Fault Tree meaning

A fault tree is a structured analytical diagram used in legal practice for risk assessment, safety cases and litigation to show how a specified adverse event could occur. It assists in demonstrating regulatory compliance and ALARP, and in evidencing causation, foreseeability and standard of care in health and safety, major accident hazards and product liability disputes. The term is not defined in legislation or case law; it is a descriptive method from safety engineering, widely used by regulators and experts. The analysis proceeds top‑down from the “top event” (for example, an explosion or system loss), often identified through event tree analysis. At each successive stage, the event is broken down into combinations of precursor events—such as equipment failures and human or operator actions—that, if they fail, lead to the postulated outcome. Logical operators (AND/OR “gates”) are used to show how these precursors combine, and the model can be qualitatively explained or quantitatively assessed to estimate likelihood. Usage and methodology are broadly consistent across England & Wales, Scotland, Northern Ireland and Ireland, and commonly arise in COMAH safety reports, nuclear site licence safety cases, rail and aviation safety management systems, and expert evidence following incidents.