A method is presented for estimating the frequency of spillage of toxic liquids from road tanker accidents. The calculation requires information about the vehicular flow of tankers, their accident rate and the probability that an accident will result in a spill. The available sources of input data are discussed.
Railway goods traffic, either involving liquids transported in tanker wagons, or hazardous freight packed in individual containers as part wagon loads, is amenable to similar analysis but relevant input data are much more difficult to obtain.
For any type of spill, the estimation of frequency should be accompanied by surface and groundwater pathway analyses, to assess the consequential damage to the aquatic environment and any possible hazard to public water supplies.
This paper serves as an outline of a subject calling for more thorough study, for which improved databases, geared to the needs of risk assessment, would be strongly desired.