Gaseous hydrogen is used in nuclear power plants, especially pressurized water reactors, for several process reasons. In this paper, we present a two steps probabilistic analysis methodology proposed by the French Institute of radioprotection and nuclear safety (IRSN), which allows for a risk informed hierarchy of the rooms in the auxiliary nuclear building through which gaseous hydrogen is circulating. Based on this analysis, the different rooms within the auxiliary nuclear building may be hierarchized, according to the evaluated frequencies of hydrogen release and explosion. This analysis may be used to prioritize the in-service controls of the venting system within this building, and to identify the needs of improvements of the venting system efficiency. In this paper, the methodology and initial lessons of the study will be presented, as well as some sensitivity studies to the main parameters. Due to the proprietary nature of the parameters (configuration of the rooms and hydrogen distribution network, operating experience feedback data, etc.) the numerical evaluations are not presented in this paper, and the discussion focus on the method.