The possibility of including mitigation systems in layout models is explored in this work. The model is based on a previous work by the authors to estimate toxic concentrations around each releasing facility surrounded by a mitigation system. The mitigation systems considered here includes water, steam, and air curtains and exponential decays are assumed for the concentrations shapes before and after the installed curtain. The selection of the mitigation system type to install is included as a variable to determine when solving the proposed MINLP model. Additional constraints include the conventional non-overlapping and risk estimations based on probit functions. The objective function includes occupied land costs, interconnection costs, risk damage costs, and mitigation costs. A software package called TROL has been developed to automatically interact with GAMS and ease the initial and final layout descriptions. Numerical results indicate that the proposed model produces more practical and optimal layouts. (C) 2013 Elsevier Ltd. All rights reserved.