Is Fire a Plasma? What is Plasma?
"Generally speaking, by the time a gas is hot enough to be seen, it’s a plasma.
The big difference between regular gas and plasma is that in a plasma a fair fraction of the atoms are ionized. That is, the gas is so hot, and the atoms are slamming around so hard, that some of the electrons are given enough energy to (temporarily) escape their host atoms. The most important effect of this is that a plasma gains some electrical properties that a non-ionized gas doesn’t have; it becomes conductive and it responds to electrical and magnetic fields. In fact, this is a great test for whether or not something is a plasma.
Even small and relatively cool fires, like candle flames, respond strongly to electric fields and are even pretty conductive."
This video demonstrates this pretty good:
"A candle flame in an electric field between two dissimilarly charged plates will be oriented sideways because a flame is a partially ionized plasma. It therefore responds more strongly to the electric force between the plates than to the thermal convective forces in a gravity field."