故障樹分析(Fault Tree Analysis, FTA)

故障樹分析或失效樹分析(Fault Tree Analysis, FTA)：為品質改善工具之一﹐以某一失效模式為起點﹐此即為故障樹或失效樹之樹根。其後﹐各種可能的原因漸次加入故障樹中﹐形成所謂的故障樹。

Fault tree analysis

In the technique known as "fault tree analysis", an undesired effect is taken as the root ('top event') of a tree of logic. Then, each situation that could cause that effect is added to the tree as a series of logic expressions. When fault trees are labelled with actual numbers about failure probabilities, which are often in practice unavailable because of the expense of testing, computer programs can calculate failure probabilities from fault trees.

A fault tree diagram

The Tree is usually written out using conventional logic gate symbols. The route through a Tree between an event and an initiator in the tree is called a Cutset. The shortest credible way through the tree from Fault to initiating Event is called a Minimal Cutset.

Some industries use both Fault Trees and Event Trees (see Probabilistic Risk Assessment). An Event Tree starts from an undesired initiator (loss of critical supply, component failure etc) and follows possible further system events through to a series of final consequences. As each new event is considered, a new node on the tree is added with a split of probabilities of taking either branch. The probabilities of a range of 'top events' arising from the initial event can then be seen.

Classic programs include the EPRI (Electric Power Research Institute)'s CAFTA Software which is used by almost all the Nuclear Power Plants in the US and by a majority of US and international aerospace manufacturers and the Idaho National Laboratory's SAPHIRE, which is used by the U.S. government to evaluate the safety and reliability of nuclear reactors, the space shuttle, and the International Space Station.

Unified Modeling Language (UML) activity diagrams have been used as graphical components in a fault tree analysis.

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