Explanation
A bowtie starts with a hazard, for example working at height, and a central event (top event): the moment you lose control, such as a fall. On the left are the threats or causes that can lead to it, with for each cause the preventive barriers that should stop the event. On the right are the possible consequences, with recovery barriers that limit the damage. The shape resembles a bow tie.
The diagram combines the thinking of a fault tree (causes) and an event tree (consequences). A barrier can be technical, such as fall protection, organisational, such as a work instruction, or dependent on human action, such as a check by the foreman. Escalation factors, such as time pressure or poor maintenance, weaken a barrier and therefore get their own control measure.
A risk matrix and a Kinney calculation give a risk a score. A TRA (task risk analysis) works out one task step by step. The bowtie does something different: it shows how many barriers surround one serious scenario and how strong they are. You mainly use it for risks with a high score or severe consequences, for situations where several causes come together, and to explain a scenario to colleagues or a client.
A bowtie takes time and works best with people who know the work, so do not use it for every risk. Choose the scenarios with the greatest impact, work out the barriers until they have owners and checks, and feed the result back into your RI&E, TRA or risk register. A barrier without an owner and a check is an assumption.
Example from practice
A contractor makes a bowtie for 'fall from height during roof work'. On the left are threats such as a slippery surface or a missing edge, with barriers such as edge protection and an approved TRA. On the right are the consequences serious injury and work stoppage, with a safety net, an emergency plan and rapid first aid as recovery barriers.
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