The Council Directive 96/82/EC of 9 December 1996 on the control of major-accident hazards involving dangerous substances, known as SEVESO II Directive, aims at the prevention of major accidents and the limitation of their consequences for human beings and environment. Although rules are well established to identify potential risk, there is no method to measure the risk level which takes into account safety devices and safety management systems implemented by operators. This paper deals with the first stage of a global methodology that aims to better assess benefits form safety devices and safety management systems through accident scenario selection.