Probit functions are part of a quantitative risk assessment (QRA), used to estimate the number of acute victims as a result of inhaling toxic substances in an accident in which dangerous substances are involved.

Third party risks: effects of toxic substances

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.

What is a probit function?

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 time.

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.