Risk Priority Number (RPN

Risk Priority Number (RPN): The risk priority number is the product of the severity (S), occurrence (O),and detection (D) rankings.

(S) x (O) x(D) =RPN

The value is between 1 and 1000 can be used to rank order the concerns in the process.
Engineering assessment for preventive/corrective action should be first directed at high severity, high RPN, and other items designated by the team.

The intent of any recommended action is to reduce rankings in the following order: severity, occurrence , and detection.

In general practice, when the severity is 9 or 10, special attention must be given to ensure that the risk is addressed through existing design actions/controls or process preventive/corrective action(s),regardless of the RPN. In all cases where the effect of an identified potential failure could be a hazard to manufacturing/assembly personnel, preventive/corrective actions should be taken to avoid the failure by eliminating or controlling the cause(s), or appropriate operator protection should b e specified.

After special attention has been given to severity rankings of 9 or 10,the team then addresses other failure, with the intent of reducing severity, then occurrence, and then detection.
Actions such as, but not limited to, the following should be considered:

1-To reduce the probability of occurrence, process and/or design revisions are required. An action-oriented study of the process using statistical methods could be implemented with an ongoing feedback of information to the appropriate operations for continuous improvement and defect prevention.

2-Only a design and/or process revision can bring about a reduction in the severity ranking.

3-The preferred method to accomplish a reduction in the detection ranking is the use of error/mistake proofing methods. Generally , improving detection controls is costly and ineffective for quality improvements. Emphasis must, however, be placed on preventing defects rather than detecting them. An example would be the use of statistical control and process improvement rather than random quality checks or associated inspection.



Articles from FMEA Third Edition DaimlerChrysler Corporation, Ford Motor Company, General Motors Corporation.