A novel real-time safety level calculation approach based on STPA

Abstract

This paper proposes a novel approach to dynamic safety level calculation for safety-critical systems based on the STAMP accident model and the implementation of a mathematical model. The proposed approach utilises (1) an STPA hazard analysis applied to the system in question, (2) system operational data from domain experts regarding process duration and reaction times, and (3) real-time system data. The STPA analysis is transformed into acyclic diagrams that graphically indicate every possible sequence of safety constraint violations that could lead to a loss (path). Based on this diagram the safety level (SL) of a system is defined as SL=p→w$ {\rm{SL}} = {\overrightarrow {\rm{p}} _w} $ where p→w$ {\overrightarrow {\rm{p}} _w} $ is the most detrimental to safety path which is active for any possible time value or context in the system’s operation. This approach is also demonstrated using as a case study the “classical” Train Door STPA analysis example. This paper aims to introduce a new perspective on the problem of measuring and managing the actual safety level of highly complex socio-technical systems in real time and discusses related limitations and future research opportunities of this approach.