Originally posted by Impediment
Just to prove how nerdy I am:Fire is a series of actions and changes that produces a result — a process. In fact, it is an oxidation process (called combustion or burning) that gives out heat and light energy as well as glowing gas and a small amount of plasma.
So, talking about fire's mass is like talking about the mass of digestion, or boiling, or getting a driver's license although it certainly makes us think about what fire is. But a process doesn't have mass.
Flames are another matter. They are burning gases and gasses certainly do have mass.
When they talk about "fire", they actually mean "flame."
And, plasma is only produced with exceptionally hot fires. (Edit - Well, that may not be completely true...I'm just not 100% positive: http://www.gordonengland.co.uk/pft.htm)