Taking Apart the Bowtie: The Inner Workings of Risk
Getting to Know the Essential Pieces of a Bowtie Diagram
At its very heart, a bowtie diagram is a visual story of a single risk. It starts with a clearly defined "hazard" — something that has the potential to cause harm. For example, in a chemical plant, that hazard might be a tank of flammable liquid. From this hazard, a series of "threats" emerge. A threat is an event that could unleash the hazard's potential, such as a worn-out valve leading to a leak of that very flammable liquid.
These threats all point towards the central "top event." This is the critical, unwelcome incident that you are earnestly trying to prevent. In our chemical plant example, the top event could be an "uncontrolled release of flammable liquid." This is the linchpin of the bowtie, the 'knot' that holds everything together. It's really important to define this event clearly and succinctly, as it becomes the main focus of the entire analysis.
To the left of this top event, you'll discover the "preventative barriers." These are the controls, systems, or actions specifically designed to stop a threat from escalating into that top event. Think of them as your protective shields. For instance, in our chemical plant scenario, preventative barriers might include regular valve inspections, systems that relieve pressure, or automated emergency shutdown procedures. Each barrier acts as a line of defense, significantly reducing the chances of that central unwanted event ever taking place.
On the right side of the top event are the "recovery barriers" and the "consequences." Once the top event has unfortunately occurred, recovery barriers are put into action to lessen the severity of the aftermath. For our flammable liquid release, recovery barriers could involve well-trained emergency response teams, robust fire suppression systems, or meticulously planned evacuation routes. The consequences themselves are simply the undesirable outcomes that result from the top event, like harm to the environment, injuries to people, or significant financial setbacks.
