Process plant layout has been an important issue in the chemical industry since it is greatly related to economic profit, saving energy. The objective of the plant layout is to provide the best arrangement of process equipment in a process plant for a given site, and to save more resources such as land occupied by facilities and energy by diminishing piping cost and pump cost.

However, only minimizing the size of the chemical complex to save the economic cost is not the best way for the optimal layout because safety issues have not been adequately addressed. Concern of safety issues, which are not easily accounted for in terms of economic cost, is growing nowadays. At this time, not only the cost of piping, land, and construction but also safety should be included when deciding about the best layout in the field of chemical engineering. Well calculated safety costs, such as losses due to injury and equipment damage, are helpful when obtaining the optimal facility layout ultimately.

This paper presents a new approach for the optimal facility siting considering the possibility of toxic releases, explosions in several facilities. A case study in Beaumont, Texas has been completed to provide a better understanding of how safety cost is assumed and involved in the optimization function. Some occupied buildings, several toxic releases and protection devises were considered here.

The proposed formulation incorporates the effect of wind speed, wind direction and environmental stability to calculate the risk via probit functions and Monte Carlo simulation. The overall problem is initially modeled as a disjunctive program where the coordinates of each facility for siting and cost-related variables are the main unknowns to determine. Then, the convex hull approach is used to reformulate the problem as a Mixed Integer Non Linear Program (MINLP). The analysis results demonstrate the potential of this approach to improve the process design activity.