A method is proposed to determine the runaway sequence of a multiple-runaway reaction using the initial temperature and adiabatic temperature rise of the individual reactions. The real-scale runaway process for MEK-oxidation was used as an example to validate this proposed approach. In order to predict the real-scale initial temperature for such a chemical reaction, an initial temperature-prediction equation was derived. The applicability of this derived equation to these reactions was verified using experimental data, with the rate equation for the reactions related to the concentrations of single or multiple reactants. In addition, the thermal-hazard model proposed previously was modified using this derived equation to predict the initial temperature. This modified model was then used to simulate the real-scale thermal hazards for H2O2 and MEKP decomposition in order to compare the relative hazards. Analysis of the results reveals that, in a commercial setting, the heat effect of MEK oxidation will probably increase the temperature of the reaction mixture enough to initiate H2O2 decomposition and, subsequently, MEKP decomposition.