The BowTie methodology is used for risk assessment, risk management and (very important) risk communication. The method is designed to give a better overview of the situation in which certain risks are present; to help people understand the relationship between the risks and organizational events. The strength of the methodology lies in its simplicity; the phrase 'less is more' is certainly applicable.

Risk in BowTie methodology is elaborated by the relationship between Hazard, Top Events, Threats and Consequences. Controls are used to display what measures an organization has in place to control the risk.

Hazard

The term 'Hazard' suggests that it is unwanted, but in fact it is the opposite: it is exactly the thing you want or even need to make business. For example in the oil industry; oil is a dangerous substance (and can cause a lot of harm when treated without care), but it is the one thing that keeps the oil industry in business! It needs to be managed because as long as it is under control, it is of no harm.

Top Event

Thus as long as a Hazard is controlled it is in its wanted state. For example: oil in a pipe on its way to shore. But certain events can cause the Hazard to be released. In the BowTie methodology such an event is called the Top Event. The Top Event is not a catastrophe yet, but the dangerous characteristics of the Hazard are now in the open. For example: oil is outside of the pipeline (loss of containment). Not a major disaster, but if not mitigated correctly it can result in more unwanted events (consequences).

Threat

Often there are several factors that could cause the Top Event. In the BowTie method these are called Threats. These threats need to be sufficient or necessary: every threat itself should have the ability to cause the Top Event. For example: corrosion of the pipeline can lead to the loss of containment.

Consequence

When a Top Event has occurred it can lead to certain consequences. A consequence is a potential event resulting from the release of the Hazard which results directly in loss or damage. Consequences in the BowTie method are unwanted events that an organization ‘by all means’ wants to avoid. For example: oil leaking into the environment.

Control

Risk management is about controlling risks. This is done by placing barriers to prevent certain events form happing. A Control can be any measure taken that acts against some undesirable force or intention, in order to maintain a desired state. In the BowTie method there are proactive Controls (on the left side of the Top Event) that prevent the Top Event from happening. For example: regularly corrosion-inspections of the pipelines. There are also reactive Controls (on the right side of the Top Event) that prevent the Top Event resulting into unwanted consequences. For example: leak detection equipment or concrete floor around oil tank platform.

Escalation Factor

In an ideal situation a Control will stop a Threat from causing the Top Event. However, many Controls are not a 100% effective. There are certain conditions that can make a Control fail. In the BowTie method 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. For example: earthquake leading to cracks in the concrete floor around a pipeline.

ALARP

If you want to be completely sure that there is no risk present you have to get rid of the Hazard. But since the Hazard is part of normal business this is simply not possible. We accept there is a risk and we try to do everything possible to keep the risk “As Low As Reasonably Practicable” (ALARP). For a risk to be ALARP it should be demonstrable that the cost involved in reducing the risk further would be grossly disproportionate to the benefit gained. What ALARP means is different for every organization; it depends on what risks an organization does or does not want to take and what an organization wants to spend (in time & money) on control measures.