In this study, prevention of rupture in organic peroxide commercial reactor during runaway reaction has been studied by estimating required vent size and by implementation of effective safety measures. In order to estimate the vent size, it is necessary to obtain the rate of temperature-rise and pressure-rise during runaway reaction, therefore experiments were carried out by ARSST following JIS B 8227 standard. For the case of model substance MEKPO used in this study, required vent size was estimated to be unrealistically large due to formation of two phase flow caused by the fast reaction and gas formation. Regarding safety measures, two methods, inherently safety measures and safety measures by controlling hazard were considered. First, it is the method to moderate runaway reaction by reducing holdup or changing the solvent to reduce the required vent size to realistic value that can be implemented. Second, it is the method to reduce probabilities of runaway occurrence by adding multiple interlock system. It is important to implement safety measures with considering process comprehensively, because available measures are limited by characteristics of processes or substances.