Field and laboratory analysis of the junction fire process in the catastrophic fire of Pedrogao Grande in June 2017

Background Two fire ignitions in Pedrogao Grande on 7 June 2017 had very fast due to unusual physical processes associated with the interaction between an overhead thunderstorm and the fire and the subsequent merging of the fires as a junction fire, killing 66 persons in 2 h.Aims Using a laboratory simulation of the merging process, we explain the fire spread conditions and verify that the junction of the two fires was responsible for the very intense fire development.Methods The real fire spread was reconstructed from an extensive field survey and physical modelling tests were performed in the Fire Research Laboratory combustion tunnel using various fuels and scale modelling laws.Key results The spread and merging of the two fires in the tests agree very well with field observations, namely the periods of rate of spread (ROS) increase and decrease, peak values of ROS and area growth process using scaling laws.Conclusions Analysis of the Pedrogao Grande fire evolution and its physical simulation at laboratory scale showed the importance of the mechanisms of two fires merging in producing very important convective processes.Implications Our study showed the validity of performing the experimental analysis of complex fire spread situations provided that the similarity conditions are fulfilled.