Safety Instrumented Systems Verification: Practical Probabilistic Calculations

Appendix E: Failure Modes Effects and Diagnostic Analysis (FMEDA)

Failure Modes and Effect Analysis (FMEA)

A Failure Modes and Effects Analysis (FMEA) is a systematic technique that is designed to identify problems. It is a "bottom up" method that starts with a detailed list of all components within the system. The overall objective is to identify design flaws, unexpected results, when components of the system fail. A whole system can be analyzed one component at a time.

Alternatively, the system can be hierarchically divided into sub-systems and modules as required. The FMEA can be done on each grouping in the hierarchy. A commonly used reference for the FMEA technique is MIL-STD-1629A (Ref. [1]). More recent standards include IEC 60812 (Ref. [2]) and SAE J1739 (Ref. [3]).

FMEA Procedure

The minimum steps required in the FMEA process are simple:

  1. List all components.

  2. For each component, list all failure modes.

  3. For each component/failure mode, list the effect on the next higher level.

  4. For each component/failure mode, list the severity (i.e., the failure mode of the higher level) of effect.

A FMEA can be very effective in identifying critical failures within a system. One of the primary reasons for doing this is so that the system design can be changed to mitigate, or reduce the likelihood of critical failures. For this reason, the best possible time to do a FMEA is during the design phase of a project. The FMEA should be done while design changes can still be made without disrupting the entire project. Ideally, the completed FMEA...

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