Balloons at the end (spoilers)

So does anyone know exactly what the deal was with the balloons when the guy was setting up the arson? I thought it was explained in a movie, but then when I watched this again recently, I realized that this is the movie I saw this in, but there was no explanation. It seems like they would hold the gasoline, and fall and burst(thus spreading the accelerant) At different times, but it also sounds like a ridiculously complex setup that would take hours upon hours to set up.

Am I wrong? Is this in another movie and explained better? If not, does anyone know if this was a valid firebug technique?