Convergence in risk assessment for Seveso sites – From Assurance results to ARAMIS method

: In the SEVESO II Directive, there is no harmonised definition of the scenarios that have to be considered for risk assessment. Typically, the chosen scenarios (total loss of containment, fire in the largest tank, explosion of the largest mass of explosive, BLEVE,etc.) can be different according to the specific risk analysts and according to the deterministic or risk-based approach of the country applying the Directive. This situation is confirmed by the results of the EC project ASSURANCE, in which 6 European organisations perform a benchmark exercise for the risk analysis of a specific plant. The partners used various hazard analysis techniques and arrived at quite different conclusions with respect to the scenarios that are relevant for the safety assessment. The ARAMIS methodology builds further on the conclusions of the ASSURANCE project and propose a structured approach that reduce the discrepancies in risk assessment. The project consisted in the elaboration of a methodology giving consistent rules for the identification of scenarios that take into account mitigation devices and safety management, and being recognised by a large number of risk experts from Competent Authorities and from Industry. The risk level of an establishment is characterised with an integrated approach where 3 independent parameters are quantified : 1) the consequence severity estimation of scenarios, 2) the prevention management efficiency and 3) the environment vulnerability. The project has brought elements to fulfil the need to establish a method that is capable to assess the risk level of an installation by integrating the preventive measures implemented by the operators. Such a method is a prerequisite in order to reach the goals of the SEVESO II Directive, that are to improve the prevention linked in particular with the safety management. The application of this method results in a more consistent risk evaluation and safety management strategy in all European Countries. The paper presents the main results of the ASSURANCE project and describes how the ARAMIS method has improved the risk assessment phase, and in particular the determination of the scenarios to be considered. It is explained how this approach helps the operator of Seveso plants to demonstrate that risks are properly identified and under control.