The issue of large-scale vented deflagration modelling and mitigation is overviewed briefly. The physics of the phenomenon of coherent deflagrations, i.e., coupled internal and external explosions, in a system vented enclosure atmosphere is studied further. Results of large eddy Simulations (LES) of coherent deflagrations for the empty 547-m(3) SOLVEX enclosure are presented. Numerical simulations of initial stages of wrinkled flame front propagation inside the enclosure and pressure generation Lip to the well-known first pressure peak demonstrate all excellent agreement with experimental observations without introduction of any adjustable parameter. The anisotropic component of turbulent combustion in all external vortical Structure after the flame touches the vent edge is thought to be responsible for the significant increase of the flame Surface density during deflagration outside the enclosure. The University of Ulster's, LES model, based on the renormalization group (RNG) analysis of subgrid-scale modelling of isotropic turbulence and premixed combustion, is developed further to account for the anisotropic component in turbulent combustion in external vortex. The simple modification of the existent LES model allowed reproducing the experimental pressure dynamics inside and outside the enclosure at distances up to 54 m as well as the shape of the external deflagration. The numerical Simulations confirmed results of former analysis that there is no extra intensification of combustion inside the enclosure. The increased second pressure peak inside the enclosure is mainly due to the pressure rise during highly turbulent external combustion and the decrease of outflow front the enclosure resulting from the pressure rise. It is concluded that in many practical cases physically sound simulations of coherent deflagrations are impossible without. proper modelling of external combustion. It is suggested that in such cases the mitigation strategy should aim primarily at the suppression of combustion outside the enclosure.