SLAB is a computer model that simulates the atmospheric dispersion of denser-than-air releases. The types of releases treated by the model include a ground-level evaporating pool, an elevated horizontal jet, a stack or elevated vertical jet, and an instantaneous volume source. Except for the evaporating pool source which is assumed to be all vapor, all of the remaining sources may be either pure vapor or a mixture of vapor and liquid droplets. Atmospheric dispersion of the release is calculated by solving the conversation equation of mass, momentum, energy, and species. The conservation equations are spatially averaged so as to treat the cloud as either a steady state plume, a transient puff, or a combination of the two depending upon the duration of the release. The mathematical description of the physics of heavy gas dispersion (gravity spread, reduced turbulent mixing, etc.) as well as the description of the normal atmospheric advection and turbulent diffusion processes, are inherently included in the conservation equations. The time-averaged concentration predicted by SLAB depends on not only the various physical phenomena associated with the dispersion equations, but also on the specified concentration averaging time. Typical dispersion simulations require only a few minutes on an IBM-AT classmore » personal computer. This report presents a theoretical description of the model, guidance for running the model and interpreting the results, and four example problems to illustrate the use of the model. 31 refs., 11 figs., 6 tabs. « less