FMEA scores each possible failure for severity (S), occurrence (O) and detection (D), usually on a 1 to 10 scale, and multiplies them to give a risk priority number: RPN = S × O × D. Rank the failures by RPN, but always act on high-severity failures even when their RPN is low.
Step by step
- List the process steps and, for each, the ways it can fail.
- Describe the effect of each failure on a critical quality attribute.
- Score severity, occurrence and detection from 1 to 10 using a written scale.
- Calculate RPN and rank the failure modes.
- Decide actions for the highest risks, then score again after the actions.
Worked example: wet granulation tablet
| Failure mode | Effect | S | O | D | RPN |
|---|---|---|---|---|---|
| Over-granulation | Slow dissolution | 8 | 4 | 5 | 160 |
| Blend segregation | Poor content uniformity | 9 | 3 | 4 | 108 |
| Compression force variation | Hardness out of range | 6 | 4 | 3 | 72 |
| Inadequate drying | High moisture, degradation | 7 | 3 | 3 | 63 |
Reading the result
- Over-granulation ranks first. Action: define granulation end point by power consumption or time, and study it in a designed experiment.
- Blend segregation has severity 9. Even though its RPN is lower, act on it: control blending time and particle size, and test blend uniformity.
- Re-score after the actions. Lower occurrence or better detection should reduce the RPN.
Tips
- Agree the scoring scales before the team starts, and keep them with the FMEA.
- Score as a team: formulation, analytical and production views all matter.
- Use the FMEA to choose the factors for your design of experiments.
QbD Risk Navigator runs this workflow in the browser, from the risk estimation matrix to FMEA, Pareto chart and experimental design.
Frequently asked questions
What is a good RPN threshold?
There is no universal threshold. Set one in your procedure, and always review failure modes with high severity regardless of RPN.
What is the difference between FMEA and a risk estimation matrix?
A risk estimation matrix is an early, qualitative screen of how material attributes and process parameters affect quality. FMEA scores specific failure modes in more detail.
Which ICH guideline covers risk assessment?
ICH Q9(R1), Quality Risk Management.
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