Guide
FMEA Explained: Failure Mode and Effects Analysis
FMEA is a systematic method for identifying potential failure modes and their effects. Learn how to perform an FMEA, calculate the Risk Priority Number (RPN), and use the results to prioritise maintenance.
9 min readUpdated July 2026
What is FMEA?
Failure Mode and Effects Analysis (FMEA) is a proactive technique for identifying potential failure modes of a system, process, or product, assessing their effects, and prioritising actions to reduce risk. Unlike RCA (which is reactive — performed after a failure), FMEA is proactive — performed before failures occur to prevent them.
The FMEA Process
- Define the system: Break the equipment or process into components or steps.
- Identify failure modes: For each component, list how it could fail (e.g., bearing wears, seal leaks, valve sticks).
- Assess effects: What happens if this failure occurs? How does it affect the system, process, safety, and environment?
- Rate severity (S): How bad is the consequence? Scale 1–10 (1 = negligible, 10 = catastrophic).
- Rate occurrence (O): How likely is this failure? Scale 1–10 (1 = very unlikely, 10 = certain to occur).
- Rate detection (D): How likely are you to detect it before it causes harm? Scale 1–10 (1 = certain to detect, 10 = cannot detect).
- Calculate RPN: Risk Priority Number = S × O × D. Range: 1 (low risk) to 1000 (extreme risk).
- Prioritise actions: Address the highest RPN items first.
Rating Scales
| Rating | Severity | Occurrence | Detection |
|---|---|---|---|
| 1 | No effect | Remote (1 in 10⁶) | Almost certain to detect |
| 2–3 | Minor, no safety impact | Low (1 in 10,000) | High chance of detection |
| 4–6 | Moderate, some downtime | Moderate (1 in 1,000) | Moderate chance |
| 7–8 | High, significant downtime or injury | High (1 in 100) | Low chance of detection |
| 9–10 | Catastrophic — safety/environmental | Very high (1 in 10+) | Cannot detect |
Example: Centrifugal Pump FMEA
| Component | Failure Mode | Effect | S | O | D | RPN |
|---|---|---|---|---|---|---|
| Bearing | Wear/fatigue | Vibration, seizure | 7 | 5 | 3 | 105 |
| Mechanical seal | Face wear | Leak, shutdown | 6 | 6 | 4 | 144 |
| Impeller | Erosion | Reduced flow/head | 5 | 4 | 6 | 120 |
| Casing | Corrosion | Leak, failure | 8 | 2 | 7 | 112 |
| Coupling | Misalignment | Vibration, bearing wear | 5 | 5 | 2 | 50 |
Using FMEA Results
- RPN above 200: Immediate action required — redesign, add redundancy, or implement condition monitoring
- RPN 100–200: Plan corrective action within 3 months — add inspection, monitoring, or maintenance task
- RPN 50–100: Monitor and review annually — consider improvement if resources allow
- RPN below 50: Acceptable risk — no action required unless severity is 9–10 (safety critical)
- Always address high-severity items regardless of RPN — a severity of 9 or 10 means potential injury or fatality