Facility layout is an important factor in designing of process plants such as petrochemical units and refineries. An appropriate design of layout ensures proper performance of corresponding departments as well as providing an equilibrium between large number and sometimes inconsistent structural design constraints. In this research, a mixed integer non-linear programming (MINLP) formulation is proposed for process plant layout problem, considering the toxic release risk and possible scenarios of fire, explosion and the domino effects of them. Then the Bat metaheuristic algorithm was employed to solve it. Finally, the model was implemented on 6th refinery, unit 101 of Iran's South Pars gas field, and the results showed the effectiveness of the model, in costs reduction and safety improvement. (C) 2017 Elsevier Ltd. All rights reserved.