A validated assessment tool for consequence analysis of accidents involving hazardous materials EXCAPE

The program ESCAPE (Expert System for Consequence Analysis using a PErsonal computer) evaluates the releases, source terms and atmospheric dispersion of hazardous materials. The model is applicable to both continuous and instantaneous releases of toxic and flammable gases into the atmosphere.

ESCAPE can be utilized in release cases which are a consequence of a sudden rupture of a container or the rupture of a pipe or container wall. An aerosol or gaseous plume or cloud will be formed, and in certain conditions, if the release scenario results in the formation of a liquid pool, its evaporation may produce either a gas cloud or a plume.

The program applies to releases from the liquefied state of refrigerated or pressurised containers and for continuous releases from the vapour phase.

The input data and model computations

A dispersion estimate requires particulars of an accident type, source, prevailing weather conditions and environment. The released substance and the location of a release point are required as input data. Meteorological input data has to include wind speed, wind direction, atmospheric stability, ambient temperature and the relative humidity of ambient air.

The ESCAPE-model evaluates releases, the formation of source term, atmospheric dispersion and resulting consequences.

The program can also be used for estimating dosages and blast wave overpressures, and the effects resulting from a BLEVE explosion. The program is applicable both to the heavier-than-air and passively-dispersing (dispersion due to atmospheric turbulence) gas and aerosol clouds.

ESCAPE-model is not applicable to the estimation of the atmospheric dispersion of pollutants emitted from typical fires in warehouses and chemical stores. Terrain effects are not considered, only in their effect on the atmospheric conditions through the surface roughness parameter. The model is not suitable for transient releases.

The contaminant plumes are shown on user-selectable maps, using the MapInfo geographic information system. In the figure, it is presented a gas plume formed in a conceived release of liquefied chlorine from a ruptured pipe. Equivalent areal distributions for dosage and blast wave overpressure are available (map (c) Genimap).

 

A separate model BUO-FMI can be used to estimate the dispersion of pollutants emitted from typical fires of warehouses and chemical stores. ESCAPE -model was evaluated in SMEDIS, which was a project, supported by the European Union, to develop a protocol for the scientific evaluation of dense gas dispersion models, and then to apply this protocol to dense gas dispersion models in use in Europe.

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