Obscuration. Block sightlines with landscaping features,
obscuration fences, walls, or noncritical structures as illustrated in
Figure 62. Consider blocking sightlines with other less critical facilities
or earth berms. Obscuration fences include chain-link fences with slats
woven through the fence fabric, and wooden fences with minimal spaces between
planks. Many other types of fences also could be effective. However, the
fence must be constructed and located such that an attacker cannot easily
overcome the obscuration features of the fence. If trees are used as part of
the landscaping, or if they already exist near the fence, locate them at a
sufficient distance from the fence so that attackers cannot use them to scale
over the fence.
Building Measures. Building elements include the building's layout
and its walls, doors, windows, and utility openings. Since bullets are fired
from line-of-sight weapons, they ordinarily pose no threat to roofs.
Layout. To reduce exposure to bullets, house critical assets
at the center of the facility. If assets are effectively concealed, no other
protective measures are needed to protect critical assets for the low level
of protection. Locate bullet-resistant walls around assets, as shown in
Figure 63, to eliminate sightlines through doorways. This arrangement allows
conventional doors to be used while providing a complete hardened enclosure
around the asset. Arrange entryways to eliminate sightlines.
Walls. Wall construction is dependent upon the threat
severity. Representative examples of types of wall construction to defeat
each threat severity level are described in the following paragraphs.
a) Low level of threat protection. There are no specific
wall requirements for the low level of protection. Standard construction,
selected for other reasons, applies. Table 46 shows a representative list of
materials that could be used for the low-severity threat. Note that all of
the materials shown are standard materials that would be appropriate for new
construction. Any single material could be used. Or, if a combination of
materials is used, such as 4-inch (101.6-mm) grouted CMU with 4-inch (101.6-
mm) brick, increased ballistic resistance will result.
b) Medium level of threat protection. Table 46 shows
representative wall materials for the medium level of threat. Note that the
material thickness increases only slightly over the low-severity threat.
Only a 1/2-inch (12.7-mm) increase in thickness is required for reinforced
concrete and only an additional 1/16 inch (1.6 mm) is required for steel.
Even the bullet-resistant fiberglass thickness only needs to be increased by
1/8 inch (3.2 mm) to defeat the medium level threat.