The manuscript focuses on the LPG railway accident occurred in Viareggio at the end of June 2009.The accident investigation highlights the uncertainties and complexities in modeling the accident inthe urban environment close to the railway station. The analysis allows assessing the sequence of events, the way they influenced each other, and the alternative possible evolutions. In particular, thepaper describes and discusses suitable models to quantify the consequences of most probable accidentdynamics and their results.