Quantitative Risk Assessment (QRA)

Introduction

Quantitative Risk Assessment (QRA) is a structured analytical method used to evaluate risks in complex industrial facilities. It estimates the likelihood and consequences of events such as fires, explosions, and toxic releases, producing numerical risk values that support safety decisions. QRA mainly focuses on risks to people, using metrics like Individual Risk Per Annum (IRPA) and societal risk (FN curves), while also considering impacts on assets, operations, and the environment.

QRA studies are essential in industries where hazardous materials and energy are handled including oil & gas, petrochemical, refining, LNG, power generation, and chemical processing facilities  providing clarity on risk exposure for personnel, assets, and the environment.

Why Quantitative Risk Assessment (QRA) Is Important

A well-executed QRA helps organisations:

• Quantify the likelihood and consequences of potential hazardous events
• Assess individual and societal risk exposure
• Prioritise design and operational mitigations
• Demonstrate compliance with international risk tolerability criteria
• Support ALARP (As Low As Reasonably Practicable) decision-making
• Strengthen emergency response and business continuity planning

QRA is also increasingly required as part of safety cases and regulatory submissions in many jurisdictions.

Types of Risk Considered in Quantitative Risk Assessment (QRA)

Quantitative risk analysis evaluates risk from multiple perspectives:

Location-Specific Individual Risk (LSIR)

LSIR is used to indicate the risk at a particular location. It is the risk for a hypothetical individual who remains at that particular location 24 hours per day for 365 days per year. It should be noted that the LSIR is independent of the manning levels. No criteria are set for risk acceptability.

Individual Risk Per Annum (IRPA)

IRPA is the combined risk to a single person, as a result of exposure to all identified hazards. Individual risk is normally calculated as the frequency of fatality per year. IRPA is the risk to which an individual worker is exposed taking into account their movement around the facilities and the time spent in facilities.

Potential Loss of Life (PLL)

PLL is a societal or group risk measure of the statistical number of fatalities that may be expected within a given time period, typically expressed as the number of fatalities per year (of operation), and is useful in tracking the major risk contributors.

Societal Risk (FN Curve)

Societal risk is used to encompass the public and identified groups of workers as a group when they are present in common purpose areas and expressed in terms of the FN curve. Societal Risk for Offshore facilities shall consider only the personnel present in the living quarters who may potentially be affected by a major incident or failure of the installation.

Objectives of a QRA Study

The primary aims of a Quantitative Risk Assessment include:

• Identifying hazards and credible failure scenarios
• Estimating potential consequences and frequency of events
• Quantifying risk levels to people, assets, and operations
• Evaluating existing safeguards and their effectiveness
• Recommending risk reduction measures where required
• Demonstrating compliance with risk acceptance criteria and ALARP principles

QRA Methodology

A robust Quantitative Risk Assessment follows a structured, stepwise process:

1. Hazard Identification

Identification of all credible loss-of-containment and failure scenarios based on process conditions, equipment inventories, and historical data.

2. Scenario Development

Defining hazardous events such as jet fires, pool fires, vapor cloud explosions (VCE), or toxic cloud dispersion that could arise from identified hazards.

3. Consequence Modelling

Using consequence modelling tools to simulate physical effects including dispersion of vapours, heat radiation from fires, overpressure from explosions, and toxic dose contours under relevant conditions.

4. Frequency Analysis

Estimation of scenario likelihood using failure data, event trees, and industry databases to determine how often each hazardous event may occur.

5. Risk Estimation

Combination of consequence severity and event frequency to compute numerical risk measures such as:

• Individual Risk Per Annum (IRPA)
• Potential Loss of Life (PLL)
• Frequency–Number (F-N) curves

6. Risk Evaluation

Comparison of calculated risk metrics against acceptable risk criteria or corporate/regulatory thresholds to determine tolerability.

7. Mitigation and Risk Reduction

Identification and ranking of risk reduction measures (RRMs), validated through cost-benefit and ALARP assessments.

8. Reporting

Preparation of a comprehensive QRA report documenting methodology, assumptions, results, risk contours, and recommendations.

This methodology ensures that all aspects of hazard, consequence, and likelihood are quantified and evaluated rigorously.

Key Deliverables of a Quantitative Risk Assessment (QRA) Study

• Defined risk acceptance criteria (Individual Risk Per Annum – IRPA and societal risk thresholds)
• Selection and justification of credible hazardous release scenarios
• Consequence modelling outputs (dispersion, thermal radiation, overpressure, toxic effects)
• Equipment failure frequency and ignition probability assessment
• Event tree development and outcome probability analysis
• Individual Risk Per Annum (IRPA) calculation
• Societal risk calculation and F–N curve development
• Individual risk contour generation
• Identification of dominant risk contributors
• Sensitivity and uncertainty assessment
• Quantitative comparison against acceptance criteria
• Identification of additional risk reduction measures
• ALARP demonstration

All of the above analyses and results are formally documented and presented within the comprehensive QRA Report.

Software and Tools Typically Used

QRA studies employ advanced, industry-standard tools such as:

• DNV PHAST / SAFETI for consequence and risk modelling
• SHELL FRED / SHEPHERD for dispersion and fire mapping

These tools help transform engineering data into quantitative risk profiles.

Standards and Acceptance Criteria

Quantitative Risk Assessments are aligned with:

• Corporate and HSE risk tolerability criteria
• International best practices for risk evaluation
• ALARP principles for risk reduction
• Recognised probabilistic risk assessment guidelines

This ensures QRA outcomes are consistent with safety management frameworks and regulatory expectations.

Industries and Applications

QRA is widely applied across high-hazard sectors, including:

• Oil & Gas upstream, midstream, and downstream facilities
• Petrochemical and chemical processing plants
• Refinery assets and storage terminals
• LNG facilities and terminals
• Manufacturing plants handling hazardous materials
• Energy infrastructure and utilities

Its application supports design, operation, modification, and safety case requirements.

Why Choose iFluids Engineering Qatar for QRA

At iFluids Engineering Qatar, we bring deep domain expertise, advanced modelling capabilities, and a practical understanding of industrial risk to deliver comprehensive Quantitative Risk Assessments tailored to your project needs.

Our team provides:

• Technically rigorous and regulator-defensible risk studies
• Clear interpretation of numerical risk results
• Risk evaluation against global and local criteria
• Practical mitigation strategies prioritised by effectiveness and cost
• Support for safety case submissions and regulatory approvals

We combine global best practices with local insights to help clients secure safe, compliant, and high-performance operations.