Root Cause Analysis Methods

Root cause analysis (RCA) looks beyond the immediate cause of an incident to find the underlying reasons.
The immediate cause is what directly triggered the event; the root cause explains why it was possible.
Common RCA methods include the 5 Whys, fishbone diagrams, fault tree analysis, and barrier analysis.
The 5 Whys technique asks "why?" repeatedly until you reach the fundamental system or management failure.
A fishbone diagram categorises causes into groups: people, process, equipment, environment, and management.
Most incidents have multiple root causes, not a single point of failure to blame.
Root causes typically involve failures in systems, procedures, training, supervision, or management oversight.
Blaming individual workers is rarely the root cause and prevents organisations from learning and improving.
Effective RCA leads to corrective actions that prevent the same type of incident from recurring.
CDM 2015 and HSE guidance expect organisations to investigate incidents thoroughly and implement systemic fixes.

Prevent recurrence	Without identifying the root cause, the same incident will happen again because the underlying failure remains in place.
Systemic improvement	RCA reveals weaknesses in management systems, training, and procedures that affect safety across the whole organisation.
Legal expectation	HSE expects organisations to demonstrate they have investigated incidents properly and addressed root causes, not just symptoms.

Do

Don't

Use the 5 Whys technique to dig beyond the immediate cause of any incident.
Look for system and management failures, not just individual mistakes.
Gather evidence from the scene, witnesses, and documentation before analysing.
Consider multiple root causes; most incidents involve more than one failure.
Use fishbone diagrams to categorise and organise potential contributing factors.
Develop corrective actions that address the root cause, not just the symptom.
Track corrective actions to completion and verify they are effective.
Share lessons learned across the organisation to prevent similar incidents elsewhere.
Involve frontline workers in the analysis; they understand the real conditions.
Record the full RCA process and findings for future reference and audit.

DON'T stop investigating at the immediate cause; always ask why it happened.
DON'T blame individual workers without examining the system that allowed the failure.
DON'T rush the analysis; thorough RCA takes time but prevents future incidents.
DON'T accept a single root cause without checking for additional contributing factors.
DON'T ignore management and organisational failures as potential root causes.
DON'T create corrective actions that only address symptoms rather than root causes.
DON'T file the RCA report without tracking corrective actions to completion.
DON'T exclude frontline workers from the investigation process.
DON'T assume training is always the answer; the problem may be systemic.
DON'T limit learning to the project where the incident occurred; share it widely.

See also: Incident Investigation Process | Near Miss Reporting and Learning

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