How do barriers relate to one another? Taking dependencies into account in Bowtie

Loss of containment could lead to fire. Having multiple barriers or controls between those events could give the impression that the operation is well-protected. But what if your barriers are dependent on each other?

Many organizations struggle with the level of detail when defining barriers in bowtie risk modeling. For example: should barriers be fully independent and therefore be more generically defined? Or does that make the barriers less useful, because fewer details are presented and assessed?

Often organizations need more than just one level of detail. It all depends on your goal. One way to do this is by using the barrier family functionality of BowTieXP. In this blog, we will give you an introduction to this functionality and show you how to set it up in the software.

The solution: barrier families

The ‘barrier families’ functionality allows for grouping individual dependent barriers together into one independent family, with a common family name. The display settings can be set to display the individual barriers, or the family as a group. There is also the possibility to manually expand or collapse specific families. All depending on the level of detail that needs to be shown. Barrier families can, for example, be used to indicate the higher level safety measures (systems) within the organization. Or the exact opposite: to show the individual barriers that are part of a larger barrier family (system).

How to use barrier families and get to the right level of detail

One way for getting the right level of detail for barriers is to make sure they follow the ‘detect, decide & act’ guideline. Let’s illustrate this by the example of ‘loss of containment could lead to fire’. To prevent this from happening, the following barriers could be implemented:

  1. Fire & gas detectors (detect)
  2. Decision by operator, based on fire alarm (decide)
  3. Manually activate sprinkler system (act)

In this specific example, barrier 1: ‘Fire & gas detectors’ influences the effectiveness of barrier 2: ‘Decision by operator, based on fire alarm’. In the same way, both barrier 1 and 2 would influence barrier 3: ‘Manually activate sprinkler system’. As all of the above-mentioned barriers could function correctly by itself, they could give the impression that the pathway to a consequence is well protected. Still, this would not be correct as one or more barriers are dependent on another barrier.

To tackle this issue, the family function in BowTieXP gives the possibility to group the three (dependent) barriers (figure 1) into one independent barrier family (figure 2). In this specific case, it would be ‘firefighting system’.

Figure 1: Example of the split out ‘detect, decide, act’ firefighting system.

Figure 2: One independent barrier family which consists of three sub-components.

TIP: Collapse the families when for instance, presenting the bowtie to the board, and fully expand for operational use in a toolbox meeting.

Benefits of grouping barriers

Grouping the dependent barriers could change the scope on a specific scenario between two events. A non-grouped barrier path could give the impression that a consequence is well protected while a grouped path would provide a more realistic scenario. In the specific example, the lesson learned would be that there is only one real, independent barrier instead of three. This could lead to a decision to implement additional barriers to protect the consequence.

Besides revealing weaknesses in your safety management system, it can bridge the gap in abstraction level between high-level barriers and specific barriers, to communicate with different audiences. Lastly, it can be used to split out detect, decide, and act barrier components, while keeping system-level barriers available in the same diagram.

How to use barrier families in BowTieXP

To use barrier families in the software, take the following steps:

  1. Decide which barriers need to be part of a family
  2. Multi-select those barriers by holding ctrl while selecting
  3. Right-click >Edit barriers, or hit F4
  4. Enter the family name (directly under the description field)
  5. Hit OK
  6. Repeat the process for other barrier families in the diagram
  7. Use the 3 icons in the menu bar for display settings (see image below)Mode: enables you to select the property to group > select ‘family’
    2nd button (from the left): expands grouped items
    3rd button: collapses items to group-level

Notes: It’s possible to put barriers on different scenario lines in the same family, but when using the visualization mode, only barriers on the same line will be visually grouped together.

In the ‘Mode’ menu there are other ways to group barriers on the same line together by various properties. For example, try selecting ‘Effectiveness’ to collapse barriers with the same effectiveness value and form a group.

What did you think of this blog?

We are very curious to hear your thoughts on this blog. What do you think about this solution? Feel free to leave a comment and we’ll get back to you as soon as possible.



2018-03-09T10:14:42+00:00Blog, BowtieXP|


  1. reinier May 6, 2018 at 1:55 pm - Reply

    I can’t multiselect and edit? Is this an add on?

    • Marko Krnjic May 18, 2018 at 11:02 am - Reply

      Hi Reinier,

      To display barriers in the grouped way you do need BowTieXP Advance, otherwise you can display to which family the specific barriers belong but you can’t display them as one grouped barrier. However, in all versions it is possible to select multiple barriers at once by holding “CTRL” (before clicking) and click on all relevant barriers in the diagram. If you then right-click on the selection you should find an option called “Edit barriers…”. Choosing this will take you to a pop up window where one of the options is “Family”. Here you can specify how the family should be named. If you are using BowTieXP standard you can click on the little eye icon in the right bottom corner of the barrier and make “Family” displayed as S (stands for short) or L (stands for long). This would specify to which family the barriers belong.

      Hope this answers your question. If not, please contact our support team (support at cgerisk dot com) and we will try to provide guidance.

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