Evolved Methods for Risk Assessment

Abstract

The foundations of risk assessment tools such as fault tree analysis and event tree analysis were established in the 1970s. Since then, research has made considerable advances in the capabilities of analytical techniques applicable to safety critical systems. Technology has also advanced and system designs, their operation conditions and maintenance strategies are now significantly different to those of the 1970s. This paper presents an overview of a new methodology developed, retaining the traditional ways of expressing system failure causality, which aims to develop the next generation of risk assessment methodologies. These evolved techniques, appropriate to meet the demands of modern industrial systems, aim to overcome some of the limitations of the current approaches. These new tools and techniques will seek to retain as much of the current methodology features as possible to reduce the learning curve for practitioners and increase the chances of acceptance. The new approach aims to increase the scope of event tree/fault tree analysis through the incorporation of Petri net, Markov model, and binary decision diagram-based methodologies. Use of these techniques incorporates features such as: non-constant failure rates, dependencies between component failure events, and complex maintenance strategies to boost the capabilities of the methods. In addition, it considers dedicated routines to analyse the accident risk of transport systems formulated as phased mission models. This type of modelling is demonstrated through the application to an aeronautical system, where the system is modelled as a mission consisting of a series of phases. Mission success requires the successful completion of each of the phases. This approach allows the requirements for success (and therefore failure) to differ from one phase to another. It is also possible to model scenarios whereby a system fault that occurs in one phase of a mission may not affect the system until a later phase of the mission.