PHAzer: An intelligent multiple models-based process hazards analyzer

Process Hazards Analysis (PHA) involves the systematic identification, evaluation, and mitigation of potential process hazards which could endanger the health and safety of humans and cause serious economic losses. It is a laborious, time-consuming, and expensive activity which requires specialized knowledge and expertise. An intelligent system for automating PHA can reduce the time and effort involved, make the analysis more thorough and detailed, and minimize or eliminate possible human errors. Towards that goal, an intelligent system, called PHAzer, has been developed in this thesis to automate PHA. PHAzer uses multiple models of process units and operations for performing HAZOP analysis, hazard assessment, and likelihood estimation. The knowledge required for performing PHA has been divided into process-general and process-specific components. The process general knowledge in PHAzer consists of multiple models--qualitative digraph-based causal models, quantitative dynamic mathematical models, and fault tree and reliability models--which provide multiple perspectives of a process plant. The process specific component consists of the plant P & ID, the process chemistry, and the operating procedure. The operating procedure is represented in PHAzer in a two tier hierarchy using high-level Petri nets. Techniques have been developed to automate HAZOP analysis of deviations and mal-operations in batch processes. The hazards identified during HAZOP can be assessed in detail using the dynamic mathematical models. A hybrid qualitative-quantitative analysis method has been developed and implemented in PHAzer for such safety verification. Methods for fault tree synthesis using the digraph and fault tree models and fault tree analysis to estimate the likelihood of hazards have also been implemented. Based on this multiple models-based framework, an intelligent system has been developed in an object-oriented architecture using the expert system shell G2. The performance of PHAzer was successfully evaluated on various industrial scale petrochemical and pharmaceutical plant case studies