areas. They also make an excellent large area fence for valuable horses. They have small openings so horses don't tend to get their hooves caught in them, and they have no exposed sharp wire ends to cut an animal. Two types of mesh wire are the diamond mesh (Figure 8a), which uses two wires twisted together in a diamond formation, and the square knot mesh (Figure 8b), which has single horizontal lines with the wire spaced 2 to 4 in. apart.
High-tensile wire fences potentially have longer life and lower costs than conventional fences. Single, smooth wires are held in tension between pressure-treated wood end-post assemblies with a combination of posts and battens or droppers to keep the wires properly spaced between posts. Tension in the wire is maintained by permanent in-line stretchers and tension springs. Best results are achieved when tensioners are used in conjunction with springs. Wires must be attached to any intermediate posts in such a way that they can move laterally and be retensioned. Wires should be retensioned at least once or twice per year. Commonly one to five or more strands of high-tensile wire are used in a fence. It is recommended that one or more of the strands be electrified in order to prevent animals from scratching on the battens and thus moving them out of position. If this happens, it could result in long unsupported lengths of wires, allowing animals to get through the fence.
Figure 9. Typical high-tensile fence brace and wire tensioner location.Typical high-tensile fence brace and wire tensioner location.
If properly designed and constructed, high-tensile smooth wire fencing has many advantages. It is easier to handle, safer for livestock, easily adapted to specific needs, has longer life, requires little maintenance, causes minimum damage to livestock hides, has a neat appearance and gives better livestock restraint and predator control when electrified.
Figure 9 shows a typical five-wire high-tensile fence with in-line wire tensioners.
Electric fences can be built for temporary or permanent use. In addition, a strand of electrified wire added to other types of fence usually improves their effectiveness tremendously. The temporary or movable fence is usually made with one or two strands of smooth wire or a rope or tape with small electric wires woven into it. Tape or rope is more flexible than smooth wire and much easier to handle and move from one location to another. It is also more visible, an important factor when a fence is to be moved periodically to new locations where livestock are not used to seeing it. An electric fence controller is used to energize the wires. The moist earth is used to allow the current to return to the controller. Alternatively, one strand of wire can be grounded, so that the circuit can be completed even when the earth is very dry and thus a poor conductor. Corners and end posts in temporary electric fences require less bracing than permanent fencing. Line posts may be small with wide spacing since the fence will generally be used for a short period of time.
Permanent electric fences may also be built. These fences have from two to eight smooth wires placed on stronger posts. Instead of using the earth for a return path, many electric fences use alternate wires as the hot wire and the grounded return to the charger. This arrangement enables a completed circuit when an animal touches any two adjacent wires and improves the performance of the fence tremendously in drought conditions. Cost of permanent electric fence is much less than that of comparable barbed or woven wire fences. Some of the advantages of electric fencing are low initial cost, low operating cost, and portability. They can be used to protect or extend the use of old permanent fences and they can be used to protect livestock or poultry from many predators.
There are a few disadvantages, however. A home-built unit can be highly dangerous. Only approved fence chargers should be used. Livestock will require training when first using electric fences. The electric fence charger must be operated full time, especially with cattle and sheep. Also, if no return ground wires are used, electric fences may not be effective in dry weather. This is especially true if the controller is not well grounded. Another potential problem is that the charged wire may short-circuit and become ineffective if heavy vegetation is allowed to contact the wires. It is imperative that electric fences be inspected and that vegetation be controlled in order to minimize short circuiting. For this reason, an electric fence may not be a good choice near wooded or swampy areas with heavy vegetative growth.
As previously stated, the type of fence needed depends on livestock, border crops, predators and other factors including cost. Table 1 shows some general comparisons for use when selecting a fence.
Table 1. Comparison of Common Fences. A. Permanent Types Types Comparative1 in. x 6 in. Treated Boards
200 10-20 Medium2 in. x 6 in. Treated Boards
350 10-20 MediumPVC Rails
500-600 20 Low High-Tensile Polymer Coated5-in. rail width
330 33 Medium Barbed-Wire Fencing (One post per 10 ft)5 strands
35 33 High Suspension Fencing (Posts 50 ft apart)5 strands
25 33 Medium Woven Wire Fencing39-in. with 2 strands barbed wire
75 33 Medium Cable Fence5 cable (5')
500 30 Low Mesh Wire12.5 gauge
150 38 Low Permanent Electric3 - (12.5 gauge) and High-Tensile Fences4 strands
20 25 Medium B. Moveable Electric Fences 3 Types Comparative12 gauge
7 33 High Reflective Tape or Rope0.5-in.
11 30+ Medium1 Cost index figures are to show relative cost, not actual costs. For example, fence with an index figure 25 costs about twice as much per foot as a fence with an index figure of 12.
2 Fence life based on combination of post and wire life expectancy.
3 Costs of electric controller not included.
Wire is covered with zinc, commonly called galvanizing, to protect it from rusting. The length of time before wire begins to rust depends on the weather but also on the thickness of the zinc coating. More zinc means more years of service before rusting starts. Fence manufacturers and the American Society for Testing Materials have established "classes" of zinc coatings for fence wire. Class 1 has the lightest coating of zinc and Class 3 has the heaviest (two to three times as much, depending on the wire size). The expected life of a fence depends on many factors, but Class 3 galvanizing can easily add 5 to 10 years of life to fence wire in a humid climate like Georgia's.
Because of competition, many suppliers of fencing materials only stock Class 1 fencing or a limited number of products in Class 3. Commonly, a light gauge Class 3 barbed wire is stocked along with a heavier gauge Class 1 barbed wire since both of these products sell for about the same price. Other products with Class 3 galvanizing may have to be special ordered, but it is usually worth the extra cost and effort, especially in the humid southeastern climate. If consumers demand a higher quality product, dealers will certainly supply that need.
Selecting the appropriate staple is just as important to the overall strength and longevity of the fence as selecting the right wire. Staple pull-out is a common fencing problem when using softwood posts. To avoid this problem, use 1.75-in. or 2-in. long, 8- or 9-gauge, hot-dipped, galvanized staples with cut points and barbs. If using hardwood posts, shorter staples can be used because they cannot be pulled out of hardwood as easily.
Wooden posts are plentiful in Georgia. Some major advantages of wood posts are strength and resistance to bending, misalignment and withdrawal. Permanent fences will require decay resistant fence posts. The most common wooden posts are pine pressure treated with CCA (chromated copper arsenate.) These posts have a greenish color, and they last longer and are harder than older treatments such as creosote and Penta (penta-chlorophenol.) This quality of hardness tends to help prevent staples from being pulled out. Some native, untreated trees are still used to a limited extent for fence posts. Table 2 shows the life expectancy of different tree varieties when used as fence posts.
Wood posts from 5.5 to 8.5 ft long and from 2.5 to 8 in. or larger diameter are readily available. The larger the top diameter, the stronger the post. Line posts can be as small as 2.5 in., but larger ones will provide for a stronger, more durable fence. Corner and gate posts should have a top diameter of at least 8 in. Brace posts should be 5 in. or more in diameter.
Be careful when buying wooden posts that the posts are properly treated for contact with the soil. Most treated lumber (including 4-by-4s often used as posts) bought in builder's supply stores is treated at 0.25 lb of CCA per cubic foot of lumber. This level of treatment will not protect against termites. Sawn lumber should be treated at 0.5 to 0.6 lb/ft3 of CCA if it is to be in contact with the earth. Fence posts can be treated at 0.4 lb/ft3. Many people are tempted to use "landscape timbers" for fence posts because they are extremely cheap at times due to over supply. These timbers are a byproduct of the plywood industry. They are what is left after the veneer has been peeled off of a large log. The danger in using these for fence posts is that many times they are not treated for ground contact since they are not designed to support a load and sometimes are not labeled, so it is unclear what, if any, treatment has been applied.
Steel posts have four major advantages. They cost less, weigh less, can be driven into the ground rather easily, and are fireproof. They also help ground the fence against lightning when the soil is moist. Steel posts vary from 5 to 8 ft long. A wide variety of steel posts are available with widely varying prices and quality, so be careful when comparison shopping to make sure you are comparing equal quality posts. Steel posts do not have as much strength against bending as wood posts. Wooden line posts can be placed every 50 to 75 ft to help keep steel posts from bending and improve fence stability.
Various kinds of posts are available for electric fence line posts as the requirements for strength are much less than for nonelectric fences. Posts are available in wood, plastic, steel, and fiberglass. Wood and steel posts require insulators to prevent short-circuiting the fence through the posts. Where available, high-density fiberglass posts (commonly known as sucker rod) make excellent electric fence posts. These posts are byproducts of the oil industry and are not always available. They are usually grey in color, are very strong and durable, and are nonconducting, so insulators are not required.
All posts must be long enough for the fence height and depth of setting. Add together the height of the top wire above the ground, the depth of the post in the ground, and 6 extra inches to get the desired length.
Table 2. Life Expectancy of Wood Fence Posts (in Years). Type of Wood Untreated Treated Ash 3-7 10-15 Aspen 2-3 15-20 Bald Cyprus 7-15 20-25 Balsam Fir 4-6 10-15 Basswood 2-3 15-20 Beech 3-7 15 Birch 2-4 10-20 Black Locust 20-25 Not necessary Box Elder 2-7 15-20 Butternut 2-7 15-20 Catalpa 8-14 20-25 Cedar 15-20 20-25 Cotton Wood 2-6 10-15 Douglas Fir 3-7 15-18 Elm 4 15 Hackberry 3-7 10-17 Hemlock 3-6 10-25 Hickory 5-7 15-20 Honey Locust 3-7 10-20 Larch 3-7 10-20 Maple 2-4 15-20 Oak (red) 5 15 Oak (white) 10 15-20 Osage Orange 20-25 Not necessary Pine 3-7 25-30 Red Cedar 15-20 20-25 Red Mulberry 7-15 15-30 Redwood 10-15 20-30 Sassafras 10-15 20-25 Spruce 3-7 10-20 Sweetbay 2-6 10-20 Sweetgum 3-6 20-30 Sycamore 2-7 20-25 Tamarack 7-10 15-20 Tupello (black) 3-7 15-20 Willow 2-6 15-20 Yellow Poplar 3-7 20-25Most people will agree that touching an electric fence is a very unpleasant experience. The experience for animals is no different. When animals come in contact with an electric fence, the shock they receive affects their nervous systems. The severity of the shock depends on the voltage and amperage, as well as the duration of the shock and the sensitivity of the animal. It takes at least 700 volts to effectively control short-haired breeds of cattle, pigs, and horses and around volts for long-haired cattle, sheep, and goats. The controller, sometimes called the charger or energizer, that delivers this shock is the heart of any electric fence and should be selected carefully.
The thing that makes controllers safe yet effective is the short duration of the charge. The charge is powerful, yet does not last long enough to damage the heart or to cause electrical burns. Modern low-impedance controllers have the capacity to power long distances of multi-wire fences and are not affected as much as earlier controllers by some contact with grass or other vegetation.
Controllers are available in battery powered models as well as 120-volt AC models. When 120-volt power is available, the 120-volt models have the obvious advantage since batteries do not have to be purchased or recharged. Cost of operation is minimal (usually less than $1 per month) for these units. If commercial power is not available near the fence to be energized, battery-powered units are available to fill this need. These units operate on 12, 24, or 36 volts (one, two, or three 12-volt batteries in series). The batteries must be recharged every 2 to 6 weeks depending on the system and amount of use. Solar collectors are also available to recharge the batteries daily. Deep cycle, marine and RV type batteries are best suited for battery-operated controllers. Batteries designed for use in automobiles will not last as long as deep-cycle batteries.
It is important to match the capacity of the controller to the fence you want to charge. Most manufacturers indicate the strength of the unit by the number of miles it will power. A good rule of thumb for sizing controllers is to determine the number of miles of electrified wire in the fence and add 25% to offset any power drain caused by vegetation touching the fence. For example, if you have 4 miles of 5-strand high-tensile wire with three of the strands electrified, you would need a controller rated for at least 15 miles (3 wires x 4 miles = 12 miles + 25% = 15 miles).
Like most construction and maintenance jobs around the farm, fence construction requires proper techniques and common-sense judgment. Every fencing job presents slightly different problems. A few basic principles are good starting points for every fencing job. Here are some to consider.
Where a permanent fence is installed on a property line, make sure of the exact location of property lines. A mistake here can be very costly. Once this is done and any trees and brush are removed, you are ready to establish the fence line.
On level ground, an end post can be installed at each end of the run and a string or a single strand of wire stretched between the two posts to establish the line. On rolling ground where hills are too high to sight from one end-post to the next, surveying equipment can be used if available to establish the location of intermediate points on the line. Alternatively, intermediate sighting stakes can be driven at the tops of hills. Two of these temporary stakes should be driven about 8 to 10 ft apart at the approximate position where the line will cross the crest of the hill. If both posts appear to be lined up when sighted from each end post, they represent a true midpoint of the line. If not, they can be moved back and forth until they are properly aligned.
Figure 10. Fence post spacing around curves.Fence post spacing around curves.
When the fence must go around a curve, place small stakes every 16 ft around the smooth curve. Then start figuring the post hole positions where the curve is greatest. The sharper the curve, the closer the posts should be. Select three stakes at a point of maximum curvature. String a line from the first to the third stake (Figure 10). Measure the distance from the center stake to the string, and space the posts as given in Table 3.
Table 3. Suggested Fence Post Spacing Around Curves. Distance fromFor any wire fence, corner-post and end-post assemblies are probably the most important structures in the entire fence. They are the foundation upon which the fence is built. When wire is first stretched, the pulling force on a corner or end may be lb. Winter cold can cause contraction of wire which increases that force to lb. Both corner and end assemblies must be strong enough to withstand these forces.
Figure 11. Double-span brace post assembly. Post depths shown are considered to be minimum.Double-span brace post assembly. Post depths shown are considered to be minimum.
Figure 11 shows proper construction of a double span H-brace assembly for wooden anchor posts. A double span assembly is more than twice as strong as a single span; use it whenever the fence span will be more than 200 ft long. A corner post will need a brace assembly for each fence line leading to it. Post depths shown in Figure 11 are minimums. Use deeper settings for sand or wet soil conditions. Figure 12 shows the proper way to secure brace wire.
Figure 12. Correct procedure for threading the nine gauge smooth wire used as diagonal in the brace assembly.Correct procedure for threading the nine gauge smooth wire used as diagonal in the brace assembly.
When a fence is more than 650 ft between corner posts, use braced line post assemblies every 650 ft in the fence line. A braced line assembly is the same as a single span braced corner except that a second diagonal brace wire is used to take fence pull in the opposite direction.
Figure 13. Types of anchor-and-brace assemblies and where to locate them. (a) For fence lengths of 160 ft or less, use single-span end construction. (b) For fence lengths of 200 to 700 ft, use double-span end construction. (c) For fences more than 700 ft long, use a brace-line-post assembly to divide the fence lengths. (d) On rolling land, fence stretching is easier if braced line-post assemblies are located at the foot and top of each hill. (e) Contour fences, more than 350 ft long, should have a braced-line-post assembly installed to keep the stretches to 350 ft or less. Install in straight section at least one post span away from a curve. Don't install on a curve; it won't hold well.Types of anchor-and-brace assemblies and where to locate them. (a) For fence lengths of 160 ft or less, use single-span end construction. (b) For fence lengths of 200 to 700 ft, use double-span end construction. (c) For fences more than 700 ft long, use a brace-line-post assembly to divide the fence lengths. (d) On rolling land, fence stretching is easier if braced line-post assemblies are located at the foot and top of each hill. (e) Contour fences, more than 350 ft long, should have a braced-line-post assembly installed to keep the stretches to 350 ft or less. Install in straight section at least one post span away from a curve. Don't install on a curve; it won't hold well.
Figure 13 illustrates anchor and brace locations for fences. Steel corner post and brace assemblies can be used in place of wood assemblies. The steel posts should be set in concrete anchors. Corner post anchors should be 20 in. square and 3.5 ft deep. Braces are anchored in 20-in.-square blocks that are 2 ft deep.
There are some other brace assemblies that are not as strong as the H-brace, but will work in many cases for short pulls and in favorable soil conditions. One is commonly called a "dead man" brace (Figure 14). The end post should be a large (10&#;12 in.) post at least 4 ft in the ground. The "dead man" is a short (4 ft) piece of post buried just under the surface perpendicular to the end post on the loaded side. This positioning supports the post such that when the post tries to lean, it must push the "dead man" through the soil sideways.
Figure 14. "Dead Man" brace."Dead Man" brace.
Figure 15. Angle brace.Angle brace.
A second type of brace, called an angle brace, is shown in Figure 15. The keys to making this brace work are (1) making sure the end post is deep in the ground (about 4 ft), (2) placing a 1 to 2 square foot rock or piece of concrete under the angle brace post, and (3) properly tensioning the tension wire. It is the tension wire that gives this brace its strength, not the angle post. If the fence starts to sag, it can usually be tightened by retensioning the tension wire.
Steel posts are almost always hand or power driven. Wood posts are frequently driven with power driving equipment. Driving posts is faster than digging holes and tamping posts in. Driving also results in a stronger foundation for the post. Posts should be driven with the small end down. The results may look strange (large end up), but they are much stronger and damage to the post during driving is minimized. Corner posts can be driven as well, but it is sometimes necessary and always advisable to drill a pilot hole about 3 to 4 in. smaller than the post before driving. The pilot hole reduces driving resistance and gives more control over the direction of lean of the post. (End posts should be driven at a slight angle away from the direction of pull so that they will be straight when tensioned.)
When setting posts in holes, center them before tamping. This makes tamping easier and gives the tightest possible soil-pack around the post. Wooden line posts should be set at least 2 ft deep, preferably deeper. In most soils, studded "T" posts need to be driven only until the anchor plate is beneath the surface. For uniform depth, mark the digging tool or steel post to desired depth. A gauge pole, cut to desired length, is handy for spacing posts. Space line posts about 10 to 12 ft apart for most fences. Narrow spacings are better over irregular ground and in contour fences.
Proper stapling techniques.
In general you will want to install and stretch wire in sections, running from one corner and/or brace post assembly to the next. Always work from the bottom up when installing wire. Install the bottom wire first, then the next highest, etc. Attach wire to the side of the post nearest livestock except where appearance is important. Use galvanized staples or the wire clips that come with steel posts to attach wire to posts. Staples should never be smaller than 1.5 in. long, preferably 1.75 or 2 in. Do not staple the vertical or stay wires of woven wire. Drive staples so the wire is held close to the post but not tight (Figure 16a). The wire should be able to move through the staple to allow expansion and contraction of the wire. Good brace assemblies should keep the wire tight. Driving staples parallel with the grain should be avoided since that will weaken the grip of the wood on the staple. Slash cut staples should be rotated in a certain direction depending on whether the staples are right or left cut (see Figure 16b). Place the staples parallel to the grain and then rotate slightly away from the flat faces of the staple points. This will result in the desired direction of staple penetration (Figure 16c) and a staple that has 40% more resistance to withdrawal than staples rotated the wrong way.
One of the best ways of assuring good performance of a fence controller is to provide a good grounding system. The controller grounding system should be separate (at least 30 ft away) from any other driven grounds. Failure to do this could cause stray voltage problems on the farm electrical system. The grounding system should consist of at least 24 ft (usually three 8-ft driven rods spaced 6 ft apart) of ground rod. In addition, a driven ground rod should be placed every ft ( ft in arid climates) of fence and attached to the grounded wires in the fence. Proper grounding will make the job of the charger easier and thus improve its performance. Lightning arresters are available and help protect the controller if the lightning strike is not too close, but will probably not prevent damage by a direct hit. Making the top wire on the fence a grounded wire sometimes helps protect the controller by shunting lightning to the ground instead of through the controller.
You can buy or build gates or cattle guards. Both should be sturdily built and adequately supported. One of the most common (and aggravating) mistakes made when building fences is inadequate bracing of gates which results in gates dragging on the ground. Several plans for gates, man passages and cattle guards are available through your local county extension office.
A fence that is properly cared for will give long and trouble-free service. Include some of the following suggestions in your regular maintenance program:
Planning Fences, American Association of Vocational Instructional Materials, .
Planning & Building Fences on the Farm, University of Tennessee Agricultural Extension Service PB , .
Status and Revision History
Published on Feb 01,
Published on Feb 20,
Published on May 14,
Published with Full Review on Feb 16,
Published with Full Review on Feb 20,
Published with Full Review on Mar 12,
Prepared by:
Royal Canadian Mounted Police
Lead Security Agency for Physical Security
Departmental Security Branch
NHQ 73 Leikin Drive Ottawa Ontario, K1A 0R2
Publication Issued: -12-02
Updated: -06-03
The Security Fencing Considerations Guide is an unclassified publication, issued under the authority of the Royal Canadian Mounted Police Lead Security Agency for Physical Security (RCMP LSA).
This is a Government of Canada publication to serve as a guide for the design and selection of security fencing for departments, agencies and employees of the Government of Canada.
Suggestions for amendments and other information can be sent to the RCMP Lead Security Agency .
The effective date of GCPSC-009 Security Fencing Considerations Guide is -01-27.
The RCMP, as the Lead Security Agency (LSA) for physical security for the Government of Canada (GC) is responsible for providing advice and guidance on all matters relating to physical security. This includes what should be taken into consideration after it has been determined that security fencing is required for a specific location or application.
The purpose of this guide is to provide GC employees with information on the appropriate selection and procurement of fence systems. It also provides considerations in the selection of alternate fence solutions.
This guide is for use by all GC employees who design and/or specify security fencing. It is intended to be updated regularly to capture new guidance or update existing information as technologies evolve.
With the constantly evolving threat landscape, and the convergence of physical and information technology (IT) security, the requirement to assess the risk of any application and/or software connected to a network to operate and support equipment in Government of Canada controlled buildings is critical. Some examples of these control systems could be for items such as, but not limited to, security lighting, perimeter gates, doors, HVAC etc.
Contact us to discuss your requirements of Ebb and Flow Bench. Our experienced sales team can help you identify the options that best suit your needs.
Before implementing any applications and/or software that will control and/or automate certain building functions, your departmental security requires the completion of a Security Assessment and Authorization (SA&A). This will ensure that the integrity and availability of the components the applications and/or software controls are maintained and that any risks highlighted will be mitigated. Starting the SA&A process early is highly recommended to ensure project delivery schedules are not affected. For more information on the SA&A process, please consult your departmental Security.
For more information, please contact:
Royal Canadian Mounted Police
Lead Security Agency for Physical Security
73 Leikin Drive, Mailstop #165
Ottawa, ON
K1A 0R2
: .
The need for a perimeter fence starts with a Threat and Risk Assessment (TRA) to determine who or what the fence(s) will deter or delay. Fences provide protection against threats; may have safety related functions and can provide both deterrent and delay functions. In order to increase fencing effectiveness, there should to be a detection element(s) included in the design.
A perimeter is not the only place a security fence can be installed. Within a given compound or area, there may be different security requirements or different security levels which may require sub-dividing the fencing elements. They can divide a compound into separate zones or create protected pathways for travelling between buildings. Higher security levels may require the use of multiple layers of security fencing to provide the appropriate security in depth.
The security fence design should consider; gates, barriers, and sally ports to control who or what may pass through the perimeter, as well as the alternatives if the system is breached. The use of Security Guards or electronic access control devices will help speed up the entry and exit process for authorized users. Reducing complications encountered when entering and exiting can make a significant difference by reducing congestion, especially for legitimate or frequent users.
All fencing installations are subject to criteria from the Authority Having Jurisdiction (AHJ). Provincial or municipal laws or bylaws may restrict, limit or demand certain construction standards for fences.
The starting point for security fences is to determine the perimeter that is to be enclosed. Some of the possible elements requiring protection from a perimeter fence could include:
The main challenge to defining a perimeter is the length of fencing required. A large perimeter is expensive and more elaborate to design. Questions to consider during the design phase are:
Access points through a security fence require significant planning. Considerations must be made for the type of access (pedestrian/vehicular), the frequency of use, and the number of access points required.
Most compounds will require at least two separate access points for vehicles, taking into consideration operational needs and fire safety. Vehicular access points can operate as secondary emergency exit points for pedestrians.
Other access point considerations include:
The threats identified in the TRA inform the choices required in fence construction. Portions of the perimeter may have different threats based on the access point, type and adjacencies. Considerations must be made given the application; vehicular entrances which may require crash prevention design options for both the gate and fence while security fences adjacent to a forested area may require a different detection technology than one adjacent to a road.
Threats to fenced areas may fall into two categories, pedestrian and vehicular. Pedestrian threats are motivation, skill and tool based, and are rated as follows:
Vehicular threats are based on the amount of kinetic energy delivered to the barrier device (F = ½ mv2). The results of this formula created the K-rating, now outdated. M-ratings have since replaced K-ratings, as the primary certification given based on how far the payload from a 15,000lb vehicle travels past the barrier. ASTM F (American Society for Testing Materials) details the requirements for the Hostile Vehicle Mitigation measures required to limit damage caused by vehicle as a weapon attacks.
Although this section deals with crash ratings for vehicles, security practitioners should note that vehicle threats are not only concerning from an impact perspective. Vehicles can also be used to pull-down the fence.
ASTM ratings are based on the mass and velocity of the vehicle hitting the barrier device. The primary goal of this rating system is to assess the strength of perimeter barriers (fencing) and gates when hit by vehicles of different masses and at varying speeds. Security fencing can also have a ballistic or blast mitigation rating based on the resistance to projectiles and explosions. The level of protection required by the fence/barrier will depend on a number of threat factors such as the size of the vehicle and payload (explosive) and the setback and standoff distances. A TRA is required to determine these threats and inform the ratings required to protect the assets. ASTM has developed crash certifications for different types of vehicles. They are as follows:
ASTM F contains a complete list of ratings however below is an example of what the required product rating would be supposing a vehicle hit a barrier at different speeds and a mass of 15,000lb (6,800kg) or M-rating:
As was stated, ASTM F base the certification on how far the payload travels past the barrier. These are P-ratings expressed as P1-P4 and Security Practitioners should note there is no limit to how far the vehicle can travel past the barrier to be certified. A P4 rating is given to any vehicle that travels beyond 98.41'. The P-ratings are as follows:
Using the above information: If a TRA recommended protecting against a vehicle threat for a 15,000lb (6,800kg) vehicle travelling at 40mph (64km/h) and requiring that vehicle to travel no further than 5' beyond the barrier, you would need to install a product with the following ASTM rating: M40 P2 - M40 (15,000lb vehicle) P2 (3.31'-23')
Setback is the distance from the property line to the fence (outer setback) plus the distance from the fence line to the buildings or other assets protected inside the fenced area (inner setback).
An outer setback reduces the total area enclosed within the fence and thus reduces the overall cost of the security fence. This outer setback area is often cleared and trimmed to provide visibility into the external area adjacent to the fence. This cleared area also allows responding personnel better visibility to observe any attackers and eliminates areas or obstacles where threats may be present. The use of Crime Prevention Through Environmental Design (CEPTED) principles are important in this area.
The inner setback can be an area for parking adjacent to a building. It can also provide a method of blast reduction by forcing any vehicle-borne explosive to be kept away from the main building. Blast pressure falls off with increased standoff; therefore making small increases in the setback distance can be very effective at reducing building damage. Inner setbacks should be kept clear of any obstructions; providing clear sight lines and good illumination aids security responders.
Using a back-filled retaining wall inside the perimeter provides two advantages. It increases the effective height of the fence on the attack side and, it provides a solid vehicular barrier. Similar advantages can be achieved using drainage ditches or berms where the slope angles can be designed to stop or slow attacking vehicles.
If there are large volumes of pedestrian traffic, it may be beneficial to use larger, more robust vehicular security barriers such as bollards, large planters or rocks. Planters and rocks, when properly anchored, provide protection while appearing aesthetically pleasing. Crime Prevention Through Environmental Design (CPTED) principles can assist security practitioners to deter attack through exposure and discovery, by removing hiding places, encouraging the proper use of the area, and improving overall visibility.
Watercourses are often subject to environmental restrictions from various levels of government. Diversion and burying of the fence fabric are preferred choices if possible. If the watercourse is seasonal, it may be possible to place a fence across it; however, the fence will likely be a collection point for sticks, leaves, and anything else that washes down with the water. The main challenge for a watercourse is to find an effective sensor that works through all the seasons and changing water levels.
Alternative methods are to fence both sides of the watercourse or bury the water run. If the run is buried, it should be buried for the complete distance through the compound, or the culverts or other water carriers need to be small enough to prevent passage by threats. Multiple, parallel pipes can be used in the immediate vicinity of the fence. The use of a culvert requires regular maintenance to remove any accumulated materials that could block the water and cause local flooding.
Shorelines are similar to watercourses. The challenge is to provide effective protection along the boundary. If the shoreline is a harbor or other area with a manmade breakwater or pier, then there is a solid base upon which to deploy a fence. The method of securing a shoreline with a fence will often call for the fence to be set well back from the water's edge to provide a solid location for the post foundations.
If the shoreline is a salt-water body, the choice of fencing materials needs to consider the threat of corrosion from salt mist and coastline erosion.
Aesthetics are a contributor to the fencing choices, especially for organizations that have public access. It can also be driven by municipal (AHJ) or architectural requirements. Often the major factor will be the fence height limit. The priority of this consideration varies greatly between projects. The use of a retaining wall to raise the interior ground level can alleviate some AHJ concerns.
Although a fence does have some effect psychologically, the physical delay factor is essentially zero if there is no sensing equipment deployed capable of detecting an attack (discussed further in paragraph 9.6). The evaluation of the delay factor for a security fence relates to the threat and the most effective defeat method for that threat. The style of security fence used will drive the defeat options, which may include:
Climbing can be deterred by (often combined):
Tunneling can be deterred by (often combined):
Pulling or pushing down attacks can be deterred by (often combined):
Through the fence fabric (physical or visual) attacks can be deterred by (often combined):
Detection is a necessary part of a fence system that acts as more than a cursory deterrent. The detection system needs to be integrated with an assessment and response system that will drive a response to any attack. A reliable sensing system that limits false positive and nuisance detections is essential. A robust system encourages a thorough assessment of any alarms and limits the complacency of responders.
Different types of sensing equipment have different methods of defeat. They will also act differently under specific situations, which may make them less reliable. Detection is more reliable when combining more than one type of sensing technology.
Detection equipment can be places in one or more locations relative to the fence line and is explained in more detail below:
Approach detection may include the following technologies:
Fence proximity detection includes the following technologies:
Fence disturbance detection includes the following technologies:
Fence deflection detection may include the following technologies:
A valid detection assessment requires properly functioning detection equipment and adequate lighting to be effective. The assessment could involve a responding security officer or some electronic surveillance such as a CCVE or thermal camera. The designed delay time required by the fence against the identified threat is part of determining the total assessment and response time.
Part of assessment is the ability to locate the threat as quickly as possible. If the threat has not yet breached the fence, the ability to see through the fabric is a prime consideration. It may also be a consideration if the perimeter has active patrols. The design of the fence may include privacy requirements to prevent or restrict the view into the enclosed area. This will affect the ability to assess and respond and may require the fence to be treated like a wall.
Upon review of the specific TRA recommendations, the design requirements for the construction of a fence become clear. The construction process involves:
Increasing the height of a fence increases the psychological and physical delay effects. It increases the time required to climb and may increase the difficulty of reaching the top of the fence to defeat any security features (such as the anti-climb topper). The height should be consistent considering terrain and other topographical features of the area.
Fences with a height of 2 meters or less should not be referred to as security fencing as they provide little delay. Most adults can reach and clear the top quickly and easily, even if topped with barbed wire. A 2-meter high fence is little more than a passive deterrent, as the barbed wire strands can easily be reached and defeated with wire cutters. The minimum height for a security fence should be 2.4 meters. High security installations should consider fences of at least 3.6 meters.
Even when deploying electronic security features, a 2-meter fence can be defeated using a short stepladder. Climbing the ladder and jumping over the fence without contacting the fence itself it is relatively simple and carries a minimal risk of harm on landing. Higher fences force the use of more obvious tools/ladders and a much higher risk of harm on landing.
The topping and the fabric choices will also increase the delay time to climb the fence. It requires mentioning again that if the fence does not include detection equipment, the effective delay time is zero. In addition, simply using CCVE, whether intermittent or even continuous video surveillance of the fence is not an effective method of detection. A combination of various types of equipment is much more effective.
As with single layer fencing, multiple fencing layers require maintenance, including in between the layers. Access between the layers should be limited to points where gates already pass through the perimeter. The access points must be large enough for maintenance equipment including snow clearing, maintenance and lift trucks for lighting and other repairs, and response vehicles.
If incorporating multiple fencing layers, design the space between fences to be resistant to the growth of vegetation. This space is also ideal for secondary detection systems. The space between the layers must be wide enough to prevent jumping or bridging between the layers with a ladder or other material. The recommended spacing is at least twice the fence height.
Fence fabrics can consist of individual slatted or solid panels that connect between posts or continuous fabrics that stretch over longer distances. Always apply continuous fabrics to posts and rails on the attack side, the fabric then covers the posts and the rails, preventing their use as a climbing aid. Attach continuous fabrics to each post, and to the top and bottom rails. Middle rails are not recommended as they provide additional climbing points.
The fabric used on a fence provides the fence's aesthetics. It is usually galvanized metal protected with zinc-coating, paint, or wrapped with polyvinyl chloride (PVC). Any of these protective coatings will extend the life of the fabric by reducing corrosion. The largest American Wire Gauge (AWG) wire with a PVC coating is often smaller than that available with a galvanized or paint finish. PVC is subject to breakdown from the sun's UV rays.
The choice of fabric must consider the ability of the responders to have visibility through the fence. When selecting the fence design, it is important to assess visibility looking parallel to the fence line. When deciding on the fencing fabric or whether a blocking material will be needed, the sensitivity of the protected compound or the need to visually monitor through the fence will need to be considered. In addition, factors such as local guidelines and heritage considerations may also determine the type of fencing material permitted input from AHJ may be required.
Previously it was noted that the fence fabric can be buried, extending below ground level. Given the climate conditions in most of Canada, this is problematic due to frost heaving the ground. Burying also increases fabric corrosion, and possibly reduces the sensitivity of the detection technology.
Figure 1: Chain link knuckle edge.
Figure 2: Chain-link twist edge.
Chain Link is the most common fabric for fence construction. It has five parameters for selection considerations:
Galvanized coatings are available in two variations. Coatings are applied to the wire before creating the fabric resulting in exposed wire ends as the fabric is manufactured &#; or &#; they may be applied after manufacturing where it can leave gaps at the wire contact points that are exposed by fabric flexing.
There are several things to consider if choosing a chain link fabric. Costs increase as the mesh size decreases and as the AWG decreases (gets thicker). A decrease in the size of the mesh openings and the thicker wire also reduce the visibility through the mesh, which makes it harder for the responding personnel to view through the fence. A smaller mesh size provides an inherent anti-climb function and makes manual tool attacks more difficult and power tool attacks slower. Large diameter (thicker) wire provides increased resistance to vehicle attacks and helps to slow tool attacks.
Continuous fabrics like chain link use tension bars inserted into the end of the fabric with straps that attach the bars to the stain or corner post. The standard method of attaching the straps to the tension bar is to use a carriage bolt and nut. The nuts must be on the secure side of the fence to prevent the attacker from undoing the straps.
If chain link fabric is used, the choice of knuckle versus twist is part of the fence top selection. Knuckle means the wires at the top edge of the fence are bent down after being twisted together. Knuckle is the only choice available for fences under 2-meters. Twist means the wires at the top edge of the fence remain pointed up. This effectively prevents straddling the top of the fence. Twist top is redundant if the fence has razor or concertina wire. If using multiple fence layers and the only effective way to move the snow is with a snow blower, the mesh size is important. Smaller meshes will catch snow while a larger mesh will allow most of it to pass through. Panel fabrics using weld mesh have the same concerns as continuous fabric meshes. Most slat panels will not let snow from a blower pass through.
Figure 3: Panel fabric with deep vertical bars and concrete extended base.
Figure 4: Panel fabric with extended base.
Panel fabrics are usually made of welded mesh or vertical metal slats. These panels have connection points at each post that their effectiveness to deal with a vehicle impact. Continuous fabric materials spread the impact load over a greater area along the length of the fabric as they stretch. Where possible, design fences perpendicular to vehicular attack angles or limit the available space so the vehicular approach speeds are low.
Panels are available in both aluminum and steel configurations. Aluminum is much lighter and may have a longer life due to lack of corrosion. These are acceptable for a pedestrian-only threat; steel is required to handle vehicle threats. In higher threat locations or locations, which require heightened security, the fence panel should be buried and anchored below ground.
Panel fabrics can achieve the necessary HMV requirements however; the construction of the posts requires secure foundations. These panels often include integral crash beams or cables that make them much heavier than the equivalent mesh fabric. All vehicle resistant fences require proper foundations to absorb the impact. The impact load requires spreading along the perimeter with continuous cables or beams, or bracing into the ground.
Panels with vertical slats are aesthetically pleasing, excellent for resisting most tool attacks if closely spaced, and provide fair anti-climb capabilities. This is a good choice for shorter fences in an urban setting such as between adjacent buildings.
The design of panel fabric fences will often include a continuous base wall that is 30 to 45 cm above ground. This provides a partial vehicular security-barrier function, especially against lower sitting vehicles such as cars, pickups, and vans. Continuous fabrics with a topping may remain intact after a low energy vehicle impact. The top of the continuous base wall should not extend beyond the fabric fence on the attack side as this may offer a foothold for an attacker.
High security fences using continuous fabric should use 9-AWG wire to tie the fabric to the posts and rails. The maximum spacing between tie points should be not more than 300mm.
Posts used in fencing must have some cover to keep precipitation out of the inside of the post. Rainwater, snow, and water that freezes and thaws will corrode or crack the posts and the foundation from the inside. This is problematic as there is little warning in advance of weakening or failing. Fence post covers are the mounting point for any fence topper such as barbed wire, concertina or razor wire. Caps must connect solidly to the post to be an effective mounting point. Bolts or attachment mechanisms must be on the secure side of the fence.
Most fence tops can be defeated with thick fabric (blankets or rugs). These spread the load of the climber and limit penetration of the topper material. Fence height and an overhang created by the topper material make climbing more difficult. To help complicate climbing, the fence topper should overhang on the attack side, as the climber must move away from the fence to clear the fence topper. Three-strand barbed wire has been a standard fence topper for many years. It is not appropriate for higher security fences as it is easily defeated with hand tools but it can be used as a stringer wire to hold various other topper material (concertina coils or razor wire) in position while providing some further deterrence.
Figure 5: Close-up of a barbed wire barb.
Figure 6: 3-wire barbed wire installation with twist end fabric and strain post.
Concertina wire is not fully effective unless the spacing of the coils is correct. Clip all loops to the adjacent loops to limit the loop spacing when stretched. Place a single wire coil on the attack side of the fence and, where possible, a second coil on the secure side. Two coils force an attacker to drop from height instead of climbing down the fabric.
The use of a tensioning wire at the top of the fencing, when barbed or concertina wire cannot be used may be considered and it should be noted that this would make the fence harder to scale, but more susceptible to being pulled down by a vehicle.
Figure 7: Helical concertina supported by barbed wire.
Figure 8: Two concertina coils in a fence line.
A fence may use a variety of post sizes depending on the location of the post such as:
Line posts are usually the smallest posts on a fence; most of the other posts are under higher stress and as such require a larger diameter. High fences require larger diameter posts with deeper foundations to offset the increased load. The spacing of posts is important for fence's overall effectiveness. Ideally, posts should be spaced no more than 2.5m apart and strain posts not more than 60m apart. The recommended post sizes for a high security fence are:
Foundations for the posts are the most important component for the longevity of the fence. The foundation provides much of the strength for vehicle resistance and keep the fence in the correct position during winter frosts. A constant sized installation is sufficient as long as it goes below the frost line. If the installation cannot go below the frost line, the use of a pear-shaped foundation will result in the frost forcing the post down instead of up.
When choosing fencing or foundations, conduct a TRA to determine the type of fencing (barrier), post or foundation needed to meet the requirement.
Figure 9: Panel fabric with narrow vertical poles, extended base, and vehicle stop behind the gate.
Figure 10: Panel fabric fence and gate with vehicle security barrier and external bollards
Figure 11: Panel gate backed with vehicle security barrier.
The selection of a gate must consider the largest object passing through it. There must be sufficient clearance height for emergency vehicles, particularly fire trucks. When selecting the appropriate gate configuration, one needs to decide whether vehicle access and pedestrian access can be together or need separation. Gates are typically the weakest portion of any fence without the addition of security features. A gate is a break in the continuous fabric and could be wider than the spacing between line posts. Considerations should be made for any National or municipal building code requirements.
If a vehicle threat is present, the first choice to protect a gate is to limit the approach speed of a vehicle. These methods cause the approaching vehicle to make direction changes and may include having the approach road run parallel to the fence until reaching the gate. The installation of an "S" curve or chicane requires vehicles to slow down in order to maneuver through fixed obstacles. If it is possible to reduce the speed of the vehicle by half, the impact force is then reduced to one quarter of the original.
It will need to be determined if gates should have integrated or separate crash barriers and what (if any) HVM measures are required. This is determined based upon the type of threat identified in the TRA. Types of barriers include:
Proper installation of these barriers is critical to their operation. If delay to personnel is required, this consideration should inform the choice of equipment selected. Many vehicle gate systems are used for vehicle only entrances and operated from a guard post providing little delay for pedestrians.
In order to maintain the strength of a gate when closed, it needs to latch at multiple points, approximately every four feet of vertical height. If multiple latches are not present, the gate can be "scissored" around the single attachment point such that a person can pass through the opening. The threats expected at the location will determine the rating of the gate required. Consideration should be given to select equipment that has been tested and certified to the rating level required for the application.
Passing through the gate at high security installations usually requires authentication and/or inspection activities. For added security, configure gates interlocked in pairs such as a sally ports, or mantraps. The use of multiple layers improves the resistance to attack, as both layers need to be defeated. The gate on the unsecured side usually requires the highest resistance to attack. (i.e. a crash barrier would only be added to the exterior gate)
Motorized vehicle gates that operate on rails or guides should have the rails heated to ensure proper operation under winter conditions. Drainage for water should also be considered. A thorough maintenance plan is required to ensure proper functionality especially in winter. Barriers at gate positions should be in the block position when not in use and restored to the blocked position immediately after a vehicle passes in or out.
All electronically controlled gate systems should be supported by backup power source that has a manual over-ride in case of mechanical failure. The gaps under and around the gate should be limited so a pedestrian cannot gain access in this manner.
Consideration should be given to securing all fastening and hinge hardware by peening or welding to prevent disassembly of fencing and gate components where warranted by the required level of protection.
Lighting on the fence line will often have limitations from various AHJs. Light pollution onto adjacent properties is a challenge. Lighting along fence lines should use LED luminaries, which require low power, provide long-life, allow for high color rendition index lighting, and good control of light spill. Lighting levels should consider the needs of response personnel and electronic detection equipment such as CCVE. Aim towards the unsecured side, which will illuminate attackers while leaving the responders less discernable in the light's glare.
Configure lighting for operation during dark hours to automatically illuminate in response to an alarm, or be controlled manually by security personnel. Locate photoelectric light sensors well away from the perimeter and shielded from any ground level light sources. This prevents "spoofing" of the sensor with a light source. These sensors also provide continuous adjustment to the changing sunrise/sunset times and automatically handle any situation, which changes ambient light levels. Continuous illumination can act as an effective deterrent and "triggered" lighting can let attackers know that they were detected.
Detection equipment must work in all weather conditions. Select the type of equipment considering heat and cold, rain, fog, and snow conditions. Place detection equipment in two possible zones, the approach area and on the fence itself. The equipment choices depend on the threats and must be evaluated along with the expected deployment environment.
Evaluate no-go areas near the fence determine if it is adjacent to a public area, road or sidewalk.
There may be situations that make certain types of sensing unreliable. Vibration sensors may not work well in proximity to an active railroad line. Buried sensors do not work optimally in all soil conditions. Line of sight technologies do not work in situations with uneven terrain. Taut wire sensors require seasonal recalibration caused by temperature swings affecting the tension. If snow collects against the wires, false alarms might occur when the snow melts and pulls on the lower wires.
Microwave sensors provide volumetric sensing and are a good choice for use between fence layers in a no-go area. The overlapping of individual transmitters and receivers is important so that there are no coverage gaps at the ends of each microwave field. Since they are a line of site technology, the deployment area must be flat with no depressions or ridges. These sensors are immune to most weather conditions, but can have reduced sensitivity in heavy precipitation. Microwave sensors have no location information along the sensing field.
Fence disturbance sensors are resistant to all weather conditions. They provide effective coverage year-round. Significant tension is required in the fence fabric in order to propagate vibrations through the mesh. Like snow removal, the higher the ratio of mesh to open areas, the more the wind will cause fence vibrations. This can generate false alarms if the sensitivity is too high or be ineffective at detecting an attacker if the sensitivity is too low. Newer vibration technology will detect if the disturbance is along most of the fence or localized and will automatically adjust the sensitivity reducing false alarms.
Infrared beam sensors have problems with fog and heavy precipitation. They must be overlapped to provide continuous coverage and only provide minimal location capabilities usually isolated to a single field. If the ground is uneven, a buried, terrain following detection system would be more useful.
Signage is subject to AHJ rules such as Heritage requirements. There may be specific requirements for the frequency, size and positioning of signs regarding trespassing and video surveillance. Signs on the secure side of a fence could act as a guide to response personnel and identify specific sectors or zones.
Wind may act upon a fence sign, and could adversely affect sensing equipment. Affix signs tightly to the fence fabric so they do not move independently and generate extraneous movement in wind.
The preparation of the ground for a fence is important in making the final product effective. Fence installations can provide dig resistance by either using a continuous foundation going several feet below ground level or adding a concrete or asphalt sidewalk adjacent of the base of the fence so that digging requires a long tunnel. Either of these methods require construction that is resistant to movement from frost heaving.
The ground along the fence line should drain well by ensuring the ground slopes away from the bottom of the fence. This area should be properly maintained as vegetation such as plants and shrubs can hide attackers. A surface that resists plants establishing themselves is ideal. The ground on either side of a fence without an anti-tunneling barrier should have compacted gravel to a depth of 300mm and extending at least 900mm on either side. This should eliminate the possibility of erosion or heaving of the fence and posts and prevent gaps from developing under the fencing. This is especially important where the fence fabric cannot be buried due to environmental conditions.
I have reviewed and hereby recommend GCPSG-009 () Security Fencing Considerations Guide for approval.
Shawn Nattress
Manager
RCMP Lead Security Agency
Date: March 16,
I hereby approve GCPSG-001 () &#; Equipment Selection Guide for Paper Shredders.
André St-Pierre
Director, Physical Security
RCMP
Date: March 16,
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