Quantitative Risk Analysis: Complete Guide for South Africa

If your site handles large quantities of hazardous materials, you need more than a colour risk matrix. You need numbers that show how often major accidents might happen and how serious they would be.
That is what Quantitative Risk Analysis (QRA) does. In South Africa it is the core method used to assess Major Hazard Installations (MHIs) under SANS 1461:2018.
In this guide you will learn:

• What QRA is and how it differs from HAZOP.
• The main steps in a QRA (with SA-specific detail).
• South African risk acceptance criteria (ALARP, 1×10⁻⁶ contour).
• Typical QRA costs in Rand and what drives them.
• How to use QRA results for land-use planning and regulatory submissions.

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What is Quantitative Risk Analysis (QRA)?

Quantitative Risk Analysis (QRA) is a specialised engineering methodology that calculates risk numerically. Unlike a HAZOP (which identifies what can go wrong), a QRA calculates how likely it is to go wrong and how bad the consequences will be.
It answers two fundamental questions:

1. Frequency: How often will this accident happen? (e.g., once in 10 000 years).
2. Consequence: What is the impact? (e.g., 1% fatality radius of 300 m from a toxic cloud).
   The output is a set of risk contours overlaid on a site map, showing where risk levels exceed defined thresholds.

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The Legal Context: SANS 1461 and MHI Regulations 2022

In South Africa, QRA is not optional for facilities that exceed hazardous-substance thresholds. The legal framework includes:

Legislation / Standard	Role
Occupational Health and Safety Act 85 of 1993	Parent Act; empowers MHI Regulations
MHI Regulations 2022	Defines MHI classification, AIA requirements, 5-year review cycle
SANS 1461:2018	Prescribes QRA methodology, risk criteria, and reporting format
SANS 1514:2018	Emergency response planning requirements for MHIs

Key SANS 1461 Requirements

SANS 1461 is the South African National Standard that outlines procedures for conducting QRAs on installations that store, use, or transport hazardous substances. It covers:

• Risk assessment procedures – methodologies for hazard identification, analysis, and risk calculation.
• Scope of work – data gathering, defining hazardous scenarios, evaluating consequences.
• Risk judgement criteria – frameworks like ALARP (As Low As Reasonably Practicable) for determining acceptable risk levels.
• Land-use planning guidance – restrictions based on hazard proximity.
• Emergency response planning – protocols for managing hazardous incidents.

Who Must Comply?

• Oil refineries, chemical plants, gas pipelines, and LPG depots.
• Mining operations using bulk cyanide, ammonia, or explosives.
• Cold-storage facilities with large ammonia inventories.
• Urban planners and municipal authorities managing land use near hazardous installations.
• Any facility classified (or potentially classified) as an MHI.

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The 5 Steps of a South African QRA

A QRA is a complex study, typically performed using specialised software (DNV PHAST, Gexcon RISKCURVES, or TNO EFFECTS) by experienced risk engineers. The process follows five main steps:

1. Data Gathering and Scope Definition

Before any modelling begins, the QRA team collects:

• Process flow diagrams (PFDs) and piping & instrumentation diagrams (P&IDs).
• Hazardous substance inventories – types, quantities, storage conditions.
• Site layout plans – equipment locations, occupied buildings, fence-line distances.
• Meteorological data – wind rose, atmospheric stability classes for dispersion modelling.
• Population data – on-site shift patterns, nearby residential or sensitive receptors (schools, hospitals).
  Tip: Facilities with well-maintained process safety information can save R50 000 – R150 000 in data-compilation effort.

2. Hazard Identification

We identify all credible loss of containment (LOC) scenarios:

• Full-bore ruptures, leaks, and catastrophic failures of vessels, pipes, and flanges.
• Overfilling, runaway reactions, and external impacts (e.g., vehicle collision).
  Example: A rupture of a 20-tonne ammonia storage sphere or a 50 mm leak on a high-pressure LPG line.

3. Consequence Modelling

We simulate the physical effects of each release using validated models:

Hazard Type	What We Model	Output
Fire	Pool fire, jet fire, flash fire	Thermal radiation zones (kW/m²)
Explosion	VCE (Vapour Cloud Explosion), BLEVE	Overpressure contours (kPa)
Toxic Release	Gas dispersion (dense/neutral)	Concentration contours (ppm), IDLH, LC₅₀
(Read more: Consequence Modeling Explained)

4. Frequency Analysis

We estimate how often each scenario occurs using:

• Generic failure-rate databases – IOGP (formerly OGP), UK HSE, OREDA.
• Plant-specific data – if your maintenance records support it.
• Fault Tree / Event Tree Analysis – for complex safeguard credit calculations.
  Example: A full-bore rupture of a generic 100 mm pipe section might occur at 1×10⁻⁵ per metre per year.
  (Read more: Fault Tree vs Event Tree Analysis)

5. Risk Calculation and Contour Mapping

We combine frequency and consequence to produce:

• LSIR contours – Location Specific Individual Risk lines drawn on a site map (like elevation contours on a topo map).
• F-N curves – Societal risk plots showing frequency vs number of fatalities.
  The key contour in South Africa is 1×10⁻⁶ per year (one-in-a-million chance of fatality). This is typically the boundary for:
• Siting new residential developments.
• Determining safe distances for sensitive receptors (schools, hospitals).

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South African Risk Acceptance Criteria

SANS 1461 and international best practice use the ALARP (As Low As Reasonably Practicable) framework:

Risk Level	Individual Risk (per year)	Action Required
Intolerable	> 1×10⁻⁴ (public) / > 1×10⁻³ (workers)	Risk must be reduced regardless of cost
ALARP region	Between intolerable and broadly acceptable	Reduce risk unless cost is grossly disproportionate to benefit
Broadly acceptable	< 1×10⁻⁶	No further action required

Practical Implications

• If your 1×10⁻⁶ contour extends beyond your fence line into a residential area, you may need to reduce inventory, add safeguards, or negotiate land-use restrictions with the municipality.
• If worker risk exceeds 1×10⁻⁴, you must implement engineering or administrative controls before the Department of Employment and Labour will accept your MHI submission.

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Typical QRA Costs in South Africa (2025)

QRA pricing depends on facility complexity, data quality, and modelling depth. Below are indicative ranges in South African Rand (ZAR):

Facility Type	Typical QRA Cost (excl. VAT)	Key Cost Drivers
Small depot (single product, < 5 scenarios)	R150 000 – R300 000	Limited modelling, straightforward layout
Medium facility (multiple products, 10–30 scenarios)	R300 000 – R600 000	More scenarios, detailed consequence runs
Large / complex site (refinery, chemical plant, 50+ scenarios)	R600 000 – R1 500 000+	Extensive modelling, domino effects, societal risk
Pipeline QRA (cross-country, per km basis)	R80 000 – R150 000 per km	Length, population density along route

What Drives Cost Up?

• Poor data quality – if P&IDs are outdated or inventories unknown, expect R50 000–R150 000 extra for data compilation.
• High scenario count – each additional scenario adds modelling and reporting effort.
• Domino effect analysis – required where multiple MHIs are adjacent (e.g., industrial parks).
• Societal risk (F-N curves) – adds complexity when sensitive receptors are nearby.
• Software licence fees – industry-standard tools like PHAST or RISKCURVES carry significant annual costs, passed through to clients.

What Drives Cost Down?

• Well-maintained process safety information – accurate P&IDs, up-to-date inventories.
• Previous QRA as baseline – 5-year updates are cheaper than greenfield studies.
• Clear scope definition – agreeing scenarios upfront avoids scope creep.

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When Do You Need a QRA?

You typically need a QRA if:

1. MHI Classification – You hold dangerous substances above threshold quantities (e.g., > 50 tonnes LPG, > 25 tonnes chlorine, > 100 tonnes ammonia). The QRA determines if you are classified as an MHI. (See: When is QRA Required?)
2. Land-Use Planning – You are planning a new development near an industrial area, or expanding your facility towards a residential zone.
3. 5-Year Regulatory Review – MHI Regulations require reassessment every 5 years or after significant change.
4. Design Decision Support – You need to compare two design options and quantify which is safer.
5. Insurance or Financing – Some insurers and lenders require QRA evidence before underwriting large industrial risks.

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Interpreting QRA Results

The output of a QRA is a decision tool, not just a compliance document.

LSIR (Location Specific Individual Risk)

• Shows the annual probability of fatality at any point on or around your site.
• Used to check if workers or neighbours are exposed to intolerable risk.
• Presented as contour lines (e.g., 1×10⁻⁵, 1×10⁻⁶) overlaid on a site plan.

Societal Risk (F-N Curves)

• Plots the cumulative frequency of accidents causing N or more fatalities.
• Used when your facility is near schools, hospitals, or dense housing.
• Regulators may require societal risk to fall within the ALARP region.

What If Risk Is Too High?

If the QRA shows risk in the Intolerable region, you generally have three options:

1. Reduce inventory – store less hazardous material on site.
2. Add safeguards – install additional layers of protection (e.g., gas detectors, deluge systems, secondary containment).
3. Relocate or restrict land use – move sensitive receptors or negotiate buffer zones with the municipality.

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Common QRA Pitfalls in South Africa

Based on our experience across hundreds of MHI assessments:

• Using outdated failure-rate data – always reference current IOGP or UK HSE databases.
• Ignoring atmospheric conditions – South African sites often have unique wind patterns; use local met data.
• Underestimating population exposure – informal settlements near industrial areas are common; ensure accurate receptor mapping.
• Skipping domino analysis – required where multiple MHIs share a fence line (e.g., Secunda, Richards Bay industrial zones).
• Poor documentation – SANS 1461 requires a structured report; incomplete submissions are rejected by AIAs and the Department of Employment and Labour.
  (See: Common MHI Assessment Mistakes)

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Conclusion

Quantitative Risk Analysis provides the hard numbers needed to manage major hazards. It moves safety discussions from "I think" to "I know." For South African facilities handling hazardous materials, a high-quality QRA aligned with SANS 1461 is the foundation of legal compliance, responsible land-use planning, and operational excellence.

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Ready to Start Your QRA?

MMRisk is an Approved Inspection Authority (AIA) specialised in high-complexity QRA studies. We use industry-leading software (PHAST, RISKCURVES) and strictly adhere to SANS 1461 to ensure your assessment is accurate, compliant, and defensible.
Typical turnaround: 8–16 weeks depending on complexity.
Request a Quote for Your MHI Assessment – we'll provide a detailed scope and cost estimate within 5 working days.