Fault Tree Analysis (FTA)

Fault Tree Analysis (FTA) is a form of causal analysis which involves starting with a high-level event (generally an accident, hazard or system failure) and looking at the immediate causes of that event, as combined through various gates (generally an AND gate or an OR gate). Each of those causes of that event are then looked at in turn until all events have been expanded sufficiently, resulting in a tree structure.

Qualitative analysis can be carried out on a fault tree, e.g., looking for single points of failure or the minimal sets of events that can cause the high-level event.

Quantitative analysis can be carried out by combining the probabilities or frequencies of the events according to the gates in the tree, deriving a probability or a frequency for the high-level event.


Poor Fault Tree Analysis in part led to the Therac-25 mistreatment.