Executive summary
- One failure must be interrogated from four separate angles.
- The mechanism lens explains what physically happened.
- The standard lens asks whether a standard existed, and whether it permitted this.
- The control lens asks whether anyone was checking compliance.
- The ability lens asks whether the person was adequately trained.
- A countermeasure drawn from one lens will be undone by the other three.
Why-why analysis is a tool nearly every plant has used and nearly every plant underuses. The familiar pattern: the team asks why five times, reaches an answer that sounds reasonable, issues one countermeasure, closes the sheet — and six months later the same failure returns.
The problem is not the number of whys but their direction. Five whys down a single path yields an increasingly detailed mechanical explanation of the same one thing.
Lens one — phenomenon and mechanism
This lens asks what physically happened: which component failed, in what manner, and what force or condition produced that failure mode. It is the lens engineers are most comfortable with, and usually the only one actually applied.
Necessary but not sufficient
Stop here and the countermeasure is always a material change or a component modification. That may fix this machine, and it does nothing to stop the same thing happening on the other twelve.
Lens two — standard, rule and regulation
Three questions in order. One: does a standard exist for this task? Two: if it does, is it written correctly, or is it written in a way that permits the failure even when followed? Three: was it actually followed? These are distinct, and they lead to entirely different countermeasures.
Lens three — control and discipline
Does anyone check that the standard is followed? How often? And when non-compliance is found, what happens? The last question matters most: if the answer is nothing, the organisation has already communicated that this standard is optional.
Lens four — ability
Was the person trained? Did the training cover the situation that actually arose? And was competence verified, rather than attendance recorded? The common finding is a training certificate with no evidence that anyone confirmed the person could do the job.
Worked case: a leak caused by corrosion
A pipe leaked after corrosion thinned the wall until it collapsed. Here is the same event analysed through all four lenses.
| Lens | What was found | Countermeasure produced |
|---|---|---|
| Mechanism | The wall thinned through internal corrosion because the fluid was more acidic than the design assumed | Change to an acid-resistant pipe grade and add wall-thickness measurement |
| Standard | An inspection standard existed but specified external inspection only; thickness was not covered | Amend the standard to require thickness measurement on lines carrying corrosive fluid |
| Control | Inspections under the old standard were fully recorded, but never spot-checked and never reviewed | Add a quarterly review of inspection results and supervisor spot-checks |
| Ability | The inspector had never been trained on localised corrosion patterns and could not recognise the early signs | Corrosion inspection training, with assessment against real samples |
Note that the first lens alone — change the pipe material — genuinely fixes that pipe. But every other line carrying the same fluid is still inspected against the old standard, by the same untrained inspector, with nobody reviewing the results. The problem simply returns on a different pipe.
The same four categories for safety incidents
The same four categories apply directly to safety incident analysis. An incident should be classified against all four rather than concluded as operator carelessness — a finding that leads to no action at all.
- Physical mechanism — a guard designed without covering the pinch point.
- Standard and rule — a lock-out procedure that does not cover in-running adjustment.
- Control and discipline — a safety inspection performed as a ritual, in which no finding is ever recorded.
- Ability — a new employee put on night shift before any on-the-job assessment.
If every countermeasure on the sheet is technical, three of the four lenses were never applied.