HAZOP is a succession of precise steps based on the identification of systems and subsystems (“nodes”, “lines”). It consists in varying certain keywords related to the functioning of the systems to observe their impact on the actual operating processes. These variations of keywords cause “drifts'' and therefore risks, the likelihood of which must be examined. ons de mots clés provoquent des “dérives” et donc des risques, dont il faut examiner la crédibilité.