Accident scenarios are the foundations of emergency responses. Hybrid Petri net is used to model emergency scenarios and responses comprehensively and systematically. Here, both the discrete events of scenarios and their evolution are characterized clearly. Elements of accident scenarios are expressed normatively using a knowledge element model and hierarchical theory, providing standardized descriptions of the different scenario stages. Then, a case study of an oil pipeline leak is examined to verify the logic of the hybrid Petri net and the expressions of attributes using the knowledge element model. The results show objective realizations of the scenario and the evolution of emergent events, enabling a formalized expression of emergency knowledge that can be used to establish an emergency knowledge base. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.