The Bow-Tie Method: A Hybrid System Safety and Risk Analysis Approach for Safety–Critical Sociotechnical Systems

Effective functioning of dynamic systems hinges upon the implementation of an in-depth Risk Management System (RMS). Central to RMS is the adoption of a rigorous risk analysis methodology. The Bow-Tie (BT) method emerges as a pivotal approach in this context, offering a structured framework to examine and elucidate complex causal relationships within high-risk scenarios. By visually delineating potential accident scenarios stemming from specific system-level hazards, the BT method furnishes a holistic overview of risk scenario landscapes. Moreover, through the identification of either preventive control measures or protective layers, it delineates actionable steps for process or organizational risk management. The BT diagram, comprising integrated Fault Tree (FT) and Event Tree (ET) components, embodies a consolidated representation of risk elements, including root and intermediate causes, preventive or protective safety barriers, and potential consequences, fostering a unified framework for accident mitigation. While the left side of the diagram delineates pre-event accident scenarios, the right side encapsulates post-event occurrences, thus encompassing both preventive and reactive measures. Leveraging the synergy of FT and ET methodologies, the BT method empowers users with a dual analytical approach suitable for both qualitative and quantitative risk assessment. This chapter elucidates the BT methodology, its variants, its primary applications within sociotechnical systems and key challenges and drawbacks associated with BT analysis. It aimed at offering deeper insights into its efficacy as a hybrid system safety and risk analysis tool to design and operate complex systems safer and resilient against system-level threats and shocks. Finally, some primary drawbacks have been highlighted, calling for further research. This chapter also offers practical guidance for researchers and risk practitioners to implement this approach in the system safety analysis of complex systems.