Control and Recovery Barriers
Barriers in the bowtie appear on both sides of the top event. Barriers on the left side interrupt the scenario so that the threats do not occur, and if they do, not result in a loss of control (the top event). Barriers on the right side make sure that if the top event is reached, the scenario does not escalate into an actual impact (the consequences) and/or they mitigate the impact.
There are different types of barriers, which are mainly a combination of human behavior and/or hardware/technology. Once the barriers are identified, you have a basic understanding of how risks are managed. You can build on this basic barrier structure further, to deepen your understanding of where the strengths and weaknesses are. Barriers can be classified and assessed beside barrier types, to include for instance barrier effectiveness. This lets you assess how well a barrier performs, or is expected to perform, based on available data and/or relying on expert judgment. After that, you can look at the activities you have specified, to implement and maintain your barriers. This essentially means mapping you Safety Management System (SMS) onto the barriers. In addition, you can determine who is responsible for a barrier and assess the criticality of a barrier in the context of all other related information. These are all things you can do to increase your understanding of the barriers. Ultimately, linking and visualizing all this information on a barrier, gives you a holistic overview of your safety measures with relevant meta data in the context of your risk scenarios.
Escalation factors & Escalation factor barriers
Barriers are never perfect. Even the best hardware barrier can fail. Given this fact, what you need to know is why a barrier will fail. This is done using the ‘escalation factor'. Anything that will make a barrier fail can be described in an escalation factor. For instance, a door that opens and closes automatically using an electrical mechanism might fail if there’s a power failure.