For the evaluation of failure modes, using the usual parameters
of the FMEA, the frequency O, which characterizes occurrence failure
modes, the severity S characterizes the duration of the outage
caused by the failure mode detectability and D, which characterizes
the probability of detecting the failure before it starts to take
corrective or preventive actions. From the three previous parameters,
we define C criticality or risk priority number RPN, which is
calculated by the product of three factors O, S and D. It allows analyzing
the risk and setting the threshold of acceptability for each
failure mode [12].