In Additive manufacturing, traceability and repeatability is a neck point for the transition from prototyping to series production. This work focuses on the interactions between the protective atmosphere and the manufactured part for Selective Laser Melting process. First, an increase of nitrogen content has been noticed for Inconel 625 part manufactured under nitrogen atmosphere. Then, Helium atmosphere on TiAl6V4 part has shown an important generation of nanoparticles and a lower quantity of spatters. Manufactured parts exhibit higher roughness on their lateral faces, with powder and spatter agglomerates. Finally, very variable moisture levels have been measured in the process chamber, as well as oxygen contamination, which can be limited by optimizing the gas flow. The importance of the gas specifications and its management has been demonstrated.