APPENDIX D (Continued)
systems will be completely destroyed. Death of personnel should be minimized, but injury level
will be high. The use of Fragment-Retention Film (FRF) is not effective at this level. The use of
blast-resistant glazing could increase damage levels to the structure.
Extended Disruption, Repairable. In this level, buildings are designed and sited for
moderate protection against an explosive threat. The building will be damaged, but damage will
be controlled and limited. The building will be out of service for an extended time (i.e., months
or years), but will probably be repairable. Death and injury of personnel should be minimal at
this level. All glazing systems will fail, but the use of FRF will limit injury by retaining glass
fragments. Some frame failure will also occur. Blast-resistant glazing could be used, depending
on the structural design and explosive-loading conditions.
Repairable. This level refers to buildings designed and sited for high-level protection
against an explosive threat. The building will be damaged, but damage will be more controlled
and limited, so the building will be repairable in a matter of weeks or a few months. Most of the
glazing systems will fail, but will remain anchored to the frame and wall. Blast-resistant glazing
could be used, depending on the structural design and explosive-loading conditions.
Quickly Repairable. These buildings are designed and sited for a very high level of
protection against an explosive threat. Damage will be very limited. Most functions will be
restored in a brief time, and the building will be fully operational in a matter of weeks. Some
glazing systems will still fail, mostly on the blast side, but will remain anchored to the wall and
frame and will resist the effects of the design basis threat.
Essentially Operable. In this level, buildings are designed and sited for maximum
protection against an explosive threat. The damage will be superficial. All functions will remain
operable without significant interruption. Windows and frames are designed to withstand the
applied pressures without failure. Allowing the glazing to fracture, while being retained in the
frame, is a cost-effective alternative at this level.
Range of Threats. Based on the desired performance goals and threat, a structural
engineer can define a set of response limits for the structure. Designing for operable/repairable
construction can be very costly. Construction required to protect against a large explosive threat
at close range would normally take the form of fully blast-hardened, bunker-type construction.
For the above performance levels, there may be a range of possible threats. These are
Maximum Event. This is the largest explosive threat, expressed as net equivalent
TNT charge at a specified standoff distance.