In order to understand gas explosion phenomena in industrial buildings, a reduced-scale vented combustion chamber is investigated numerically. In this configuration, a flame is ignited in an initially quiescent flammable mixture and propagates past solid obstacles, generating a strong pressure increase. The aim of this numerical study is twofold: The first objective is to show how large eddy simulation manages to reproduce the parameters of critical relevance for this multiscale problem, in particular the overpressure generated during the flame propagation. The second objective is to highlight that, even if large- to small-scale turbulence effects play a crucial role in the flame development and the resulting overpressure, it is also needed to correctly account for thermo-diffusive scale phenomena.