The systematical and thorough analysis of the hazard scenario is the foundation and core not only for analyzing and finding the solution for safety issues，but also for process hazard analysis（PHA）and fault diagnosis.The hazard scenario was defined and was categorized into five groups.On the basis of the above categories，the algorithm for intelligent selfinterpreted alarm，single and multiple fault root cause detection was presented by using signed directed graph(SDG).The results could play an important role in the development of the intelligent hazard and operability study（HAZOP），layer of protection analysis（LOPA），self-interpreted alarm and on-line fault diagnosis system for process industry.