While many will agree that the oil and gas and process industries have been very successful in improving occupational safety, improvements in process safety management are lagging. Process hazard assessment has become a recognized tool to assess process design and production operations around the world even though it has a tendency to concentrate on the design phase only rather than considering all aspects of the integrity of operating systems in the total life cycle of the asset. In response, barrier management based on the bow tie model is being widely promoted in the oil and gas industry to understand operational risk in more detail and influence potential results.
The structured approach of the bow tie model forces an assessment of how well all initial threats are being controlled and how well-prepared the organization is to mitigate consequences should things start to go wrong in the total life cycle of the asset. It highlights the direct link between the controls (preventive and corrective) and the management systems. But, how can risk based on the performance of these process safety barriers be managed?
In general, barriers are not fully reliable. They have common causes of failure (e.g., human factor, organizational deficiencies), there are paradigm shifts in barrier expectations (e.g., shallow-water vs. deepwater drilling), and multiple barriers are required to assure an acceptable level of risk. In the event of a major process safety incident, the scenario is investigated in-depth and the failures of the barriers are analyzed by using methods such as 5-why, TRIPOD, and SCAT. The lessons learned include optimizing barriers and defining missing barriers.
From a preventive point of view, however, it is even more important to investigate failed barriers individually as Tier 3 or Tier 4 incidents as defined in the American Petroleum Institute Recommended Practice 754. This paper reviews the process and results of such an effort. The author has used this method for oil and gas operating companies and discusses the lessons learned from this experience. The results of this application show that the bow tie method, in combination with incident analyses on barriers, can be adapted for understanding, monitoring, and influencing barrier performance.
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