I'm not going to jump on the bandwagon against the neighbor because I know personally how quick it can happen. Just about this time last year, my wife was burning some leaves and limbs in our backyard. We have burned in this area many times before, there is a tree stump right in the center of it, we pile the debris on top of the stump and burn it. This time of year, our grass is dead, but since the ground is usually saturated with rainwater, only the grass will sometimes flare up in a spot or two, then go out. Now behind our yard, is a cleared area that was logged a few years back, full of dead limbs and undergrowth, a lot of what we call "sage grass". Some people call it broom straw grass, because people used to make brooms from it. Anyways, this particular Sat, I was working on my pickup out in the yard, and the wife was burning the pile. There was no wind whatsoever when she started burning, but suddenly, a cold front that was forecast to move in that night started moving in. The wind picked up, blew a few embers around, and that was that. She yelled at me, I ran and got the water hose and started spraying, but too late. It got to the sage grass, and exploded like gas. There are about 36 acres total on the homeplace, 9 or so of it is ours, and it started moving toward the back of the property, away from our house. We called the local VFD, they got there in about 5 minutes, and in about 30 minutes had it out. A few more minutes wasted, and we would have had to have had the Forestry Service out with a bulldozer to plow a fire line around our property.
Even if you're being careful, it only takes a puff of wind to change things in a heartbeat. Like I said above, it was a totally calm day to start with. We still burn in that spot, but now only after a rain.
You can see how close it got to the propane tank!