In order to improve risk analyses and influence the design of the future hydrogen systems, an experimental study on leaks qualification and quantification was performed. In H2 energy applications, fittings appear as a significant leakage potential and subsequently explosion and flame hazards. Thus,as part of the 'Horizon Hydrog ne Energie' French program [1], four kinds of commercial fittings usually employed on H2 systems were tested thanks to a new high pressure test bench - designed, set-up and operated by INERIS allowing experiments to be conducted for H2 pressures up to 700 bar. The fittings underwent defined stresses representative of H2 systems lifetime and beyond. The associated leaks when existing are characterized in terms of flow rate.