Selection guidance
PHAST is commonly used for consequence modelling of individual releases; SAFETI integrates frequencies, weather and population to calculate individual-risk contours and societal-risk F-N curves; ALOHA supports selected screening and emergency-planning scenarios; and specialist CFD tools may be required for complex dispersion or explosions. The correct tool depends on the release physics, required outputs and regulator or client expectations.
QRA software turns process and site inputs into consequence distances and numerical risk estimates, but tool selection is only one part of a defensible study. Scenario completeness, frequency data, population inputs and independent checking are equally important.
For the complete workflow, see the QRA methodology guide. For study delivery, visit Elion’s QRA service.
QRA software comparison
| Tool type | Typical use | Important limitation |
|---|---|---|
| PHAST | Discharge, dispersion, fire and explosion consequence modelling | Individual scenarios alone do not constitute full risk integration |
| SAFETI | Individual and societal risk using frequencies, weather and population | Quality depends on the scenario and frequency model |
| ALOHA | Selected toxic, flammable and thermal consequence screening | May not provide every capability needed for a full facility QRA |
| CFD tools such as FLACS | Complex dispersion and explosion behaviour in congested geometry | Requires detailed geometry and specialist competence |
| Spreadsheet or custom calculation | Frequency analysis, event trees and transparent checks | Requires strong verification and version control |
PHAST: consequence modelling
PHAST is used to calculate discharge, dispersion, jet fire, pool fire, flash fire, BLEVE and explosion effects. The modeller must still select correct material, phase, hole size, duration, weather, surface and endpoint assumptions.
SAFETI: integrated risk calculation
SAFETI combines consequences with initiating frequencies, event-tree outcomes, weather, ignition, occupancy and population to generate individual-risk contours and societal-risk F-N curves. The underlying scenario-frequency register must remain reviewable.
ALOHA: screening and emergency-planning support
ALOHA can support selected atmospheric, flammable and toxic consequence assessments. A full QRA may require additional frequency, population and risk-integration calculations.
When specialist CFD may be appropriate
Complex congestion, confinement, terrain or building geometry can make simplified models unsuitable. Specialist CFD may then be justified, provided the geometry, boundary conditions and additional complexity are validated against the decision need.
Software-selection checklist
- Define consequence analysis versus full QRA.
- List every physical outcome that must be modelled.
- Confirm required individual and societal risk outputs.
- Identify regulatory and client expectations.
- Check material-property and model availability.
- Assess congestion, confinement, terrain and building effects.
- Define weather, population and occupancy treatment.
- Confirm native files or reviewable outputs.
- Assign an independent model checker.
Minimum input data
- Substance composition and physical properties
- Operating and storage temperature and pressure
- Inventory and connected volume
- Equipment, line and orifice dimensions
- Isolation, detection and shutdown behaviour
- Release direction, elevation and surface conditions
- Weather and wind-direction distribution
- Plot plan, congestion, terrain and receptors
- Occupancy and population data
Model quality-assurance checks
- Reconcile inputs with PFDs, P&IDs and equipment data
- Check units, phases and material properties
- Benchmark selected scenarios with hand calculations or alternative methods
- Review unexpected discontinuities and outliers
- Confirm contour coordinates and map scale
- Trace integrated risk to the scenario register
- Lock software version, model files and revision history
Common software mistakes
- Choosing a tool before defining the decision
- Using default weather or surface values without justification
- Calling consequence distances a complete QRA
- Ignoring isolation time and connected inventory
- Applying an explosion model without evaluating congestion
- Presenting screenshots instead of reviewable inputs
- Treating output as more precise than the data
Which QRA tool should be used?
Tool-selection summary: Use the tool that matches the decision and the physics. PHAST is commonly used for consequence modelling; SAFETI integrates scenarios, frequencies, weather and population into risk results; ALOHA supports defined screening and emergency-planning tasks; CFD tools are considered when congestion, confinement or complex geometry can materially change dispersion, fire or explosion behaviour.
| Tool or method | Best-fit role | Typical outputs | Important limitation |
|---|---|---|---|
| PHAST | Loss-of-containment consequence modelling | Discharge, dispersion, fire, explosion and toxic-effect distances | Consequence results alone are not a complete QRA |
| SAFETI | Integrated facility or transport QRA | Individual-risk contours, risk contributors and F-N curves | Quality depends on frequencies, population, weather and assumptions |
| ALOHA | Screening and emergency-planning support | Threat-zone estimates for selected chemical-release hazards | Screening results do not satisfy every regulatory QRA scope |
| FLACS or other CFD | Complex geometry, congestion and confinement | Three-dimensional dispersion, fire or explosion behaviour | Requires justified geometry, boundaries, mesh and validation |
| GIS | Spatial data and risk presentation | Population overlays, receptors and georeferenced contours | A map cannot correct weak source data or calculations |
| Spreadsheets or custom code | Event trees, frequency integration and independent checks | Traceable calculations and sensitivity tests | Needs version control, formula review and verification |
What software cannot prove
Software output does not by itself prove that a QRA is complete, accurate or acceptable. The study must still justify scenario selection, release sizes, isolation and detection assumptions, failure frequencies, ignition probabilities, vulnerability models, occupancy, weather data, uncertainty treatment and the applicable risk criteria.
Required QRA model handover files
- Scenario register and equipment-to-scenario mapping
- Native model files or an agreed reviewable export
- Software name, version, modules and model options
- Material-property basis, weather cases and surface parameters
- Frequency, ignition, escalation, population and occupancy inputs
- GIS layers, coordinate system and receptor data
- Verification checks, sensitivities and limitations
- Result tables, contours, F-N data and revision history
Official software sources
- DNV: PHAST consequence-analysis software
- DNV: SAFETI for quantitative risk analysis
- US EPA: ALOHA software
- Gexcon: FLACS-CFD
See Elion’s QRA calculations, F-N curve and ALARP guide and design-stage QRA input checklist.
Frequently asked questions
Which is the best QRA software?
There is no universal best tool. Select the model suite that represents the release physics and produces the outputs required for the facility and decision.
Can PHAST generate a complete QRA?
PHAST is primarily used for consequence modelling. Full QRA also requires frequencies, event outcomes, weather, population and risk integration.
Is ALOHA acceptable?
ALOHA may be suitable for defined screening or emergency-planning applications. Acceptance depends on scope and the reviewing authority.
Should clients receive native files?
Define this contractually. If native files cannot be supplied, provide enough input, assumption and result detail for independent review.
Elion selects the modelling basis after reviewing the facility, inventory and required outputs. Share the project brief for a tool and deliverable recommendation.
Continue by application: See QRA for hydrogen, ammonia, LNG, BESS and emerging-energy facilities, and confirm the governing basis with the international QRA standards and acceptance-criteria guide.