firestorm; fire whirl
A large, intense fire that creates its own wind system, often associated with wildfires or large-scale urban fires.
A firestorm occurred during the large-scale wildfire.
Firestorms are caused by intense updrafts generated by the fire.
旋風 means 'whirlwind' in general, while 火災旋風 specifically refers to a fire-induced whirlwind or firestorm.
火事 is a general term for 'fire' (as in a building fire), whereas 火災旋風 is a specific meteorological phenomenon.
Compound of 火災 (kasai, 'fire disaster') and 旋風 (senpū, 'whirlwind').