FaultTreeAnalyse

FaultTreeAnalyse, also known as Fault Tree Analysis (FTA), is a systematic, deductive method used to identify the combinations of hardware, software, and human failures that can lead to a defined undesired state, called the top event. The method is used to analyze safety, reliability, and security concerns in complex systems.

A fault tree is built from the top event downward. It represents causal relationships with logical gates such as AND, OR, and XOR connecting basic events (low-level failures or events) and intermediate events. Basic events typically have no further cause within the tree and are assigned failure data. Gates describe how failures combine to produce higher-level events.

Qualitative analysis seeks to enumerate minimal cut sets—the smallest combinations of basic events that suffice to cause the top event. Quantitative analysis uses probability data for basic events to estimate the likelihood of the top event and to rank critical components. Sensitivity and importance measures help identify drivers of risk.

Applications of FTA span aerospace, nuclear, chemical processing, automotive safety, rail, and information technology, where it supports design, risk assessment, and incident investigation. The method is also used in fault tolerance studies and failure reporting analyses.

Limitations include the need for accurate data and modeling assumptions, with independence among basic events often assumed unless modeled otherwise. Common cause failures, dynamic or time-dependent effects, and scope boundaries can complicate analysis. The quality of results depends on the completeness of the fault tree and the data available.

Standards and guidance include IEC 61025, which provides formal guidance on fault tree analysis, and related risk management references such as ISO 31010. Tools exist to facilitate both qualitative and quantitative analysis.