Last reviewed 11 May 2015

Infographics or information graphics are visual representations of information, data or knowledge, intended to help to communicate complex information in a concise manner, quickly and clearly. Justin Tyas examines how infographics, specifically “bow-tie” diagrams, can be used to express health and safety risk analysis to non-technical personnel, including board members.

Infographics are not a new concept. Some of the earliest known examples of infographics date back to the Late Stone Age, when humans depicted animal portraits on cave walls in the south of France. The ancient Egyptians provide good examples of infographics from around 3000 BC, where hieroglyphics were used to convey language through graphic symbols and icons.

In 1786 the Scottish engineer William Playfair pioneered data visualisation in his book The Commercial and Political Atlas and Statistical Breviary. Numeric data were explained through the use of linear graphs, pie charts and bar graphs.

Today, many people are familiar with statistics being represented by infographics because of the popularity of data visualisation and its use in the traditional media.

Safety communication

Safety communication has been considered to be the foundation of an effective health and safety culture, with ES Gellar suggesting in People-based safety: the source that “the status of safety in your organisation is largely determined by how health and safety is talked about from the boardroom to the breakroom”.

The Health and Safety Executive (HSE) recognise that monitoring and reporting are vital parts of health and safety culture. Monitoring systems must allow the board to receive both specific, as well as routine, reports on health and safety performance. For numerous organisations, health and safety is a corporate governance issue and is incorporated into the main governance structures.

Many organisations have to communicate risk to the board, but this is often in a descriptive written format. The board of an organisation may be made up of senior managers who have differing perspectives of risk in their own areas of expertise, but not necessarily health and safety risks. Therefore, one of the challenges of a health and safety manager is to find simple but effective means of communicating risk to the board. Diagrams of one kind or another are a good way of getting your message across.

What is the bow-tie method?

The bow-tie method provides a readily understood visualisation of the relationship between causes and consequences analyses into one simple diagram. When plotted, the diagram resembles a bow-tie.

The theory behind the bow-tie approach can be found in Reason’s “Swiss Cheese Model of Accident Causation” (also known as the cumulative act effect). This model posits that a system is similar to slices of Swiss cheese: there are holes in it that represent opportunities for failure, and each slice is a layer of the system. When holes in the layers line up, a loss (or accident) occurs. Each layer of the system is an opportunity to stop an error; the more layers, the less likely an accident is to occur.

Figure 1: Simplified bow-tie diagram

The left hand side of the bow-tie diagram, ie causes, is produced by plotting a Fault Tree sideways, and the Event Tree, ie consequences, is plotted sideways on the right.

The barriers required to control the hazardous event as well as mitigate the consequences are then plotted onto the bow-tie diagram:

Figure 2: Simplified bow-tie showing controls (barriers and mitigation) to manage risk

he bow-tie diagram has several advantages for use in health and safety situations.

  • The full range of initiating events is shown.

  • The intervening safeguards are clearly shown.

  • The actual ways in which these combine and escalate is displayed.

  • The consequence side shows barriers in an equivalent manner.

  • The many possible consequence outcomes are defined.

  • The linkage of barriers to the safety management system can be made explicit.

The linkage of barriers to the safety management system can be made explicit.

Developing bow-tie diagrams should be carried out in a structured and methodical manner, in order to obtain quality information and best represent the actual risk control arrangements in practice.

One of the best ways to achieve this is through the use of facilitated workshops involving the professionals who are regularly confronted with the risks. They are often more likely to identify the actual controls and have knowledge of past incidents as well as current practices. It is important that workshops are conducted in an open manner and it is important that any weaknesses in controls are identified.

The construction of a bow-tie diagram involves asking a series of structured questions, including the following.

  • What is the hazard, ie the thing that could cause harm?

  • What happens when hazard control is lost?

  • What safety event (threat) could release the hazard?

  • What are the potential outcomes?

  • How and the hazard / undesired event be avoided?

  • How can we recover if the event occurs?

  • How can the potential outcome likelihood or consequence severity be limited?

  • How might controls fail and/or their effectiveness become undermined?

  • How do we make sure that controls don’t fail?

Practical uses for bow-ties, and their limitations

Bow-tie diagrams should be kept simple, as their main function should be to demonstrate mechanism and allow senior managers and others to understand how major hazard events can occur, the controls in place to prevent the event occurring and the preparedness measures in place to limit the consequences.

The bow-tie approach provides a structured approach to risk analysis where quantification is not possible or desirable. Risk assessments can have a tendency to focus on the level of risk only, rather than considering all aspects of the management of risk. However, the bow-tie method highlights the direct link between the controls and elements of the safety management system. Bow-ties have been used successfully in Safety Reports produced for compliance with the Control of Major Accidents Hazards (COMAH) Regulations 1999 (as amended).

Bow-ties are not the panacea for all risk management problems; there are other methodologies that are better suited to particular situations or problems. Bow-tie methodology is not applicable where risk quantification is required, and if modelling of complex inter-relationships between risk controls are required then there are better techniques that can be applied. Bow-ties also require a facilitated and multidisciplinary approach in their development.

Conclusions

The bow-tie approach lends itself well to risk communication. The format is not overly complex, and as such non-specialists such as board members can readily understand the approach. All the controls relating to the hazards are shown. By careful use of colour coding it is possible to differentiate between technical and procedural safeguards, and potentially the role of specific groups or individuals, as well as linking to the overall safety management system.

Bow-tie methodology is extremely versatile and has been successfully used in various applications from the control of major hazards, process safety reviews and auditing, and assessing the adequacy of controls to communicating risk to non-technical personal including third parties. Bow-tie diagrams do provide an effective means of visually communicating risk information to non-technical personnel. As such, health and safety professionals may find the approach effective in succinctly communicating complex risk information to the senior managers and board members.

Further information

ES Gellar (2005): People-based Safety: The Source, Coastal Training Technologies Corporation

Health and Safety Executive / Institute of Directors (2013). INDG417 Leading Health and Safety at Work: Actions for Directors, Board Members, Business Owners and Organisations of all Sizes (Rev 01)

S Lewis and K Smith (2010): Lessons Learned from Real World Application of the Bow-tie Method, American Institute of Chemical Engineers

M Smiciklas (2012): The Power of Infographics, Pearson Education Inc.