Hazard assessment involves the retrieval of appropriate chemical hazard data and the production of an assessment which complies with relevant regulations. This is a complex process requiring detailed knowledge of chemical hazards and hazard assessment regulations. The purpose of this project is to investigate the use of an expert system approach for hazard assessment of complex systems. The approach has focused on the design, development and evaluation of an expert hazard assessor after appropriate modelling of chemical database retrieval, and legislative knowledge base. An "intelligent form" was designed to link the legislation to the chemical hazard data. To facilitate ease of use, the program was extended to include an on-line help facility, and a user friendly interface to address local and remote databases. The feasibility and benefits of the Expert Hazard Assessor ( EHA ) have been demonstrated through system testing and evaluation using sample regulations, and available chemical data, by groups of inexperienced users. Comparison with a previous standard expert system, also shows the EHA to be more comprehensive in output, more efficient, easier to use for the non-expert assessor, and provides better help support. The results suggest that an EHA such as the one detailed in this work is of significant benefit in providing appropriate hazard assessment.