Accidents and disruptions in chemical process installations can, in principle, lead to the rare events in which the release of flammable and/or toxic substances occurs, and which at particular distances from the installation can result in a hazard potential due to thermal radiation, blast wave effects or the concentration of toxic substances. The possibilities and limits of deterministic and probabilistic estimation methods for appropriate distances from hazardous installations, based on the example of an ammonia release and a large surface fire, are shown. In this, it is demonstrated that the deterministic and probabilistic approaches are in no way conflicting or unnecessary, but rather that they are complementary. The use of a deterministic estimation method leads to a maximum set radius of effects which only take account of the damage impact. Depending on the selection of the appropriate and suitable consequence models, critical distances are calculated which are in some cases much larger than the current standardised distances, as is shown by the example of large-scale fires. The use of a probabilistic estimation method leads to a range of distances for which the individual risk can be given in addition. In principle, iso-contours joining points of same risk or areas of same risk may be defined through the use of such estimations.