Bow Tie Accident Investigation

There are numerous techniques available to methodically investigate incidents and help identify the “root causes”. In this article we explore the 8-step process for what is referred to as “bow tie” analysis. The shape of the analysis diagram below gives this technique it’s name.

The bow tie method is a visual way that helps to understand the factors leading up to an (adverse) event and the post-incident mitigation factors, per the diagram below.

                                                                            Visual presentation of the bow tie analysis

I like this techniques at it visually maps out aspects that act as reminders in your analysis of the incident. For example, it highlights there may be numerous potential causes, and pre-event controls that have failed, and then prompts us to consider post-event mitigation factors we could or should have had in place, and finally the factors that effect the potential outcome of the event in question.

In essence, the eight steps are:

Step 1 - Hazard & Event Scenarios

Step 2 – Causes or Threats

Step 3 – Potential Outcomes

Step 4 – Logical Flow & Completeness Test

Step 5 – Prevention Controls

Step 6 – Mitigation Controls

Step 7 – ID Safety Critical Activities & Equipment

Step 8 – Review & Test Reliability of Controls

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