The World of Warcraft is always expanding. You may know how to play the game and how to combat the bosses but you may not know why all these happen. The way to make clear the above question is from the background story behind wow.
The factor of fire, which seems to be harmful mortal lives, was introduced on Azeroth by the dread Ragnaros the Firelord. It is doomed to be controlled by the Old Gods before recorded history. Ragnaros is one of the most hostile elemental lords who helped the Old Gods in the war against the Titans, and the falling of elementals and the locking Old Gods, the Titans produced a prison for the soldiers of the elemental lords and those lords as well, abandoned them to a place called the Elemental Plane.
Imprisoned in a narrow area and having no outside enemies, the elementals began to fight with each other. This was known as the Elemental Sundering. For certain reason, there are some difficulties for elementals in wholly dying. Because of the link to element, Ragnaros cannot fully absorb Thunderaan’s essence. However, it is unclear how long the Elemental Sundering lasts. Actually, it is probably continuous. The only thing that is clear is fire elementals is perhaps more hostile to those fire than air.