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The Bowtie Method: Ten Golden Rules for Building Better Bowtie Diagrams

The following ten ‘Golden Rules’ provide practical guidance for developing effective bowtie diagrams bringing some consistency into the bowtie development process.

  1. Know from the start what you want to achieve with the bowtie since this will affect how you approach the exercise (have a look at our resource for additional uses of bowtie diagrams)
  2. In general, bowtie diagrams are not quantified and their primary purpose is to represent hazard management arrangements
  3. The ‘top event’ represents the point at which control of the hazard is lost
  4. Threats are states, conditions or occurrences which could lead directly to a top event
  5. Consequences are discrete worst-case outcomes of the top event with no mitigation barriers in place
  6. Barriers must be tangible and must have an effect substantially to prevent or mitigate the top event
  7. Escalation factors should be used sparingly representing only barrier failure modes presenting a major threat
  8. Human error should not be treated generically, but should be included as specific threats to the top event or to barriers
  9. Bowties should be developed and reviewed by personnel with practical knowledge of the systems being described
  10. Break the rules where necessary to improve risk communication, these rules are intended to provide guidance not a straitjacket