Model-based Safety Risk Assessment using Behaviour Trees

For complex engineered systems, it is important to conduct technical risk assessment early in the system development life-cycle, in order to identify critical system requirements, such as safety requirements, that should be included in design. This paper proposes a model-based approach to such assessment, which can be applied from the system requirements analysis stage onwards. The approach starts with the application of the Behaviour Trees modelling notation to natural language functional requirements. The BT model is then extended to include the events and conditions that might contribute to hazards, and automated model checking is used to identify the mechanisms by which component or subsystem failures can lead to hazardous system failures. The approach is intended to be used iteratively in design and analysis, to assist system designers in assessing the effectiveness of system safety requirements. A hypothetical bushfire-fighting management system is used to illustrate the approach