The aim of this thesis is to extend the current techniques available for the analysis of
non-coherent fault trees. At present importance analysis of non-coherent systems is
extremely limited. The majority of measures of importance that have been developed
can only be used to analyse coherent fault trees. If these measures are used to
analyse non-coherent fault trees the results obtained are inaccurate and misleading.
Extensions for seven of the most commonly used measures of importance have been
proposed to enable accurate analysis of non-coherent systems.
The Binary Decision Diagram technique has been shown to provide an accurate and
efficient means of analysing coherent fault trees. The application of this technique for
the qualitative analysis of non-coherent fault trees has demonstrated the gains to be
made in terms of efficiency and accuracy. Procedures for quantifying a non-coherent
fault tree using this technique have been developed; these techniques enable
significantly more efficient and accurate analysis than the conventional techniques for
Fault Tree Analysis.
Although the Binary Decision Diagram technique provides an efficient and accurate
means of analysing coherent and non-coherent fault trees, large trees with many
repeated events cannot always be analysed exactly. In such circumstances partial
analysis must be performed if any conclusions regarding system safety and reliability
are to be drawn. Culling techniques employed in conjuncfion with the Binary Decision
Diagram method have been developed for the partial analysis of both coherent and
non-coherent fault trees.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.