Consequence Modelling
Consequence Modelling Services
Precise modelling of how a release behaves — and how far its effects reach.
Dispersion, fire, explosion and toxic release modelling in DNV Phast and ALOHA to quantify physical effect zones.
Request a ConsultationWhat is Consequence Modelling?
In short: Consequence Modelling is the quantitative simulation of the physical effects of a loss-of-containment event — gas/vapour dispersion, pool fires, jet fires, flash fires, vapour cloud explosions (VCE), and BLEVEs — to determine hazard footprint distances such as toxic dose contours, thermal radiation contours, and explosion overpressure contours.
Scenarios we model
A consequence modelling study starts from the loss-of-containment scenarios that matter for the decision at hand — siting, emergency planning, building occupancy or QRA input. Typical scenario types include:
- ●Toxic gas dispersion — neutral and heavy (dense) gas releases such as ammonia, chlorine, hydrogen sulphide and phosgene
- ●Flammable dispersion to the lower flammable limit (LFL) and ½ LFL for flash fire and gas detection coverage
- ●Jet fires from pressurised gas and two-phase releases
- ●Pool fires from liquid spills, including rainout and pool spreading and evaporation
- ●Vapour cloud explosions (VCE) using congestion-based methods such as TNO Multi-Energy or Baker-Strehlow-Tang
- ●BLEVE and fireball events for pressurised liquefied gas storage
- ●Hydrogen releases, where high buoyancy, wide flammability limits and low ignition energy change the picture
Ammonia consequence modelling case study →What is consequence modelling? →
Harm criteria and end-points
Hazard distances are only meaningful against stated end-points. The criteria are agreed at the start of the study and reported with every contour. Values commonly used in industry practice include:
- ●Thermal radiation: 37.5 kW/m² (process equipment damage), 12.5 kW/m² (significant chance of fatality for extended exposure), and around 4–5 kW/m² (pain and injury threshold for short exposure)
- ●Explosion overpressure: about 0.3 bar (heavy damage to process plant), 0.1 bar (repairable structural damage), and about 0.02–0.03 bar (window breakage and glass injury)
- ●Toxic exposure: concentration end-points such as ERPG-2/ERPG-3, AEGL or IDLH for emergency planning, or probit-based dose–response models where a QRA needs fatality probability
Tool selection: matching the model to the release
Process Pulse runs consequence studies in DNV Phast and US EPA/NOAA ALOHA. Phast is our main tool for detailed studies: it models discharge, two-phase and dense-gas dispersion, rainout and pool evaporation, jet, pool and flash fires, fireballs and vapour cloud explosions in one validated workflow, and produces the QRA-grade consequence results used for siting, FERA and emergency planning. ALOHA is a fast screening tool, well suited to early toxic and flammable threat-zone estimates and to the emergency-planning distances that response teams use on the ground.
No single model is right for every scenario. Where a release falls outside what integral models handle well — for example a vapour cloud explosion in highly congested or confined geometry — computational fluid dynamics tools such as FLACS or FDS are the appropriate next step, and we will say so rather than stretch a model beyond its validity.
Every report states which tool was used for each scenario, its version, the key input assumptions and the limits of its validity — so the results can be reviewed or reproduced by a third party.
What drives the accuracy of the results
Most of the uncertainty in a consequence study comes from the inputs, not the software. The source term — hole size, release pressure and temperature, phase, and isolation time — sets the release rate and duration, and an error there propagates into every downstream contour.
Weather is the next biggest driver. Studies normally run at least a neutral, moderately windy case (for example Pasquill stability D with 5 m/s wind) and a stable, low-wind case (F with 2 m/s), because stable night-time conditions often produce the longest toxic and flammable distances. Release orientation, surface roughness, averaging time and the presence of bunds or impingement surfaces are also stated explicitly, so the client knows which contours are conservative and why.
Why It Matters
- ●Underpins QRA, HAZID siting decisions, and emergency response planning distances
- ●Validates whether existing separation distances and mitigation systems are adequate
- ●Required input for fire and explosion risk assessments and ERDMP
- ●Supports plant layout optimisation and inherently safer design reviews
Our Methodology
- 1Source term modelling — release rate, duration, phase (gas/liquid/two-phase)
- 2Dispersion modelling under range of atmospheric stability and wind speed conditions
- 3Fire and explosion modelling for ignited release scenarios
- 4Hazard footprint mapping for toxic, thermal and overpressure end-points
- 5Sensitivity analysis across weather categories and mitigation credits
Deliverables
Industries We Serve
FAQ
Consequence Modelling Frequently Asked Questions
What is consequence modelling?
Consequence modelling is the quantitative simulation of physical effects — dispersion, fire, and explosion — resulting from a loss-of-containment event, producing hazard footprint distances used in QRA, siting, and emergency planning.
What software is used for consequence modelling?
Widely used tools include DNV Phast, ALOHA, EFFECTS, and dense-gas models such as SLAB and DEGADIS, chosen by release type and scenario. Process Pulse uses DNV Phast for detailed consequence studies and ALOHA for screening and emergency-planning threat zones.
Which software does Process Pulse use for consequence modelling?
Process Pulse uses DNV Phast for detailed discharge, dispersion, fire and explosion modelling, and US EPA/NOAA ALOHA for rapid screening and emergency-planning threat zones. Each report states the tool and version used for every scenario.
What is a source term in consequence modelling?
The source term defines the rate, duration, phase and physical state of material released from a loss-of-containment event — it is the critical input that determines the accuracy of all downstream dispersion and fire/explosion modelling.