Decomposition of cumene hydroperoxide (CHP) can occur easily and may lead to runaway reactions, which have resulted in fire and explosion incidents in the chemical industry. Therefore, it is important to understand the effects of process conditions on runaway reactions, which is necessary for the development of inherently safer measures to minimize risks associated with the runaway reactions. In this paper, the effects of CHP concentration on runaway reactions were studied using a systematic methodology, a combination of molecular simulation and experimental calorimetric study. Results showed that the concentration of 40 wt% can be regarded as a critical CHP concentration. Below the concentration of 40 wt%, CHP concentration shows significant effect on the parameters representing exothermic behavior of runaway reactions. The dominant reaction pathway associated with the concentration range of 0-40 wt% and some possible explanations of the reaction mechanism for concentration above 40 wt% were proposed. Results can be applied for the development of safer process conditions and other facilities to minimize the risk of runaway reactions. (C) 2010 Elsevier By. All rights reserved.