What is Bow tie Analysis.
Bow tie analysis is a simple process for identifying where new or enhanced controls may be worthwhile. It is a core part of risk treatment planning, particularly where there is a high level of risk or where control effectiveness is assessed as low.
It is a visualization of the path a hazard may take to cause a severe consequence and the combination of preventive and mitigative barriers required to reduce the process safety risk.
A Bowtie diagram is a simplified combination of a fault tree that analyses the cause of an event or risk, the left-hand side of the tree, and an event tree that analyses the consequences on the right-hand side.
A Bow Tie diagram is created by combining two established risk analysis tools, the fault tree, and the event tree. Fault trees picture all possibilities that lead to an event. Event trees work inversely, starting with a single event and modelling all its consequences. In Bow Tie, like for a HAZOP scenario, fault and event trees are joined together so that the diagram shows causes and consequences around a central (or top) event.
Objectives:
- To analyze and evaluate Hazards
- Suggest
Methodology:
It’s worth reminding everyone that a hazard is something that has the potential to cause harm or trigger an Event, for that to happen something must occur to allow the hazard to occur and the event take place.
- Creating the Bow tie
This begins in the middle with the hazard identified during HAZID and the Event to be analysed, make sure it’s written in plain English to ensure that everyone understand what they are trying to analyse.
On the left had side list all the potential causes or threats that would lead to the event happening, ranging from things that are almost certain to happen to things that are remote. On the right-hand side all the consequences that could happen if the event linked to the hazard was to occur will be listed, again there will be a range of them to consider.
Walk through the logical flow of the chart i.e., if this potential threat happens, then this event (linked to the hazard) could happen, and the consequence listed could happen.
- Control & Mitigation
Starting on the left, for each Potential cause a control measure should be put in place that would eliminate that possible cause. Controls are rank high, medium, or low in terms of their effectiveness in being able to stop the potential cause from occurring. On the right-hand side, the same should be done with emphasize on mitigatory steps for if the event actually does occur that would limit or stop the potential outcome or consequences from impacting.
