Methodology for Aircraft Crash Release Frequency Evaluation.

DOE-STD-3014-96

Step 2. From the list of impact frequencies compiled for the impact frequency evaluation,

delete the impact frequencies corresponding to the aircraft categories/subcategories

identified in Step 1.

Step 3. Sum the impact frequencies for the remaining aircraft categories/subcategories.

The calculated sum is the release frequency screening value.

Step 4. Compare the release frequency screening value to the guideline. If the guideline

is met, the safety risk associated with aircraft impact is below the level of concern and no

further analysis is needed; document the results. If the guideline is exceeded, proceed to

the release frequency evaluation (Section 5.5).

Methodology for Aircraft Crash Release Frequency Evaluation. The release frequency

5.5

screening does not take into account the fact that, even if a particular aircraft category or

subcategory can cause damage that could potentially lead to a release, only certain

impact locations will have that effect. By making better use of the structural analysis and

the impact frequency calculations, the analyst can define specific release scenarios and

estimate the frequency associated with those scenarios. This makes it possible to

determine the extent to which the actual release frequency may be lower than the initial

release frequency. This section addresses the evaluation process for making this

determination.

For each impact location which is determined in the structural response analysis to exceed

the structural response guideline, a release scenario associated with the level of damage

resulting from the impact should be developed. The intent is to specify the most realistic

conditions that can be justified. The scenario selected should be physically possible and

rational within the physical constraints of the level of damage incurred (including the

occurrence of process accidents as a result of system failures). Once it has been

determined that a release can occur, the overall facility dimensions used to assess the

impact frequency are replaced with a partial facility dimension representing the impact

location (a new effective area) for the specific release scenario. The new effective area is

input into the four-factor formula (Equation 5-1) for the appropriate aircraft subcategory,

resulting in a revised impact frequency specific to the impact location being evaluated.