Risk-Based Approach – Quantitative Risk Assessment

The Process Safety and Loss Prevention field was born out of the need to avoid personnel injury, i.e., workforce and public, property damage, environmental impact and operation interruption (i.e., economic impact, due to several relevant accidents during the last 50 years, e.g., Bhopal, Seveso, Buncefield, Flixborough, etc.). A Quantitative Risk-Based Assessment (QRA) is considered to be the foundation of process safety and loss prevention. Generally, there are two main approaches to conduct a risk assessment: consequence-based or risk-based. The issue that arises by using a consequence-based approach is that the likelihood of occurrence is not considered, and therefore, it does not account for the frequency of an undesired event.

A complete Quantitative Risk Assessment (QRA) consists of six main steps:

  1. Hazard Identification, which consists of the identification of all Loss Of Containment scenarios (LOCs) with the potential to lead to an explosion, fire, or toxic hazards in a process facility;
  2. Frequency Analysis, which estimates the likelihood of occurrence of all LOCs via analysis of historical data, specific plant data (if available), worldwide references with generic process equipment failure rates, and/or dedicated fault and event trees; i.e., bow-tie analysis;
  3. Consequence Analysis, which quantifies the effects and impacts of all potential outcomes that could occur from a given LOC, based on damage criteria for fires, explosions, and toxic hazards for personnel, structures, and process equipment; 
  4. Risk Analysis, which quantifies the risk level as a function of the likelihood of occurrence (i.e., frequency analysis) of possible undesired events (LOCs) and the magnitude of their associated impacts (i.e., consequence analysis), and it can be divided into two (2) categories: individual risk and societal risk;
  5. Risk Tolerability Criteria, which consists of comparing the estimated risks to a worldwide recognized risk tolerability criteria to determine if the risk levels are deemed to be tolerable or not; and
  6. Risk Reduction, which consists of implementing risk reduction measures such as inherent safer process design, prevention, and/or mitigation in order to decrease the individual and/or societal risks to at least a tolerable if ALARP (As Low as Reasonably Practicable) risk region.

Some examples of applicable safeguards or Independent Protection Layers (IPLs) are Safety Instrumented Systems (SIS), Fire and Gas Detectors (FGS), etc.,

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