Steps for Performing FTA
The purpose of fault tree analysis is to evaluate the probability of occurrence of the top event. To perform such an analysis, you construct the tree and perform qualitative analysis by determining the minimal cut sets. To perform quantitative analysis, you must supply reliability or maintainability information, such as failure probability, failure rate, or repair rates, for the lowest-level events.
This topic provides guidance on the steps you take to effectively and efficiently perform fault tree analysis. In addition to supplying general instructions and descriptions, this topic references other topics where appropriate. These referenced topics typically describe how to perform the actions indicated.
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The actions in the following table are numbered to indicate that they are performed sequentially. For accurate analyses, you must complete these actions in the order in which they are listed.
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Action
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Description
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1.
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Create the system definition and clearly and concisely define the top event.
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The system definition must define all functional interconnections, components, dependencies between components, reliability parameters, and conditions when components are considered to be failed. The top event definition must include what the specific undesirable event is as well as a description of when it might occur. For more information, see Fault Tree System Definition.
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2.
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Create or open the System file and insert the fault tree.
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In a newly created System file, the FTA Table and FTA Diagram panes display a default tree with only one OR gate. You use these panes to construct a graphical representation of the relationship between lower-level events and the top event. For more information, see Fault Tree Construction. You insert additional trees by inserting new top gates in the FTA Table. For more information, see Inserting New Top Gates (Fault Trees).
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3.
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Insert gates and events to construct the tree.
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Insert gates and events to construct the tree. For more information, see Inserting Gates and Events. Gates with no inputs are ignored in FTA calculations.
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4.
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Edit the properties for the gates and events. To perform quantitative analysis, enter reliability or maintainability data for each event.
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Each gate and event in the tree has its own properties. To view and modify the properties for a gate or event, you double-click it. Although you can change gate and event properties at any time, after constructing the tree, you should carefully review all properties to ensure that they meet your current needs. To perform quantitative analysis, in the Properties window for each lowest-level event, enter the calculation data to use. For more information, see Gate or Event Properties.
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5.
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Calculate FTA results.
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Once all available data has been entered, run calculations. For more information, see FTA Calculations.
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6.
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Generate FTA reports and graphs.
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Generate FTA reports and graphs. For more information, see FTA Custom Graphs.
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