Quantitative Risk Assessment (QRA) Services

Let us understand how we can help you

We Help You Manage Safety In Your Premises Successfully!

INDSAFE provides Quantitative Risk Assessment (QRA) services to systematically evaluate major accident hazards, model potential consequences, estimate event frequencies, and characterize risk for industrial facilities and operations.

QRA combines hazard identification, frequency analysis and consequence modelling to provide a quantitative understanding of risk. The results can support risk-based decision-making, facility design, emergency planning, risk reduction measures and other process safety activities.

QRA can be applied to new projects, existing facilities, plant modifications and other situations where quantitative risk information is required, depending on the objectives and scope of the assessment.

What is Quantitative Risk Assessment (QRA)?

Quantitative Risk Assessment (QRA) is a systematic process used to estimate the risk associated with defined hazardous scenarios by combining the likelihood or frequency of events with the potential consequences of those events.

For major accident hazards, QRA may consider scenarios such as:

Flammable material releases
Toxic material releases
Pool fires
Jet fires
Vapour cloud explosions
Fireballs/BLEVE scenarios
Unignited gas or vapour dispersion
Other credible major accident scenarios relevant to the facility

Depending on the study scope, consequence modelling can estimate effects such as thermal radiation, explosion overpressure and toxic exposure.

The resulting information can then be used to characterize measures such as individual risk and societal risk, where applicable.

Objectives of QRA Study

The objectives of a QRA depend on the facility and assessment scope, but commonly include:

Identifying and evaluating major accident scenarios
Estimating the frequency or likelihood of relevant hazardous events
Quantifying potential consequences of selected scenarios
Characterizing individual and/or societal risk where applicable
Identifying major contributors to overall risk
Supporting risk-reduction decisions
Supporting facility layout and siting decisions
Supporting emergency planning and preparedness
Providing quantitative input for engineering and process-safety decisions
Supporting applicable regulatory or project requirements

QRA is therefore not simply a calculation of consequence distances. It brings together scenario development, frequency estimation, consequence modelling and risk evaluation.

Our QRA Methodology

A QRA methodology is developed according to the facility, hazardous materials, study objectives, available data and applicable requirements.

A typical assessment may include the following stages:

Data Collection → Hazard Identification → Scenario Selection → Frequency Analysis → Consequence Modelling → Risk Calculation → Risk Evaluation → Recommendations

The exact methodology and level of detail may vary from one assessment to another.

Step 1: Data Collection and Site Understanding

The first stage is to establish a clear understanding of the facility, process, inventories, equipment and surrounding environment.

Depending on the study scope, inputs may include:

Site layout
Process Flow Diagrams (PFDs)
Piping and Instrumentation Diagrams (P&IDs)
Process conditions
Equipment information
Material inventories
Storage capacities
Operating conditions
Pipeline and transfer information
Relief-system information
Meteorological data
Population or occupancy information
Surrounding land use
Building and enclosure information
Emergency response information
Existing safety and mitigation systems

For existing facilities, a site visit may also be conducted where required to understand actual site conditions and verify relevant information.

The quality and completeness of input data can have a significant effect on the assessment results.

Step 2: Hazard Identification and Scenario Selection

Potential hazardous events are identified based on the process, materials, equipment, operating conditions and study objectives.

Existing studies such as HAZOP, HAZID, What-If analysis or other process hazard assessments may provide important inputs for scenario identification.

However, QRA scenario development should be based on the objectives and boundaries of the QRA rather than assuming that every HAZOP finding automatically becomes a QRA scenario.

Typical major accident scenarios may include:

Loss of containment from process equipment
Pipeline or piping failure
Flange or connection leakage
Storage tank release
Vessel release
Loading/unloading incidents
Transfer-line failures
Toxic releases
Flammable gas or liquid releases
Other credible scenarios relevant to the facility

The selected scenarios are then developed for further frequency and consequence analysis.

Step 3: Frequency and Likelihood Analysis

The frequency of relevant hazardous events is estimated using appropriate failure-frequency data, initiating-event frequencies, release-frequency information, historical data, engineering models and/or recognised industry sources, depending on the methodology.

The analysis may consider:

Equipment failure
Pipe and pipeline failure
Valve and flange leakage
Vessel or tank failure
Human or operational factors where relevant
Ignition probabilities
Other scenario-specific event probabilities

The selected data sources and assumptions should be documented because uncertainty in frequency data can influence the resulting risk estimates.

QRA results should therefore be interpreted in the context of the assumptions, data quality and modelling methodology used in the assessment.

Step 4: Consequence Analysis

For selected scenarios, consequence modelling is used to estimate the physical effects of potential releases and hazardous events.

Depending on the scenario, consequence analysis may include:

Dispersion Modelling

Estimation of the movement and concentration of released gases, vapours or toxic substances under defined atmospheric and release conditions.

Thermal Radiation

Assessment of thermal radiation effects from scenarios such as:

Pool fires
Jet fires
Fireballs/BLEVE scenarios

Explosion Modelling

Assessment of potential explosion effects and overpressure for applicable vapour cloud or other explosion scenarios.

Toxic Exposure

Assessment of toxic concentration and exposure distances for relevant hazardous releases.

Software such as DNV PHAST may be used for consequence modelling where appropriate to the study scope and methodology.

For enclosed or indoor facilities, additional considerations such as ventilation and HVAC air-change characteristics may be relevant to the modelling.

Step 5: Risk Calculation

Once scenario frequencies and consequence results have been developed, they are combined to characterize risk.

Depending on the assessment objectives, QRA may evaluate:

Individual Risk

Individual risk represents the risk to a hypothetical individual at a particular location, based on the defined hazardous scenarios and exposure assumptions.

Results may be presented as risk contours showing how estimated risk varies across the site and surrounding area.

Societal Risk

Societal risk considers the relationship between the frequency of accidents and the number of people potentially affected.

It may be represented using an F-N curve, which describes the frequency of accidents involving different numbers of fatalities or affected people, depending on the methodology and study scope.

The appropriate risk metrics depend on the purpose and requirements of the assessment.

Step 6: Risk Evaluation

The QRA results are reviewed to understand:

Major contributors to overall risk
Dominant accident scenarios
High-risk locations
Areas affected by thermal radiation
Areas affected by explosion overpressure
Toxic exposure zones
Population or occupancy exposure
Potential risk-reduction opportunities

Where defined risk criteria or acceptance criteria are applicable, the calculated results can be compared with those criteria.

The interpretation should clearly distinguish between calculated results, modelling assumptions and the criteria used for decision-making.

Step 7: Recommendations and Risk Reduction

Based on the QRA findings, practical risk-reduction measures may be identified.

Depending on the scenarios and facility, recommendations may address:

Process design
Equipment selection
Inventory reduction
Isolation systems
Detection systems
Emergency shutdown systems
Fire and gas detection
Passive or active fire protection
Layout and separation distances
Ventilation
Emergency response
Operating procedures
Inspection and maintenance
Emergency planning
Other engineering or administrative controls

The recommendations should be proportionate to the identified scenarios and aligned with the objectives of the assessment.

Typical QRA Scenarios

Depending on the facility and materials involved, QRA may evaluate scenarios such as:

Pool Fire

A flammable liquid release forms a pool and subsequently ignites, producing thermal radiation.

Jet Fire

A pressurized flammable release ignites and produces a directional flame and associated thermal radiation.

Vapour Cloud Explosion

A flammable vapour cloud forms following a release and subsequently ignites under conditions capable of producing explosion effects.

Fireball / BLEVE

Certain pressurized or liquefied flammable inventories can produce fireball scenarios under specific failure conditions.

Unignited Gas Dispersion

A released gas or vapour disperses without immediate ignition. The resulting concentration field can be evaluated against relevant concentration criteria.

Toxic Release

A hazardous or toxic material is released and dispersion is modelled to estimate concentrations and potential exposure zones.

Not every scenario is applicable to every facility. Scenario selection should reflect the actual process, materials, equipment and assessment objectives.

QRA Outputs and Deliverables

Depending on the agreed scope, a QRA study may provide:

Hazard and scenario register
Release scenario definition
Frequency/failure data and assumptions
Consequence modelling results
Thermal radiation contours
Overpressure contours
Toxic dispersion contours
Risk contours
Individual risk results
Societal risk / F-N analysis where applicable
Major risk contributors
Risk evaluation
Risk-reduction recommendations
QRA report
Supporting modelling files or calculations where included in the agreed scope

The final deliverables depend on the project requirements and assessment methodology.

Where QRA is Used

QRA can support a range of engineering and process-safety decisions, including:

Facility Layout and Siting

Risk contours and consequence zones can provide quantitative information for evaluating equipment locations, occupied buildings and surrounding areas.

Emergency Planning

Consequence and risk information can support emergency response planning and identification of areas potentially affected by major accident scenarios.

Risk Reduction

QRA can help identify scenarios that contribute significantly to overall risk and support evaluation of potential mitigation measures.

Project Development

QRA can provide quantitative risk information during the development or modification of industrial facilities.

Existing Facility Assessment

For operating facilities, QRA can support review of existing risk profiles and potential risk-reduction opportunities.

Regulatory and Project Requirements

Where applicable, QRA can provide quantitative information required by project specifications, regulatory frameworks or other defined assessment criteria.

QRA and Other Process Safety Studies

QRA is part of a broader process safety and risk-assessment framework. It is not a replacement for every other hazard-analysis technique.

QRA and HAZOP

HAZOP systematically examines process deviations from design intent and identifies causes, consequences and safeguards.

QRA quantitatively evaluates selected hazardous scenarios using frequency and consequence analysis.

HAZOP findings may therefore provide useful inputs to QRA, but not every HAZOP deviation necessarily needs to become a QRA scenario.

[Explore HAZOP Study Services → Click Here]

QRA and HAZID

HAZID provides broader hazard identification at the project, facility, system or activity level.

It can help identify scenarios that may subsequently require more detailed analysis.

[Read more about HAZID → Click Here]

QRA and LOPA

LOPA is a semi-quantitative method used to evaluate selected hazardous scenarios and the effectiveness and independence of protection layers.

QRA and LOPA address risk using different approaches and levels of quantification.

QRA and SIL Assessment

SIL assessment addresses the required performance of safety instrumented functions for specific hazardous scenarios.

QRA results may provide useful information for broader risk assessment, while SIL determination requires a suitable functional-safety methodology and scenario-specific analysis.

[Explore Functional Safety & SIL Studies → Click Here]

These studies are therefore complementary rather than interchangeable, and the appropriate combination depends on the facility, hazards and assessment objectives.

Industries We Serve

QRA can be applied across a wide range of process and industrial facilities, subject to the characteristics and requirements of the project.

INDSAFE provides QRA services for applications including:

Oil & Gas
Chemicals and Petrochemicals
Pharmaceuticals
Manufacturing
Food & Beverage
FMCG
Power and Energy
Other process and industrial facilities

The scope of the assessment is adapted to the process, hazardous materials, facility configuration and objectives of the study.

Why Choose Indsafe for QRA?

INDSAFE approaches QRA as an engineering and process-safety assessment rather than simply a software-based modelling exercise.

Our QRA methodology focuses on:

Understanding the facility and process
Identifying credible major accident scenarios
Selecting appropriate modelling assumptions
Applying suitable frequency and consequence data
Quantifying relevant risk measures
Identifying dominant risk contributors
Developing practical risk-reduction recommendations

Where appropriate, specialised consequence-modelling software such as DNV PHAST may be used as part of the technical assessment.

The specific tools, data sources, modelling assumptions and methodology are selected according to the requirements and scope of each project.

Common QRA Challenges

A meaningful QRA depends on more than running consequence models.

Poor Input Data

Incomplete process information, inventories, equipment data or meteorological information can affect the quality of the assessment.

Inappropriate Scenario Selection

Including every conceivable event or excluding relevant major accident scenarios can distort the purpose of the assessment.

Unclear Frequency Data

Failure frequencies and probability assumptions need to be selected carefully and documented.

Over-Reliance on Software

Software can perform complex calculations, but the quality of a QRA also depends on scenario definition, engineering judgement, data selection and interpretation.

Ignoring Uncertainty

QRA results contain uncertainty associated with frequency data, assumptions, models and input information. These limitations should be recognised when interpreting the results.

Treating QRA as a One-Number Answer

Risk is often better understood through scenario-specific results, risk contours, F-N relationships and identification of dominant contributors rather than a single headline value.

Frequently Asked Questions About QRA

What is QRA?

QRA stands for Quantitative Risk Assessment. It is a systematic approach for estimating risk by combining the likelihood or frequency of hazardous events with the consequences associated with those events.

What is the difference between QRA and HAZOP?

HAZOP is a structured qualitative hazard and operability study that examines deviations from design intent. QRA uses quantitative frequency and consequence analysis to characterize risk for selected scenarios.

Does QRA always require a HAZOP?

No. HAZOP can provide valuable input for scenario identification, but whether a HAZOP is required depends on the facility, project stage, hazards and objectives of the QRA.

What is individual risk in QRA?

Individual risk represents the estimated risk to an individual at a particular location under defined assumptions. It is commonly represented using risk contours.

What is societal risk?

Societal risk considers the frequency of accidents in relation to the number of people potentially affected. An F-N curve is one common way of representing societal risk.

What software is used for QRA?

Consequence modelling and QRA may involve specialised software such as DNV PHAST, depending on the study methodology and requirements. Software selection should follow the assessment objectives rather than being treated as the defining feature of QRA.

What information is required for QRA?

Typical inputs include process and equipment information, PFDs, P&IDs, inventories, operating conditions, site layout, meteorological information, population/occupancy information and relevant safety-system data.

What scenarios are considered in QRA?

Depending on the facility, scenarios may include pool fires, jet fires, vapour cloud explosions, fireballs/BLEVEs, unignited dispersion and toxic releases, as well as other credible major accident scenarios.

What are the outputs of a QRA?

Typical outputs include scenario frequencies, consequence distances, thermal radiation and overpressure results, dispersion results, risk contours, societal-risk analysis where applicable, identification of major risk contributors and risk-reduction recommendations.

Can QRA be performed for an existing plant?

Yes. QRA can be applied to both new and existing facilities, provided the assessment has appropriate information about the actual facility, operations, inventories, surrounding population and other relevant conditions.

When should a QRA be conducted?

QRA may be appropriate during project development, facility siting and layout decisions, major modifications, existing-facility risk assessment, emergency planning or other situations where quantitative risk information is required.

Technical References

The specific references and methodologies used for a QRA should be selected according to the facility, jurisdiction, industry and study objectives.

Relevant technical sources may include:

Recognised process-safety and risk-assessment guidance
Applicable industry standards and regulatory requirements
Established consequence-modelling methodologies
Appropriate equipment failure and incident-frequency data sources
Project-specific risk criteria and acceptance criteria where applicable

The selected data sources, assumptions, models and criteria should be documented within the QRA methodology and final report.

Discuss Your QRA Requirements with INDSAFE

Whether you are developing a new industrial facility, evaluating an existing plant, assessing a modification, or reviewing major accident risk, a properly scoped QRA can provide quantitative information to support engineering and process-safety decisions.

Contact INDSAFE to discuss your QRA requirements, facility details and the appropriate risk-assessment methodology for your project.