Ten rules are presented to assist in the development of robust bowtie diagrams, providing clarity, definition and guidance to ensure that the objectives of the study are met.

Bowtie diagrams are a well-established and increasingly widespread tool for risk management, providing a concise summary of a complex process safety situation. Experience of reviewing bowtie diagrams has made clear that the quality and depth of bowtie diagrams are extremely variable. These problems may stem from a lack of clarity around the objectives of the bowtie exercise, with no clear understanding of the ultimate use to which a bowtie will be put. Problems may also arise from a lack of understanding or loose definition of the various component parts of a bowtie. A lack of rigor identifying barriers may result in an overestimate of the strength and number of safeguards.

For this reason, ten ‘golden rules’ are presented for ensuring robust bowtie diagrams. These rules provide: clarification of the objectives of the exercise; guidance on choosing clear study boundaries; definition of the elements of bowties; and clarity on what constitutes a barrier. In addition the rules provide guidance about the incorporation of human factors; an area prone either to neglect or over-simplification.

Whilst the concept of a bowtie diagram is simple to grasp, producing bowties which are of a consistent standard is notoriously difficult. The rules presented in this paper provide a framework for standardizing and quality-checking bowties, with the intention of improving their effectiveness in managing major hazards.

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