Attention should be paid to both Lmax and the duration time of the external flame, which can be used to estimate the hazardous area where equipment or personnel will be at risk from the venting; however, there are few investigations concerning the two factors. EN 14994 (2007) suggests that Lmax can be calculated as when static activation pressure of vent is below 10 kPa. However, current experiments show that the behaviors of the external flame were affected significantly by higher pv, as investigated in the current experiments. As shown in Fig. 11, with an increase in pv, Lmax increases approximately linearly, whereas the duration time of external flame decreases.