Failure mode and effects analysis (FMEA)
Posted by isoeasy on May 11, 2006
Failure mode and effects analysis (FMEA) is a method that examines potential failures in products or processes. It may be used to evaluate risk management priorities for mitigating known threat-vulnerabilities.
FMEA helps select remedial actions that reduce cumulative impacts of life-cycle consequences (risks) from a systems failure (fault). It is used in many formal quality systems such as ISO/TS 16949.
FMEA is most commonly applied but not limited to design (Design FMEA) and manufacturing processes (Process FMEA).
Design failure modes effects analysis (DFMEA) identifies potential failures of a design before they occur. DFMEA then goes on to establish the potential effects of the failures, their cause, how often and when they might occur and their potential seriousness.
Process failure modes effects analysis (PFMEA) is a systemized group of activities intended to:
> Recognize and evaluate the potential failure of a product/process and its effect,
> Identify actions which could eliminate or reduce the occurrence, or improve detectability,
> Document the process, and
> Track changes to process-incorporated to avoid potential failures.
The basic process is to take a description of the parts of a system, and list the consequences if each part fails. In most formal systems, the consequences are then evaluated by three criteria and associated risk indices:
1. severity (S),
2. likelihood of occurrence (O), and (Note: This is also often known as probability (P))
3. inability of controls to detect it (D)
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Each index ranges from 1 (lowest risk) to 10 (highest risk). The overall risk of each failure is called Risk Priority Number (RPN) and the product of Severity (S), Occurrence (O), and Detection (D) rankings: RPN = S × O × D. For a failure with a severity of 6, a detection of 3 and an occurrence of 6, the RPN will be 108 (6 * 6 * 3 = 108). The higher the RPN, the more attention that particular step of the process or that characteristic of the product should get.
The templates used for FMEAs are not always the same but the items above (Severity, Detection, Occurrence and RPN) should always be present since they are the basis for corrective actions.
Since the purpose of an FMEA is to forestall failures, after determining the list of potential failures and their RPNs, the next step should be the planning of the actions to take to avert their occurrence. The strategic actions to take are above all based on the nature of the failures but their preseance is contingent upon the RPN. After finishing the first phase of the FMEA, preventive tasks are assigned to stakeholders according to their aptitude, but the priority of execution should be subject to the RPN ranking.
All FMEAs do not follow the same pattern of Action Plans but the following steps are usually considered.
The recommended preventive actions are generally suggested by the FMEA team during a brainstorm session. It consists of all the suggested proceedings that need to be followed to prevent failures. The reasons for failures are multifaceted; every failure can have several causes, that is why recommended preventive actions are better generated by cross functional team.
Task owner and projected completion date:
The task owner is the person or people who have been assigned the task of mending the aspects of the product, process or design that is subject to failure. Even though the suggested preventive actions are the result of a collegial brainstorm, the task of executing the actions is performed at an individual or departmental level. A person or a group of people are selected and assigned the task of forestalling failures.
The projected completion date should also be determined to avoid procrastination and enforce accountability.