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Bowtie diagrams are increasingly used throughout the oil and gas industry to represent and communicate the measures in place to prevent or mitigate hazardous events. They are used to identify safety critical equipment, define process safety metrics and highlight safety critical competencies. At their simplest, they provide an overview of safety arrangements. More complex bowties include information about accountabilities, performance standards, procedures, etc. They have been used primarily as a descriptive tool but can also be used to convey information about the effectiveness of the safety measures represented. Assessment of this “barrier strength” is often either subjective—relying on judgment—or complex, requiring detailed assessment of failure modes of barriers. This paper presents a methodology for undertaking a structured, qualitative barrier effectiveness assessment that allows a “first-pass” screening process. The method considers such factors as whether the safety measure is fail-safe, the complexity of the system, and whether overrides are possible. For existing facilities, operating history and condition can be taken into account. If this assessment is conducted early enough in a project lifecycle, it can be used to support design (not just to record design decisions), by assessing the adequacy of protection and whether additional (or different) barriers should be considered. In operations, it allows the key assurance processes and metrics to be identified that collectively provide a view of the current condition of critical barriers and consequently a “quasi real time” view of the risk level of a facility, compared to that calculated in “static risk assessments.” This work is applicable across the industry in any site that has the potential for major accident events. This approach supports operational managers in making risk-based decisions based on their current risk profile (e.g., about where to focus resources) and facilitates the development of meaningful dashboards that can be rolled up or down depending on the viewer’s role in an organization. This allows otherwise static risk assessments to be recalibrated based on the latest data available on the condition of barriers, informing the operational decisions that could have a major impact in reducing major accidents.

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