Currently, there is a strong demand for quantitative risk analysis. There is a challenge in describing the process dynamic behaviour in case of failures. We suggest a methodology that combines dynamic simulation (with ASPEN PLUS DYNAMICSTM 9.0 tool), lessons learnt from accidents to identify the most likely deviations and risk matrices. In fact, there is a real interest in knowing the system behaviour during malfunctions for safety analyses. For this purpose, dynamic simulation is an efficient tool to predict the time evolution of process parameters during deviations from normal operating conditions. Moreover, the knowledge of the process dynamic behaviour and the profiles of the operating parameters during a degraded mode permits adequate safety barrier recommendations. The case study concerns a continuous process of propylene glycol (C3H8O2) production. The synthesis reaction involves three consecutive competitive reactions leading to the formation of by-products: di and tri glycols (C6H14O3 and C9H20O4 respectively). The process is composed of a CSTR reactor and two distillation columns in series. The objective is to study the propagation of deviations along the process. This work provides a new perspective on risk quantification through the analysis of deviation propagation along a process involving cascade distillation columns.