Risk Priority Number
The Risk Priority Number (RPN) is a numerical scoring metric used in Failure Modes and Effects Analysis (FMEA) to quantify and prioritize risk by multiplying three factors: Severity (S), Occurrence (O), and Detection (D). Each factor is rated on a 1 to 10 scale, yielding a total score from 1 (negligible risk) to 1000 (maximum risk).
In shop floor maintenance, RPN is applied within CMMS platforms like ServiceGrid to rank asset failure modes by criticality. Maintenance teams input S, O, and D ratings for specific failures, generating an RPN score that automatically prioritizes assets. High RPN scores trigger priority work orders, directing reliability engineers to address safety hazards, production losses, or costly downtime before medium- or low-risk items. This converts subjective engineering judgment into an actionable ranked list, enabling planners to allocate resources to the most critical corrective actions first, optimizing maintenance efficiency and reducing unplanned downtime.
Why is RPN criticized in modern reliability engineering?
RPN is criticized because the multiplicative formula can mask critical severity; a failure with Severity=10 (safety hazard) might have a lower RPN than a non-critical failure with high Occurrence/Detection, leading to dangerous prioritization errors.
How does RPN differ from Risk Priority Code (RPC)?
RPC often uses non-multiplicative logic (e.g., separate tables for S, O, D) to avoid the masking effect of RPN, providing a more accurate reflection of high-severity risks.
What is the standard scale for RPN components?
The industry standard is 1–10 (ISO/AIAG), though some organizations use 1–5 scales; the scale must be consistent to ensure valid comparisons across assets.
How is RPN integrated into predictive maintenance strategies?
High RPN failure modes are targeted for predictive maintenance (PdM) sensor deployment, while low RPN modes may remain on preventive lubrication schedules, optimizing asset reliability budgets.