The process layout of chemical plants is usually designed in a compact configuration for economic efficiency. However, n n most of the chemical process units are vulnerable to accidents such as fires and explosions, and these accidents can cause severe damage to humans. In this study, direct risks to humans from such hazards were quantitatively assessed as individual risk and converted into safety distances for each piece of process equipment. Then, a process layout optimization problem was

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... ulated with risk zones constructed using those safety distances. Boundary factors accounting for land uses around the process site and protection factors from additional protective devices were also considered. A case study for an ethylene oxide plant was conducted. With the proposed methodology, a cost-efficient and inherently safe layout can be provided in f f the early stage of the design of a process plant.