Application to a case study of the Aramis methodology for the identification of reference accident scenarios

In the framework of the European ARAMIS project, two complementary approaches were developed to serve as a basis for the whole risk assessment process. On the one hand, through a Methodology for the Identification of Major Accident Hazards (MIMAH), according to a bow-tie approach and on the basis of the equipment type and the properties of the substance handled, the major accidents (without considering safety systems) are identified through generic fault and event trees. On the other hand, a Methodology for the Identification of Reference Accident Scenarios (MIRAS) was developed to study the influence of safety systems on the occurrence probability of the accident and on the extend of its effects. Finally, thanks to a "Risk Matrix", the Reference Accident Scenarios are selected on the basis of their frequency and their potential consequences, evaluated qualitatively. The Reference Accident Scenarios are those which are the most representative of the actual risk level of the plant. These methods were tested on five companies across Europe. One case study will be presented here. The feed-back from these case studies demonstrates that MIMAH and MIRAS are consistent and applicable. They provide a conceptual and methodological framework for risk analysis. The main difficulties met come from the lack of reliable data about frequencies and performances of safety systems, even if some various bibliographic data were obtained. These methods can have promising applications in other fields and are strongly connected with other parts of ARAMIS such as severity computation or management efficiency assessment.