Buildings can significantly affect atmospheric dispersion. There is an infinite number of possible configurations of release and obstacle arrangements, and no general theory exists to predict the dispersion of gas releases for all conditions. In this paper, two ＇classes＇ of configurations, i.e. dispersion in the lee of buildings and dense gas dispersion over a fence, are discussed in detail and simple models are described. An example of the effects of multiple building arrangements is also presented.