Linguistic Assessment Approach for Hierarchical Safety Analysis and Synthesis

Engineering systems in industry are most often concerned with safety issues. Many of these systems are intended to work properly even in contexts where information is missing, incomplete or unreliable. This chapter introduces a safety model based on the concept of approximate reasoning for safety analysis. Parameters of the safety level, including failure rate, failure consequence severity and failure consequence probability, are all described by fuzzy linguistic variables. A fuzzy rule-base is used to capture the uncertainty and the non-linear relationships among these parameters. A safety estimate for possible causes of a technical failure can be obtained by the approximate reasoning approach. A safety synthesis is then applied to integrate all possible causes for a specific technical failure, or applied at the safety estimate made by a panel of experts. The synthesis is based on an ordinal fuzzy linguistic approach by means of a direct computation on linguistic values instead of the approximation approach by their associated membership functions. The use of the ordinal fuzzy linguistic approach makes the safety analysis more effective. Subsequently, the ranking and interpretation of the final safety synthesis of a concerned system are also described. Application of this proposed approach is demonstrated by a realworld case study in the offshore engineering. ________________________________________________________________