Securing the Perimeter

July 7, 2004
New technology is smarter and more reliable, but are security personnel trained for today
Securing the perimeter has taken on a new importance in the age of suicide bombers. High-security barricades, like this hydraulically operated system from Delta Scientific Corp., are lowered to allow cars to pass. Raising it will stop the charge of a 10-ton truck dead in its tracks.
Redirock concrete blocks anchored by a steel cable provide discrete yet effective penetration against truck ramming attacks.
Taut wire fences announce their presence and use sophisticated electronics to help defeat intruders.
Southwest Microwave's Micropoint cable locates intruders by detecting vibrations caused by cutting or climbing. For More Information
Perimeter Security Sensor Technologies Handbook. Written by the Space and Naval Warfare Systems Center in 1997, it is an excellent survey of perimeter sensor technologies, including limitations and integration methods. You can find it at

Critical Information Protection (CIP) Resources is a Dept. of Homeland Security Website that contains links to Federal, state, and industry organizations looking at CIP protection issues.

The International Security Industry Organization (ISIO) is a major organization of security professionals at

Since 9/11, America's understanding of security has changed, says Dick Williams, the former Department of Defense security director and now a consultant based in Stafford, Va.

Organizations have taken information on building plans and construction contracts off the internet, says Williams. They have begun to treat office buildings as critical command centers. They have started doing detailed threat and vulnerability assessments for offices, factories, and critical infrastructure. They have increased surveillance, kept cars and trucks from getting too close to buildings and hired more security guards.

“Things are definitely changing,” agrees Moshe Levy, CEO of Hackensack, N.J.-based perimeter security manufacturer Safeguards Technology Inc. “But have they changed enough?”

“Look at airports,” says the animated Levy. “We spend hundreds of millions of dollars to protect the terminal, but the perimeter is wide open. It's like closing the doors in a house but leaving the windows open.”

“If you're a terrorist, you explode a bomb in a terminal and maybe kill 10 or 15 people. But at the 407 airports with no perimeter safety, you can go right onto the runway where the planes are lined up waiting to take off and create an explosion.”

Levy is just getting warmed up. He points to a November 2003 60 Minutes episode that told how Pittsburgh Tribune-Review reporter Carl Prine had waltzed into 60 large U.S. chemical plants without authorization in the two years since 9/11.

“There are 15,000 chemical plants in the United States, and they may have chemicals that can affect thousands or even millions of people if there's an explosion,” says Levy. “There are refineries. What about power plants? They could blow up a power plant and create a blackout that disrupts the economy.” Levy, a decorated former Israeli soldier, warns that 9/11 is just the beginning. “It's been three years since 9/11 and we've become complacent,” he says. “But the terrorists waited seven years between the first unsuccessful attack on the Trade Center and 9/11. They planned major attacks before the Israeli and Spanish elections. I hope I'm wrong, but I believe they will try again here.”

The solution, he says, begins at the perimeter.

According to Michael Rack, head of marketing for Senstar-Stellar Corp., which is owned by Israel's Magal Security Systems, Ltd., a good outdoor perimeter security system fulfills five basic functions:

  • Deterrence. It discourages access to clearly defined boundaries.
  • Detection. It sounds an early warning of unauthorized entry.
  • Delay. It slows intruders so security personnel have time to react.
  • Assessment. It includes procedures to determine if the alarm is valid.
  • Response. Security personnel must take action.

Most systems consist of three parts: (1) a physical barrier to deter and delay; (2) sensors to detect intrusion; (3) and security personnel to assess and respond.

A fence or concrete wall with a barbed wire outrigger on top are examples of physical barriers. Vibration detectors running along a fence or microwave and infrared detectors and video cameras behind a wall are examples of sensors. Ultimately, though, a man or woman will have to assess the alarm and decide how to respond.

Physical Barriers
The first piece in any perimeter security system is usually some sort of wall or fence. All do a good job of defining the perimeter, but vary in their ability to delay penetration. Someone could easily climb a conventional chainlink fence, by pushing their shoes into the space and spreading the wires.

Welded mesh fences are more secure. Their wires are spaced closer, so it takes longer to cut through. Intruders also find it harder to get a toehold, and the welds keep the wires from spreading apart. Expanded metal fences, whose sections are made from a single piece of slitted steel, also defend against climbing. Running an outrigger of razor or barbed wire along the top provides additional protection. For even greater security, razor mesh fences include barbs or razors welded to the wire.

While these fences define the perimeter, they are not likely to delay a truck barreling at them. There are several solutions to that threat, such as iron palisade fences and concrete barriers. They are effective but ugly.

Many managers of government monuments and business facilities want to disguise or downplay perimeter security. They have traditionally used concrete bollards (posts) and planters to block direct access and keep potential car and truck bombs far enough away to prevent serious damage. A number of new products now give them more options.

One of them comes from Redi-Rock International LLC of Charlevoix, Mich. It uses 1,400-pound concrete blocks shaped and colored to look like natural stone to form walls up to 7.5 feet high. Unlike natural rock, they are anchored by a steel cable running through them.

“Because of the cable, a truck bomb trying to break through would have to pull the mass of the entire wall and not just one area,” says company president Ben Manthei. He says the product is very price competitive when compared with poured-in-place concrete, and that he has received queries from airports, government buildings, and military bases.

Security gates have changed to meet increased threats as well. Some secure facilities now use heavy-duty sliding and hydraulic steel gates capable of stopping a speeding truck.

Because public buildings in cities are not easily fenced off, they are more vulnerable to blasts and attacks. Since 1995, when a bomb exploded in a truck parked in front of the Oklahoma City Murrah Federal Building, many security officers have sought to improve security.

“A particular challenge for public buildings is blast protection,” says Tom Gillette, a director in the Asset Protection Systems Div. of Radian Inc. (Alexandria, VA). “In facilities with free public access, it's hard to create a greater standoff zone. Instead, we try to control vehicular access. People have to park further away. In airports, for example, you can no longer park near the terminal. That's to mitigate a blast.”

Physical barriers have evolved only gradually. Sensors, on the other hand, have changed dramatically over the past decade. The use of high-tech electronics has made them smarter and more reliable. Still, like most complex systems, their use involves tradeoffs.

On one hand, users want alarms sensitive enough to detect intruders in darkness, dusk, rain, snow, fog and heavy winds. They must be able to pick up large, fast objects, like trucks, and also intruders crawling slowly on the ground.

A good outside sensor will hit the mark from 95-99 percent of the time, but will never reach 100 percent. Any sensor that sensitive would alarm due to small animals, debris, wind, blowing rain or snow, or even trees swaying in the summer breeze. These nuisance alarms do more than waste resources, warns Levy.

“You cannot keep sending guards back and forth or they won't believe in the system any more,” he explains. “If the alarm keeps going off on a rainy day, by the third time they will just shut down the system and pull the plug. We've seen it happen and then you don't have an alarm any more.”

Nor is any sensor infallible. A team of intruders can bridge a fence with ladders and no vibration sensor will detect them. They may be able to crawl under microwave sensors, or reduce their signatures on passive infrared (IR) sensors by wearing a wet suit. Or they may simply spoof a system by setting off a series of false alarms until security stops responding, then go over.

The most common way to deal with false alarms and smart intruders is to use layers of sensors and barriers. Highly secure facilities often use two fences: the first one keeps out wildlife and debris while the second one acts as a tripwire for rapid response. Another common solution is to use more than one type of sensor. An intruder who uses a ladder to avoids a fencemounted vibration sensor will stand out on microwave, IR or video surveillance.

There are many different types of sensors. They can be visible and even obvious, such as IR units and cameras mounted on fenceposts, or covert, such as units in trees or wires underground. They can also be passive, such as vibration and some IR detectors, or actively radiate energy

Vibration Sensors
Fences are often equipped with vibration sensors. These not only warn of intruders but can help pinpoint the location of a breakthrough. They usually consist of a metal or optical fiber wire strung along a fence.

There are many ways to do this. Strainsensitive devices produce small electrical signals when cut, climbed or spread. Fence vibration systems use electromechanical or piezoelectric transducers to detect the motion of a sensor wire. Taut wire sensors are microswitches that detect changes in tension in tightly strung barbed wire running between them. Fiber optic systems detect small changes in light running through a glass fiber when it breaks or bends.

These systems all have strengths and weaknesses. Most vibration detection systems are economical, easy to install and work well as long as the fence lines are well maintained. A swaying or sagging fence will set off alarms. So will animals and high winds, especially when accompanied by rain or snow. Some strain sensors are sensitive to electromagnetic interference (EMI).

Commercial vendors have found ways around some of these issues. DeTekion Security Systems Inc. of Vestal, N.Y., for example, has developed a cable that consists of magnetic wires that are precisely twisted to improve their EMI resistance. The wires are lubricated to move freely when disturbed. This creates a disturbance in the field created by sending electrical pulses down the cable. Timing when and where those pulses occur enables the system to pinpoint the site of the intrusion to within 5 feet.

Southwest Microwave Inc. of Tempe, Ariz., provides a similar system. “It can distinguish between a nuisance alarm caused by weather, wind-blown debris or a stray animal and permits quick assessment and response,” says company director of government and international project sales Terry McGhee. The system's strength is the software. If it sees a moderate disturbance along the length of the fence, it assumes it is caused by rain, wind or nearby vehicles. A more violent and prolonged disturbance could be an intruder. Software also enables users to calibrate the system to work even with fences that might sway in the wind.

Volumetric Sensors
Volumetric sensors are devices used to survey a clear area and detect movement. Microwaves are the leading volumetric sensors, says McGhee. Technically, they act like radar but operate at lower frequencies. Monostatic systems work like radar guns, using a single device sending and receiving the signal. They are usually used for short zones.

More common are bistatic units, which post transmitter and receiver on opposite ends of an area. Any movement between them triggers an alarm. By using several sets of bistatic units, it is possible to overlap coverage to eliminate dead zones below and to the sides of the transmitters. Bistatic transmitters can easily extend coverage to 1,500 feet or more.

Microwaves handle wind and rain but do not do well with snow, sand, moving vegetation and debris. Fluorescent lights and devices that generate electric fields, such as radio transmitters, large electric motors and generators, can interfere with signals. Microwaves have a difficult time picking up intruders who advance slowly and take cover behind such obstructions as metal dumpsters.

IR systems are often used inside fences. Passive IR detects body heat. Active IR works like the safety systems on garage doors. It shines a thin beam of light in a straight line to a transmitter. When someone walks through the beam, the alarm goes off. Systems require precise alignment and they are vulnerable to fog, heavy rain and blowing sand and dust. Intruders can tunnel under or climb over them, or grab onto the transmitter and receiver posts and vault over unless the site is carefully thought out.

Some sensors serve as covert tripwires. Geophones, for example, detect low-frequency seismic energy created by motion over the soil or asphalt above them. Underground glass fibers are sensitive to pressure. Coaxial cables with holes through their outer shield create an electrical field that detects motion above. All can be bridged, and all have limitations. Optical fiber, for example, will pick up pressure generated by trees stretching in the wind. Geophones require well-compacted soil. Coax can falter in snow and water.

“One of the best things to happen in detector technology is the ability of cameras to sense motion without sounding a false alarm,” says Williams.

Video motion detection (VMD) works by analyzing the thousands of pixels in a digital image for small changes that even a trained eye would never pick up. It then uses patternrecognition software to identify and track the direction of the motion.

Safeguards, for example, has introduced a VMD system developed by the Israeli Defense Force at a cost of $20 million. “It lets you know exactly where the intruder is so you can respond faster,” says Levy. “It can detect someone walking by at night in starlight, or a person in a white suit crawling over snow.” He plans to begin selling the system after it completes performance testing at Sandia National Laboratory.

VMD is important because it helps overcome the biggest problem with closed circuit television (CCTV): boredom. “Studies show the human mind wanders every 20 seconds and can't concentrate for long periods of time,” says Williams. “The technology compensates for that. If I have a guard watching 30 consoles and someone flashes past, would they see it? They might or they might not. But if the video detects the motion automatically, they would know where to look.”

Gillette is not a particular proponent of exterior VMD because of its potential for nuisance alarms. “It works better for more controlled environments,” he says. VMD advocates, on the other hand, claim they have made great strides cutting down on false alarms. Gillette, however, does admit that accurate motion tracking is a powerful tool for assessing a situation.

Because sensors all have weaknesses, they are often combined to improve their likelihood of detection and reduce the vulnerability to defeat. For example, microwave systems often back up vibration alarms on a fence. A concrete wall might contain taut barbed wire on top and video surveillance around its boundaries. Passive IR is often combined with monostatic microwave.

Yet no matter how much technology a site puts in place, someone, somewhere is going to have to assess the situation and respond to it. Instead of trying to circumvent sophisticated sensors, criminals and terrorists often attack people and procedures. They may set off what look like false alarms to try to degrade security's trust in its alarm system, or set off many alarms at once and try to break through during the confusion.

Stevan Layne, a well-known consultant in Dillon, Colo., is not very confident about what happens then. “A site is only as well protected as the professionalism of the people protecting it,” he says. “You can put alarms on all the doors, video throughout the building and light up the perimeter, but if the security guy behind the desk is reading a magazine, it does you no good.”

In doing security evaluations, Layne has found a very broad range of responses. “I went to visit a supposedly secure facility with lots of high-value items inside located in a metropolitan area,” he recounts. “The facility had a contract security force and an extremely expensive electronic security management system with video surveillance and access controls.

“The building was closed to the public. I went around back, knocked at the outer door in the rear and told the guard I was there to meet somebody. Security just let me walk right in. I wasn't even wearing a tie. There was a major robbery of artwork in Boston where security just opened a door in the middle of the night for two guys dressed as Boston cops.

“The level of protection directly relates to the level of training given to people in charge of security,” Layne continues. “Compared with Australia, New Zealand or even Great Britain, we pay our guards less and only a few states and municipalities require mandatory training. And with those training programs I personally reviewed, either the programs or the results would not cut it in industry.”

Some contract security agencies, such as Allied Security, Wackenhut and Guardsmark, have outstanding training programs. Others do not. Some security firms claim they have training programs, but they consist almost entirely of videos and on-the-job training. Many facilities that hire their own guards do the same because they do not have the budget or staff to provide effective training.

“Up until a few years ago,” says Layne, “that might have been all right. It's not all right now. We're seeing a higher level of threat than ever before, and we're not prepared to meet it.”

Layne certainly agrees that things have changed greatly since 9/11. Surveillance equipment has grown smarter and more reliable. More facilities are controlling access and monitoring their perimeters. But it still comes down to people.

Layne wonders, “Is a guy who is making $7 an hour going to step in front of a truck carrying a bomb?”

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