Standards Development

Scope

This document describes the Fault tree analysis (FTA) technique and provides guidelines for its application. FTA is used to identify and analyse combinations of events, conditions and factors that cause or can potentially cause or contribute to the occurrence of a defined undesirable outcome, referred to as the "top event".

The document includes:

–        definitions and descriptions of commonly used terms and symbols;

–        the purpose, applications and limitations of fault trees (FTs);

–        a description of basic concepts and principles;

–        a description of the steps involved in scoping, constructing and developing the FT;

–        guidelines for on performing qualitative and quantitative analysis of the FT, including discussion of requirements and limitations of the associated mathematical models;

–        identification of basic items to be included when documenting and reporting the FTA;

–        methods for performing FTA when some of the commonly used assumptions are not satisfied (e.g. non-coherent FTs, dynamic FTs);

–        example applications in support of the above;

–        procedures for calculating dependability measures (unavailability, failure frequency and unreliability) for different types of system, with constant or time-dependent probabilities or with non-repaired or repaired items).

In annexes, the document also describes:

–        the relationship of FTA with other related techniques such as reliability block diagram analysis (IEC 61078 [1]), failure mode and effects analysis (FMEA) (IEC 60812 [2]), event tree analysis (IEC 62502 [4]) and Markov techniques (IEC 61165 [6]);

–        methods by which the importance of various events included in the FT can be established;

–        automated fault tree construction;

–        the application of FTs to the estimation of dependability parameters

–        mathematical models necessary for large and more complex FTs;

–        numerical examples demonstrating the use of FTs in dependability.