How does The Undertakers pyro get so HOT?

If u have ever been to a live WWE event, and you were there to witness The Undertakers entrance live, then you know that it is literally HOT AS HELL, i was on the other side of the arena kind of in the upper level, and the heat from those flames were out of this world, before the flames shoot up u can see the gas or something come out first, and u can actually hear the flames. I've searched everywhere for those type of flame projectors and i cant find them anywhere, can someone please help me?