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The bow tie method
- 1. Bow tie method JohnBaker
- 2. Objective • Explain thebow tie method • Consider whether it is a useful tool for safety event investigation Slide 2
- 3. Initiating event Success event 1 Success event 2 Failure event2 Failure event 1 Success event 3 Failure event 3 Accident Failure 3 Failure 1 Failure 2 Failure 5Failure 4 Fault and event trees Slide 3 FAULTTREE EVENTTREE Bow ties use the principles of both fault trees and event trees, forming a ‘bow tie’ shape:
- 4. Bow tie principles Slide4 Recovery preparedness Preventive controls CONSEQUENC ES CAUSE S System vulnerability System resilience
- 5. Bow tie models Bowties: • are graphical, not numerical • link to known threats • Provide qualitative indication of how sufficient a control measure is Slide 5
- 6. Origins • First developedin late 1970s • Royal Dutch/Shell first organisation to make full use of technique • Now widely used in high-hazard sectors Slide 6
- 7. Sector applications • Oil& gas • Aviation • Mining • Marine • Healthcare • Rail (fairly recently) Slide 7
- 8. Creating a bowtie Slide 8 HAZARD TOP EVENT CONTROL 1 CONTROL 2 CONTROL 3 THREAT 1 THREAT 2 ESCALATIO N FACTOR 1 CONSEQUENC E 1 CONSEQUENC E 2 HAZARD Situation with the potential to cause harm TOP EVENT The point where control over the hazard is lost THREAT Unsafe acts or conditions that would lead to the top event ESCALATIO N FACTOR Anything that would cause a control barrier to fail
- 9. Process 1. Identify thehazard and resulting top event 2. Identify the threats that can cause the top event 3. Show the control barriers that should prevent the threats 4. Describe the possible consequences 5. Identify the control barriers that limit or remove the consequences 6. Identify escalation factors that could weaken or remove the control barriers 7. Identify the controls for the escalation factors 8. Identify people responsible for the controls 9. Link the controls to the safety management system Slide 9
- 10. Example – confinedspace training Slide 10 Smoke/fume s Pressure gauge Insufficient air in BA cylinder Death or major injury Discomfort Insufficient breathable air for firefighter to get to safety Warning whistle Routine charging BA cylinder valve switched off Buddy checks Moisture in system causes freezing Compressor filters Filters blocked Maintenanc e schedule Safety doors Safety Officer Safety doors Safety Officer
- 11. Bow tie –object hazard Slide 11
- 12. Bow tie –fire on train hazard Slide 12
- 13. Bow tie –moving train hazard Slide 13
- 14. Bow tie –station fire hazard Slide 14
- 15. Bow tie inaccident investigations • Useful visual aid to brainstorming possible causal factors and controls • Useful for understanding possible incident sequences and consequences • If a bow-tie already exists, helps an investigator understand what controls the organisation believes are in place, and how effective they are Slide 15
- 16. Bow tie asa risk assessment tool - strengths • Provides a way of visualising risk assessments • Gets people involved – promotes understanding of hazard management and their role in it • Helps make the distinction between preventive controls and resilience controls • Includes all credible scenarios ***** • Structured approach where quantification is not possible or desirable Slide 16
- 17. www.silvermoorconsulting.co. uk Silver Moor BusinessConsulting LLP t: 01934 824609 | m: 07551 124383 Registered in England and Wales, OC389666. Registered office: Cannaways Farm, Banwell, North Somerset, BS29 6LQ