BowTie Method Tip:                                      The (not so) mysterious world of Hazards and Top Events

Differences between traditional risk registers and the BowTie method.

If you’re new to the BowTie method it’s likely that you will have encountered ways of defining various aspects of your risk landscape that you have not used before. Traditional risk registers didn’t usually differentiate between a Hazard and a Threat and it is rare indeed to have seen a column entitled Top Event. So it’s no surprise that people often struggle with the use of these parts of the BowTie when they are getting started. These are the first elements that we need to define when we create a new BowTie and they shape the risk assessment that will be built upon them, so it’s crucial that we get them right.


The basic principle to keep in mind is that the Hazard will define the scope of what you are assessing and will be a description of a potential source of harm. It is used in the BowTie method to set the scene of what the risk assessment is about and defines appropriate boundaries. Hazards can be an object, a condition or an activity.

More often than not, it is a description of one of your normal processes (or things you do in order to achieve your business goals). So lets look at three examples: it could be something like landing an aircraft, having passengers in an airport terminal, or even a process like project management.

In risk management we used to talk about eliminating hazards but as we see in the above examples, these are not things that we want to eliminate; rather they are things we want to manage appropriately and actually keep doing (hence the point of doing a risk assessment in the first place!). The things that we want to eliminate form our business are the Threats (which often equate to what we used to call hazards in traditional risk registers). Remember that the hazard is just a potential source of harm, not how it causes a problem (again, that is where threats come into the method).

Top Events

Next is the Top Event. People get tied up in all sorts of knots about this (please forgive the attempted pun), but its really not that mysterious. We are defining the point at which we are no longer happy with how we are managing the Hazard. It depends on your perspective and the type of business you are in but 99 times out of 100 it is fair to say that the Top Event will not be a disaster yet, it will be the loss of control moment that precedes a disaster.


Looking back at the three examples used earlier (landing an aircraft, passenger handling in an airport terminal and project management) the Top Event could be something like a loss of direction control on the runway, a breach of security in the terminal or getting behind the curve on a project delivery schedule.


The great thing about defining a Top Event is that we can then consider all of the Threats that could cause a Top Event and all of the Consequences that may flow from it. Therefore we can look at multiple pathways to disaster all in one place and develop a clearer picture of our risk landscape.   


·      If the Hazard describes how we get to an accident it is probably a Threat.

·      If a Hazard describes something that sounds like a disaster, it’s probably a Consequence.

·      If the Hazard describes something that is already out of control it is probably a Top Event.

·      If the Top Event describes an accident it is probably a Consequence.

·      If the Top Event describes how we lose control it is probably a Threat.