Why are there no bowties in rail?
Liam McBride
Technical Assurance Engineer
15 April 2021
First of all, we should caveat this to say that we are not talking about the piece of cloth you place round your neck at a fancy event however excellent that would look as part of standard PPE!
We are talking about the hazard management tool ’Bowties’. These are, as you probably guessed it, bowtie shaped. They are used to explore in detail, your most significant hazards.
While HAZIDs and HAZOPs are your first step in risk management to understand operational and design risks, their function is not to delve in great detail the leading events and consequences of any single hazard, rather they are intended to identify all hazards across the system and provide a qualitative assessment against them. The Bowtie is an excellent tool to allow a spotlight to be shone on those risks that have high risk, be that the consequences are significant, or that the hazard presents itself frequently. Using these you are able to identify, target and manage safeguards (referred to as barriers in Bowtie risk management) against each of the identified causes and consequences. This method can also allow you to target in more detail causes and consequences so they can have more specific controls placed against them; think “Extreme Weather Conditions” against:
Dense Fog (Visibility under 100m)
Snow (over 10cm)
Rain (flooding)
Low temperatures (<-10oC)
Significant ice build up
And the differing ways in which these are managed.
These bowties give you a simple, graphical view on what would lead to the top event (worst case) and what comes of it, as well as the mitigations and safeguards you have in place to prevent / reduce it. Bowties are primarily a qualitative method and have a number of advantages over other hazard identification methods for the exploration of high consequence events:
Focus on a single event.
Further identification of leading causes.
Further identification and exploration of barriers and mitigations.
Identification of events / issues that would degrade your barriers.
Flexible application so can be used in design or operations.
Bowties can be used as a qualitative method for showing that all of your hazards have been managed, the effectiveness of your barriers and the current state of your barriers. All of which gives you a case to determine how safe your system is. A simplistic (and rudimentary) bowtie can be seen below relating to a relatively common railway hazard.
To read this, you need some context:
The hazard here is: Fixed Obstacles adjacent to line.
The top event is: Impact of Vehicle on Fixed Obstacles
To read the bowtie, you simply go left to right, taking “New Infrastructure” as an example. You would ensure you have designed it to not infringe on the Kinematic Envelope of allowable vehicles in that section. If you did impact, the result could be to damage or derail the train, potentially mitigated using speed restrictions as well as designing your train to be crashworthy.
This is a simple method that allows you to visualise what could cause, and what will result of realisation of a hazard. The Bowtie drawing above took around 15 minutes to create in PowerPoint. During this time an assessment was performed on a hazard which is extraordinarily common in the railway environment but could have disastrous consequences if realised. Design and operational experts could easily perform a comprehensive analysis of this (and any other significant event), noting any gaps and prioritising actions to further eliminate the risk.
So, going back to the original question, why is there little use of bowties in rail?
This method is used widely in other industries, Renewables, Oil and Gas, Aviation being a few that come to mind. The only thing I can think of is the sheer number of hazards facing a railway operator which could carry significant risk and the broad range of causes and consequences to mitigate, then again this is the application where bowties shine bright.
They are a simple visual way of viewing hazards, causes and consequences. Don’t let the simplistic nature of the bowtie above fool you, the application of these can be extremely powerful in the management of these hazards and the assurance that all barriers have been identified which could reduce your risk ALARP.
Further reading:
CGE Risk Management Solutions
