Environmental Engineering Reference
In-Depth Information
interior space of a facility by detecting an intruder who is attempting to enter
or who has already entered a room or building. In contrast, exterior intrusion
sensors are designed to detect an intrusion into a protected outdoor/exterior
area. Exterior protected areas are typically arranged as zones or exclusion
areas placed so the intruder is detected early in the intrusion attempt before
gaining access to more valuable assets (e.g., into a building located within
the protected area). Early detection creates additional time for security forces
to respond to the alarm.
Buried Exterior Intrusion Sensors
Buried sensors are electronic devices designed to detect potential intrud-
ers. The sensors are buried along the perimeters of sensitive assets and are
able to detect intruder activity both above and below ground. Some of these
systems are composed of individual, stand-alone sensor units, while other
sensors consist of buried cables.
Fences
A fence is a physical barrier that can be set up around the perimeter of an
asset. Fences often consist of individual pieces (such as individual pickets in
a wooden fence or individual sections of a wrought iron fence) that are fas-
tened together. Individual sections of the fence are fastened together using
posts, which are sunk into the ground to provide stability and strength for
the sections of the fence hung between them. Gates are installed between
individual sections of the fence to allow access inside the fenced area.
Fences are often used as decorative architectural features to separate phys-
ical spaces from each other and to mark the location of a boundary (such as
a fence installed along a properly line); however, a fence can also serve as an
effective means for preventing intruders from gaining access to a water or
wastewater asset. Many utilities install fences around their primary facili-
ties, around remote pump stations, or around hazardous materials storage
areas or sensitive areas within a facility. Access to the area can be controlled
through security located at gates or doors in the fence (e.g., posting a guard
at the gate or locking it). To gain access to the asset, unauthorized persons
would have to find a way either around or through the fence.
Fences are often compared with walls when determining the appropriate
system for perimeter security. Both fences and walls can provide adequate
perimeter security, and fences are often easier and less expensive to install
than walls; however, they do not usually provide the same physical strength
that walls do. In addition, many types of fences have gaps between the indi-
vidual pieces that make up the fence (e.g., the spaces between chain links
in a chain-link fence or the space between pickets in a picket fence); thus,
many types of fences allow the interior of the fenced area to be seen. This
may allow intruders to gather important information about the locations or
defenses of vulnerable areas within the facility.
