The data about illegal activities connected to the waste cycle refer to an alarming situation linked to the development of waste fires in Italy and the world in the last few years. Hence the interest in implementing new methodologies to study fires in piles of waste, understand the incidental dynamics, and draw scientific evidence on the nature of combustion is crucial. The investigation focused on a real case waste disposal fire in a company in northern Italy. Initially, the trigger involved a heap of unsorted municipal waste, with flames spreading to other heaps of twigs, wood, and paper and plastic storage areas. The damage was limited by the prompt intervention of the Fire Brigade, who took a few hours to tame and extinguish the flames. The entire dynamic was captured by internal security cameras and made available for investigations. This key element made it possible to compare the real evolution to model estimations. Therefore, the present work aimed to approach an actual case study via numerical simulation to give insight into the fire accident. To this end, it was decided to use the Fire Dynamics Simulator (FDS) for an open field application. The application produced interesting results and paved the way for further research questions and debates regarding the effectiveness of this strategy for investigating incidental scenarios. In particular, it was possible to recreate the incidental dynamics assuming different compositions of the initial fuel matrix and their impact on the fire dynamics. However, some issues have emerged, including the lack of reliable data concerning fuel matrixes and their behaviour in open spaces. Another limitation is linked to the software unsuitability to implement heterogeneous material properly. On the contrary, internal safety distances among piles of stored waste were defined through empirical models and compared to what is embodied in the technical fire prevention rule draft concerning waste disposal facilities.