Conference on Railway Excellence CORE 2026
ESR Consulting's principal consultant Steven Gibson attended CORE 2026 in Adelaide where he presented on Effective Bowtie Diagram Development - Supporting Safety and Risk Management.
Abstract:
Bowtie diagrams have been utilised for some years as relatively simple aides to understanding and communicating safety hazards. However the simple structure of the Bowtie diagram belies the complexity in developing models beyond the text-book examples, particularly at the operational system level where there may be many interrelated hazard scenarios.
In this paper, the authors draw on many years’ experience developing risk models to share practical techniques for developing logical, structured and robust Bowtie diagrams to effectively characterise accident scenarios: their causes, potential consequences, and those control measures designed to prevent or minimize the risk.
The authors discuss some of the pitfalls and how to identify them, including:
- Bowtie terminology and its relationship to common risk management elements.
- The distinction between hazards and Bowtie ‘top events’.
- Effective top event selection and why this matters.
- Consideration of the relationship between Bowtie top events, direct threats and consequences in more complex event sequences.
- Threat identification, and how distinguishing these from risk control failures leads to a better understanding of risk.
- Effective identification of independent risk controls, and why more is not necessarily better.
Drawing on examples from real-world railway systems, the authors demonstrate how the Bowtie diagram technique can be applied including: qualitative and semi-quantitative risk assessments, identification of safety-integrity requirements, risk-reduction control verification, and supporting the argument that risks have been reduced so-far-as-is-reasonably practicable.
The authors conclude with a brief overview of available software tools and open-source options.
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