This report documents the methods to calculate the risks due to dangerous substances in the Netherlands using the models and data available. Calculation of the risks relates, on the one hand, to stationary installations and, on the other, to transport and related activities.
The report consists of two parts. Part 1, describing the methods to calculate the risks of stationary installations, was written by the National Institute of Public Health and the Environment (RIVM) under a supervisory committee of representatives from the subcommission on Risk Evaluation of the Committee for the Prevention of Disasters (CPR-RE). Part 2, drawn up under the responsibility of the Ministry of Transport, Public Works and Water Management, describes the calculation of the risks connected with the transport of dangerous goods, based on the approach developed in accordance with the Ministry of Housing, Spatial Planning and the Environment and set down in the last few years in various commissions.
Although the report describes the present-day calculation methods (in practice, no better methods are currently available), discussions on a number of subjects in the supervisory committee led to the conclusion that additional research would be necessary to guarantee the quality of the calculation methods in the future. Three subjects for study were indicated: A. The failure frequencies of stationary installations. Failure frequencies are based on the so- called COVO study from 1981. Additional failure frequencies have been determined in various studies carried out for the Dutch government over the years. Recently, new studies have been published, reporting different figures – mostly higher – for a number of failure frequencies. A more detailed study on the failure frequencies will be carried out, concentrating especially on the original data sources.
B. The meteorological model. Dispersion calculations are carried out as part of the risk analyses using generally accepted meteorological models and the corresponding meteorological data.
The national model used in air pollution calculations has recently been adapted to include new insights. At the moment, meteorological statistics are not sufficiently available to apply this new meteorological model to risk analyses. The relevance of the new model to risk analyses should be ascertained; furthermore, the consequences which the new model, including the model parameters, could have on the results of calculating risks should be examined. The study on these consequences will be started up in the short term.
C. Differences in risk calculations for transport and for stationary installations. The method to calculate the risks of transporting dangerous goods is comparable to the calculation method applied to stationary installations. During the last few years, the basic principles of risk analysis have been discussed and established with the parties involved. Since developments in the risk calculation methods for transport and stationary installations were separate, several differences exist between the basic principles in risk calculations for transport and for stationary installations. These differences relate, among other aspects, to the frequency of catastrophic failure of tank wagons relative to stationary tanks and to certain loss of containment scenarios.
The Committee for the Prevention of Disasters considers it important to have reliable risk calculations for stationary installations and for transport of dangerous goods; these should, as far as possible, also be founded on similar basic principles. It is therefore advisable to analyse the basic principles of the calculation methods and to study the consequences of removing the differences in the calculation methods. Both the Ministries mentioned above can then decide whether these differences should actually be reduced.
The discussions show that the methods of risk analysis are still being further developed. The Committee for the Prevention of Disasters is pleased that with the publication of this report a substantial contribution will be made to the further development of this risk analysis instrument.
The Committee thanks the government experts, research institutes and industry for their contributions. The Committee for the Prevention of Disasters is convinced that the report will be of great value for all those dealing with risk analysis and risk management.
