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Acceptability and safety objectives, use of concepts through various areas

Final Report EU/ DG XXIV under contract N° B5-1030/99/094994, october

Summary

The definition and use of the acceptability concept has not been developed in an homogeneous way among all sectors of activities, and various interpretations have emerged. Many policy documents have been issued that allow to identify goals and criteria for safety policy. However, such documents may fail to reveal the practical use of the concepts, and complementary information may be available in administrative guidance and in some studies already made by research teams. The purpose of this study is to review these existing acceptability concepts and to suggest, if possible, some harmonization in the concepts and the vocabulary used in the different areas.
Though this review cannot be exhaustive, one must agree that there are many words and values in different areas for the definition and quantification of risk acceptability. Figures found in the literature search in are not all presented, but the examples given here are representative of what was found.
The figures for the individual lifetime risk of death due to a life long exposure cover many orders of magnitude, ranging from 10-8 to 10-3. However most figures for an acceptable or a tolerable risk range between 10-6 to 10-4 but either for one year of exposure or a whole life exposure. Clearly enough two acceptability concepts emerge behind such figures, the “negligible” level and the “intolerable" level.
One fundamental condition for a proper definition and use of quantitative risk acceptability criteria is to be really convinced that numbers and figures do not solve all issues. After the increasing use of quantitative assessments, there is now a trend to moderate this approach by giving more importance to all the qualitative aspects of risk management. In its recommendations, the US Presidential/Congressional Commission on Risk Assessment and Risk Management insists on the weight of the qualitative information of a risk to make it acceptable.
Finally, and in order to suggest some harmonization of the acceptability frame, it can be drawn from this study a proposal hierarchy of terms to qualify risks. This is a suggestion that is consistent and more or less used in different sectors. It needs to be approved by all risk assessors and managers. If agreed and used, this qualitative hierarchy would give some consistency to all risks analysis and without associated figures, it would still allow the integration of specific quantitative aspects in a particular situation, for a particular risk.
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