Fault Tree Analysis
1 FAULT TREE ANALYSIS 1. Introduction
FTA is a deductive, failure-based approach. As a deductive approach, FTA starts with an undesired event, such as failure of a main engine, and then determines (deduces) its causes using a systematic, backward-stepping process. In determining the causes, a fault tree (FT) is constructed as a logical illustration of the events and their relationships that are necessary and sufficient to result in the undesired event, or top event. The symbols used in a FT indicate the type of events and type of relationships that are involved. The FT is a qualitative model that provides extremely useful information on the causes of the undesired event. The FT can also be quantified to provide useful information on the probability of the top event occurring and the importance of all the causes and events modelled in the FT. This handbook leads the reader through FTA. Particular details can be skipped if the reader desires only an overview of FTA and instead wants to focus on its uses to assist decision-making. In addition to FTA, inductive approaches are also used in safety analysis and in risk and reliability analysis. In contrast to the deductive approach used in FTA, inductive approaches are forward-stepping approaches that begin with a basic cause or initiating event and then investigate (induce) the end effects. Both FTA and inductive approaches are failure-based. The advantages of failure-based approaches are also discussed. A FT can be transformed into its logical complement; a success tree (ST) that shows the specific ways the undesired event can be prevented from occurring. The ST provides conditions that, if assured, guarantee that the undesired event will not occur. The ST is a valuable tool that provides equivalent information to the fault tree, but from a success viewpoint. Techniques for transforming the FT to its ST are described along with uses of the ST. The uses of FTA to assist decision-making are described in this AFTH. FTA
FTA is a deductive, failure-based approach. As a deductive approach, FTA starts with an undesired event, such as failure of a main engine, and then determines (deduces) its causes using a systematic, backward-stepping process. In determining the causes, a fault tree (FT) is constructed as a logical illustration of the events and their relationships that are necessary and sufficient to result in the undesired event, or top event. The symbols used in a FT indicate the type of events and type of relationships that are involved. The FT is a qualitative model that provides extremely useful information on the causes of the undesired event. The FT can also be quantified to provide useful information on the probability of the top event occurring and the importance of all the causes and events modelled in the FT. This handbook leads the reader through FTA. Particular details can be skipped if the reader desires only an overview of FTA and instead wants to focus on its uses to assist decision-making. In addition to FTA, inductive approaches are also used in safety analysis and in risk and reliability analysis. In contrast to the deductive approach used in FTA, inductive approaches are forward-stepping approaches that begin with a basic cause or initiating event and then investigate (induce) the end effects. Both FTA and inductive approaches are failure-based. The advantages of failure-based approaches are also discussed. A FT can be transformed into its logical complement; a success tree (ST) that shows the specific ways the undesired event can be prevented from occurring. The ST provides conditions that, if assured, guarantee that the undesired event will not occur. The ST is a valuable tool that provides equivalent information to the fault tree, but from a success viewpoint. Techniques for transforming the FT to its ST are described along with uses of the ST. The uses of FTA to assist decision-making are described in this AFTH. FTA