Five whys at the workface: follow the evidence and test a countermeasure
A rebar cage was assembled using an old drawing revision. The foreman initially writes that the worker failed to check. The next conversation reveals that the current sheet remained in the trailer and the bench set has no clear update owner. The team needs to examine those facts rather than end the investigation at its first explanation.
Ask why repeatedly to move from an observed problem toward supported explanations and a useful countermeasure. The Lean Enterprise Institute explains that the number five is not the point; IHI notes that a problem can have multiple causes and different perspectives. Use the technique as a structured inquiry. A fluent chain of answers is still a hypothesis until the relevant evidence supports it.
Keep the cause path beside its evidence
- State the observed gap. Locate the event and expected condition before asking why. Gather the people with relevant knowledge and use safe, permitted access to the work context. A brief discussion may start the inquiry, but fifteen minutes or one day is not a required limit for completing it.
- Ask for an explanation and its basis. Record the answer, supporting reference and unresolved question. Check drawing versions, actual handovers or other appropriate records rather than accepting memory alone. Describe decisions and actions accurately without turning a person's name into the complete explanation or assuming every problem has only a process cause.
- Branch where the evidence branches. Follow separate contributing paths when answers differ. A bench-set update gap and an unclear release instruction may both matter. Mark untested ideas as such and seek the appropriate review for technical questions. Do not force a single chain, a fifth answer or agreement merely to fill a form.
- Choose an assessed countermeasure and follow-up. Link the proposed action to the supported condition, its owner and receiving point. Check any required authority before changing technical or safety arrangements. Define what later observation would show the change worked, then review actual results and remaining causes. A new rule on paper does not establish prevention.
Common mistakes
- Stopping at a person's name without examining the conditions.
- Treating a plausible answer as verified evidence.
- Forcing one chain or exactly five questions.
- Calling an issued countermeasure proof of prevention.
Action list
Retain a five-whys record with
- A located gap and expected condition.
- Explanations linked to evidence and uncertainty.
- Separate contributing paths where needed.
- An assessed action, owner and receiver.
- A result check and remaining questions.
Check your understanding
The team agrees on a convincing cause chain, but no one has checked the drawing handover. Is the cause established?
