Bowtie risk assessment is broadly used in high hazard industries. The bowtie modeling has proven to be a successful method to: 1) visualize risk scenario’s and control measures, 2) facilitate structured brainstorming and 3) identify gaps in risk control, by highlighting information that is lacking or unknown.

Human Factors: a greater threat than technical failures

The general opinion nowadays states that Human Factors represent a greater threat to complex hazardous systems than technical failures do. This means that if Human Factors are not present in your risk modeling tool, then you are lacking and ignoring crucial information.

Human Factors can directly cause incidents, but can also affect risk controls. Therefore, Human Factors can be found in two elements in the bowtie diagrams; as a threat (also called cause) and/or as the escalation factor (also called degradation factor).

Taking Human Factors into account in BowTieXP

Threats are possible causes for the loss of control over the hazard or hazardous process. Threats can be grouped into four main categories: primary equipment failures, environmental influences, concurrent operation conflicts, and Human Factors. Human Factors appear as a threat in a bowtie diagram when the human act has the ‘causal power’ to directly influence the hazardous operation to result in a loss of control. The threat is not described in general terms such as ‘Human Factors’, but is described as the act that could cause the top event. An example is a crane operator who accidentally presses the wrong button which causes an unwanted release of the load.

Figure 1: an example of Human Factor as a threat.

Escalation factors are conditions or acts that defeat or reduce the effectiveness of a safety barrier. Escalation factors refer to the holes in the cheese in the Swiss cheese metaphor. As the Human Error Theory tells us, barrier failures are often caused by substandard human acts or omissions. An example is a crane operator who is overriding a barrier system that is designed to prevent the crane operator to (accidentally) release the load during lifting.

Figure 2: example of Human Factor as escalation factor

Some practical tips

Adding Human Factors into your bowtie diagram under threats or escalations factors helps create a more comprehensive picture. Key here is to get the wording right: don’t just write down ‘human factors’, but phrase it as a specific action (see Figure 2) that can cause the top event or reduce the effectiveness of a barrier. By phrasing it in such a manner, the diagram reads more as a story which helps people’s thought processes. This will help everyone involved come up with better threats, barriers, actions, recommendations, etc.

Learn about Human Factors from Prof. Dr. Jop Groeneweg

In this blog, we’ve shown you how to visualize the human factors in BowTieXP, but to find and name the specific human factors is a wholly different skill. For this, we trust our partners in the academic world such as Prof. dr. Jop Groeneweg from Leiden University.

Curious to find out what Prof. Dr. Jop Groeneweg has to say about Human Factors? Check out the trailer of Risk Expert Sessions 2: The Human Factor, or sign up for the Risk Management Master Class where Prof. Dr. Jop shares his insights during the Safety Culture & Human Factor course.

Of course, there are many different insights and views on how to include human factors in the bowtie method. We are very curious to hear your thoughts on this subject, so feel free to leave a comment below or to contact us in case of any practical questions.