Development of modern safety standards for hydrogen infrastructure requires fundamental insight into the physics of buoyant gas dispersion into ambient air, from realistic flow geometries. In the present study, inert compressible air and helium releases from a round opening in a curved pipe were considered, experimentally. Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) techniques were employed simultaneously to provide instantaneous and timeaveraged patterns of flow velocity and gas concentrations. A range of gas densities and Reynolds numbers were considered in order to quantify their effects on the resulting flow structure. Significant differences were found between the spreading rate of round jets and those considered here. The findings indicate that use of conventional round jet assumptions are inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of the gas leak.