A 4-zone concept for operational risk assessment in ship-ship encounters incorporating human performance and data analysis

This paper reviews and synthesises operational methods for assessing ship-ship collision risk, with particular emphasis on human performance and data-driven analysis, within a 4-zone concept inspired by ALARP (As Low As Reasonably Practicable) principle. An integrated conceptual approach is proposed that combines an expert-based declarative arena defining outer risk zone with the Collision Avoidance Dynamic Critical Area and the Event Horizon to delimit inner risk zone. The central challenge addressed is the representation of risk progression within the middle zone, with specific attention to the role of human performance. Selected qualitative and quantitative approaches are reviewed, including Human Reliability Analysis, Event Risk Classification Methods, systems-theoretic methods, and AIS-based (Automatic Identification System) traffic analysis. Their applicability, limitations, and compatibility with the Event Horizon concept are critically discussed within the 4-zone concept tailored to ship-ship collision scenarios. The paper concludes that no single method is sufficient. However, an AIS-based approach, enhanced by a selected human reliability approach, provides the most promising basis for a meaningful and operationally relevant assessment of collision risk progression.

Keywords: Ship-ship collision risk, Operational risk assessment, ALARP principle, 4-zone concept, Collision avoidance, Risk gradient, Ship-ship encounters, Human performance, Maritime safety, Navigational safety.