as an aid to decision-making, so that with a combination of criticality and
severity, priority for action to mitigate or minimize effect of certain failures
may be set.
Relationship Between FMECA and Risk Analysis
Criticality combined with severity is a measure of risk, which differs from the
usually accepted measures of risk only in less rigorous, and hence often less
costly, approach to its evaluation. The difference shows not only in the
manner of prediction of the severity of a failure effect but also that far less
complex interaction between the contributing factors can be modelled in a
typical bottom-up procedure applied in FMECA. Also, FMECA usually results in
a relative ranking of the contributions to the overall risk, while a risk analysis
for a high-risk system generally aims at risk acceptability. However, for low-
risk and low-complexity systems FMECA may be a very cost-effective and
appropriate method. Whenever during the FMECA the likelihood of high-risk
effects is recognized it is advised that a probabilistic risk analysis (PRA) should
be used in preference to a FMECA.
Therefore, FMECA should not be used as the single basis for judging whether
or not the risk of a particular effect of a high-risk or high-complexity system is
acceptably small, even if the estimate of frequency and severity is based on
trustworthy data.
Summary Procedures for FMECA
See Appendix C1 for Summary Procedures for FMEA and FMECA.
Figures 18 show a simplified version of FMECA (sFMECA) and Figure 19 shows
an example of Asset FMECA.
Figure 18 : simplified Failure Mode, Effects, and Criticality Analysis (sFMECA)