When calculating the risk of a Seveso-establishment with toxic substances, probit functions are used to have a relationship between the human lethality on one hand and the concentration of the toxic substance on the other hand. These probit functions have a substantial impact on the calculated effect of a toxic release and so the risk of the establishment. Probit functions are derived from animal experiments with a lot of assumptions, among others the classification of the acute inhalation studies and the extrapolation factors for animal to human extrapolation.
In this paper, the methodology to derive probit functions will be described for Flanders and The Netherlands with emphasis on the differences. The probit function for the toxic substance hydrogen chloride (HCl) will be studied more in detail, because, in this case, there is another important assumption, namely whether or not considering a specific study about baboons.