A Goal based methodology for HAZOP analysis

This paper presents a goal based methodology for HAZOP studies in which a functional model of the plant is used to assist in a functional decomposition of the plant starting from the purpose of the plant and continuing down to the function of a single node, e.g. a pipe section. This approach leads to nodes with simple functions such as liquid transport, gas transport, liquid storage, gas-liquid contacting etc. From the functions of the nodes the selection of relevant process variables and deviation variables follows directly. The knowledge required to perform the pre-meeting HAZOP task of dividing the plant along functional lines is that of chemical unit operations and transport processes plus a some familiarity with the plant a hand. Thus the preparatory work may be performed by a chemical engineer with just an introductory course in risk assessment. The goal based methodology lends itself directly for implementation into a computer aided reasoning tool for HAZOP studies to perform root cause and consequence analysis. Such a tool will facilitate finding causes far away from the site of the deviation. A Functional HAZOP Assistant is proposed and investigated in a HAZOP study of an industrial scale Indirect Vapour Recompression Distillation pilot Plant (IVaRDiP) at the DTU-Dept. of Chemical and Biochemical Engineering. The study shows that the goal based methodology using a functional approach provides a very efficient paradigm for facilitating HAZOP studies and for enabling reasoning to reveal potential hazards in safety critical operations.