It is necessary to obtain accurate values of both the time of vent failure (tb) and the vent burst pressure (pv) to investigate the characteristics of the pressure profile and the propagation of the explosion flame before and after vent failure. tb was determined from the interruption of an electrical circuit by the breakage of a thin metal strip fixed onto the vent cover (Cooper et al., 1986). As shown in Fig. 3, when the thin metal strip was interrupted, the voltage fell sharply to zero, indicating vent failure. At the same time, the pressure near the vent (PT2) can be regarded as approximately pv because PT2 is only 2 cm away from the vent cover. tb and pv determined by the above method are given in Fig. 4. As shown in Fig. 4, pv increases nearly linearly as d increases from 0.075 mm to0.9 mm. tb also increases as d increases, but the difference becomes very small for d 0.6 mm; the reason for this observation may be that the pressure rise rate just before vent failure increases with the increase of d.