Liquid releases pool formation

If the material released to the atmosphere is not ignited, the spill can be accompanied by flash vaporization, liquid entrainment, and/or liquid accumulation (with pool formation and evaporation), and associated vapor dispersion. Absence of an immediate ignition source allows a vapor cloud to form as the vapors disperse downwind. A portion of this vapor cloud may be flammable, and if the gas has any toxic components, it can also pose a toxic hazard. The downwind extent of the flammable hazard depends on the size of the release, the upper and lower flammability limits of the material, and the air entrainment rate. 

Note The factor of 2 in items a, b, and c above is to account for the aerosol formation and entrainment in the flashing release. Also, when determining the material in the cloud resulting from a two-phase or flashing release, consideration should be given to the contribution to the cloud from liquid pool evaporation. 

Furthermore dispersion is influenced by the initial momentum of the released fluid. Gas or vapours released with low initial momentum lead to plume formation. If the initial momentum is high, turbulent jets result. Releases of liquids produce a stream with low initial momentum and a liquid jet, if the momenrnm is high. In both cases eventually a pool is formed. 

Source models are used to quantitatively define the release scenario by estimating discharge rates (Section 2.1), total quantity released (or total release duration), extent of flash and evaporation from a liquid pool (Section 2.2), and aerosol formation (Section 2.2). Dispersion models convert the source term outputs to concentration fields downwind from the source (Section 2.3). The relationship between source and dispersion models, and the various model types, is shown schematically in Figure 2.1. As shown in Figure 2.1, source and dispersion models are highly coupled, with the results of the source model being used to select the appropriate dispersion model. 

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