Fires in tunnels

The problem of fires in tunnels is reviewed and new experimental data are presented which show for possibly the first time that the established correlations between fire size and critical ventilation velocity appear to be incorrect at large fire sizes; the dependence of these data upon the particular tunnel geometry is also evident. The departure from previous expectations is attributed to non-Boussinesq effects and tilting of the fire plume in the downstream direction. The Boussinesq approximation, implicit in standard correlations, is considered to be inappropriate for a study of the dynamics of hot smoke layers due to the significant effects of large density gradients on the horizontal momentum equation.