In laser-based powder bed fusion of metals (PBF-LB/M), the atmospheric residual oxygen plays a key role, particularly for highly reactive materials like Ti-6Al-4V. Oxygen concentrations present in commercial machines are still too high to effectively prevent oxidation of the powder and oxygen take-up into built parts deteriorating the part quality and mechanical properties. In this work, to reduce the residual oxygen content to a range adequate to an extreme high vacuum (XHV) while maintaining normal pressure, a silane-doped argon atmosphere ( 0.001 vol.-\% silane in argon) is introduced. Ti-6Al-4V powder was processed both under a conventional argon atmosphere ( 0.01 vol.-\% oxygen) and argon-silane atmosphere ( 10-20 vol.-\% oxygen). The influence on the resulting porosity was investigated using a central composite design. Additionally, the tensile properties were analyzed. High tensile strengths > 1290 MPa and low porosities 0.02 \%, but no significant influence of the atmosphere was found.