Definition
In FMEA, the product of severity × occurrence × detection (1–1000 on a 1–10 scale; a 1–5 scale is calculated separately), used to rank risk priority. Because it is the product of three ordinal numbers with no physical meaning, it cannot be used alone as a criterion. The source material's requirement for severity 9/10 is "special attention"; putting high-severity items on a mandatory action list is an ABS adopted policy with a configurable threshold, not a universal hard rule.
In detail
Risk Priority Number (RPN) is a quantitative metric used in Failure Mode and Effects Analysis (FMEA) to rank risks, calculated as the product of Severity, Occurrence, and Detection, ranging from 1 to 1000 on a 1–10 scale (a 1–5 scale is calculated separately, and the two scales are not comparable). It helps teams identify which failure modes need priority attention, but because it is merely the product of three ordinal numbers, it has no physical meaning and cannot be used alone as a decision basis; the source material's requirement for severity 9/10 is "special attention," and ABS by default puts high-severity items on a mandatory action list with a customer-calibrated threshold, not a universal hard rule. RPN typically outputs a ranked list to guide subsequent improvement actions.
Example in practice
During the new product design phase, a cross-functional team uses FMEA to analyze potential failure modes. For each failure mode, they assess severity, occurrence, and detection, calculate the RPN value, and rank them from high to low (comparing only within the same scale). High RPN items are prioritized for improvement plans, while items with a severity of 9 or 10 are flagged for special attention as the source material requires, and the team then decides which of those must be acted on immediately using an internally calibrated threshold. The final output is a risk priority list that guides design changes and test resource allocation.