"My brother has been working on a way to make large explosions without the inherit danger of real explosives. Sawdust ignites well when mixed with the right ratio of air, so he devised this contraption. I hope to have an example of this at night- which is a truly spectacular effect! The intent of this is for special effects in a low-budget war film I'm scheming to start soon... err, someday."
This video is featured in the MythBusters' "Viral Videos" episode, aired on Sept. 3, '08.
Why did they make this gigantic explosion? Because they could, and its fucking awesome. They are never going to make a "low budget war film." They just wanted to make a BIG FIERY BOOM that towers over the surrounding area, and no man should hate on that.