Fault tree analysis
Fault Tree Analysis (FTA), according to DIN EN 61025 also Fault State Analysis, can be used as a safety and reliability analysis for plants and systems of all kinds, including Common Mode Failures and Human Errors. This is a deductive analysis based on Boolean algebra. The logical connections of component or subsystem failures that lead to an unwanted event (top event) are determined (see next figure presenting an example fault tree). The results of the analyses enable a system assessment with regard to reliability, availability and safety.
The following figure shows the representation of a series and a parallel system as a reliability block diagram and as a fault tree. For the parallel system, basic event 1 AND basic event 2 must occur for the top event to occur. The top event on the production system is taken by the occurrence of basic event 1 OR basic event 2.
Picture: Fault Tree Analysis Basics
The objectives of theFTA are detailed:
- The systematic identification of all possible failure causes and failure combinations that lead to an undesirable event.
- The determination of reliability parameters (e.g. occurrence frequencies of the failure combinations, occurrence frequencies of the undesired event or non-availability of the system in case of requirements).
- The creation of the graphical representation in a kind of tree structure (logical switching network) with input and output variables.
- To compare different design proposals by probabilistic reliability and safety predictions, to point out weak points, to analytically prove required reliability and safety requirements.
The FTA is particularly suitable for the reliability and safety relevant representation and analysis of large complex systems, which usually consist of thousands of minimum sections (these are event combinations, which lead to the undesired top event). The creation and evaluation is computer-aided accordingly.
Further information on the system considered during the FTA can be obtained via importance measures. These evaluation parameters can be used to determine the influence of individual basic events (often component failures) on the reliability or safety, in order to objectify and quantify issues such as system optimization, vulnerability analysis, error detection or maintenance strategies.
IQZ employees use qualitative and quantitative fault tree analyses, among other things in the area of functional safety, in order to obtain initial estimates of the probability of a defined top event occurring at a very early stage of the product development process. The software-supported creation and calculation allows different system configurations to be compared with each other in order to achieve optimum safety, reliability and cost-effectiveness.
As a basis, IQZ can access all common failure rate databases. In addition, the use of the Wuppertaler Zuverlässigkeitsprognosemodell enables the inclusion of customer-related failure rates