A ternary flame system is presented that allows observations of soot oxidation in a hydrogen diffusion flame in the absence of hydrocarbons. A propylene/air laminar jet diffusion flame emits a soot column with a diameter of 3 mm that passes through a ring burner supporting a hydrogen diffusion flame. The soot oxidizes in a region that is 60 mm long, laminar, steady, axisymmetric, and accessible for optical and sampling diagnostics. Temperatures and soot loading can be controlled nearly independently in this region and a broad range of mixture fraction is encountered without interference from soot formation.