A New Line on Perimeter Security
The Pease Air National Guard Base in Portsmouth, N.H., had a perimeter security problem. As an air refueling station for the Air Force, Pease stores four million gallons of jet fuel in two large tanks located on base property. Each tank occupies the space of a three-story building. Even if the words “Jet Fuel” were not painted on the sides of the tanks, their size and shape would be impossible to miss.
For years, a conventional fence has surrounded the two-mile perimeter of the tanks, where base guards patrol. But fences and guards do not provide enough protection in today’s uncertain security climate. Reliable perimeter security also requires technology capable of instantly sensing and locating intrusions.
Perimeter security technology has always been an expensive and problematic undertaking. Closed circuit television (CCTV) systems have traditionally required constant — and constantly attentive — monitoring. A second option is motion detection devices, but they tend to set off alarms when animals approach or brisk breezes blow through. Combining the two technologies to overcome the problems of each can make for an expensive and complex system requiring continual maintenance and adjustment. A third option, buried coaxial cable, also tends to catch a lot of animals — and the cost is high.
After considering these technologies, officers at Pease ran across a product developed by Sandia National Laboratories and Fiber Instrument Sales (FIS) Inc., a fiber-optic company based in Oriskany, N.Y. Called Fiber Fence, the perimeter security technology mounts all-weather fiber optic cables on the outside of a chain link fence. At Pease, a Fiber Fence 1000 system loops three cables around the fenced perimeter of the fuel tanks. The loops trace around the top, middle and bottom perimeter of the fence. A control unit in the base security station connects an optical time domain reflectometer (OTDR) to the fiber loops. The OTDR shoots rapid pulses of infrared light through the glass strands in each of the three cables.
At 50-foot intervals along the fence, each loop of cable passes through boxes the size of clock radios. Called mouse-trips, the boxes contain spring-loaded arms set just below the cable. If someone attempts to cut through the fence, the physical vibration will trip the spring-loaded arm, which crimps the cable and alters the flow of light.
Back at the control unit, the OTDR senses a change in the light moving through the fiber, calculates the distance from the control unit to the change and displays a distance on a screen. A read-out of 2,000 feet means that something has set off the mouse trip at that distance from the control unit.
According to Lieutenant Colonel Scott Normandeau, communications flight commander at Pease, the Fiber Fence system has proven economical. “We installed it for about $10,000 a mile,” he says. “So we have $20,000 in it. That’s not much. Another important benefit is that Fiber Fence requires no power. The mouse trips are simple mechanical devices that trigger when the fence moves. So we haven’t had to go to the trouble or expense of installing power.”
The system triggers an alarm when someone climbs the fence, cuts the fence or bumps the fence trying to crawl underneath it. It has required a few adjustments, however. “We had to figure out how to set the tension on all the trips so that things like wind and ice storms don’t alarm the system,” Normandeau says.
The fiber has broken several times when tree limbs have fallen on the fence or when contractors have backed into it. “The alarm has gone off each time that’s happened,” Normandeau continues. “And that’s what we want. It lets us know that the system works. Repairing the cable is no big deal. We repair the fiber ourselves.”
More important, the Fiber Fence installation has freed Pease security personnel from patrolling the fuel tank fence line.
According to Mike Cammiso, test equipment manager and installation specialist for FIS, Fiber Fence is available in three models. Pease purchased Fiber Fence 1000, the mid-range model. A smaller system, designated the 100, is designed for small perimeters, the size of a utility substation, for example. “The 100 gives you an alarm, but no distance calculation,” Cammiso says. “But you don’t need to know the distance in a small perimeter, you just need to know there’s a problem.”
On the high end, the Fiber Fence 2000 can monitor up to 30 kilometers or 18.5 miles. Unlike the other two systems, the 2000 does not require a fiber loop that flows out of the control unit and back to the control unit. “The 2000 just has fiber going out,” Cammiso says. “The technology that comes with the 2000 also enables you to put digital pictures or bit maps of your site into the system. When an intrusion occurs, the visual pops up on a monitor showing an icon of that location.”