Major accidents hazards not only may lead to losses of life and properties, but also may cause irrecoverable damages to the environment. HAZard and OPerability (HAZOP) study is one of the most widely used and accepted techniques to assess the risk of process upset and search for the required safeguards. However, the method is a qualitative approach subjective to engineering judgement of the HAZOP team. In this paper integration of mathematical modeling with the HAZOP study, called quantitative dynamic HAZOP study, is investigated for a complex polystyrene polymerization process to provide quantitative analysis. This paper presents the role of quantitative dynamic HAZOP and its capabilities. It then identifies the shortcomings of this integration which needs to be addressed in order to achieve the full potential of this approach (i.e. specially for complex systems). Finally, some suggestions are provided to meet these challenges.