Barriers are the safety measures or controls in a bowtie diagram. Barriers interrupt the scenario so that the threats do not result in the top event when control is lost over the hazard. Barriers can also ensure that the top event does not escalate into an actual impact (the consequences). Barriers in the bowtie appear on both sides of the top event.
Type of barriers
Barriers can be categorized using any classification system desired. A common classification system is if the functioning of the barrier is dependent on human behavior or technology. Categorizing barriers very often creates a greater understanding of how risks are managed. You can build on this basic barrier structure further to deepen your understanding of where the weaknesses are. Barrier categorizing your barriers as a certain type, it is also advised to include information on barrier effectiveness.
Barrier effectiveness lets you assess how well a barrier performs. If you have barriers in place that are not performing well, the risk exposure is only slightly reduced. To keep barriers performing adequately, the barriers need to be implemented and maintained. In bowtie diagrams, barrier effectiveness is often indicated by a stoplight system, where green barrier perform well, and red barriers are under performing.
After that, you can look at the activities you have to implement and maintain you barriers. This essentially means mapping your Safety Management System (SMS) on the Barriers. Also determining who is responsible for a barrier and assessing the criticality of a Barrier are things you can do to increase your understanding of the Barriers.