Occurrence
How is the Occurrence score differentiated from 'Current Likelihood' in RCM?
Occurrence in FMEA/PFMEA is a scored probability (1–10) based on historical frequency, whereas RCM 'Current Likelihood' is the specific failure frequency with existing preventative maintenance plans in place.
What is the standard time window for calculating Occurrence?
Typically 3 years of work order history is used to count failure events for the 1–10 FMEA scale.
How does Occurrence drive 'Bad Actor' identification?
High Occurrence scores combined with high Severity identify bad actor candidates (chronic failure modes) for Root Cause Analysis (RCA) to minimize recurrence.
What is the threshold for a 'High' occurrence rank?
Rank 7 corresponds to a 1/100 failure rate (High failure rate), while Rank 1 is 1/10,000 (Remote probability).
Occurrence is a numerical score (1–10) in FMEA and reliability engineering that represents the likelihood or frequency of a specific failure mode, calculated from historical work order data and manufacturer reliability stats. It is used to compute the Risk Priority Number (RPN) = Severity × Occurrence × Detection for prioritizing corrective actions.
In shop floor maintenance, reliability engineers use Occurrence to prioritize corrective actions by analyzing breakdown records from the CMMS. They count root cause events for a specific asset and failure mode over a defined period (e.g., 3 years) to assign an Occurrence score. This score, combined with Severity and Detection, forms the RPN, which guides decisions on which failure modes to address first. High Occurrence scores, especially with high Severity, identify 'bad actor' candidates for Root Cause Analysis (RCA) to minimize recurrence. Accurate Occurrence scoring relies on proper failure code tagging and recurrence analysis, avoiding guesses or manual errors.
Dormant CMMS Data: Failing to use recurrence analysis to surface repeats, leaving intervention history 'dormant' and preventing accurate occurrence scoring.
Manual Tagging Errors: Relying on technicians to manually select failure codes without strict validation rules, causing occurrence counts to be inaccurate or inconsistent.
Unscored Root Causes: Assigning Occurrence scores based on guesses or experience rather than pulling documented failure frequency from the CMMS, leading to misrepresentative RPNs and wrong prioritization.