Читать книгу System Reliability Theory - Marvin Rausand - Страница 165

A systematic investigation of a failure or a fault to identify its likely root causes, such that they can be removed by design, process, or procedure changes.

The root cause analysis is reactive, starting with (i) a failure that has happened, or (ii) a potential failure that has been identified. The root cause analysis should continue until organizational factors have been identified, or until data are exhausted. Root cause analysis may be used to investigate a wide range of undesired events, not only failures and faults but also our description is delimited to failure/fault analysis.

The main steps of a root cause (failure) analysis are:

1 Clearly define the failure or fault. Explain clearly what went wrong.

2 Gather data/evidence. The evidence should provide answers to the following questions:When did the failure occur?Where did it occur?What conditions were present prior to its occurrence?What controls or barriers could have prevented its occurrence but did not?What are the potential causes? (Make a preliminary list of likely causes).Which actions can prevent recurrence?

3 Ask why and identify the true root cause associated with the defined failure/fault.

4 Check the logic and eliminate items that are not causes.

5 Identify corrective action(s) that will prevent recurrence of the failure/fault – and that address both proximate and root causes.

6 Implement the corrective action(s).

7 Observe the corrective actions to ensure effectiveness.

8 If necessary, reexamine the root cause analysis.

The root cause analysis is done by a team using idea generation techniques, such as brainstorming, and is often started by a cause and effect analysis link: (see Section 3.7.1). To identify root causes, it is usually recommended to ask “why?” at least five times for each main cause identified. The five whys are illustrated in Figure 3.14.

The root causes must be thoroughly understood before corrective actions are proposed. By correcting root causes, it is hoped that the likelihood of failure recurrence is minimized.

Figure 3.14 Repeatedly asking why?