b) Penetration times for existing stud/girt construction.
Estimated penetration times for the seven basic types of stud/girt walls are
all less than 2 minutes (see Table 39).
c) Retrofit options for medium-severity threats. Limited
data is available on retrofit options for hardening against medium-level
Table 40 shows the delay times achieved by adding 9-gauge (3.8-mm)
metal fence material, 1/4- to 3/4-inch (6- to 19-mm) thick plywood, 9-pound
(19-kg) expanded metal, or 3/16-inch (4.8-mm) steel plate to a wood panel.
d) Retrofit options for high-severity threats. The steel-
ply retrofit options shown in Figure 48 and Table 32 or the riveted or welded
steel grating shown in Figure 49 can be affixed to the interior of the stud-
girt wall to increase the effective delay time. See par. 18.104.22.168(1)(d) for
Roof/Floor Retrofit Construction for Low to High Threats