Because of economical processes that tend to move the frontiers of firms salaried relations of uncertain status are found coexisting inside the very same working world. From a qualitative investigation mixing employees' interviews and observations made on SNCF and GrDF working sites our research offers to think about the relations linking subcontracting, maintenance, safety and security. Considering subcontracting as a particular way for professional bodies to be associated allows us to wonder about its effects within a same firm (the "integrated" subcontracting) as much as between a principal and a provider. Our thesis shows that when change occurs inside the organization — like the creation of new committees of experts or the reorganizing of an old service — security and safety can be impacted because thus professional bodies tend to be reconfigured while modifications affect practices, professional identities and work division. The relations between subcontractors and principal are complicated and their consequences depend from the context they are placed in,
determined by a combination of various characteristics such as the confidence level, the available time, the reputation, the position occupied by the subcontractor.
Our investigation makes clear that there is no direct link between subcontracting, security and safety. Their effects, in spite of their reality, are submitted to the altering mediation of legal factors (related to economic national and European issues) and concern the working organization as well as the professional identities.