v1.0.0 to v1.0.0

---

name: neqsim-consequence-analysis

version: "1.0.0"

description: "Quantitative consequence analysis for oil & gas hazards — jet fire, pool fire, vapour cloud explosion (VCE), BLEVE, Gaussian plume and heavy-gas dispersion, probit-based fatality probabilities, individual and societal risk roll-up. USE WHEN: a task requires fire-radiation contours, dispersion to LFL/IDLH/ERPG, BLEVE thermal/missile assessment, or QRA-style risk integration of multiple release outcomes. Anchors on neqsim.process.safety.fire, neqsim.process.safety.dispersion, neqsim.process.safety.qra."

last_verified: "2026-04-26"

requires:

java_packages:

- neqsim.process.safety.fire

- neqsim.process.safety.dispersion

- neqsim.process.safety.qra

---

# 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)

```java

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):

| Flux (kW/m²) | Effect | Use |

| ------------ | --------------------------------------- | -------------------------- |

| 1.6 | No discomfort for long exposure | Public area limit |

| 4.7 | Sufficient for evacuation in 30 s | Escape route |

| 12.5 | Wood ignites, equipment failure (5 min) | Process equipment limit |

| 37.5 | Structural failure of process equipment | Damage to steel structure |

## Method 2 — Pool Fire

```java

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)

```java

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

```java

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)

```java

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):

```java

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

```java

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

```java

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:

| Criterion | Limit | Source |

| ---------------- | ---------------------- | ------------------- |

| Worker IRPA | 1·10⁻³ /yr (intolerable) | UK HSE R2P2 |

| Worker IRPA | 1·10⁻⁶ /yr (broadly acceptable) | UK HSE R2P2 |

| NORSOK FAR | 10 fatalities / 10⁸ h | NORSOK S-001 |

| Public 1 % fatal | 35 m typical for 12.5 kW/m² | API 752 |

## 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:

```bash

```

## 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