Kapitel – Arbejdsrapport fra Miljøstyrelsen Nr. 8 2008

Acceptkriterier i Danmark og EU

Summary and conclusions

This report describes the use of risk acceptance criteria in order to identify conflicts between major hazard establishments (establishments covered by the major hazard (“Seveso”) directives) and surrounding land use with respect to protection of human life and environment.

The report explains relevant notions in risk assessment and a glossary is included. The report describes different types of risk acceptance criteria based on individual or location-based risk, societal risk and potential loss of life. The different types of risk assessment methodologies are described.

Earlier Danish studies are reviewed, including ”Environment Project 112”, in order to identify the background for the present practice in Denmark, and the practice for risk acceptance in a number of other European countries is summarised.

Conclusions are drawn where European practice has converged towards consensus regarding risk acceptance criteria, viz. the order of magnitude for individual or location-based risk (fatality risk of an individual shall be less than 10^-6 per year for the protection of the general population) and societal risk (the probability of an accident shall be less than 10^-3 per year for major accidents with up to 1 fatality, dropping with a factor 100 when consequences are ten times bigger). These values are in the middle of the “grey” zone proposed by “Environmental Project 112”.

The ALARA (As Low As Reasonably Achievable) principle states that all safety precautions should be implemented that are reasonable in view of technical and economical possibilities. The ALARA principle should always be applied, and therefore it is not necessary to define separate intervals of risk where ALARA has to be used.

The report concludes that in Denmark no guidance is available on how safety distances should be determined using the available qualitative risk analysis methods, nor is a method to assess environmental damage available. It is proposed to define accident classifications for environmental damage similarly to those used for qualitative assessment of societal risk, by using the size of the area affected by the accident.

The report’s conclusions give some recommendations on risk acceptance criteria. These criteria have to fulfil requirements regarding:

Consistency, proportionality and transparency.
All accident possibilities to be considered.
Environmental damage to be considered.
Reasonable safety distances (for land-use limitations) to be determined as well as the consequence distance for the worst-case accident (for emergency planning).
Societal risk for land use outside the safety distances to be assessed.
Specific safety measures at the establishment to be considered.

It is necessary to consider the probability of events in the assessments, as probability is elementary in the notion of risk. Inclusion of probability can be either quantitatively or qualitatively.

Limitations in land use distinguishes between vulnerability of different objects such as residential areas, hospitals, schools or natural reserves; generally higher levels of risk are accepted in industrial areas as compared to residential areas, while hospitals and emergency support facilities should be given the best protection possible. The same risk criteria should apply, if needed after en transitional period, for existing land-use situations and new developments.

The use of quantitative and qualitative risk analysis methods should be possible side by side, but efforts should be directed into making the results more comparable. This means that among others there should be obtained consensus about the relation between verbal descriptions and the numerical values of accident probabilities. The French risk assessment method, which includes both quantitative and qualitative elements, could be used as a basis for a relatively simple and transparent risk assessment method in Denmark.

Further work is required in order to develop the qualitative methods to determine safety distances, to develop criteria and methods to deal with risks for environmental damage, and to develop a practical guideline for the use of the ALARA principle.