This publication is intended to provide guidance to HAZOP (Hazard and Operability) and What-If review teams associated with the petroleum, petrochemical and chemical industries. It describes the nature, responsibilities, methods and documentation required in the performance of such reviews. This ensures the reviews are conducted in a timely, effective and professional manner as may be prescribed by a company's Process Safety Management (PSM) Policy. This book can be used as a practical reference to prepare the safety review requirements for these industries and their process safety management systems.The safety of petroleum and chemical facilities is an important part of a company's operations. Recent worldwide petrochemical safety regulations and a company's own process safety management policies would require that a process hazard analysis (PHA) review of its existing and proposed petroleum operations be accomplished. The limits of hazardous sub-stances cited by both the US Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) regulations dictate the applications of process safety management elements at almost all of a company's facilities.These reviews are intended to reduce the probability and/or consequences of a major incident that would have a detrimental impact to the employees, the public's well being, onsite or offsite properties, the environment, and most important to a company itself, its continued business operation and survival. Process hazard analysis reviews are not intended to identify the minor ""slips, trips, or falls""; these are the responsibility of the company's general safety requirements and are well established. The process hazard analysis is looking for the major incidents, which have the potential for severe impacts.HAZOP and What-If reviews are two of the most common petroleum and chemical industries qualitative methods used to conduct process hazard analyses. Up to 80% of a company's process hazard analyses may consist of HAZOP and What-If reviews with the remainder 20% from checklist, Fault Tree Analysis, Event Tree, Failure Mode and Effects Analysis, etc. An experienced review team can use the analysis to generate possible deviations from design, construction, modification, and operating intent that define potential consequences. These consequences can then be prevented and/or mitigated by the application of the appropriate safeguards.