The Bow Tie Risk Assessment Methodology

What is the Bow Tie Concept?

Bow Tie methodology is a fresh and coherent approach within the Risk Analysis arena. As accidents do not just happen and instead follow a multifaceted causation path in relation to the complexity of “triggered” risks, we desperately needed a Scenario Based and also a qualitative Analysis tool for mitigating risks and that is what exactly Bow Tie is.

How does a Bow Tie Diagram looks like?

Bow Tie idea brought in an effective graphical representation of all potential interactions between (e.g. people, equipment, time, weather and mostly of organisational factors, etc) which might lead into an accident, in a measurable and understandable way, aiming at safety promotion within High Reliability Organisations. Bow Ties do that efficiently because they are constructed in a way to submitting a better overview for each hazard and the specific threats that release the danger altogether   with the involved barriers in place to prevent or mediate the potential negative outcomes. An ultimate tool for risk communication and training from top to bottom within the organisation.

Risk in Bow Tie methodology is elaborated by the relationship between Hazards, Top Events, Threats and Consequences. Barriers or Controls are used to display the exact mechanism, an organisation has employed for risk mitigation. The parts in the diagram are laid out in a sequential order and also time factor is accounted as well. Their definition follows:

A hazard is defined as: “The condition, object or activity with the potential of causing injuries to personnel, damage to equipment or structures, loss of material or reduction of ability to perform a prescribed function”.

Hazards are commonly part of the accepted operating environment as in fact their existence offers a Key business advantage that is highly esteemed. Rather than being something, that an organization seeks to take off its function it is more convenient to focus on effective management instead.

During the time that a hazard is under control nothing really happens and everybody is happy .Trouble really starts when something causes the beginning of a LOC (Loss of Control) situation. Then a sequence of events is ready to start rolling and that specific moment is called as the Top Event.

In Bow Tie methodology such an event is not catastrophe yet because still we maintain a control, based on the preparations we have done before.

The fact is that although a major disaster requires far more to arrive, the open air is full of dangerous characteristics which in case they will not be satisfactory mitigated; a set of unwanted events shall be expected.

In occasions several Top Events might get involved with a solo hazard.

Often the Top Events can be released by a series of factors that in Bow Tie methodology we call Threats.

There is a cause and effect relationship between the two and the prerequisite for Threats to be named like that is their strength to incur that release individually, without any additional contribution by elements of an external factor being simultaneously present.

Threats according to the previous thoughts require the customisation of a set of Barriers which in occasions will sufficiently hinder Top Events from bursting.

When a Top Event has occurred it can lead to certain consequences.

A consequence is every potential event stemming from the release of the hazard which results directly in loss or damage.

Consequences in Bow Tie methodology are unwanted events that an organisation “by all means” wants to avoid. In case that cannot be happened the organisation itself will start suffering up to a point that it might cease operations.

A Threat Barrier is anything that can holistically remove the Threat or might prevent the Top Event from happening.

A Barrier or Control can be any measure taken that acts against some undesirable force or intention, in order to maintain a desired state.

That type of Barriers play their role after the time line crosses Top Event eruption. Again there are two different kinds of measures that could be taken. The first kind takes effect between the Top Event and the Consequence.

On the contrary the last one takes effect after initial release of Top Event to minimize further consequences.

There is no need saying that we can put in place several Barriers that could do the job with a different efficiency level which shall be taken account before and monitored as well.

Life unfortunately does not follow identical pathways, instead it is full of surprises and Barriers as well sometimes fail.

There are certain conditions that can make a Control fail. In Bow Tie methodology these are called Escalation Factors.

An Escalation Factor is a condition that leads to increased risk by defeating or reducing the effectiveness of a Control. By examining the Escalation Factors (and the Escalation Controls that are used to manage them), the methodology reveals important factors that many other types of risk analysis fail considering.

Overall, Bow Tie methodology and Bow Tie diagrams, in colour depict all information that is needed to present the current safety status of each operation, as it had been decided to function, assists the determination of the effectiveness of each Control, therefore they give us the opportunity to estimate the exact risk exposure.

After having that, each organisation establishes its opinion on how happy it is with measures already taken and has already obtained the means to train all its personnel and a template to modify as organisational learning improves and learning curves become more efficient.