While in high school I went to a pep rally/bonfire. They had piled up a bunch of old pallets, cardboard boxes and other trash to make the bondfire with. A couple of older guys, propably 20somethings at that time, started pouring 5 gal cans of gas on the pile. Even way back then I knew that was a bad ideal and told everyone around me that we needed to move back. Some listened and some didnt, but I moved way back. To start the fire they poured a trail of gas a few feet fro the gas soaked pile and threw in a match. You guessed it, big whoose and the pile exploded sending burning piles of trash everywhere. It flattened the burn pile. Lucky, no one was hurt, but the bon fire turned into a bust.
I replied to a continuation of this thread over on arborist site. I see some here also start brush piles in a similar method as I what I use. I have a propane weed burner with about 20ft or so of hose. I simply light the burner and place it under the pile of brush. I then take a backpack leaf blower and aim the air blast at the flame. This will start any brush pile, no matter how wet in just a few minutes. No danger of explosions, no petroleum byproducts left soaking in the soil. I dont know how long a 20# bottle of propane will last using it to start brush piles. I just borrow the bottle off my gas grill when I need to burn a brush pile. The weed burner cost me about $20 at Harbor freight several years ago. With the price of gas, I suspect buying a weed burner would be a cheaper method of starting brush piles than pouring out gallons of gas, diesel or oil mixes, I know its a lot safer.