Understanding risk calculation methods in FMEA

The risk calculation method determines how the risk priority number (RPN) is calculated when a failure cause has multiple failure effects. Understanding these methods helps you choose the most appropriate approach for your FMEA analysis.

In FMEA, you can calculate risk using the following methods. Each method serves different business scenarios and offers specific advantages in risk assessment.

• Risk calculation using the highest failure effect severity When a failure cause has multiple effects, this method looks at all the severity values of these effects and picks the highest one. It then uses this highest severity value to calculate a single RPN. This means all effects of the same cause will show the same RPN value. This is the default method in FMEA.Example Consider a damaged filter seal causing two different effects where the highest severity is used for both the effects.
  Failure effects Severity Occurrence Detection RPN
  
  
  Engine damage due to dust penetration 10 4 5 10 × 4 × 5 = 200
  
  Reduced engine performance due to partial clogging 6 4 5 10 × 4 × 5 = 200

• Risk calculation using individual failure effect severity This method calculates risk separately for each effect of a failure cause. Instead of using one severity value, it considers each effect's individual severity to calculate its own RPN. This gives you different RPN values for each effect, allowing for a more detailed analysis of risks.Example Consider a damaged filter seal causing two different effects where individual severity values are used to calculate separate RPNs.
  Failure effects Severity Occurrence Detection RPN
  
  
  Engine damage due to dust penetration 10 4 5 10 × 4 × 5 = 200
  
  Reduced engine performance due to partial clogging 6 4 5 6 × 4 × 5 = 120
  
  Note This approach is applicable specifically while performing failure mode effect analysis within the formsheet.