the FUNCTIONAL RESONANCE
Using a FRAM model for retrospective analysis (event analysis)
The common purpose of an accident investigation / event analysis is to find the causes for the observed outcome(s) (the injury). (In some methods, the purpose is even to find the root causes.) An accident investigation therefore typically starts from the observed (adverse) outcome, and traces the developments backwards in order to find out what went wrong or malfunctioned, i.e., the conditions (events) that were necessary and sufficient for the outcome to happen. The reasoning is usually contra-factual, such as: 'If X had not happened, then this (the accident) would not have happened. Therefore X is the cause of the accident.'
Accident analysis based on functional resonance
In consonance with the principles of Safety-II (q.v.), the purpose of a FRAM analysis is to identify how the system should have functioned for everything to succeed (i.e., “everyday” performance), and to understand the variability of functions which alone or in combination prevented that from happening. This is typically the variability that existed in the situation being analysed, but it could also be the variability that possibly might exist under other conditions.
A FRAM model describes a system’s functions and the potential couplings among functions. The model does not describe or depict an actual sequence of events, i.e., an accident scenario. The basic steps in building a FRAM model of the activity (or performance) that is to be analysed have been described here. The development of the model ended by describing the potential variability.
An accident scenario corresponds to an instantiation of the model. A FRAM model includes a description of the potetial variability of the functions. The instantiation is a “map” of how the potential variability became real (or actual) variability in a given situation. An instantiation shows how functions were coupled under given – favourable or unfavourable – conditions. The analysis of the instantiation of the FRAM model comprises the following steps:
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