Safety is the second nature of chemical processes. Process security is the extended concept and practice of process safety. In large-scale chemical manufacturing, unit operations interact closely through various mass, energy, and momentum transfers. This may cause many possible occurrences of "chain-reaction" type disasters, which should be rooted out completely. To ensure process security and safety, the first step is the accurate assessment of security status of the processes. In this paper, a security-bearing, large-scale process dynamic modeling and simulation method is utilized to perform security assessment of an ethylene oxide production process involving various units, including a multi-tubular plug flow reactor operated under high pressure and temperature, adsorption and separation units, heat exchangers, recycle stream, and purge stream. The chemicals involved in this process possess serious environmental and health hazards. By simulating process behavior under various scenarios, this method can be used to classify the operational space, assess process security status quantitatively, foresee possible security failures, and give a critical review of design and operation policy to secure operation. (c) 2006 Elsevier Ltd. All rights reserved.