Quantitative Risk Assessment (QRA)

A Quantitative Risk Assessment (QRA) is a formal and systematic risk analysis approach to quantifying the risks associated with the operation of an engineering process.

A QRA is an essential tool to support the understanding of exposure of risk to employees, the environment, company assets and its reputation. A QRA also helps to make cost effective decisions and manages the risks for the entire asset lifecycle.

The main objectives of a QRA are:

• To identify the hazards associated with a facility;
• To determine the potential frequencies and consequences of the identified hazards;
• To determine the system availability of the protection systems;
• To quantify the risks associated with a facility (e.g. Risk Contours, Individual Risk Per Annum (IRPA), Potential Loss of Life (PLL) and F-N Plots).

A typical QRA study conducted by Rizzo Engineering consists of the following processes:

• A HAZOP study to identify a series of hazardous scenarios that could lead to significant adverse consequences;
• A SIL Allocation study, typically done using the the Layers of Protection Analysis (LOPA) method;
• A Fault Tree Analysis (FTA) to determine the event frequencies associated with the hazardous scenarios from the HAZOP and LOPA study;
• A consequence analysis to determine the consequences of the hazardous release from a facility (including flammable, explosion and toxic);
• An Impact Analysis to determine the frequency of a specific hazardous impact using Event Tree Analysis (ETA). ETAs are ‘bottom up’ analytical tree diagrams that determine the overall likelihood of a particular impact following a hazardous release (i.e. Jet Fire, Flash Fire Vapour Cloud Explosion (VCE));
• A Risk Assessment to determine the risks associated with hazardous scenarios;
• Risk Reduction Measures to identify the options to reduce or mitigate the risks;

Lifecycle Cost Analysis to provide a Cost Benefit Analysis (CBA) based on different risk mitigation measures.