In brief
Root cause analysis ensures that an accident investigation does not stop at a first answer such as "carelessness" but reaches the system cause that management can change. The 5 Whys follows a single chain in depth; the fishbone diagram makes all contributing factors visible under the headings of people, machine, method, material, measurement and environment. Using both methods together on the same incident provides both depth and breadth.
Why should root cause analysis not stop at "carelessness"?
After a workplace accident, the quickest answer is usually "the employee was not careful". This answer may be partly true, but it does not prevent the next accident. On the same machine, under the same shift pressure and with the same missing instruction, another employee will make the same mistake. Root cause analysis is the general name for methods used to find the cause behind an incident that management can change.
This analysis is not optional; it is a duty arising from the legislation. Art. 14/1 of Law No. 6331 requires the employer to keep a record of workplace accidents and to prepare a report after carrying out the necessary investigations. Art. 9 of the Regulation on the Duties, Powers, Responsibilities and Training of OHS Specialists gives the specialist the duty of investigating the causes of workplace accidents and occupational diseases and proposing measures to prevent recurrence. Incidents that do not cause injury but have the potential for harm fall within the same scope; the methods below therefore also apply to near miss events.
We cover the management of the first hours after an accident in our article on what to do after a workplace accident. This article focuses on the analysis stage, after the scene has been made safe and information has been collected.
Example incident: hand trapped on a press line
The following incident is a fictional example of the kind that may occur in metal and automotive supplier businesses in Bursa:
On the night shift, two hours after a die change, an eccentric press operator trapped two fingers of the left hand while trying to remove by hand a part stuck in the die. The light curtain in front of the press had been bypassed.
The first impression is "the operator switched off the light curtain and put a hand in the die". Now let us apply two methods to the same incident. In both methods, the answers must not be guesses; they must be verified information based on statements, records, photographs and trials on site.
5 Whys analysis step by step
The 5 Whys analysis opens up the cause behind a problem layer by layer by repeatedly asking "why?". The number five is a guide, not a rule; sometimes the system cause is reached in three questions, sometimes in seven.
- Why were the fingers trapped? The operator put a hand into the die area while the ram was descending.
- Why did the operator put a hand in the die? The part was sticking in the die and the operator tried to remove it without stopping the line.
- Why was the part sticking? The ejector had not been adjusted after the die change; the part was staying in the die every few strokes.
- Why did production start without adjustment? There was no written checklist for commissioning after a die change; there was no die setter on the night shift.
- Why was the light curtain bypassed? Because the line had to be stopped frequently to remove the stuck part, the curtain had been bridged during the shift. The bypass key switch was not locked and its use was not recorded.
Two root causes emerge from this chain: the absence of a commissioning procedure after die changes and the possibility of disabling the safety device without authorisation. The operator's behaviour is a real factor, but the same behaviour will recur unless these two conditions are removed.
The same incident with a fishbone (Ishikawa) diagram
The fishbone diagram writes the incident at the head of the fish and divides contributing causes into categories along the bones. The categories most commonly used in workplace safety are people, machine, method, material, measurement and environment; some teams add "management" as a separate heading. The diagram uses teamwork to make visible the factors that the 5 Whys may miss in a single chain.
| Category | Finding in the example incident | Evidence |
|---|---|---|
| People | The operator has worked on this press for three months and does not know what to do about sticking after a die change | Training records, operator statement |
| Machine | The light curtain bypass key switch is not locked; the ejector setting goes out of adjustment easily | Site inspection, maintenance records |
| Method | No commissioning checklist after die changes; no "stop, lock out, remove" instruction for stuck parts | Instruction file |
| Material | The thickness of the newly delivered sheet batch is at the lower tolerance; the part tends to stick in the die | Incoming quality records |
| Measurement | No first-part inspection was carried out after the die change | Quality form blank |
| Environment | Night shift, no die setter, target raised for end-of-line shipment | Shift plan, production target |
The table revealed two factors not visible in the 5 Whys chain: the tolerance difference in the material batch and shipment pressure. These may not be root causes, but they should go on the action list.
Using both methods together
The two methods are not alternatives but complements. In practice, we recommend the following order:
- Information gathering: scene photographs, statements, maintenance and training records, shift plan.
- Fishbone: in a one-hour session with the specialist, workplace physician, department head, operators and employee representative, write all factors under the categories.
- Prioritisation: select the two or three factors that appear most decisive in causing the incident.
- 5 Whys: for each selected factor, follow the chain down to the system cause.
- Verification: for each root cause, ask "If this cause had been removed, would the incident have happened?"
| Method | Strength | Limitation | Best use |
|---|---|---|---|
| 5 Whys | Quick, in-depth, can be applied even by one person | Focuses on a single chain; limited by the knowledge of the person doing the analysis | Simple incidents, near misses, initial assessment |
| Fishbone | Broad view, team participation, catches overlooked factors | Does not show the depth of factors on its own | Accidents with serious injury, recurring incidents |
Check questions for an analysis that does not stop at human error
When the analysis approaches the conclusion "employee error", ask these questions:
- Why did this behaviour make sense to the employee at that moment? Was there time pressure, habit or missing information?
- Would another employee have done the same thing under the same conditions?
- Was the safe way more troublesome than the unsafe way?
- Was the rule known, written down and workable?
- Had managers seen this behaviour before and said nothing?
These questions are not meant to remove responsibility but to find the condition to be corrected. In an environment that punishes the person who reports, employees hide incidents and the analysis is carried out with incomplete information. We discuss this approach in detail in our article on how to build an OHS culture.
From finding to action: the hierarchy of controls and effectiveness tracking
For the example incident, the actions can be ranked according to the hierarchy of controls as follows:
- Engineering: Making the light curtain bypass key switch locked and subject to authorisation; a mechanism to eject stuck parts without manual intervention. For guard selection, see our article on machine guards.
- Administrative: A commissioning checklist after die changes, first-part approval, a "stop, isolate energy, lock out, remove" instruction for jams, and a permit to work for maintenance work.
- Organisation: Not scheduling die changes on the night shift, or having an authorised die setter on that shift.
- Training: Practical training for press operators specific to the new instructions.
For each action, write the person responsible, the deadline and the effectiveness verification: "In one month, the bypass key switch will be checked on site; die change forms will be reviewed." An accident is one of the situations requiring the risk assessment to be renewed regardless of its validity period; be sure to enter the results of the analysis into the risk assessment. We carry out accident investigation and action tracking together with the workplace physician as part of our OHS specialist service.
What should the analysis report contain?
Recording and reporting the accident is the employer's responsibility under Art. 14/1 of Law No. 6331. A good root cause analysis report allows the reader to reconstruct the incident and the decisions. The report should contain the following sections:
- Description of the incident: date, time, shift, location, equipment, injured person and nature of the injury.
- Evidence collected: photographs, statements, maintenance and training records, instructions, shift plan. Which information was obtained from whom is written down.
- Sequence of events: a short timeline starting from the hours before the incident.
- Analysis: fishbone diagram and 5 Whys chains.
- Root causes and contributing factors: listed separately.
- Action plan: for each action, the person responsible, deadline and method of effectiveness verification.
- Similar risks: whether the same hazard exists on another machine, line or shift. In the example, the condition of the bypass key switches on the other presses in the factory should also be checked.
- Participants and signatures.
The results of the report should be linked to the findings the specialist writes in the approved logbook and to the annual evaluation report. The closure of actions is recorded at the next site visit.
Frequently Asked Questions
Who should carry out root cause analysis?
The OHS specialist leads the analysis but does not do it alone. The participation of the workplace physician, department manager, employees who experienced and witnessed the incident, and the employee representative brings the real conditions to light.
Are five questions always asked in a 5 Whys analysis?
No. Five is a guiding number. You stop when you reach a system cause that management can change; sometimes this takes fewer questions, sometimes more.
Which categories are used in a fishbone diagram?
In workplace safety, people, machine, method, material, measurement and environment are commonly used. A management or organisation heading can be added as needed. What matters is that every finding is supported by evidence.
Is root cause analysis also needed for near misses?
Yes. Near misses are an opportunity to see the same causes without an accident. For simple incidents, a short 5 Whys analysis is often sufficient.
How quickly should the analysis be completed?
The legislation sets no separate deadline for the analysis; the accident notification to the SGK (Social Security Institution) within 3 working days is an obligation independent of the analysis. Collect initial information on the day of the incident before evidence is lost, complete the analysis in the first few days, and keep temporary measures in place until permanent actions are implemented.
A certified specialist matched to your hazard class: site inspections, approved logbook, training plan, annual plan and report follow-up.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.