In the past 4 decades in Japan and Taiwan, many thermal explosions have been caused by methyl ethyl ketone peroxide (MEKPO) subjected to external heating including fire. Thermograms of commercialized MEKPO dimers were first screened by differential scanning calorimetry (DSC) to determine the heat of decomposition and exothermic onset temperature. Thermal runaway phenomena were then thoroughly investigated using Vent Sizing Package2. Instead of the normal one-reaction peak for the MEKPO dimer seen in the adiabatic calorimeter, two distinct exothermic peaks occurred in the DSC thermograms near 110 and 170 degreesC, indicative of series reactions. The onset temperature of the MEYPO monomer was determined to be about 40 degreesC, showing it to be extremely reactive under storage or process conditions. Thermokinetic and related data were obtained that can be used for hazard analysis to prevent thermal explosions in both the monomer and the dimer.