Fire risk in historical buildings. The case study of the arson of a Savoy residence during restoration works

The fire that destroyed a tower in the Savoy residence in Moncalieri, Turin, Italy, on 5 April 2008 is described in this paper. The results of the field inquiry made it possible to describe the fire dynamics. The fire started from a very interesting char combustion which was ignited from restoration works on a wooden floor. The works were suspended at 16.30 pm and the fire was observed at 5.00 a.m. from the town outside the castle. Char combustion occurred in the space between the false ceiling on the 3rd floor and the floor above. The structure was made completely of wood. Transition to flaming combustion occurred when the ambient on the fourth floor was heated by the char combustion, which quickly led to the flames spreading to the 4th floor ambient. Vertical spreading was also facilitated by vertical walls made of a wooded structure filled with bamboo. The flames thus spread to the attic, where they then spread to the roof structure. No continuity solution in the wood structure was found at this level. In order to verify the assumptions and the fire hypothesis made on the basis of the investigation, a CFD fire dynamics simulation has been performed using FDS 5. the simulation input data has been derived from field observations and specialized literature. A three-stage simulation has been conducted to deal with the complex mechanism of fire dynamics in this situation, where each fire step takes input data from the previous. This approach also makes it possible to avoid the calculation of steady times, which were not useful to represent the evolution of the fire. Three main phases, each characterized by precise behaviour, have been identified and simulated for a suitable time to be able to characterize their evolution and the transition to the following phase. The three main phases were: a) smouldering combustion, b) flaming combustion with surface flame spreading and c) general involvement of the main compartment. During the activities the authors also investigated the reduction of the fire risk by fire detectors in order to understand whereas, in this particular case, such prevention measures would have significatively changed the evolution of the fire.