The manuscript analyzes the accident that occurred in the railway station of Viareggio (Italy) on June 2009. A freight train carrying LPG went off the rails and five out of fourteen wagons derailed and overturned. A hole formed in the first tank car due to the impact with a signaling stake. The pressurizedLPG was released as a two-phase jet: the liquid phase formed a boiling pool on the ballast while the dense gas dispersed in the atmosphere. The dense cloud spread and moved towards the neighboring houses. Afterwards, the cloud was ignited and exploded. The overpressure destroyed some residential buildings in the area closest to the explosion epicenter, while glasses were shattered in a larger area. Thirty-one people died and a number of residents were injured due to the fires that engulfed the surrounding houses. Starting from the data related to the tank cars, meteorological data, pictures of the site after the accident, aerial photos, witnesses of both civilians, and rescue teams, the manuscript reconstructs the dynamics of the accident by means of a dedicated software.