We played around with what were known as 'Flame Effects Generators', also known as 'Fire Cannons', for years out at Burning Man. We even shot them directly at people, clad in fire suits of course (search YouTube for 'Dance Dance Immolation'). As far as I know no one ever got hurt, or even burned a little, and we compared notes a lot. But these were all pressurized propane. The subject line above was something of a motto. These things use liquid, and the potential for an accident is pretty high. I've used FEGs for years, but I wouldn't want to be within a city block of a liquid based flame thrower.
One early year a guy had a kerosene-based torch, a big one. I heard him tell the Black Rock Rangers, "You know, if anything goes wrong here you're gonna have to move 2,000 people 100 yards in about 20 seconds".