Neqsim Consequence Analysis

NeqSim Consequence Analysis Skill

Quantitative consequence modelling that converts a release scenario (mass flow, inventory, ignition probability) into thermal radiation contours, overpressure contours, dispersion footprints, and finally individual / societal fatality risk per ISO 17776, NORSOK Z-013, API 752 and the CCPS Guidelines for Chemical Process Quantitative Risk Analysis.

When to Use

• Jet-fire, pool-fire, VCE or BLEVE source-term modelling
• Toxic / flammable dispersion to LFL, IDLH, ERPG-2/3 or 1 % fatality contours
• Probit-based fatality probability for thermal radiation, overpressure or toxic dose
• QRA roll-up: combine release frequency × ignition probability × fatality probability
• Source-term generation as input to PHAST / FLACS / KFX

Distinct from neqsim-process-safety (HAZOP / LOPA / SIL — frequency side) and neqsim-relief-flare-network (PSV sizing / flare radiation — design side). This skill is the consequence side of QRA.

Standards

• API 521 §6 — flare and vent radiation, fire heat input
• API 752 / 753 / 756 — facility siting, occupied buildings
• NORSOK Z-013 / S-001 — risk acceptance, fire & explosion loads
• CCPS QRA Guidelines — probit constants, ignition probabilities
• TNO Yellow Book — multi-energy / Baker-Strehlow VCE
• EI 15 — hazardous area classification

Method 1 — Jet Fire (API 521 + CCPS solid-flame)

import neqsim.process.safety.fire.JetFireModel;
import neqsim.process.safety.dispersion.ProbitModel;

// 30 kg/s gas leak, 50 MJ/kg HoC, 25 % radiative fraction
JetFireModel jet = new JetFireModel(30.0, 50.0e6, 0.25);
double flux50m = jet.radiationFluxAt(50.0);   // W/m²
double dist125 = jet.distanceForFlux(12500.0); // m where flux = 12.5 kW/m²

Typical thermal radiation criteria (API 521 / NORSOK S-001):

Method 2 — Pool Fire

import neqsim.process.safety.fire.PoolFireModel;

// 500 kg liquid, burning rate 0.05 kg/m²·s, dike diameter 8 m, η = 0.30
PoolFireModel pool = new PoolFireModel(0.05, 8.0, 50.0e6, 0.30);
double flux = pool.radiationFluxAt(25.0); // W/m² at 25 m

Method 3 — Vapour Cloud Explosion (TNO Multi-Energy)

import neqsim.process.safety.fire.VCEModel;

// 200 kg flammable in cloud, congestion class 7 (heavy)
VCEModel vce = new VCEModel(200.0, 50.0e6, 7);
double overpressure = vce.overpressureAt(60.0); // Pa at 60 m
double safeDist = vce.distanceForOverpressure(20684.0); // m for 3 psi

Method 4 — BLEVE

import neqsim.process.safety.fire.BLEVECalculator;

// 50 t propane vessel
BLEVECalculator bleve = new BLEVECalculator(50000.0, 50.0e6, 0.40);
double fireballDiameter = bleve.fireballDiameter();   // m
double fireballDuration = bleve.fireballDuration();   // s
double thermalDose = bleve.thermalDoseAt(150.0);      // (W/m²)^(4/3)·s

Method 5 — Gaussian Plume Dispersion (Briggs σ)

import neqsim.process.safety.dispersion.GaussianPlume;

// 10 kg/s leak, ground-level source, 4 m/s wind, neutral stability D
GaussianPlume plume = new GaussianPlume(10.0, 0.0, 4.0,
    GaussianPlume.Stability.D, GaussianPlume.Terrain.RURAL);
double conc = plume.centerlineGroundConcentration(200.0); // kg/m³
double distLFL = plume.distanceToConcentration(0.044);    // m to methane LFL

Stability classes: A (very unstable) … F (stable). RURAL vs URBAN selects Briggs σ coefficients per Pasquill-Gifford. Use Stability.F for worst-case dispersion analysis (calm night, low wind).

Method 6 — Heavy-Gas Dispersion

For dense releases (CO₂, propane, butane) the Gaussian model under-predicts near-field concentrations. Use HeavyGasDispersion (Britter-McQuaid screening):

import neqsim.process.safety.dispersion.HeavyGasDispersion;

HeavyGasDispersion hgs = new HeavyGasDispersion(
    50.0,    // continuous release rate [kg/s]
    1.98,    // gas density at release [kg/m³]
    1.20,    // ambient density [kg/m³]
    4.0);    // wind speed [m/s]
double distLFL = hgs.distanceToConcentration(0.05); // m

Method 7 — Probit Fatality Probability

import neqsim.process.safety.dispersion.ProbitModel;

// Thermal: Y = a + b·ln(t·F^(4/3)), 60 s exposure at 12.5 kW/m²
double pFatality = ProbitModel.thermalFatality()
    .fatalityProbability(60.0, 12500.0);

// Toxic H2S: Y = -31.42 + 3.008·ln(C^1.43·t)
ProbitModel h2s = ProbitModel.h2sFatality();
double pH2S = h2s.fatalityProbability(600.0, 5.0e-4); // 10 min, 500 ppm

// Overpressure (lung haemorrhage): Y = -77.1 + 6.91·ln(P)
ProbitModel ovp = ProbitModel.overpressureFatality();

Built-in factories: thermalFatality(), overpressureFatality(), h2sFatality(), cl2Fatality(), nh3Fatality(), coFatality(). The ToxicLibrary class centralises probit constants for common toxic gases.

Method 8 — QRA Roll-up

import neqsim.process.safety.qra.ConsequenceAnalysisEngine;

ConsequenceAnalysisEngine e = new ConsequenceAnalysisEngine(
    "10 mm gas leak", 1.0e-4); // release frequency [/yr]
e.addJetFire(0.05, jet, ProbitModel.thermalFatality(), 60.0);
e.addJetFire(0.02, pool, ProbitModel.thermalFatality(), 60.0);
e.addToxicCloud(0.01, plume, ProbitModel.h2sFatality(), 600.0);

double IRPA = e.individualFatalityRiskPerYear(50.0); // at 50 m
String text = e.report(50.0);

The engine sums:

IRPA(d) = Σ_outcome f_release · f_branch · P_fatality(d, outcome)

Compare against acceptance criteria:

Method 9 — Flare Flame Radiation & Noise (API 537)

import neqsim.process.safety.fire.Api537FlareFlameModel;

Api537FlareFlameModel flame = new Api537FlareFlameModel(
        50.0, 50.0e6, 0.20, 200.0)   // mDot[kg/s], HoC[J/kg], radiantFrac, vExit[m/s]
    .setStackHeightM(40.0)
    .setWindSpeedMPerS(10.0);

double r473 = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_4_73_KW); // property line
double q75  = flame.heatFluxAtGroundDistance(75.0);  // W/m²
double spl  = flame.soundPressureLevelDb(100.0);     // dB at 100 m

Use this instead of the point-source jet-fire form when the source is an elevated flare tip (it accounts for stack height, wind tilt, and flame geometry).

Method 10 — Hazardous-Area Zone Classification (IEC 60079-10-1)

import neqsim.process.safety.dispersion.HazardousAreaCalculator;
import neqsim.process.safety.dispersion.HazardousAreaCalculator.ReleaseGrade;

HazardousAreaCalculator calc = new HazardousAreaCalculator(
        0.1,      // release mass flow [kg/s]
        6.0,      // process pressure [bara]
        340.0,    // temperature [K]
        0.044,    // LFL [volume fraction]
        0.01604)  // molar mass [kg/mol]
    .setReleaseGrade(ReleaseGrade.SECONDARY)  // CONTINUOUS / PRIMARY / SECONDARY
    .setSafetyFactor(0.5);

double dHaz = calc.hazardousDistanceM();
String zone = calc.zoneClassification();   // "Zone 0" / "Zone 1" / "Zone 2"

Maps the dispersion result to an Ex zone for electrical-equipment selection. CONTINUOUS → Zone 0, PRIMARY → Zone 1, SECONDARY → Zone 2.

Method 11 — Passive Fire Protection (PFP) Demand (API 521 / NORSOK S-001)

import neqsim.process.safety.fire.PfpDemandCalculator;
import neqsim.process.safety.fire.PfpDemandCalculator.FireType;
import neqsim.process.safety.fire.PfpDemandCalculator.PfpDemandResult;

PfpDemandResult pfp = new PfpDemandCalculator(
        100.0e3,   // fire heat flux [W/m²] (pool ~100 kW/m², jet ~250+ kW/m²)
        0.012)     // wall thickness [m]
    .setFireType(FireType.POOL)               // POOL / JET
    .evaluate(3600.0);                        // required survival time [s]

boolean need = pfp.isPfpRequired();
double thkMm = pfp.getRequiredPfpThicknessMm();
PfpDemandResult.PfpRating rating = pfp.getRating(); // NONE / H60 / J120 ...

Determines whether unprotected steel reaches its critical temperature before the required survival time, and if so the intumescent thickness and H/J rating.

Source Term for External CFD

ConsequenceAnalysisEngine.exportSourceTerm() writes a JSON block usable by PHAST, FLACS, KFX or DNV Safeti containing release rate, momentum, density, duration and chemistry — the standard handoff format described in neqsim-agent-handoff.

Common Pitfalls

• Stability class — using class D ("typical") instead of F for hazard contours under-predicts safe distance by 2–3×. Always run F at low wind for siting.
• Heavy gas — applying Gaussian to CO₂ / LPG releases under-predicts near-field concentration. Switch to HeavyGasDispersion when density ratio > 1.2.
• Probit constants — different sources give different (a, b, n). Always cite the source; the factories in ProbitModel use CCPS values.
• Ignition probability — small leaks (< 1 kg/s) often use 1–5 %, large leaks (> 50 kg/s) up to 30 % delayed. Use scenario-specific values, not 100 %.
• Flame view-factor — the simple 1/(4πr²) point-source form is conservative near the flame; use API 521 solid-flame for distances < 2 × flame length.

Verification Tests

src/test/java/neqsim/process/safety/{fire,dispersion,qra}/ contain JUnit 5 tests for every model. Run:

./mvnw test -Dtest=FireModelsTest,GaussianPlumeTest,ProbitModelTest,ConsequenceAnalysisEngineTest,Api537FlareFlameModelTest,HazardousAreaCalculatorTest,PfpDemandCalculatorTest

See Also

• neqsim-process-safety — frequency side (HAZOP / LOPA / SIL)
• neqsim-relief-flare-network — PSV sizing and flare radiation
• neqsim-depressurization-mdmt — emergency depressurization source terms
• neqsim-agent-handoff — source-term JSON schema