To execute the Seveso III Directive, appropriate safety distances must be maintained between Seveso establishments and some specified areas accessible to the general public. This with the objective of limiting the consequences of major accidents for human health. One benefit of maintaining a safety distance is that it is a reciprocal criterium: it works both ways. The distance between a vessel and a school is the same as the distance between the school and the vessel. As this kind of reciprocity is (luckily) rather the rule than the exception in daily life, this also applies when a risk tolerability criterium (with respect to one risk source) with territorial reflection is used: When there is no school inside a certain individual risk contour (IRC) of a dangerous facility it is implied that the school is not within the individual risk contour of the same facility. Several countries/regions use a risk tolerability threshold for land-use destinations in the realization of safety distances according to the Seveso directives, and do this for the siting of dangerous facilities and new developments in the vicinity of these facilities.
However it becomes more difficult when using a societal risk as parameter in the evaluation to limit the consequences of major accidents: The societal risk calculated for a dangerous facility, incorporates the risk of every possible major accident with its lethality and its expected frequency of appearance. Therefore, in a non-zero risk world, it is an excellent tool to evaluate whether the possible consequences of siting a dangerous facility in a particular environment is tolerable or not. However, to use the societal risk of a dangerous facility in the evaluation of a new development is less obvious: The calculated societal risk is not only dependent on the risk source and the development, but also on the entire population present in the environment of this risk source. This makes it not only practically complex to deal with, but also more arbitrary and not transparent. On top of this, one can see that although societal risk criteria for siting of dangerous facilities is differ between countries/regions in order of magnitudes, they are all (rightfully) rather stringent, as compared to individual risk acceptancy criteria that are used in facility siting and real life. The combination of more tolerable individual risk acceptance with a non-reciprocal less tolerable societal risk leaves the door open for some very counterintuitive outcome in land-use planning processes. This paper goes deeper into detail on the principles and consequences of societal risk and how they can be used benefic