Fault Tree Analysis

Fault tree analysis (FTA) works backward from an undesirable event (the 'top event') to identify all possible combinations of component failures that could cause it. Using Boolean logic gates (AND gates, where all inputs must fail; OR gates, where any input failing causes the top event), FTA maps the logical relationships between root causes and system failure. For a 'reactor coolant loss' top event, the fault tree might show that this requires pump failure AND valve failure (both must fail simultaneously) OR a pipe rupture (single cause sufficient). This distinction is crucial: AND-gate failures require multiple simultaneous failures (safer — redundancy works), while OR-gate failures can be triggered by any single component (less safe — single points of failure).

When to use it

When analyzing complex systems to find single points of failure, designing redundancy into critical systems, investigating which combinations of failures could cause catastrophic outcomes, or prioritizing investments in system reliability by identifying the most vulnerable failure pathways.

How it can help

FTA thinking applies to any situation where you need to understand the causal pathways to failure. In business, a 'loss of major client' fault tree might reveal that this requires both service quality decline AND competitor offering (AND gate — losing the client needs both, so redundant quality checks help) OR a single data breach (OR gate — one event is sufficient, making this the vulnerability to prioritize). The AND/OR logic helps you distinguish between failures requiring multiple simultaneous causes (invest in redundancy) and failures with single points of failure (invest in prevention). This distinction changes your risk mitigation strategy entirely.