Methodology for Aircraft Crash Release Frequency Evaluation. - Continued

DOE-STD-3014-96

In this context, the word "could" should be taken to mean "is it mechanistically

possible, given the level of damage." The possibility that failures occurring away

from the material could cause system failures resulting in process accidents should

also be considered. Therefore, intersystem dependencies and support system

interactions should be explicitly evaluated. If there is any doubt about the answer

to any of the three questions listed in this step, the answer should be assumed to

be "yes." If, for the given crash location, the answer to any of these questions is

"no," the scenario can be designated as a nonrelease scenario and eliminated from

further consideration.

Step 5. If the scenario has not been eliminated (i.e., the analysis has shown that it could

lead to a release), calculate the impact frequency by rerunning the four-factor formula for

the appropriate aircraft subcategory, using facility dimensions specific to the impact

location associated with the scenario. The analyst will need to better define the location

as an area (rather than just a single point) where impact could result in the release

scenario. This requires judgement and consultation with the analyst(s) who conducted the

structural response evaluation. Use this information to develop a set of "scenario facility

dimensions" that represents what the target would look like if it encompassed an area

equal to the target area associated with the release scenario being evaluated. Credit

should be taken for shielding effects from other facilities to further reduce the scenario

facility dimensions (Appendix B, Section B-4). The development of the scenario facility

dimensions should be well justified and documented in detail. Once these dimensions

have been established, run the appropriate four-factor formula to calculate the scenario

release frequency.

Step 6. Repeat Steps 1 through 5 for all of the impact locations that exceed the structural

response guidelines. Adding together the scenario release frequencies from each pass

through Step 5 gives the final release frequency for the evaluation step.

Step 7. Compare the final release frequency value to the guideline. If the guideline is

met, no additional analysis of aircraft impact is required. If the guideline is not met, a more

detailed analysis of the exposure associated with each release scenario needs to be

performed in accordance with Section 7.3 of this standard. For the purpose of that