QRA
Quantitative Risk Assessment (QRA) Services
Numbers that withstand regulatory and insurer scrutiny — individual risk, societal risk, F-N curves.
Full quantitative risk assessment including dispersion, fire and explosion modelling, individual and societal risk contours.
Request a Consultation
What is QRA?
In short: Quantitative Risk Assessment (QRA) is a rigorous, numerical methodology for estimating the risk to people, assets and the environment posed by major accident hazard scenarios. QRA combines failure frequency data, consequence modelling (dispersion, fire, explosion, toxic effects) and population/exposure data to generate individual risk contours, societal risk (F-N curves), and risk ranking against tolerability criteria such as ALARP.
QRA meaning: what the abbreviation stands for
QRA stands for Quantitative Risk Assessment. In process safety it is sometimes written CPQRA — Chemical Process Quantitative Risk Assessment — the term used by the CCPS guidelines that define the method. It should not be confused with the business-risk or software-testing uses of the same acronym.
A QRA answers one question in numbers: how likely is a person at a given location to be harmed by the major accident hazards of this facility, and is that likelihood tolerable? Qualitative studies such as HAZOP and HAZID identify what can go wrong; QRA quantifies how often and how badly, so that siting, layout and risk-reduction decisions can be made on a defensible basis.
When a QRA study is needed
A QRA is usually triggered by an external decision that needs numbers rather than a qualitative ranking:
- ●Siting a new unit, storage area or occupied building near an existing hazardous inventory
- ●Land-use planning around a Major Accident Hazard (MAH) installation, or new development near the fence line
- ●The risk assessment chapter of an Environmental Impact Assessment (EIA) for a hazardous project
- ●Safety reports and emergency planning for MAH sites under the MSIHC Rules
- ●Insurer, lender or corporate-parent requirements for a quantified risk picture
- ●Demonstrating that risk has been reduced As Low As Reasonably Practicable (ALARP) before investment in further safeguards
Risk tolerability criteria
QRA results only mean something when compared against agreed criteria. India does not publish a single statutory set of individual-risk criteria, so studies commonly reference the UK HSE framework from Reducing Risks, Protecting People (R2P2): an individual risk of death of 1 in 1,000 per year is the usual upper limit of tolerability for workers, 1 in 10,000 per year for members of the public, and 1 in 1,000,000 per year is generally treated as broadly acceptable.
Between those bounds lies the ALARP region, where further risk reduction is expected unless its cost is grossly disproportionate to the benefit. Societal risk is assessed separately on an F-N curve, which plots the frequency (F) of events causing N or more fatalities against criterion lines. The criteria are agreed with the client — and where applicable the regulator or insurer — before any modelling starts, so the conclusion is not chosen after the numbers are seen.
Where failure frequency data comes from
The frequency side of a QRA is as important as the consequence side, and it is where weak studies most often cut corners. Generic leak frequencies are taken from recognised, documented sources such as the IOGP Risk Assessment Data Directory, the UK HSE Failure Rate and Event Data (FRED) set, and the Dutch Purple Book (CPR 18E). Equipment counts, pipe lengths and leak-size distributions are built up from the P&IDs and plot plan rather than assumed.
Event trees then split each release into outcomes — jet fire, pool fire, flash fire, explosion, toxic exposure or safe dispersal — using immediate and delayed ignition probabilities, isolation and detection success, and weather and wind-direction frequencies for the site. Every assumption is listed in an assumptions register so a reviewer can trace any risk figure back to its inputs.
Why It Matters
- ●Required for land-use planning approval near Major Accident Hazard (MAH) installations
- ●Demonstrates ALARP (As Low As Reasonably Practicable) to regulators and insurers
- ●Informs emergency response planning radii and mutual aid arrangements
- ●Provides defensible basis for siting decisions and risk-cost trade-off justification
Our Methodology
- 1Hazard inventory and representative leak/release scenario selection
- 2Frequency analysis using fault tree and recognised failure rate databases
- 3Consequence modelling in DNV Phast — dispersion, pool fire, jet fire, flash fire, VCE, BLEVE as applicable
- 4Risk integration to generate individual risk contours and societal risk F-N curves
- 5ALARP demonstration and risk reduction recommendation
Deliverables
Industries We Serve
FAQ
QRA Frequently Asked Questions
What is QRA in process safety?
QRA (Quantitative Risk Assessment) is a numerical risk assessment method that combines failure frequencies with consequence modelling of fire, explosion and toxic dispersion scenarios to calculate individual and societal risk levels for a facility.
What is ALARP?
ALARP (As Low As Reasonably Practicable) is a risk management principle stating that risk should be reduced until the cost of further reduction is grossly disproportionate to the benefit gained, used as the tolerability test in QRA studies.
What outputs does a QRA produce?
A QRA typically produces individual risk contour plots overlaid on the site plan, societal risk F-N curves, ranked contributing scenarios, and recommendations for risk reduction measures where risk exceeds tolerability criteria.