Release Mechanism

DOE-STD-1027-92

Accident analysis consists of the four distinct elements highlighted in Figure 4.1: (1)

Release Mechanism Analysis, (2) Sequence Selection, (3) Engineering Analysis, and

(4) Consequence Analysis. Figure 4.1 displays the relationships between the

analysis techniques available to evaluate accident consequences, and the hazard

and complexity parameters associated with the graded approach. The decision

criteria blocks shown immediately after each of the distinct elements provide for

immediate consideration of the information learned in that step of the analysis. For

example, if the Release Mechanism Analysis identifies information concerning an

obvious flaw in the design or operation of a facility, immediate action should be taken

to correct the flaw, and the release mechanism analysis would be appropriately

modified. This same iterative consideration to correct problems identified in the

analysis would occur throughout the accident analysis process.

Thus, accident analysis is used not only to provide insight into the vulnerabilities in

the system, but also to improve the systems and reduce the consequences of

accidents. The following discussion highlights the four key elements of the accident

analysis.

Release Mechanism

This element provides the analysis for determining the vulnerabilities in the structures,

systems, and components to create conditions for or cause releases of hazardous

material. There are several Hazard Analysis techniques used to identify these

vulnerabilities. They range from simple techniques such as checklists to complex

techniques such as Hazard and Operability (HAZOP) Studies or integrated fault trees

and event trees. The analysis technique should be selected on the basis of the

significance of the potential hazards in the facility and the complexity of the processes

which could affect the hazard. A summary of the levels for the preferred analysis

technique as a function of the hazard and complexity of the facility is shown in Figure

4.1. The objective of the identification of release mechanisms is to provide an

evaluation sufficiently detailed to identify potential releases which could adversely affect

the worker, the public, or the environment. The results of the release mechanism step

are a comprehensive set of potential accident sequences which provide the basis for

the next element, sequence selection.