Radical polymerization methods are prone to runaway under extreme process conditions. A review of case histories of polymerization incidents indicate that human error coupled with equipment failures,loss of cooling, temperature control and mischarging of reactants are the primary cause for triggering runaway accidents, Many of these accidents can be reduced or eliminated by changing the materials, alternative synthetic chemistry routes and process variables. Runaway hazard evaluation is the principle approach to assess and eliminate the inherent hazards. In this paper, hazard characterization of bulk and suspension methods of styrene polymerization, by microcalorimetric techniques is studied. The investigation indicates that suspension polymerization of styrene is less hazardous than the bulk polymerization method. The kinetics autocatalytic nature of suspension polymerization is presented. The coolant requirements for safe operation, as well as the temperature shoot up profiles for its failure for a typical 4000-kg batch commercial styrene polymerization reactor is simulated by employing reaction calorimetric data. ARC study indicates that a large excess of water present in the reaction mixture acts as a thermal sink and rules out the possibility of severe thermal hazards.