Calculators›Toxic Gas Dispersion (Pasquill-Gifford)
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Toxic Gas Dispersion (Pasquill-Gifford)
Process safety · Gaussian plume w/ Briggs σ · ALOHA-class
Continuous Gaussian-Plume Dispersion
Ground-level centreline concentration from a steady point release using the Gaussian plume with Briggs (1973) urban/rural dispersion coefficients, compared to user ERPG/AEGL endpoints.
⚠ Safety-critical — screening, neutral-buoyancy only. Passive plume, flat terrain, steady wind ≥ 0.5 m/s. INVALID for dense gases (chlorine, LPG vapour), complex terrain, building wakes, or calm winds — use a dense-gas model (DEGADIS/SLAB/Phast). Concentration vs endpoints (not dose/probit). Not for safety case submission or regulatory filing without SME review.
Release & Met
g/s
m/s
Geometry & Substance
m
m
°C
Toxic Endpoints (ppm, optional)
Engineering Basis
C = Q/(π·u·σy·σz)·exp(−H²/2σz²) — ground-level centreline, continuous source.
Briggs (1973) open-country & urban σy, σz vs distance and Pasquill class A–F.
ppm = C[mg/m³]·Vm/MW, Vm = 22.414·(T/273.15) L/mol.
Compare to ERPG-1/2/3 or AEGL endpoints (user input).