Fig. 9 shows typical flame images outside of vessel after vent failure for pv = 20 kPa and 131 kPa, and the times in the figures denote the moment after ignition. Fig. 10 presents the location of flame front as a function of time. As shown in Fig. 9, the volume of the internal flame bubble just as the vent cover bursts increases with the increase of pv. After vent failure, turbulent jet combustion occurs outside of the vessel. The jet flame appears as a “mushroom”, as reported by previous researchers (Harrison and Eyer, 1987; Zhihua et al., 2006). The external flame propagates quickly and reaches its maximum length Lmax. Subsequently, the flame length decreases and then increases again. The oscillation phenomenon of external flame can be easily identified for two or three cycles.