Dispersion and Consequence Analysis

The neqsim.process.safety package provides the building blocks for a quantitative risk assessment (QRA): dispersion footprints, fire/explosion radiation and overpressure contours, probit-based fatality probabilities, and an aggregate IRPA (individual risk per annum) calculation.

Dispersion

GaussianPlume implements the standard Pasquill–Gifford / Briggs model. Stability classes A (very unstable) through F (stable) are encoded as the Stability enum; terrain is RURAL or URBAN.

GaussianPlume plume = new GaussianPlume(
    10.0,                 // mass release rate [kg/s]
    0.0,                  // source height [m] — use 0 for ground-level release
    4.0,                  // wind speed [m/s]
    GaussianPlume.Stability.D,
    GaussianPlume.Terrain.RURAL);
double cAt100m = plume.centerlineGroundConcentration(100.0); // kg/m³
double rLfl    = plume.distanceToConcentration(0.025);       // m to 2.5 % CH4

For dense releases (CO₂, propane, chlorine), use HeavyGasDispersion (Britter–McQuaid screening).

Fire and explosion

Model Class Citation
Jet fire JetFireModel API 521 §6.4.4, Chamberlain solid-flame
Pool fire PoolFireModel API 521 §6.4.3
VCE VCEModel TNO multi-energy / Baker-Strehlow
BLEVE BLEVECalculator TNO Yellow Book Ch. 6 
JetFireModel jet = new JetFireModel(30.0, 50.0e6, 0.25);  // ṁ, HoC, η
double q50 = jet.radiationFluxAt(50.0);          // W/m² at 50 m
double r12 = jet.distanceForFlux(12500.0);       // m to 12.5 kW/m²

Probit fatality

ProbitModel exposes ready-made factories for thermal radiation, overpressure, and toxic gases. The form is

\[Y = a + b \ln\!\left(C^{n}\,t\right), \qquad P_{fatality} = \tfrac{1}{2}\!\left[1 + \mathrm{erf}\!\left(\tfrac{Y-5}{\sqrt{2}}\right)\right]\] 
ProbitModel pr = ProbitModel.h2sFatality();           // -31.42, 3.008, 1.43
double pFat   = pr.fatalityProbability(60.0, 500e-6);  // 60 s @ 500 ppm

QRA roll-up

ConsequenceAnalysisEngine aggregates branches (each with branch probability, hazard model, probit, and exposure time) into an IRPA at a receptor distance.

ConsequenceAnalysisEngine eng = new ConsequenceAnalysisEngine(1.0e-4); // base freq
eng.addJetFire(0.30, jet, ProbitModel.thermalFatality(), 60.0);
eng.addToxicCloud(0.10, plume, "h2s", ProbitModel.h2sFatality(), 600.0);
double irpa = eng.individualFatalityRiskPerYear(50.0);
String json = eng.exportSourceTerm();   // for PHAST / FLACS / KFX handoff

Acceptance criteria

Criterion Limit Source
Process equipment radiation 12.5 kW/m² API 521
Personnel egress radiation 4.7 kW/m² API 521
Occupied building overpressure 0.21 bar API 752
Broadly acceptable IRPA < 1·10⁻⁶ /yr UK HSE R2P2
Tolerable IRPA (worker) < 1·10⁻³ /yr UK HSE R2P2

See also