Quantitative Risk Assessment (QRA) in South Africa
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20+
years of experience
- Quantitative
Risk Assessments
If your site handles hazardous materials, high-pressure systems, flammable gases, combustible dust, or toxic chemicals, you already know this truth: the risk is never “zero” — the only real question is how big the risk is, who it affects, and whether it’s tolerable. That’s exactly what a Quantitative Risk Assessment (QRA) or Major Hazard Installation (MHI) Risk Assessment answers.
At MHI Risk Engineers, we deliver quantitative and MHI risk assessment services that help you measure, model, and visualise the risk of fires, explosions, and toxic releases. The outcome isn’t just a report for the shelf. It’s decision-quality information you can use to:
- justify safety spend with confidence
- prioritise upgrades (the right actions, not “everything”)
- support compliance and defensible engineering decisions
- demonstrate ALARP (As Low As Reasonably Practicable) where required
Whether you call it QRA, risk assessment quantitative, or probabilistic risk assessment, or MHI Risk Assessment, the goal is the same: turn uncertainty into numbers you can act on.
- What is a QRA
What a QRA actually does
A quantitative risk assessment or MHI risk assessment is a structured process that answers:
- What can go wrong? (credible loss-of-containment scenarios)
- How often could it happen? (frequency / likelihood based on failure data)
- What happens if it does? (consequence modelling)
- Who is exposed and how much? (individual and societal risk)
- What should we do about it? (mitigation measures or ALARP justification)
Unlike a qualitative approach that uses categories like “low/medium/high,” a QRA or MHI provides numbers and risk visualisations such as risk contours and FN curves — the kind of outputs regulators, boards, and technical authorities can evaluate consistently.
- Who needs this service
When you should commission a QRA
A quantitative or MHI risk assessment is especially valuable when you need to:
- support a Major Hazard Installation (MHI) risk assessment scope
- evaluate changes (MOC) that could materially impact risk
- justify separation distances / land-use planning decisions
- choose between safety investments (e.g., detection vs isolation vs bunding)
- demonstrate that controls bring risk into tolerable/ALARP range
- respond to incidents, near misses, or audit findings with defensible analysis
- What we do:
Our QRA methodology
Our quantitative or MHI risk assessments typically follow this flow:
01
Hazard identification
(inputs from your studies)
We start by identifying credible hazards using results from:
HAZID, HAZOP, and related studies
This ensures the QRA is based on real process hazards, not generic assumptions.
02
Frequency estimation
(how likely is it?)
We estimate event frequencies using recognised failure data sources, such as:
OREDA (where appropriate)
This is where the “probabilistic” part of probabilistic risk assessment comes in — we quantify likelihood using evidence-based data and event logic.
03
Consequence modelling
(what happens physically?)
We model outcomes using industry-standard consequence modelling tools, including:
- PHAST
- Gexcon
This allows us to simulate thermal radiation, blast overpressure, toxic dispersion, escalation potential, and impact distances under credible conditions.
04
Risk calculation & visualisation
We calculate and present risk in formats that decision-makers actually use, such as:
- risk contours (individual risk over a site map)
- FN curves (societal risk and tolerability)
- scenario ranking (what contributes most to the risk)
05
Mitigation recommendations or ALARP justification
Finally, we provide:
- targeted mitigation measures (engineering, procedural, detection, isolation, etc.)
- or defensible ALARP justifications where further reduction is disproportionate
The end result: you can clearly see what drives risk, and you can invest in the controls that reduce it most.
- Certifications
Standards and guidelines we follow
Our QRA and MHI work is aligned to recognised international and South African guidance, including:
- CCPS RBPS Guidelines
- UK HSE R2P2 (risk tolerability principles)
- API 754 (process safety performance indicators)
- SANS 1461 (relevant to risk assessment context within SA)
This gives your assessment credibility across internal governance, audits, insurers, and regulatory engagement.
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Get in touch with us
Reach out for any inquiries, support, or to discuss how we can meet your industrial needs.
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FAQ: Quantitative risk assessment explained
What is the difference between quantitative and qualitative risk assessment?
A qualitative or MHI risk assessment uses descriptive rankings like low, medium, high based on judgement and broad criteria. A quantitative risk assessment (QRA) assigns numerical values to likelihood and consequence, then calculates risk as measurable outputs (like individual risk contours and FN curves). Qualitative is faster and simpler; quantitative is more rigorous and defensible for high-hazard decisions.
What best describes a quantitative risk assessment?
A quantitative risk assessment is a structured method that identifies hazards, estimates how often events occur, models consequences, and then calculates risk numerically so it can be compared to tolerability criteria and used for investment decisions.
What are the 4 types of risk assessment?
A practical way to group risk assessment types is:
- Qualitative (descriptive categories)
- Semi-quantitative (scoring systems / matrices with numbers but not true frequencies)
- Quantitative (QRA) (numerical frequency + consequence modelling)
- Dynamic/Continuous (ongoing assessment as conditions change, often operational)
Different industries name these slightly differently, but the concept is consistent.
What is a qualitative risk assessment?
It’s a risk assessment that uses judgement-based ratings rather than calculated frequencies and consequence models. It’s useful for screening hazards, prioritising actions, and lower complexity environments.
What is an example of a quantitative risk assessment?
A classic QRA example is modelling a toxic release (e.g., ammonia or chlorine), estimating the release frequency using failure data, simulating dispersion in PHAST, then producing risk contours showing risk levels at various distances and an FN curve showing societal risk.
What are qualitative and quantitative assessments?
They’re two ways of measuring risk:
- Qualitative: category-based, faster, less data-heavy
- Quantitative: data-based, numerical, defensible for high-hazard sites
Most mature programmes use both: qualitative to screen and prioritise; quantitative where the risk is complex or high.
- Qualitative: category-based, faster, less data-heavy
How to perform a quantitative risk assessment?
In short:
- Define scope, inventory, and receptors (people, property, environment)
- Identify credible scenarios (often from HAZID/HAZOP)
- Assign frequencies using data sources and event trees
- Model physical effects (thermal, blast, toxic dispersion) using software
- Calculate individual and societal risk (contours + FN curves)
- Compare results to criteria and evaluate risk reduction options
- Provide mitigation recommendations or ALARP justification
What are the 5 things a risk assessment should include?
A solid risk assessment should include:
- Hazard identification (what can go wrong)
- Likelihood/frequency (how often)
- Consequences (what happens)
- Risk evaluation (is it tolerable / ALARP?)
- Controls and actions (what you’ll do, by when, and who owns it)
What are the 4 elements of risk assessment?
A common four-part breakdown is:
- Identify hazards
- Analyse risk (likelihood + consequence)
- Evaluate risk (compare to criteria)
- Control risk (implement and verify measures)
What are the 5 P's of risk assessment?
“5 P’s” varies by organisation, but a useful operational version is:
- People (competence, exposure)
- Plant (equipment integrity)
- Process (procedures and controls)
- Place (layout, environment, surrounding receptors)
- Product (materials, properties, quantities)
For QRA work, those P’s map neatly to data collection and scenario definition.
What is a type 2 risk assessment?
“Type 2” is not a universal standard label. In many workplaces it refers to an issue-based or task-level risk assessment (more detailed than baseline, less complex than full quantitative modelling). If your internal system uses “Type 2,” we align the QRA scope and terminology to your framework so the outputs are easy to adopt.
What is a type 3 risk assessment?
Similarly, “Type 3” often refers (in some systems) to a high-detail, specialist assessment—which is where QRA frequently sits. The key is not the label but the method: if you need numerical risk outputs, consequence modelling, and defendable ALARP reasoning, you’re typically in “type 3” territory.
What is the major difference between qualitative analysis and quantitative analysis?
Qualitative analysis relies on descriptive judgement; quantitative analysis relies on numerical data, models, and calculations. Quantitative results can be compared more consistently across scenarios, sites, and time — especially when stakes are high.
What is the difference between qualitative and quantitative impact assessment?
A qualitative impact assessment describes impacts in words or categories (minor/moderate/major). A quantitative impact assessment estimates impacts with numbers (e.g., predicted overpressure at distance, thermal dose thresholds, concentration-time exposure), which is essential in high-hazard environments.
What is a detailed quantitative risk assessment?
A “detailed” QRA typically means:
- more complete scenario set
- refined frequency modelling (event trees / fault trees where required)
- validated assumptions and sensitivity checks
- detailed consequence modelling
- clear breakdown of risk contributors (what drives the FN curve / contours)
- defensible mitigations and ALARP arguments
Which is a better tool for risk measurement, qualitative or quantitative risk management?
Neither is “better” universally — they’re different tools for different decisions:
- Use qualitative for fast prioritisation, early screening, and simpler hazards.
- Use quantitative risk assessment (QRA) when decisions are high-impact, complex, regulated, or require defensible numeric outputs.
For MHI-related and major hazard contexts, quantitative methods are often the most credible way to justify safety decisions.
Quantitative Risk Assessments build on HAZOP studies and LOPA reviews to model credible worst-case scenarios for Major Hazard Installations. This evidence-based approach strengthens regulatory defensibility and supports informed risk management decisions.