Sensitivity Analysis Applied to Multiple Fault-trees

Fault-tree analysis is applied to technological systems to determine the probability of system’s failure modes with unacceptable consequences, called “critical states”. As many Fault-trees as the number of system’s critical states are constructed and analysed; when their probabilities are deemed not acceptable, the Importance and Sensitivity Analysis (ISA) is applied to improve the system safety through design modifications. This paper describes a novel approach based on the ISA method aiming at supporting the designer in achieving the objective of obtaining a uniformly protected system satisfying the predefined design goals in a cost-effective way. It is based on the concurrent analysis of all relevant system’s Fault-trees. This approach aims at overcoming the limitations of the current approach, which is based on the sequential analysis of Fault-trees. In addition, it extends the ISA application also to “over-reliable” or “over-protected” system functions on which the reliability/maintainability characteristics of the involved components can be relaxed with consequent cost saving.