Analysis of the Flash-fire Scenario in the Viareggio Accident

On the 29th of June, 2009 the derailment of a rail-tanker containing liquefied petroleum gas (LPG) in the Viareggio station produced a large cloud of flammable vapours, which ignited in a flash-fire, causing 31 fatalities and extensive property damage. The literature models applicable to the simulation of flash fires differ for the hypothesis made and the complexity. The majority of models assume homogenous clouds, usually at stoichiometric concentration. However the dispersion of the substances released in accidental events frequently results in non-homogeneous stratified clouds. Computational Fluid Dynamics (CFD) models have limited applicability due to the large scale of the scenario, yielding extremely high computational burdens. Integral models based on empirical parameters are necessary for routine quantitative risk assessment practice, and more generally, for prevention and mitigation of the scenario. In this study the models for simulating flash fires of stratified vapour clouds are applied to the study of the Viareggio accident. The model by Raj & Emmons was modified to include the correct description of the combustion of pre-mixed and diffusive flame. The considerations underlying the models by Feng and Kaptein & Hermance for flame velocity were implemented. The comparison with the actual outcomes of the accident, as recorded by an on-site survey, allowed for model validation.