When an accident or near miss happens, the temptation is to blame the person closest to it. An effective incident investigation asks a different question: why did the system allow this to happen? Finding the root cause is what prevents repeat events.
What should be investigated?
Every injury, but also near misses, property damage, environmental releases and dangerous occurrences. Near misses are free lessons — the same causes sit behind most serious accidents.
Step 1: Make the scene safe and respond
Look after the injured, secure the area and notify those who need to know. Only then begin the investigation.
Step 2: Gather evidence quickly
- Photograph and sketch the scene before it is disturbed.
- Secure equipment, permits, work instructions, training and maintenance records.
- Interview witnesses separately and promptly with open, non-blaming questions.
- Note conditions: lighting, weather, noise, workload and time of day.
Step 3: Build the timeline
Establish what happened, in order, from the start of the task through the event. Gaps show what you still need to find out.
Step 4: Analyse causes
The 5 Whys
Ask "why?" repeatedly until you reach a cause you can fix. Example: the worker fell → the guardrail was missing → it was removed for a job and not replaced → there was no inspection after the job → the permit did not require a final check.
Fishbone (Ishikawa) diagram
Group contributing factors under People, Equipment, Materials, Methods, Environment and Management.
Immediate causes vs root causes
Immediate causes are unsafe acts or conditions. Root causes are the management system failures behind them — missing procedures, poor training, weak supervision, inadequate maintenance or production pressure.
Step 5: Write effective corrective actions
- Each action targets a cause, not a person.
- Prefer elimination and engineering controls over retraining or reminders.
- Assign an owner and a due date and check the action worked.
Step 6: Share the learning
Publish the lessons across sites and update risk assessments, procedures and training.
Key takeaway: Investigate to learn, not to blame, and fix the system.
Frequently asked questions
How soon should an investigation start?
As soon as the scene is safe — evidence and memories fade quickly.
Who should lead it?
A trained investigator with workers' representatives and supervisors. See our incident investigation course.