Methodology for Aircraft Crash Release Frequency Evaluation. - Continued

DOE-STD-3014-96

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