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Page Title: Methodology for Aircraft Crash Release Frequency Evaluation. - Continued
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This process is performed on each of the impact locations that exceeds the structural
response guidelines, following the steps listed below.
Step 1. From the results of the structural analysis, take the description of the level of
damage. This description will provide a conservative estimate of the structural damage
that has occurred, including the path and location of penetrators; the damage state of
walls, barriers, and equipment; the location of the aircraft fuel; and other pertinent
information, as described in Chapter 6.
Step 2. Assume that all available fuel burns, as well as any other combustibles that are in
the path of the penetrators. Assume also that any high explosive material undergoes a
high explosive violent reaction (HEVR). High explosive material includes such things as
TNT, ion exchange resins, and the like, but not highly flammable materials that are subject
to burning (i.e., prompt thermal releases) rather than true explosion (e.g., aircraft fuel,
hydrogen gas). Note that this assumption pertains only to combustibles and explosives
that are directly affected by the penetrators; that is, they are in areas or compartments that
are actually breached by the penetrators.
Step 3. Evaluate the extent to which secondary effects cause the scenario to spread
beyond the area directly damaged by the crash. Comprehensive guidance cannot be
provided for this step because situations will vary greatly from facility to facility. However,
these are some questions to consider:
Is there sufficient combustible material to breach additional barriers and spread
further through the facility? Remember that fire can also spread through ducts and
along wiring conduits. Credit can be taken for the existence of fire barriers and
breaks, if they have not been damaged by the crash. The basis for taking credit
(e.g., short duration of the fire) should be documented. Therefore, a
characterization of fire duration will almost certainly be required, although the level
of detail will depend on how much sophistication is required to determine the
duration of the fire relative to the capability of the fire barriers. Due to the difficulty
of demonstrating that active systems can function following a crash, credit should

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