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 MIL-HDBK-1013/1A
3) Wall Ventilators. All wall ventilators should be externally
shrouded using, as a minimum, 3/8-inch (9-mm) steel plate (see Figure 58).
The shroud should extend well below the bottom edge of the ventilator, and
the minimum possible distance should be between the wall face and the shroud
plate. It should be noted, however, that a solid steel plate placed in front
of the ventilator will restrict the air flow because of the blockage in front
of the open area. Compensation for this air flow reduction should be made.
The security engineer should determine whether the distance between the wall
face and the shroud plate and the shroud attachment mechanism permits the
required air flow. Internally, a cost-effective method of increasing
resistance is to use riveted steel grating, MIL-G-18014, Type A, Class B, cut
with a minimum 6-inch (150-mm) overlap on all sides of the ventilator
opening. Two installation techniques are shown in Figure 58. One technique
requires welding the steel grating to an existing steel frame surrounding the
vent. The other technique requires no welding. Flat steel bars, 1/4 by 2
inches (6 by 50 mm), drilled to accept 1/2-inch (13-mm) expansion fasteners,
should be used to hold the grating to the wall. Any concrete anchor meeting
the requirements of ASTM or military specifications may be used. To ensure
maximum pullout strength, the holes must be drilled carefully to ensure tight
fit of the fastener. The fastener must not be installed closer than 4 inches
(100 mm) to the edge of the concrete. The bolt should be welded to the
frame.
4) Roof Ventilators. Roof ventilators in older magazines may open
directly into the magazine ceiling or may open high on the rear of the
magazine wall. These ventilators should be protected through the internally
mounted vent covers. The light sheet metal and ceramic tile construction of
the older magazine vents precludes reinforcing the roof ventilators at any
point other than the inside opening. In concrete arch magazines, use of
riveted steel grating mounted as shown in Figure 59, similar to the technique
used for wall ventilators, can be used for enhanced penetration resistance.
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