Apart from these previous reports, many aspects of the effect of pv on explosion venting have not been studied or solved yet. For example, how does external flame propagate after vent failure? How does pv determine the maximum length of the external flame? Thus, work should be performed to identify the hazardous area into which the explosion is vented because it must be sufficiently far from other equipment to prevent fire and explosion hazards (EN14994, 2007). In this paper, first, the propagation of internal flame was investigated using high-speed photography before and after vent failure. Second, the pressure-time histories in a vessel were measured to elucidate the effect of pv on the maximum internal overpressure and the behavior of an internal flame bubble. Third, the propagation of an external flame was examined to determine the dependency of the maximum flame length on pv