HAZOP (Hazard and Operability) is a preliminary and systematic approach for identifying hazards and suggesting hazard mitigation measures in a process facility. A knowledge-based expert system. ExPHAZO(+), has been developed to automate the manual HAZOP analysis and accelerate the process. ExpHAZOP(+) comprises a graphical user interface (GUI), a knowledge-base and an Inference engine. One of the unique features of ExpHAZOP(+) is the fault propagation algorithm, an aspect of the inference engine, which defines the propagation of deviations to all downstream equipment. The dynamic knowledge-base of ExpHAZOP(+) allows a user to update knowledge while performing the HAZOP analysis and to use that knowledge in the result. ExpHAZOP(+) is easy to use and provides results in a standard report format. Crown Copyright (C) 2009 Published by Elsevier Ltd All rights reserved.