Reasoning with failures

TL;DR

This paper introduces a formal model for analyzing faults and failure modes in Safety Instrumented Systems (SIS), improving safety analysis accuracy by systematically considering complex program behaviors.

Contribution

It presents the concept of Failure Mode Reasoning and demonstrates its application in safety analysis of SIS programs, addressing limitations of traditional fault tree methods.

Findings

Formal model effectively captures complex program failure modes

Application to a practical example shows improved safety analysis

Enhances fault analysis beyond experience-based methods

Abstract

Safety Instrumented Systems (SIS) protect major hazard facilities, e.g. power plants, against catastrophic accidents. An SIS consists of hardware components and a controller software -- the ``program''. Current safety analyses of SIS' include the construction of a fault tree, summarising potential faults of the components and how they can arise within an SIS. The exercise of identifying faults typically relies on the experience of the safety engineer. Unfortunately the program part is often too complicated to be analysed in such a ``by hand" manner and so the impact it has on the resulting safety analysis is not accurately captured. In this paper we demonstrate how a formal model for faults and failure modes can be used to analyse the impact of an SIS program. We outline the underlying concepts of \emph{Failure Mode Reasoning} and its application in safety analysis, and we illustrate the ideas on a practical example.