The following ten ‘Golden Rules’ provide practical guidance for developing effective bowtie diagrams bringing some consistency into the bowtie development process.
- 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)
- In general, bowtie diagrams are not quantified and their primary purpose is to represent hazard management arrangements
- The ‘top event’ represents the point at which control of the hazard is lost
- Threats are states, conditions or occurrences which could lead directly to a top event
- Consequences are discrete worst-case outcomes of the top event with no mitigation barriers in place
- Barriers must be tangible and must have an effect substantially to prevent or mitigate the top event
- Escalation factors should be used sparingly representing only barrier failure modes presenting a major threat
- Human error should not be treated generically, but should be included as specific threats to the top event or to barriers
- Bowties should be developed and reviewed by personnel with practical knowledge of the systems being described
- Break the rules where necessary to improve risk communication, these rules are intended to provide guidance not a straitjacket
