Proceedings of the

The 33rd European Safety and Reliability Conference (ESREL 2023)
3 – 8 September 2023, Southampton, UK

The Extension of Commonly used Measures of Importance for Dynamic and Dependent Tree Theory (D2T2)

Sally Lunta and John Andrewsb

University of Nottingham, Resilience Engineering Research Group, UK.


Traditional Fault Tree Analysis (FTA), known as Kinetic Tree Theory (KTT), was derived by Vesely et al (1970) to model and analyse engineering systems. The tree structure provides a clear visual representation of the causes of system failure. FTA has two stages, qualitative and quantitative analysis. Part of the quantification process is to calculate measures of importance. FTA is limited by the necessary assumptions of constant component failure and repair rates and independence of component failure and repair rates. The D2T2 methodology overcomes these assumptions, but a new methodology to calculate measures of importance when such assumptions are not met is required. This paper proposes extensions to 5 common used measures of importance.

Keywords: Importance measures, Fault tree analysis, Quantitative analysis, Dependencies.

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