ACTIVE BOW TIE
Version 1.7 launched in September 2007
Bow tie approach was originally devised to energise the safety management system. In its original formulation it was used in the hazard identification and the development of hazard register, but has recently been extended to operational risk analysis to link risk barriers to the day-to-day tasks of personnel. In the bow tie approach it is assumed that each specific hazard can be represented by one or several threats that can trigger the hazard and cause an initiating (top or accidental) event. Each initiating event (loss of control situation) may lead to unwanted consequences. Risks can be assessed for each consequence (as shown). For each threat one or several barriers can be specified to prevent or minimise the likelihood of hazard release.
For any barrier there may be internal or external factors which can cause barrier erosion and influence its effectiveness. These factors are modelled as barrier decay modes (failure modes) each of which can be controlled by a suitable secondary barrier. Similarly, if all barriers are breached, and the top event (loss of control) is reached, then mitigation barriers and recovery measures should be provided to mitigate unwanted consequences and recover from the accident situation. The barriers with different coloured bars on the right hand side are intended to represent different groups of workers, subcontractors, or different types of barriers. The example below shows barriers under port control (black bar), vessel control (blue bar), and non-existent barriers (grey bar). The numbers in barrier boxes denote post indicator of the responsible person and the corresponding task which ensures that the barrier is operational at all times.
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