Occurrence ( O ) : Occurrence is the likelihood that a specific cause/mechanism of failure will occur.The likelihood of occurrence ranking number has relative meaning rather than an absolute value.Preventing or controlling the causes/mechanisms of failure through a design or process change is the only way a reduction in the occurrence ranking can be effected.
Table 2. Suggested Process Failure ‘s Occurrence Evaluation Criteria
| Probability | Likely Failure Rates | Ranking |
| Very High : Persistent Failures | ≥ 100 per thousand pieces | 10 |
| 50 per thousand pieces | 9 | |
| High : Frequent Failures | 20 per thousand pieces | 8 |
| 10 per thousand pieces | 7 | |
| Moderate: Occasional Failures | 5 per thousand pieces | 6 |
| 2 per thousand pieces | 5 | |
| Low: Relatively Few Failures | 1 per thousand pieces | 4 |
| 0.5 per thousand pieces | 3 | |
| Remote:Failure is Unlikely | 0.1 per thousand pieces | 2 |
| ≤0.01 per thousand pieces | 1 |
Articles from FMEA Third Edition DaimlerChrysler Corporation, Ford Motor Company, General Motors Corporation.
