Root cause analysis is a structured investigation method that looks past the immediate cause of an incident to find the underlying system failures that allowed it to happen, so they can be fixed.
Root cause analysis (RCA) is a structured method for finding the underlying reasons an incident, near miss or failure occurred. Instead of stopping at the most obvious cause, such as a worker slipping or a valve leaking, it keeps asking why until it reaches the management, design, planning or organizational failures that allowed the event to happen.
OSHA's guide for employers on incident investigations compares the two levels of cause to weeding a garden: fixing only the immediate cause is like cutting weeds, while fixing the root cause is like pulling out the roots. The guide also states that human error is the starting point of an investigation, not its conclusion.
Root cause analysis is a core part of incident investigation and feeds directly into corrective action. It is used across safety, quality, engineering and healthcare.
These are the conditions or actions present at the moment of the incident, such as a missing guard, an oil spill on the floor or a worker standing in the line of fire. They are often described as unsafe conditions and unsafe acts.
These are conditions that made the incident more likely or more severe, such as fatigue, poor lighting, time pressure or unclear instructions.
These are the system-level reasons the immediate causes existed. Examples include no process for inspecting guards, a maintenance backlog, training that did not cover the task, or production targets that encouraged shortcuts. Fixing a root cause should prevent a whole class of similar incidents, not just a repeat of the same one.
The team asks "why" repeatedly, usually around five times, until it reaches a cause that management can fix. It is quick and works well for simple incidents, but it can follow a single path and miss other causes if used alone.
Possible causes are grouped under categories such as people, methods, equipment, materials, environment and management. This helps the team consider several types of cause at once.
A top-down logic diagram that maps how combinations of failures could lead to the event. It is useful for complex equipment and process incidents.
The team compares the incident situation with the normal, incident-free situation to find what was different. It works well when something that usually goes right suddenly goes wrong.
The team identifies the barriers that should have prevented the incident and asks why each one was missing, failed or was bypassed.
A warehouse worker's hand was caught in a pallet wrapper while clearing a film jam. The first report concluded that the worker "failed to follow lockout procedure."
The safety team ran a root cause analysis. Asking why the worker did not lock out, they learned that jams happened several times per shift, that the lockout point was at the far end of the machine, and that supervisors had been told to keep the wrapper running to meet shipping deadlines. No one had reported the frequent jams because they were seen as normal.
The root causes were a known equipment problem that had never been fixed, a machine layout that made lockout slow, and production pressure. Corrective actions included replacing the worn film carriage, adding an interlocked guard that stops the machine when opened, and making clear in writing that stopping the machine to clear jams is expected.
OSHA does not require root cause analysis for every incident. The process safety management standard requires incident investigations that identify contributing factors, and OSHA strongly recommends root cause analysis as part of any incident investigation program.
Most incidents have more than one. Serious incidents usually result from several failures lining up, so an analysis that finds only one cause may not have gone far enough.
Include someone who knows the work, a supervisor or manager who can approve changes, and someone trained in the method. Including frontline workers improves the quality of findings.
Yes. Near misses often share the same root causes as serious incidents, and investigating them lets you fix problems before someone is hurt.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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