MODEL RELEASED. Welding. Man welding a pipe using an oxyacetylene torch. In his left hand he is holding a piece of wire which is being melted onto the joint to help strengthen it. He is wearing goggles and an apron to protect himself from sparks. At lower left are the two tubes which separately deliver oxygen and acetylene to the torch. The acetylene burns in this oxygen to form carbon monoxide; this reaction provides most of the heat. The carbon monoxide then reacts with atmospheric oxygen to give the blue flame. The flame from an oxyacetylene torch burns hot enough to melt most metals and it is neutral, which means it burns without leaving oxides in the cut region.