The bottom of the fabric will extend to within 2 inches (50.8 mm)
of firm soil. Where stabilization of the soil cannot be accomplished, a soil
engineer should be consulted and involved in developing the fence specifi-
cation. In unstable or shifting soil such as sand, the fabric should either
be buried to compensate for the shifting soil or a minimum of 2 inches (50.8
mm) of the bottom selvage of the fence anchored in concrete curbs, sills,
hooked steel bars, or similar types of anchoring devices extending below
ground level as recommended by the soil engineer. (Frost levels should also be
considered when placing curbs, sills, etc.) Even in unstable and shifting
soil, the height of fabric and posts must be designed to assure that the top
of the fence fabric will be maintained at 7 feet (2.1 m) above existing or
anticipated ground level. This often may require that the fabric be 8 feet
(2.4 m) or greater, so that sufficient material is buried below the surface or
embedded in concrete sills.
At nuclear weapons storage facilities, the bottom 2 inches (50.8
mm) of the fabric will be encased in a 6-inch (152.4-mm) wide concrete sill
extending approximately 12 inches (304.8 mm) into the soil around the entire
perimeter. In areas where freezing is experienced, the curb must extend below
the local frost level for the facility.
Outriggers. Steel outriggers will be installed to conform with
RR-F-191/4 with their overhang facing outward (away from the protected site),
except where the fence must be mounted directly on the property line (instead
of at least 18 inches (457.2 mm) back), in which case outriggers can be
modified (with exception approval) to be vertical or angle into the site. As
a minimum, the outriggers will provide an additional 12 inches (304.8 mm) to
the fence height. The top guard fencing adjoining gates may range from a
vertical height of 18 inches (457.2 mm) to the normal 45-degree outward
protection, but only for sufficient distance along the fence line to open the
gates adequately. Outriggers will be permanently affixed to the fence posts
with screws or by spot welding.
Nuclear weapons storage facilities will have two steel outriggers
installed at opposing 45-degree angles along the top of the fence to form a
"V" or a "Y" configuration.
Secure all fastening and hinge hardware in place by
peening or welding. This allows proper operation of components, while
preventing disassembly of fencing components or removal of gates.
Special Security Features.
Clear Zones. Maintain unobstructed areas or clear zones on both
sides of, and between, physical barriers surrounding restricted and non-
restricted areas. These areas must be cleared of all vegetation and man-made
or natural obstructions that exceed 8 inches (203.2 mm) in height. All clear
zones will be clear of visual obstructions such as vines, shrubs, tree limbs,
electrical and telephone poles or junction boxes, steam pipes, fire hydrants,