Natural Phenomenon

What is a fire tornado?
A fire tornado is a combination of heat, ash, and fire into a spinning mass of air.
Actually, fire tornado are more closely related to whirlwind than they are to full-fledged tornado because the vortex in most cases does not extend from the surface to the cloud base. But because they also involve a mass of rotating air rapidly around a central axis, similar to tornado, we can still call it fire tornado although the most exact name should be fire whirl. They form in certain situations, such as wildfires, large fires spawned by natural disasters, and, in some cases, house fires.

There are 3 types of tornado, that is supercell (can cause significant damage), non-supercell (any other tornadoes beside supercell), and whirlwind (tornado-like storms). Fire tornadoes are in the last cathegory. 

How did a fire tornado form? First a very big heat source near the ground existed, and causing a column of superheated air. When the fast wind high above the ground met the slower one near the ground, it will create a mass of spinning air alongside with the column of superheated air. When it met an updraft and the updraft is strong enough, it will raise the spinning air from horizontal to vertical.

Fire tornadoes are dangerous. That's why we should maximize our effort to prevent it, such as not making a wildfire in the forest, and not letting a very big heat source exist uncontrollably in the open air.