AbstractThe problem of diagnosing faults in chemical plants can be efficiently addressed by a hierarchical procedure involving successive narrowing of the space in which the fault search is conducted. A technique is presented for narrowing diagnostic focus useful in the first stages of a diagnostic search. Based on a decomposition of the process according to function, the technique assesses the functionality of process systems based on measurements of controlled and manipulated variables. A procedure for identification of possibly faulty systems and units from the system states is outlined. Detailed diagnosis, not treated in this paper, would be applied after candidate systems or units are located. An example is presented using a hypothetical chemical reaction process.