Five Whys Analysis
The Five Whys is a simple but powerful root cause analysis technique. Learn how to use it, when it works, and when you need a more structured approach.
What is the Five Whys?
The Five Whys is a root cause analysis technique that involves asking 'why?' repeatedly until you reach the fundamental cause of a problem. The idea is that most problems have multiple layers of causes, and asking 'why?' five times (or however many times needed) peels back the layers to reveal the root cause.
It was developed by Taiichi Ohno, the architect of the Toyota Production System. It is simple enough that anyone can use it, without special training or tools.
How to Use It
- State the problem clearly and specifically.
- Ask 'Why did this happen?' Write down the answer.
- Ask 'Why did that happen?' Write down the answer.
- Continue asking 'why?' for each answer, drilling deeper.
- Stop when you reach a root cause that, if fixed, would prevent the problem from recurring.
- Verify: if I fix this root cause, would the original problem be prevented? If yes, you have found the root cause. If no, keep digging.
Example
Example: Pump seal failure
Problem: Mechanical seal failed on Pump 3. Why? The seal ran dry. Why? The pump lost prime. Why? Air was drawn in through the suction flange. Why? The flange gasket was degraded. Why? The gasket was the wrong material for the fluid. Root cause: wrong gasket material specified at installation. Fix: replace gasket with correct material and review the specification process.
When It Works and When It Doesn't
- Works well for: Single-cause problems, mechanical failures, procedural issues, straightforward cause-and-effect chains.
- Does not work well for: Complex problems with multiple interacting causes, human factors, organisational issues, or systemic problems. For these, use more structured methods like fishbone diagrams or FMEA.
- Common pitfall: Stopping too early. If you stop at 'the operator made a mistake' without asking why the mistake was possible (poor training? confusing procedure? inadequate supervision?), you haven't reached the root cause.
Don't blame people
If your Five Whys analysis leads to 'the operator made a mistake' or 'someone was negligent', you have stopped too early. Ask why the system allowed the mistake: Was training inadequate? Was the procedure unclear? Was there time pressure? Was the equipment designed for error-free operation? Human error is a symptom, not a root cause.
Tip: Document every Five Whys analysis in your maintenance log. Even simple problems benefit from documentation. Over time, patterns emerge that reveal systemic issues. PlantLogica's maintenance logging system can store these analyses with the asset record for future reference.