4 Blocker

1. Define scope, baseline, requirement, measurable target and timeframe. Use the same denominator for comparisons.
2. Protect the customer immediately. Identify suspect material, stock, work in progress and delivered product.
3. Use 5 Why, fishbone, process observation or experiments to develop and test causes. Distinguish occurrence, escape and systemic causes.
4. Link permanent actions to verified causes. Update controlled instructions, training, PFMEA and control plans as appropriate.
5. Verify implementation, then verify effectiveness over an agreed period or sample. Record recurrence, side effects and residual risk.
6. Obtain approval and hand over routine monitoring to the process owner.

Specify the characteristic or parameter, acceptance limits, measurement method, frequency, responsible person, record and reaction plan. Ensure equipment is suitable and calibrated or verified as required. Apply measurement-system analysis where appropriate.

Specification limits define acceptance. Statistical control limits describe process behaviour. A stable process may still be incapable. An unstable process needs investigation before capability indices can be interpreted reliably.

Special processes may require validation and revalidation when output cannot be fully verified later. Periodic testing, approved process parameters and competent personnel support assurance; final inspection alone may not detect latent failures.

• Writing “operator error” without examining the system and working conditions.
• Calling sorting or rework a permanent corrective action.
• Closing actions without evidence or confusing completion with effectiveness.
• Changing the denominator or mixing unlike products in a trend.
• Using a 4 Blocker to replace a required 8D, concession, control plan or customer form.

The fictional coating project addresses 8 adhesion failures in 100 panels. Investigation identifies inconsistent cleaning and an uncontrolled delay before coating. An absent periodic test review allowed the issue to escape. Containment protects existing material; revised process controls address recurrence. The lower failure rate is encouraging, but the example remains under effectiveness review.