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  • Writer's pictureErik Lindén | Consultant

Bowtie Analysis - An Introductory Guide to the Methodology and How It Can Be Used in Industrial Risk Assessment

Updated: Mar 18

In this article:


Bowtie analysis in industrial risk management.

What is a bowtie analysis?

A bowtie analysis is a graphical risk assessment method focusing on activity risks considered as Major Accident Hazards (MAH), where there is a potential for fatalities, significant damage on assets as well as environmental impact. The idea is to systematically go through all systems in a production series to spot any kind of weaknesses that could trigger an accident and further increase the consequence severity.


As a part of hazard management and based on the identified high-risk scenarios, the procedure of the bowtie method is to allocate resources and add control measures where they are needed.


The bowtie analysis is known for providing precise visibility as it gives the assessor the possibility to easily overview major risks. In addition, a bowtie analysis can indicate flaws and vulnerabilities related to the integrity levels of a system.


Bowtie diagram - Characteristics and common terms


First look

Like other risk analysis tools, e.g., the fault tree or the event tree analysis, the Bowtie analysis is illustrated by an object that most people can relate to. Naturally, the bowtie method is illustrated in accordance with its name, namely like a "bowtie". The knot in the middle of the bowtie represents the hazard along with the top event. Common top events are loss of containment, blowout, leak, fire, and explosion.


The left-hand side and the right-hand side indicate threats and impacts (consequences) respectively. Common threats are high pressure, high temperature, fatigue etc. For impacts, this usually means consequences related to serious injuries/fatality, harm to the environment, or loss of material assets/lost production.


Example of typical hazards and subsequent top events.
Example of typical hazards and subsequent top events.


Controls

A threat or an impact can be reduced based on the presence and effectiveness of controls/barriers. A typical scenario involves two types of control: preventative and mitigative. The preventative barriers belong to the left-hand side of the bowtie, while the mitigative barriers belong to the right-hand side.


Controls are usually divided into three major categories: passive, active, and behavioral controls. A passive control is associated with protective design, i.e., dimension criteria for components with built-in tripping points in case of a component failure. An active control refers to a mechanism that at a certain point in a system process activates to ensure functionality. A behavioural control does not relate to a technical function itself, but to a person who ensures functionality to operate the system.


A simple diagram illustrating the bowtie model.
A simple diagram illustrating the bowtie model.



Escalation factors

The control effectiveness can also be affected by the presence of so-called "escalation factors". An escalation factor, as per its name, has the potential to escalate the effectiveness of controls. In common cases, this means that existing controls either are weakened or prevented from functioning successfully.



Left side of the bowtie including a control with an escalation factor.
Left side of the bowtie including a control with an escalation factor.


Typical escalation factors are related to the design of components, i.e., equipment failure, or personnel behaviour (human error), i.e., lack of competence. Escalation factors can occur in all three control varieties and can be hard to prevent from influencing the original control. To manage escalation factors, specific controls can be added to reduce the influence.


Not uncommonly, escalation factors are related to human error. These escalations are often problematic since they are the most complicated and hardest to solve by design. If the control effectiveness ultimately is dependent on human accuracy, without the possibility of eliminating the risk by using a machine, then the only effective controls are routine procedures and training of personnel.


Application and use of the bowtie analysis


Bowtie analysis is most effective as a group assignment

In practice and according to company standards, a typical bowtie analysis is conducted through a multidisciplinary workshop, where relevant representatives are gathered to commonly assess the bowtie(s) and the risk(s) associated with each of them. This way, with different takes and perspectives on subjects, more detail can be added to the discussion making it more holistic and diverse.


The workshop team usually consists of disciplines from various engineering divisions (e.g., chemical, civil, electrical, mechanical engineers, etc). Besides this group, there are often other disciplines working with environment and quality assurance, i.e., Quality, Health, Safety, and Environment (QHSE) managers/engineers. Moreover, the ultimately responsible managers in the project are present at the table to ensure that the right information is provided and also to approve that possible action points are listed and delegated to the correct discipline(s)/stakeholder(s). The workshop session is facilitated and organised by a representative from either the study organiser or a third-party company.



Bowtie analysis performed as a multidisciplinary workshop.
Bowtie analysis performed as a multidisciplinary workshop.


Risk management practices for bowtie analysis

The bowtie study starts by analysing a few observed threats and impacts with their existing controls. It is not uncommon that these threats, impacts, and controls are prefilled prior to the workshop by the study organiser or a third part company. Furthermore, the idea is to fill out possible gaps in terms of control measures on both sides of the bowtie. The idea is to enrich the bowtie diagram as much as needed so that no unclarities are left from the workshop session. Issues and flaws should be well stated and documented along with their corresponding action points to be followed up.


What are the advantages of bowtie analysis?


Overview, transparency, and zoom in

The application of bowtie analysis comes with several advantages. Its holistic overview along with its precise and simple process makes it easy for the project stakeholder(s) to visualize the potential outcomes of an event and how to manage risk. The reader can zoom in on contributing threats to see where in the series of controls there is a gap that needs to be filled. This can be both time and cost-saving since it is clearly stated where there is a need for action. The explicit and concise message in each box of a bowtie delivers a message to the reader. That way, it becomes completely clear what it is referring to. Consequently, the bowtie analysis provides transparency to every reader, even for someone who did not attend the workshop.


Ability to zoom in on each threat and its corresponding controls.
Ability to zoom in on each threat and its corresponding controls.



Systematic technique

Just like a normal wear-on bowtie, the bowtie method follows a systematic procedure. It can almost be compared with a food recipe that follows a strict preparation order with some room for flexibility. Unlike a Hazard Identification (HAZID), where the scope is generally large and more open for broad discussions, the bowtie analysis narrows the scope and focuses on the most critical aspects with the greatest impact. Due to this, a bowtie analysis can normally be performed over a short amount of time.



Systematic step-by-step solution to finalise the bowtie.
Systematic step-by-step solution to finalise the bowtie.



Focus on major business values

From an industrial risk management perspective, there is usually an interest to investigate where in a project's design there might be a need for actions or improvements. Faults and flaws in a system are usually indicating that there will be issues in one way or another. Since flaws and faults normally result in undesirable results that tend to harm or decrease the profit of a company, these are of great priority to work against.


Causes of people's death and serious harm to the environment have previously shown, e.g., from the Deepwater Horizon disaster in 2010, that the consequences are major in several aspects. The reputational impact due to media monitoring can also lead to a company boycott, resulting in a financial crisis. In the worst case, the effects of such an event can be so devastating that the company falls.


Bowtie analysis in today's businesses


Oil and gas industry

The bowtie method was brought to life in conjunction with the tragic catastrophes in the oil and transportation industries, e.g. the Deepwater Horizon disaster. From the starting point until this point, the bowtie method has been a priority tool for worldwide operations whenever there has been a need to effectively identify and assess risks on a larger scale.


Bowtie analysis in oil and gas industry.
Bowtie analysis in oil and gas industry.


Chemical industry

In chemical industries, the demand for effective controls to prevent any hazards from happening is the be-all and end-all in project planning. In similarity with the oil and gas industry, chemical industries involve several common parameters, e.g., major varieties of pressures and temperatures. As standards and demands become sharper and more specified, there is a need to implement more often and refine the methods for analyzing the risks related to the process. As an initial step of the concept design phase, the bowtie analysis could be seen as the way forward to clearly identify the risks related to new installations in complex systems.



Bowtie analysis used on chemical production facilities.
Bowtie analysis used on chemical production facilities.


Renewable energy sector

Since the launch of bowtie analysis, the concept has spread to other sectors and nowadays the requests are more frequently coming from companies within the renewable energy sector. As technical solutions that are promoting the green transition claim larger market shares within the energy sector, bowtie analysis is getting more and more common. With the knowledge and experience from earlier major accident hazards in hand, bowtie analysis is now part of the whole energy sector.


In terms of using bowtie analysis, the major difference between oil and gas and renewable energy, is the difference in major accident hazards. Each specific energy sector will have its specific major accident hazards and associated controls, but the general approach and methodology for the bow tie analysis will be the same.



Offshore windfarm.
Offshore windfarm.


Conclusion

In summary, the bowtie method is a graphical risk assessment method focusing on major accident hazards. The method's main purpose is to identify high-risk events that could have the potential for either fatalities, significant damage on asset or impact on the environment. Examples of such events are loss of containment, blowout, leak and fire/explosion.


Performing a bowtie analysis is done by organising a multidisciplinary workshop where the attendees collaborate to find any kind of flaws, faults, or trigger points in a system that could initiate a hazardous event. This is done by following the logical flow of the bowtie method. In the bowtie diagram, the trigger points are defined by threats on the left-hand side of the bowtie, while the consequences of an event are stated as impacts on the right-hand side of the bowtie. To prevent the threats from triggering a hazardous event from occurring and/or mitigate the degree of impacts, controls/barriers are added on both sides of the bowtie. The idea is to create a package of control measures that is as waterproof as possible.

Finally, the bowtie technique is applicable on a broad scale where actors in various industries can implement this method as part of their risk analysis tools.


Hopefully, you and your colleagues now know more about bowtie analysis and how it can be used. If you have questions or want ORS Consulting to help you and your company in a barrier management project, please do not hesitate to contact us.

Image by Thought Catalog

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