A quantitative risk assessment (QRA) is a tool for the
provision of insight into the risks of the use, transport and
storage of dangerous substances. The calculation methods used in
the analysis provide insight into the expected number of victims in
an accident involving dangerous substances. The use of probit
functions is prescribed for the model-based estimate of the acute
lethal effects of toxic substances. This information is used in the
granting of permits and spatial planning concerning activities
involving dangerous substances.
Probit functions indicate the relationship between the
concentration of a substance, the exposure time and the effect on
(in this case) human beings. This way, a probit function for a
substance can be used to estimate the percentage of fatalities in
the direct vicinity of an accident caused by exposure to the toxic
substance, in any random combination of concentration and exposure
Probit functions are based on toxicological information from animals that are converted into exposure-response relationships for humans. Probit functions have been formally determined for a number of substances, and included in the Reference Manual Bevi Risk Assessments (NL). For substances for which no probit function is available, a probit function is derived, evaluated and formalised according to a determined process.