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.
A bow tie is a graphical depiction of pathways from the causes of an event or risk to its consequences in a simple qualitative cause-consequence diagram. It is a simplified combination of a fault tree that analyses the cause of an event or risk, the left hand side of the diagram, and an event tree that analyses the consequences, the right hand side. It is represented as a bow tie (Figure 1), where the knot of the bow tie is of the point where the fault tree paths converge and the event tree spans out. While bow tie diagrams can be constructed from fault and event trees, they are more often drawn directly from a brainstorming session, providing a fruitful basis for a group exploration of controls.
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