The bowtie method
Figure 1 – A bowtie diagram showing all elements
The bowtie method is a risk assessment method that can be used to analyse and communicate how high risk scenarios develop. The essence of the bowtie consists of plausible risk scenarios around a certain hazard, and ways in which the organisation stops those scenarios from happening. The method takes its name from the shape of the diagram that you create, which looks like a men’s bowtie.
The bowtie method has several goals:
- Provide a structure to systematically analyse a hazard.
- Help make a decision whether the current level of control is sufficient (or, for those who are familiar with the concept, whether risks are controlled to an acceptable level.
- Help identify where and how investing resources would have the greatest impact.
- Increase risk communication and awareness.
The next section will introduce the elements that make up a bowtie diagram. Building a bowtie happens in the same order.
Stpe One: Identify the hazards
A bowtie starts with a hazard we want to analyse. The word ‘hazard’ has a negative connotation in daily life. Let’s take as an example associated to the above video, a part of a BowTie model published by the UK CAA, referred to Runway Excursion on landing.
Figure 2 – An example of a Hazard
In the bowtie method however, hazards are part of normal business and are often necessary to run a business. What makes a hazard special is that this part of the business introduces the possibility for harm to occur. Most hazards are introduced into an organisation for good reasons, otherwise they could simply be eliminated and no harm would be possible. Hazards can be operations/activities (operating rotating machinery, driving a car), substances (chemicals, hot fluids, etc.) or situations (a load suspended at height) we deal with in the normal processes of our business. As long as these hazards are under control, they will not cause harm, but they introduce the potential for harm.
Step Two: Identify Top Events
When control over a hazard is lost, it is usually possible to identify the moment when a normal situation changes to an abnormal situation. That point is called the top event in bowtie and is the centre event of the diagram.
Figure 3 – An example of a Top Event
The top event is not a catastrophe yet, but the company is now exposed to the potential harm of the hazard. It should
be possible for the organisation to bring the situation under control again. If control is regained after the top event has occurred, it will be thought of as a narrow escape that could have led to more serious unwanted events.
Step Three: Identify Threats
There are often several factors that could cause the top event. These are called threats in the bowtie.
Figure 4 – An example of a Threat
Threats lead directly to the top event and should be able to cause the top event independently.
Step Four: Identify Consequences
When a top event has occurred, it can lead to certain consequences. Consequences are unwanted scenarios that could be caused by the top event.
Figure 5 – An example of a Consequence
They should be realistic and specific. Consequences are mainly unwanted because they will lead to loss or damage.
Step Five and Six: Identify Preventive and Recovery Barriers
Risk management is about controlling risks. This is done by implementing barriers to prevent certain events form happening. A barrier (sometimes also called a control) can be any measure taken that acts against some undesirable force or intention, in order to maintain a desired state. Barriers can be hardware systems, design aspects, human behaviour and so on. Barriers are placed on both sides of the top event.
Preventive barriers on the left side of the bowtie prevent the top event from happening.
Figure 6 – An example of Preventive Barriers – Remember: they are the cheapest and the most effective.
Recovery barriers on the right side of the bowtie can either prevent the top event from resulting in unwanted consequences or mitigate further consequences.
Figure 7 – An example of Recovery Barriers – Remember: they are expensive and least effective.
Step seven and eight – identify escalation factors and escalation factor barriers
Once the control measures are identified, the bowtie method takes it one step further and identifies specific conditions or actions that make it more likely that a barrier will fail. These are called escalation factors.
Figure 8 – An example of Escalation factors. Remember: they can be either side of the BowTieXP model.
In case of any question, please connect: firstname.lastname@example.org
Source: UK CAA Significant Seven Risks BowTie diagrams.