Occupational Safety and Health –OS&H- Risks Assessment and Management is a particularly demanding task: the European Directives - and the derived Italian laws and regulations - stress the importance of a pro-active approach, the one able to reach effective results. To simply focus on localized situations, and carry out a bird’s-eye survey cannot ensure a systematic evaluation of the operating contexts in complex settlements such as the Large Public Facilities, where the most serious criticalities are not of direct identification. The paper –developed within The General Safety Issues and Goals in Turin Universities research program, funded by Politecnico di Torino, discusses a special sub-part of the well-tested Guideline set up, for Large Public Facilities, in cooperation between Politecnico di Torino and Università degli Studi di Torino, aimed to grant a sufficient detail in the aforesaid situations. The approach is based on an original development for OS&H Risk Assessment and Management of some Forensic Investigations techniques for a thorough Hazard Identification on shell, services and interior spaces of settlements containing workplaces, and on their not-operative content. The analysis of some case histories confirms the effectiveness of the approach in terms of completeness and repeatability, and makes possible to draw suggestions on the selection of the better investigation technique in different scenarios.