Geothermal is believed a cleaner and more environmentally friendly energy source than fossil fuel. Indonesia whose has the largest geothermal potency in the world just be able to utilize around 5% of her potency. This research is about geothermal power plant area layout optimization considering one of process safety aspect, i.e.Toxic gas dispersion particularly H
S gas spreading. Results of this study hopefully can be used to promote geothermal energy utlilization further especially at Indonesia. For the purpose, the optimization problem was formulated as a mixed integer non linear programming and solved with excel solver using GRG non linear algorithm. The objective function of the model is to minimize total plant layout cost yet still to take into consideration toxic gas dispersion. In this case, H
S gas dispersion was computed through computational fluid dynamic simulation. To show the applicability of the model, layout of two geothermal power plants, with and without following process safety standard spacing requirements, have been optimized. The results show that this proposed model is capable to reduce total plant layout cost of existing layouts up to 36%.