Passive, Non-Lethal and Lethal
Types and Methods of Implementation
(this is all very academic)
(more information to be added, I just never know how much I’ll add)
Passive Barriers and Walls
There are a number of types of walls or barriers that might make for a good fence. Two very important factors in determining the construction method is the terrain and the ambient conditions. As an example, the barrier used in a hot and dry desert climate would be far different from one used in a jungle, a mountain range or a temperate forest. Seasonal changes dramatically impact the use of barrier systems.
Combinations of basic systems are generally used to provide reasonable difficulty, preventing easy passage past the barrier. Items like height, friction, surface hold points at connecting members are taken into consideration to prevent scaling the barrier. In many cases, poured concrete foundations are used to assist against tunneling. Depending on necessity, based on security requirements, anything from barbed wire to concertina loop wire might be strung along the crest to increase the amount of deterrent.
Link fences of the ‘tight mesh’ or “un-cut-able” variety have become popular. These fences are easy to erect but require a solid foundation to prevent passage under the fence. They are less expensive than concrete or steel walls and have lower maintenance cost rates, especially when they are coated in a rubberized compound (to prevent oxidization and decay). The drawback of course is that the foundation must be continuous and the fence secured at the base. In addition, in order run a crest deterrent such as concertina (loop), an additional horizontal brace or support member must be used between the poles supporting the fence.
Crest Deterrent Types
- Piano Wire - This is a thin stainless steel capable of cutting tissue (much like a garrote) and is generally strung between fastening points at the fence poles in either a vertical or angular fashion. This type of deterrent provides a low level of security.
- Barbed Wire - This is a medium thickness galvanized steel double wire twisted to produce “barbs” at a symmetrical distance, point to point. This is a reasonable deterrent for most low security applications dependent on the manner deployed, eg. the number of strung lines, their tension, spacing and angular orientation to the fence.
- Concertina - Also know as “barb-tape” or “razor-wire” due to its razor sharp formed barbs and heavy rolled tubular loop construction, formed in a horizontal spiral pattern. In a medium to high security application, this product fits nicely. If constructed properly, a concertina fence will drop into itself under heavy assault and if constructed of stainless steel, can even jam tank treads.
- Deterrent Stringing - The construction of a secondary deterrent in the case of piano wire or barbed wire is very straight forward. The lines are strung with reasonable tension (to keep them parallel to the fence) between fasteners attached to the fence poles or supports. In the case of concertina, which is a loop, mounting on the crest of a new or existing fence is a little more problematic. Concertina must be secured at the bottom of every loop in such a manner as to prevent the concertina from falling sideways. In many cases a second single wire can be run on the inside of the top of the concertina and fastened between poles to insure vertical stability. Again, the loops should be attached to the top wire to insure mounting integrity.
- Disabling - There are many disabling features, regardless of which “packaged system” you use, always include a kill switch tied to a relay and your ECM or ignition system.
- Protected Power Sources - For alarms, keep a spare battery in the trunk that runs the security system. This is also a nice touch if you need to boost your vehicle from behind.
- Restrictive Access - The addition of restriction plates can be helpful near your battery and any security devices that can be accessed from under the vehicle.
- High Voltage Blankets - A wire grid blanket can be mounted in security sensitive areas under the hood. This blanket system will shock and/or disable a would-be thief.
- Catching a Thief - One method that was used was to string additional fishing wire with fishing hooks around the battery and/or security equipment. A would-be thief would attempt to disconnect the battery and once done on trying to remove his/her arms would find that they were trapped as the fishhooks dug in. This won’t deter a potential thief as they don’t know the hooks are they, but they probably won’t get away.
Voltages and Current Used
- Ranges and Reasons - The HV Blanket system uses a multiple horizontal loop of hot wires and returns and a small 12vdc to 10,000vac PWM boost system. Energy output is limited to a maximum of 20 joules to stay below lethal thresholds.
Electrified Non-Lethal Barriers
The construction of an electrified deterrent system is much the same as any perimeter barrier as outlined under “Passive Barriers” with the exception that secondary and/or tertiary systems will be employed to perform electrification and/or detection. In all systems, electrically energizing a fence or hot wires requires isolation from ground.
- Wooden Fence - These can be electrified by stringing the ‘shock wire’ mounted on glass insulators. Wood, especially wet wood is not a good insulator and creates high reactance to ground.
- Link Fence - A metal link fence can be properly electrified by isolating the fence poles and fence itself from ground. If there are ground points (faults) along the fence however, electrical energy will be channeled to ground based on the reactance of the ground connection. This of course will become more prevalent during ambient conditions involving moisture (rain and snow).
- Isolated Wall or Fence - As with the “Wood Fence” isolators are used. This can be set up as a barrier wall of strung electrically active wires or on the peak of a fence or wall.
- Wall Peak/Top Mounted - Again, this is an isolated system that uses electrical insulators, generally made of glass to isolate the active wires from the balance of the fence.
- Interior Attic/Roof Space - Wires are strung back and forth alternating between, hot and return path wires with a spacing of about 1 foot horizontal and 6 inches vertical. The spacing creates a semi-impenetrable maze of electricity preventing someone breaking through your roof, from gaining entry to your building through an attic.
Voltages and Current Used
- Ranges and Reasons - Bear in mind that current kills. Once the skin has been breached even a small amount of current can kill a person. Non-lethal system voltages can range from 1,000 volts to 100,000 volts as long as the amount of energy delivered follows specific rules. The amount of energy required to cause a lethal arrhythmia can be 50 to 300 joules and energy transfer efficiency is a function of skin resistance. Cooking cells is simply based on i=e/r. Assuming a watt/second rate or joules, the maximum energy to safely shock or disable a person would be 25 joules (or 25 watt/sec). Current limiting is done in the boost circuit to prevent excessive currents from entering a target. One method to limit current is to collapse the boost transformer’s magnetic field during lower resistive/higher current loads, this is a transformer design consideration. A secondary method is current limiting systems that are employed electronically to stabilize the maximum output current. Resistors, although they will provide current limiting also act as 1/2 a voltage divider circuit which of course lowers the output voltage to the target.
Electrified Lethal Barriers
The construction of an electrified deterrent system is much the same as any perimeter barrier as outlined under “Passive Barriers” with the exception that secondary and/or tertiary systems (or more) will be employed to perform electrification and/or detection. In all systems, electrically energizing a fence or hot wires requires isolation from ground.
- Supported Concertina Loops - In this case the loops are secured to a base and top line at each loops intersection point. The supporting wires are adjusted with tension between fence posts too keep them true to the direction of the fence. Hot wires are strung on insulators in the center of the concertina loops to protect the hot wire from accidentally being touched. We used 3,300 volts at 1 amp AC or 3,300va
- Self Supporting Concertina Loops - In this case, the bottom loops are supported in a formed concrete tray or the loops are linked through small “loop fasteners” horizontally. The next two loops are supported only by the bottom 3 loops. The top loop is semi supported by the two loops below. Any additional loops on top of the 3rd level loop require a “supported’ type connection as above. Hot wires are strung on insulators in the center of the concertina loops to protect the hot wire from accidentally being touched. We used
3,300 volts at 1 amp AC or 3,300va (4,000va max)
- Active Wall - Hot wires are strung with tension on insulators between fence posts
- Wall Peak/Top Mounted - Hot wires are strung with tension on insulators between fence posts generally with an angular deviation from vertical. We used 3,300 volts at 1 amp AC
or 3,300va (4,000va max)
- Interior Attic/Roof Space - Wires are strung back and forth alternating between, hot and return path wires with a spacing of about 1 foot horizontal and 6 inches vertical. The spacing creates a semi-impenetrable maze of electricity preventing someone breaking through your roof, from gaining entry to your building through an attic. Hot wires are used in all cases coming of an AC boost transformer (we used 4000v at 1800va AC).
Voltages and Current Used
- Ranges and Reasons - A good rule of thumb for lethal systems is 3 times the normal maximum number of joules required or around 900 joules (900 watt/seconds) per potential intruder. Since “groups” trying to enter a facility are usually limited to 2 or 3 persons, in an attempt to avoid detection, one can assume a lethal energy of around 1800 to 2700 joules. Inclement weather will effect the way the fence and its current is passed to a potential intruder. A 2700 joule fence could actually kill a few dozen people prior to being cleared enough to allow mass intrusion. This of course depends on a number of factors, the constant current circuit being used, the voltage used, the field collapse current of the boost transformer and is the weather wet or dry, etc.
Notes on Electrification
In all cases we used AC voltages for both non-lethal and lethal electrification solutions. There is a very simple reason for this, it’s called electrolysis, the migration of electrons. If a high voltage DC source is used in an electrified fence, electron migration occurs and the wire increases in diameter on one end, while shrinking on the other. Eventually the wire breaks. Even though it may be difficult and costly to produce an accurate detection system (later in the web page), it is considerably more costly and difficult to restring a 5 to 50 mile long fence. Another interesting effect in electrified fences is the voltage under varying ambient weather conditions. Voltages can be driven up and down by changes in barometric pressure and humidity. Although this doesn’t adversely effect the operation of the fence in performing its primary function, it can play hell with poorly designed detections systems.
So far, I imagine you can see a host of ways to circumvent basic systems. It will get a little more difficult as we delve deeper into the types of detection available and their deployment.