Risk-Based Approach – Risk Reduction Basics

This manuscript is intended to provide an overview of layers of protection capable of reducing the risk level of a given process facility, i.e., measures intended to prevent and/or mitigate the identified hazardous scenarios. Based on the development and results of a risk-based quantitative assessment, regions, zones, or more detailed locations (e.g., occupied buildings, critical process equipment) with an intolerable risk level can be identified and the associated hazardous scenarios that most contribute to the risk of these zones. Sensitivity analysis and cost-benefit analysis can be conducted with the goal to find which safeguards achieve reducing risk to an acceptable level while ensuring that the investment is not in gross disproportion.

Introduction

ISO 17776 defines the concept of risk as the combination of the frequency of occurrence of an event and the consequences of that event. Its estimation is used to take decisions, usually supported by using graphical tools (e.g., F‐N curve, risk profile, risk contour, exceedance curves) to show risk and the relationship between frequencies and consequences. Taking into account most of the factors that contribute to the total risk of a process facility, the risk values will highlight the major sources of risk and will give the decision‐maker objectives for re‐design or other loss prevention efforts. Techniques to achieve these goals are, for example, the risk based quantitative assessment (see Figure 01).

However, actual risk results are not very useful if there are no criteria for comparison. The decision-making process should be based on internationally recognized tolerability criteria with the aim to compare the actual risk level and therefore, take the appropriate actions. This paper provides criteria on risk reduction measures for the Chemical Process Industry (CPI) and provides guidance for answering the following question: Which are the most appropriate safeguards for reducing risk to a tolerable level?

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