Mechanisms of flame spread and burnout in large enclosure fires

Knowledge of the first principles defining fire behaviour in large enclosures remains limited despite their common use modern tall buildings. The evolution a can be defined by relationship between flame front and burnout velocities (VS/VBO). This classified into three distinct spread modes being Mode 1 (VS/VBO ? ?), 2 > 1), 3 ? 1). mechanisms governing are investigated using four full-scale enclosure experiments with high porosity wood cribs similar geometries. Flame positions estimated video data. Velocities affected heat feedback from smoke layer to fuel. velocity shows two regimes, minimum external flux above which there is surface (q?s,min?) that defines onset very rapid (q?rs,crit?). A phenomenological model developed help identify underlying controlling transition different modes. Both data show for cribs, dependence radiation weak, whereas strong. 1) occurs increasing fluxes q?s,min?. ?) further once q?rs,crit? attained due sudden increase changing ventilation condition, or significant increases enclosure.