System-Theoretic Analysis of Hazard Causal Factors and Scenario Development for Complex Systems

This paper proposes a system-theoretic process and analysis (STPA) for complex systems (STPA_CS) to analyze the hazard factors arising from interactions between multiple components in a system. STPA_CS is realized by adding the following features to STPA: (1) using class diagrams to define control signal inputs and outputs of components, (2) defining component configurations by using composite configuration diagrams, (3) clarifying hazard occurrence processes by tracing the control signal exchange paths, and (4) facilitating seamless hazard analysis by detailing the class diagrams and repeating the hazard analysis. When STPA_CS and STPA are applied to a chiller system, STPA_CS clarifies fifty-one hazard factors and scenarios, while STPA clarifies thirty hazard factors and scenarios. This represents an improvement of 60% in the analysis results and demonstrates the advantages of STPA_CS.