Flame propagation means the speed at which the fuel gas will travel:

Flame propagation refers to the speed at which the flame front moves through a combustible mixture, which is a crucial concept in welding and gas applications. Understanding flame propagation helps in determining the behavior of various gases when mixed with air and ignited.

In this context, the statement suggests that flame propagation means the speed at which the fuel gas will travel in isolation, which is not an accurate description. Flame propagation involves not just the fuel gas but also the surrounding air or oxidizer, and how these interact during combustion. Thus, solely stating that flame propagation is equated to the speed of fuel gas traveling oversimplifies the concept.

Although factors like the type of gas and temperature can influence flame speed, those details are part of broader discussions regarding combustion dynamics rather than the fundamental definition of flame propagation. Consequently, the answer indicates a misunderstanding of this significant principle in welding and combustion theory.