Mistake Proofing Levels classify controls by strength, from warnings and detection to prevention, forced sequencing, and automatic shutdown at the source.
Definition
Mistake Proofing Levels describe the relative strength of error-proofing controls. Weak controls warn or remind. Stronger controls detect and stop defects. Strongest controls prevent the error from occurring or make the correct action automatic.
The hierarchy helps teams avoid overreliance on training, inspection, and signs when process design can eliminate the error path.
History
The concept grew from poka-yoke and quality-at-the-source practice. As organizations applied FMEA and Lean methods, they needed a way to compare countermeasure strength beyond simply adding inspections.
When to Use
Use the levels when selecting FMEA actions, reviewing corrective actions, improving control plans, or evaluating whether a proposed control is strong enough for the risk.
Step-by-Step
- Define the error and defect effect.
- Identify current control level.
- Prioritize based on severity and occurrence.
- Seek elimination or prevention first.
- If prevention is not feasible, use detection and stop controls.
- Use warnings only as supplemental controls.
- Verify effectiveness with data or trials.
- Maintain and audit the control.
Examples
- Warning: A label reminds the operator to check orientation.
- Detection: A sensor detects missing part.
- Stop: The machine will not cycle unless the part is seated.
- Prevention: Fixture geometry makes wrong orientation impossible.
Common Pitfalls
- Treating training as error proofing.
- Using weak controls for high-severity risks.
- No bypass control.
- No verification of effectiveness.
- Ignoring maintainability of devices.
- Not updating FMEA and control plan.