Application of dispersion models to flammable cloud analyses

Abstract

The accidental release of flammable gases may result in a gas cloud which presents a hazard due to heat exposure (from burning), mechanical damage due to generated overpressures (from explosion), or both. The damage potential in such incidents depends not only on the material released but also on the spatial gas distribution as a function of time and the degree of confinement. Estimates of the temporal and spatial distribution of gas clouds formed from accidental releases can be made using physical (wind or water tunnel) models or mathematical models. This article discusses the application of mathematical dispersion models to the prediction of the spatial and temporal distribution of gas in the vicinity of an accidental release. A primary objective of such analyses is to estimate the amount of gas which exists at concentrations above the lower flammability limit and the amount of gas which exists at concentrations between the upper and lower flammability limits. Based on experiments performed by Shell Research Limited on the ignition of denser-than-air flammable clouds, examples of the application of the DEGADIS and FEM3A models are described, and the sensitivity of DEGADIS model predictions to gas release rate and windspeed is examined.