Cause (Causal Factor): An event or condition that results in an effect. Anything that shapes or influences the outcome.

Proximate Cause(s): The event(s) that occurred, including any condition(s) that existed immediately before the undesired outcome, directly resulted in its occurrence and, if eliminated or modified, would have prevented the undesired outcome. Also known as the direct cause(s).

Root Cause(s): One of multiple factors (events, conditions or organizational factors) that contributed to or created the proximate cause and subsequent undesired outcome and, if eliminated, or modified would have prevented the undesired outcome.  Typically multiple root causes contribute to an undesired outcome.

Root Cause Analysis (RCA): A structured evaluation method that identifies the root causes for an undesired outcome and the actions adequate to prevent recurrence.  Root cause analysis should continue until organizational factors have been identified, or until data are exhausted.

Event: A real-time occurrence describing one discrete action, typically an error, failure, or malfunction.  Examples: pipe broke, power lost, lightning struck, person opened valve, etc…

Condition: Any as-found state, whether or not resulting from an event, that may have safety, health, quality, security, operational, or environmental implications.

Organizational Factors: Any operational or management structural entity that exerts control over the system at any stage in its life cycle, including but not limited to the system’s concept development, design, fabrication, test, maintenance, operation, and disposal. Examples: resource management (budget, staff, training); policy (content, implementation, verification); and management decisions.

Contributing Factor: An event or condition that may have contributed to the occurrence of an undesired outcome but, if eliminated or modified, would not by itself have prevented the occurrence.

Barrier: A physical device or an administrative control used to reduce risk of the undesired outcome to an acceptable level.  Barriers can provide physical intervention (e.g., a guardrail) or procedural separation in time and space (e.g., lock-out-tag-out procedure).