The aim of this study is to perform a model-based analysis of various accident scenarios effects and consequences involving two high risk neighbouring chemical plants, by employing a ¿worst credible case¿ rule corresponding to accidents of low frequency but of worst consequences. Simulations investigate the influence of the distance between the two plants and the plant production capacity on the accident outputs including the domino accident scenarios. Accident consequences are evaluated in terms of a proposed joint probability of causing human fatalities as a result of a concomitant biological action of thermal radiation and toxic gas doses.