ATOS is an experimental project based on 3 simple guiding principles aimed at integrating several disciplines for a risk analysis. The three guiding principles are: a vision of the organisation with a balance between an formal (centralised, or what is written) and an informal (decentralised, or unwritten rules) part; "you do not manage what you cannot measure"; a focus on the quality of the barriers for the risk control. The disciplines involved in this project are, respectively to these principles, the organisational sociology, quality management and engineering. In this paper, the approach is explained and the result of a first application is presented. ATOS is designed to be a transferable tool for managers who have in charge the management of major hazard prevention.