It is common practice in organizations where Failure Mode Effect Analysis (FMEA) is used as a quality improvement tool, to set thresholds on the Risk Priority Numbers (RPN’s), above which actions should be taken to reduce the RPN. I don’t believe that setting such thresholds is good practice. I propose instead that responsibility should be placed on the team to decide whether action is appropriate. In the event that the team decides that it is not necessary to take action on a particular identified cause of the failure mode, then the team leader should sign off on this decision on behalf of the team; i.e. the team will take responsibility for proposing no corrective action be taken, should that be the decision.
The reality is that the choice of the values (Severity, Occurrence, and Detection ratings) which go to make up the RPN is very much based on the judgement of the team members, and there is wide scope for variability in the values that will be chosen. It is a virtual certainty that if two teams with identical backgrounds are given the same failure mode to analyse, even if the causes are agreed among them, they will come up with different RPN’s. That is the nature of FMEA. In these circumstances, I don’t believe it makes sense to have fixed RPN thresholds for action on causes. One of the teams may well have RPN’s below the threshold whereas the other team working on the same failure mode may not.
I think there tends to be too much emphasis and reliance on the RPN values in FMEA in making decisions on whether or not corrective actions should be implemented. I believe the real benefit of the FMEA is the intense discussion that takes place between the team members. I believe that by the time the team has reached the stage of calculating the RPN, the discussion that has taken place up to that point should be sufficient to inform the team’s decision on whether or not corrective action is to be taken, and the responsibility for the decision, should rest with the team.
Learn more about FMEA techniques by attending our Failure Mode Effect Analysis training course.