Publisher Summary This chapter discusses the use of hazard studies at critical stages of a project. The first or concept stage seeks to provide a database and context for the plant being designed. The hazard study level 1 comprises identification of basic hazards of the materials and the operations; collection of information (if any) on previous hazardous experiences with the processes; definition of SHE criteria; identification of the information that is needed, and that of the needed studies to address safety, health, and environmental issues; and evaluation of suitability of proposed sites and their constraints. The second level hazard research is particularly important for the identification and treatment of potentially severe risks. This research takes place during the project definition stage or “Front engineering design.” It corresponds to a typical “Preliminary PHA” in terms of the United States. The study is usually performed on the draft flow sheets for the design at a stage where design changes and the introduction of additional safety measures will not incur penalties of wasted design effort.