4.5.2. Colour Coding of Barriers

To support the core function of Bowtie, being a communication tool that is easy to understand, we propose colour coding the barriers by 6M category. The colour assignment was to some extent random and did not follow a particular scheme. In addition, each barrier should have a colour that has not been used before for any other element of the Bowtie diagram. The colour assignment of each M category is shown in Figures 7 and 8. If greater emphasis is necessary, either to draw attention to specific categories, or to provide greater clarity for the visually impaired, additional demarcation could be added in the form of a symbol. Some suggested symbols are illustrated in Figures 7 and 8 below, though it should be noted that these have been added manually as this is not currently a feature of the BowtieXP software used here. Alternatively, hatching may be added to the Bowtie elements.

**Figure 7.** Threat path with coloured barrier categories.

**Figure 8.** Consequence path with coloured barrier categories.

### 4.5.3. Escalation Factor Paths with a 6M Structure

In principle, the escalation factor path on the prevention and mitigation side of the Bowtie diagram could follow the same 6M structure as demonstrated for the threat and consequence path in Figures 7 and 8. The result would look like Figure 9. After the higher-level structure of the Bowtie has been completed, it may in some situations be necessary to extend the analysis to the escalation factors, and in this case, the methodology proposed here o ffers a way this may be approached.

**Figure 9.** Escalation factor path with coloured barrier categories.
