A mission oriented accident model based on hybrid dynamic system

As a conceptualization of the characteristics of an accident, the accident model indicates the hazard factors in the systems and describes the process of system accidents. Therefore, accident models are the basis of system safety analysis and assessment. This paper presents a mission-oriented accident model to adopt the complex characteristics in the socio-technical system. Based on the principles that an accident is regarded as an emergent phenomenon and the dynamic relationships and interactions between the system entities are the key to building a systemic accident model, a two-stage modeling procedure is described in the paper including the qualitative and quantitative models. First, to build a qualitative conceptual model of the accident, the system mission process is decomposed to identify the system entities, such as equipments, facilities and human, involved in the mission, as well as their states and behaviors. By classifying the types of entity behaviors, the interactions between them are defined and utilized to construct the qualitative conceptual model based on Systems Modeling Language (SysML). Secondly, the accident systemic model is built for quantity analysis based on hybrid dynamic system (HDS) theory, which includes the discrete state transformation of the system and the continuous or discrete behaviors of the system entities. The entity behaviors promote the changes of system states that can be used to determine the system hazard, and the accident process is modeled through the interactions between the entities along the mission process. A case study is also presented including an analysis conclusion to verify the feasibility of the accident model.