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2 Scientific Journal of Gdynia Maritime University

2 2023

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Hazard analysis of an autonomous container handling system – a comparison of STPA and HAZOP methods

Heikkilä Eetu, Malm Timo, Tiusanen Risto, Ahonen Toni

Scientific Journal of Gdynia Maritime University

2023

nr 125

25--39

Increasing automation is a major trend in container terminals. In automated container handling systems, safety has been previously ensured by segregating the automated machinery from other traffic and workers moving on foot. Currently, further increases in flexibility are sought by developing autonomous systems that are capable of mixed-traffic operations without the need for separate operating areas. This increases the complexity of the systems and introduces new safety hazards. In addition to traditional hazard analysis methods, new approaches are needed to address the emergent risks related to autonomous operations. This paper studies the applicability of the STPA (system-theoretic process analysis) method in hazard analysis of an autonomous machine system. To support the evaluation, we define evaluation categories for comparison of the analysis methods. We also compare STPA with an established method, HAZOP (hazard and operability study). To perform the comparison, both STPA and HAZOP are applied to an autonomous container handling system concept. The study suggests that both STPA and HAZOP are well suited to support the development of autonomous machinery. However, we also highlight some notable differences in the methods, mostly related to the different underlying accident models that they utilise. HAZOP is an established method with tools and standards available. STPA, on the other hand, provides a well-defined syntax to ensure the analysis quality and a system modelling approach that supports the system development.

Formal verification of STPA with model checking

Kwon Ryeonggu, Kwon Gihwon

Scientific Journal of Gdynia Maritime University

2023

nr 125

7--24

As technology advances, hardware-centric systems are rapidly moving towards software-centric ones, and their complexity is rapidly increasing. In particular, systems directly related to safety require thorough verification. Model checking exhaustively explores the state space of the abstracted system to check whether properties written in a logical formula are achieved. In this paper, the control algorithm of the controller is verified using model checking to discover risk scenarios during the STPA steps. Two case studies are conducted using the widely used model checkers NuSMV and UPPAAL. We then explain the empirical results and compare two model checkers based on their characteristics. Finally, we discuss the benefits of applying model checking in the process of STPA.