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Models have been applied to stages of two phase releases following the failure of pressurized vessels. The initial expansion stage has been modeled using an experimental apparatus involving the measurement of pressure histories and of Freon-11 aerosol droplet sizes and velocities. The experimental data combined with a thermodynamic analysis has allowed estimations of the time dependent processes. The analytical description of the critical pressure decrease on the opening of the vessel is presented. The later evolution stage has been mathematically modeled by assuming that the two phases have separate velocities. The cloud motion characteristics have been shown to depend upon the degree of hydrodynamic interactions between the particles via the gaseous phase. For small particles' fractional volumes, this interaction is small and each particle behaves as a single particle corresponding to a "filtration" regime. However, for large concentrations the air between the particles becomes entrained due to the particle motion and the cloud velocity exceeds that of the single particle. In this "entrainment" regime large scale vortex motion occurs.