# FTA - Fault Tree Analysis ME4214 Design for Product Safety...

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1 ME4214 Design for Product Safety Modeling System Failures Part III: FTA Dr. David Yuen Department of Mechanical Engineering The Hong Kong Polytechnic University 2 Fault Tree Analysis • Fault trees were first developed in 1962 at Bell Telephone lab to facilitate analysis of the Minuteman missile launching system • Fault trees provide a good framework for both qualitative and quantitative analysis because they have both a logical (Boolean algebra) and probabilistic basis. 3 What is a fault tree? • A fault tree is a logic diagram that displays the relationship between a potential event affecting system performance and the reasons or underlying causes for this event. The reason may be failures (primary or secondary) of one or more components of the system, environmental conditions, human errors and other factors. 4 Example of a Fault Tree

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5 Why use fault tree analysis? • A fault tree model provides a logical framework for analyzing the failure behaviour of a system. • A fault tree model precisely documents which failure scenarios have been considered and which have not. • Fault tree analysis can be used to support engineering and management decisions, trade-off analysis and risk assessment. • The fault tree model has a well-defined Boolean algebraic and probabilistic basis which relates probability calculations to Boolean logic functions. • Fault tree analysis provides a logical framework for understanding the ways in which a system can fail, which is often as important as understanding how a system can succeed 6 FAULT TREE ANALYSIS According to Fussel (1976) the value of a fault tree are as follows: 1. Directing the analysis to ferret out failures. 2. Pointing out the aspects of the system important to the failure of interest. 3. Providing a graphical aid in giving visibility to those in systems management who are removed from design changes. 7 FAULT TREE ANALYSIS 4. Providing options for qualitative and quantitative system reliability analysis. 5. Allowing the analyst to concentrate on one particular system failure at a time. 6. Providing an insight into system behaviour. 8 FAULT TREE ANALYSIS A fault tree analysis involves the following steps: 1. Definition of the TOP event 2. Construction of the fault tree 3. Qualitative (and quantitative) analysis of the fault tree
9 Preparation for FTA • The starting point of an FTA is often an existing FMECA and a system block diagram • The FMECA is an essential first step in understanding the system • The design, operation, and environment of the system must be evaluated • The cause and effect relationships leading to the TOP event must be identified and understood 10 Preparation for FTA 11 Boundary conditions • The physical boundaries of the system (Which parts of the system are included in the analysis, and which parts are not?) • The initial conditions (What is the operational status of the system when the TOP event is occurring?) • Boundary conditions with respect to external

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FTA - Fault Tree Analysis ME4214 Design for Product Safety...

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