BC proposes a detailed assessment aimed to:

 

(1) Minimize the economic investment during the decision-making process.

(2) Maximize the effectiveness of Layers Of Protection (LOP) to be implemented after identifying target locations with intolerable risk levels.

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The assessment was developed by Dr. Dunjó and published in reference [1], and it is a clear methodology for linking the Quantitative Risk Assessment (QRA) results with Functional Safety principles.

 

The potential accuracy of the decision-making process associated with the QRA results depends on the level of the information taken into account for its development, and the efforts for acquiring in-depth and reliable results. After confirming target locations with intolerable risk levels, the following three (3) questions from the decision-makers require an appropriate answer:

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1. Which pieces of equipment generate Loss Of Containment (LOC) scenarios with the potential to impact the target location with intolerable risk level?; i.e., list of LOCs to be addressed for risk reduction?

 

• Identification of most contributing LOCs.

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2. What should be the Risk Reduction Factor (RRF) for each identified LOC?

 

• Quantification of RRFs for selected LOCs.

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3. What are the most suitable and practicable risk reduction measures that can be implemented based on decision-maker needs?; e.g., minimizing changes to the current process design; thus, mitigation measures rather than preventive measures.

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• Definition of LOP that meet the RRFs.

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The methodology:

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The most contributing LOCs are identified by using selected risk indices statistics already calculated during the QRA development.

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The RRF is determined by evaluating the ratio of the actual risk index value and a desired constant target risk index threshold. The definition of the target risk index threshold consists of applying the guess-estimated RRFs and then re-evaluating the QRA risk profiles through an iterative procedure. The iterative procedure is completed when the target location is confirmed to be within a tolerable risk level.

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Once the new QRA risk profiles ensure the new risk level at the target location is tolerable, the discussion of which LOP can satisfy with the estimated RRF is performed. Examples of LOP are the following:

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• Safety Layers

• Active Protection Layers

• Passive Protection Layers

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[1] J. Dunjó, M. Amorós, N. Prophet, G. Gorski. “Advanced QRA Methodology: Quantifying Risk Reduction Measures to Minimize Economic Investment”. 14th Global Congress on Process Safety, Orlando, FL. April 2018.

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