Life support networks are vital structures, as they are significant in size and essential in nature for the entire society. A network failure may thus involve serious consequences. The analysis of the needs of those in charge of emergency measures has established that the behaviour of life support networks had to be studied not only for extreme events but also for all possible situations of failure. In this context, the role of civil engineers is crucial, since they must assure the safety of infrastructures from design to dismantling. The proposed approach consists of characterizing networks according to the importance and efficiency of their missions, operations, and essential infrastructures. This allows approaching network vulnerabilities from an exhaustive and global perspective. Based on the degree of efficiency of a mission, it is possible to identify the dysfunctioning operations and infrastructures, from which the internal and external causes of faults or failures could be defined. Instead of starting from a hazard and asking the question "What-if", as is currently done, this new approach aims at determining the vulnerabilities of a network by asking the question "Why". Once the potentialities of failures are defined, it will be possible, by using a global method of fusion, to determine the vulnerabilities of the various components of a life support network (missions, operations, infrastructures). This paper describes this new approach and the required criteria for the development of a global methodology for the assessment of anthropic hazard. Our article illustrates this approach with an application to a hydroelectric facility.Key words: risk, vulnerability, reliability, life support network, hydropower.