Fire devils or “firenados” are not really tornadoes at all.
A tornado forms downwards from a cloud base when warm, moist air collides with colder air.
A “firenado” actually has more in common with a whirlwind or dust devil, as they form from the ground upwards.
When a wildfire intensely heats air close to the ground, it can rise rapidly and start to spin into a narrow vortex. As more hot air gets drawn in around the base of the vortex, wind speeds accelerate inwards, like an ice skater pulling in their arms.
While most whirlwinds pick up dust and debris, a fire whirl is characterised by flames, ash and smoke which are whipped upwards in the rotating shaft.
Typically firenadoes grow up to around 100ft (30m) tall but are usually only a few feet wide. They are often very short-lived but can be extremely dangerous, as winds can blow as fast as in a tornado, though on a much smaller scale.