Abstract: In order to solve the problems oflimitation in description of fault logicand time-consuminganalysis in the traditional safety analysis method, a formal safety analysis method based on Petri net model was proposed. Firstly, the system physical hierarchy was divided, and the functional structure model of systemwas established. Secondly, considering the functional failure state of the component exceptfor normal state and physical fault state, and the transition relationship between multiple states, combined with dynamic logic and fuzzy logic, the fault mode were combed, and the probability value was quantified. A fault Petri net model was established and the safety analysis was carried out. Finally, the feasibility of the proposed method was verified by a case study of the ATP subsystem of urban rail transit. The results show that the Petri net model analyzes the fault source of the subsystem logic output function as the speed motor interface fault, and deduces the fault propagation path to guide the hazard identification and fault diagnosis.

Key words: Petri net, formal safety analysis, automatic train protection(ATP), fault propagation, hazard identification, fault diagnosis faultdiagnosis