Risk evaluation considering common cause failures in FMEA

Common cause failures (CCFs) are potentially critical contributors to the failure of redundant systems. Hence, correct evaluation of failure risk is an important part to mitigate system failure. FMEA (failure mode and effect analysis) is risk evaluation tool, risk priority number (RPN) is used to evaluate risk of failure, but RPN may not be suitable in evaluating risk of CCF due to its qualitative assessment. To quantify risk of CCF, this study focused on follows: (i) CCFs were identified systematically using fault tree (ii) Critical importance (CI) was adopted to measure risk of failure precisely (iii) New risk priority metric (RPM) is proposed based on CI, occurrence probability, and detection probabilities. Finally, new approach is demonstrated with an example.