Several models are currently available to model the discharge and dispersion of toxic or flammable materials to the environment. A few of the Gaussian dispersion modeling tools allow the representation of the complex environment within a manufacturing plant or urban area in determining the impact of continuous releases from a plant. For atmospheric dispension of dense gases, a correction is made for the presence of the buildings and other complexity by using a surface roughness parameter, which is only a crude approximation. A need exists to obtain realistic estimates of plume dispersion in a complex environment, particularly accounting for buildings/obstructions at a plant and the associated turbulence. With the advance of computational technology, and greater availability of computing power. computational fluid dynamics (CFD) tools are becoming more available for solving a wide range of problems. A CFD model, called FLACS (flame acceleration simulator), developed originally for explosion modeling, has been upgraded for atmospheric dispersion modeling. CFD tools such as FLACS can now be confident used to understand the impact of releases in a plant environment consisting of buildings, structures, and pipes. and accounting for all complex fluid flow behavior in the atmosphere and predicting toxicity and fire explosion impacts. With its porosity concept representing geometry details smaller than the grid, FLACS can satisfactorily represent geometry even when using a coarse-grid resolution to limit The simulation time. The performance of FLACS has recently been evaluated using a wide range of field data sets for sulfur dioxide (Prairie Grass), carbon dioxide (Kit Fox), and ethylene (EMU), for example. In this paper, details about the improvements made to FLACS, model validation exercises', and results from the modeling of releases from an industrial facility are presented. (c) 2005 American Institute of Chemical Engineers Process Saf Prog 24: 316-327, 2005.