Flamethrowers ?
Well, for the really big concussion, just get a six-foot piece of 8" pipe, and get out your trusty ol' oxy-acetylene torch, some newspaper and some masking tape.
Tape a cou[le layers of newspaper over each end, and punch a pencil-hole in one of the paper caps.
Light your torch, adjust for a complete combustion flame (neither oxidizing nor carburizing) and then wipe the flame out from off the end of the torch with a gloved hand.
Then, while the perfect combustion mixture is still flowing, insert the torch tip into the hole in the paper and let the gas flow for around 30-40 seconds.
Ignition of the charge is accomplished with some sort of glowing object pressed into the paper. A cigarette taped to a yard-stick works well , but be sure you stand to the side of the pipe, not in front of it.
Of course, the above is actually theoretical, Understand.
Me? Why I have never even seen it done, I've only heard the big kids talking about it.
I doubt that it would be well received in populated areas.
Flash