What will cause the flame of a halide torch to turn yellow?

The flame of a halide torch turning yellow is indicative of an improper fuel-to-oxygen ratio, specifically an excess of fuel relative to the available oxygen in the combustion process. When there is excessive oxygen, the flame tends to burn hotter and more efficiently, which usually does not result in a yellow flame. Instead, a yellow flame often suggests a deficiency of oxygen or an abundance of fuel, leading to incomplete combustion.

In contrast, conditions like a restriction in the tubing, high temperatures, or the presence of refrigerants may affect how the torch operates, but they do not specifically contribute to the changes in flame color associated with fuel combustion. These factors could cause other issues, but the yellow color specifically points to an imbalanced combustion situation, where not enough oxygen is present for the complete burning of the fuel. Therefore, understanding the relationship between oxygen levels and flame characteristics is crucial in operating a halide torch properly.