Quality managementReading time 12 min

How to write an 8D that does not come back rejected

8D is not a form. It is a test of whether you really found the cause. Filling in the boxes is easy; passing review is not.

01The eight steps

Step	Name	Deliverable
D1	Form the team	Cross-functional list with responsibilities and an owner
D2	Describe the problem	5W2H, the symptom, quantity, lot numbers, occurrence rate
D3	Interim containment	Disposition and completion time for shipped, in-stock, WIP and in-transit material
D4	Root cause	Occurrence cause plus escape cause, each verified
D5	Permanent corrective action	The chosen action and verification of its effectiveness
D6	Implement and confirm	Implementation date, lot number, tracking data
D7	Prevent recurrence	Standardisation: SOP, FMEA, control plan, gauges
D8	Close and recognise	Horizontal deployment to similar processes and part numbers

D3 has to be complete within 24 to 48 hours; everything from D4 onward usually gets 15 to 30 days.

02D4: two causes, not one

A sound 8D answers two questions and cannot skip either:

Occurrence. Why was the defect produced?
Escape. Why, having been produced, was it not caught?

An 8D with only the occurrence cause will be sent back. Even with the process fixed, the hole in the detection system remains, and the next different problem will escape the same way.

Ask why until you reach something you can control

Level	Example	Assessment
Symptom	Dimension out by 0.05 mm	Not yet a cause
Direct cause	Tool wear past the limit	Getting closer
System cause	Tool changes judged by experience, with no defined limit	Now at a level you can change
Management cause	The work standard sets no tool change criterion	Root cause

Stopping at “the operator was careless” is the most common failure. People will always be careless; the system has to absorb it.

03D5: the action has to be verifiable

The quality of a permanent action depends on which level of the error-proofing hierarchy it sits at.

Level	Approach	Effectiveness
1. Eliminate	Change the design so the problem cannot occur	Highest
2. Mistake-proof	Get it wrong and it will not assemble, or the machine will not run	High
3. Detect	Automatic detection that stops the line	Medium
4. Control	SPC monitoring of the trend	Medium-low
5. Procedure	SOP, training, extra patrol inspection	Lowest

A corrective action that stops at level 5 will usually not be accepted.

04Five things a reviewer will look for

Are quantity and scope clear in D2? Affected lots, date range, quantity already shipped.
Does D3 cover everything in transit? The customer, the warehouse, WIP and the supplier all need a disposition.
Does D4 give both causes? Occurrence and escape.
Is D5 high enough in the hierarchy? Stopping at training gets it rejected.
Did D7 go back and change the documents? FMEA, control plan, SOP and gauge list must all be updated, with revision and date.

The last of these is the most often missed. If the FMEA is not updated once the 8D is closed, the same failure mode will come round again on the next project.