Hazard and operability analysis (HAZOP) is widely used in process hazard analysis of chemical processes. But it is time and effort consuming. To aid human experts in conducting HAZOP analysis in a more thorough and systematic way, a software system (PHASuite) for automated HAZOP analysis has been developed. PHASuite can greatly increase the efficiency of the HAZOP analysis, support best analysis practices, and provide foundation for reuse of the safety knowledge generated from the analysis. Given the knowledge intensive nature of HAZOP analysis, a knowledge engineering framework was developed. From the point of view of functionality, the framework consists of four main parts: information sharing, representation, knowledge base and reasoning engine. Ontology based information sharing schemes are developed to share process information and results with other systems. Coloured Petri Nets based representation, created from process information, is used to represent chemical processes as well as the methodology for HAZOP analysis. In this framework, a process is decomposed into two abstraction levels, operation level and equipment level, which are bridged using functional representation. Analysis is carried out on both the levels. Knowledge used in this system is stored in models. Case-based techniques are adopted for knowledge management. Knowledge base is stored externally in structured databases. A two-level, two-layer reasoning engine has been designed to operate on the Petri Nets representation of the process using the knowledge base to perform HAZOP analysis.