At lifewater ranch we have tons of wood and often have to burn it to keep the place safe from fire. I have gained much experience, having had 3 fires get away from me, or my caretaker, since I got this place. A great burn pile is TALL. At least 4′ in height is generally needed in order for the pile to burn completely. What happens is the flame gains sufficient height to create an upward pull with the heat that pulls in oxygen from around the base and channels it into the fire and up with the smoke. Once such a vortex is set up the pile burns quickly while most of the heat goes straight up.
In the pile above I had hoped to save the tree to its right. That tree did fine till the fire burned down to coals. At that point the heat began to radiate rather than flow as described above and the sheer proximity of the coals caught the tree on fire spontaneously.
Another important point is to get the area around the pile as clean as you can and with a diameter at least twice that of the pile itself. It’s always much safer and easier to build a good pile BEFORE you light it. A large pile will quickly get so hot you won’t be able to get within 20′ feet of it before being VERY uncomfortable. So make that pile as perfect and safe as you can while its nice and cool.
Only if the fire is going to be less than 4′ in diameter is it small enough to burn as you pile – which is a good idea if you are trying to safely make a burn are for a later larger fire but this method, I have found, is generally more work overall for the amount of fuel burned.
Here’s a pile right next to the first one that was not made nearly as well. This was built by using a dozer to push the pile up into place. I did a little cleanup of this one but not nearly as well as I did on the first one, which took me two full days to complete. Because this is much dryer material the height is not as needed but its surroundings were never cleaned up nearly as well.
When lighting the fire it’s important to get a sufficiently large enough flame in the middle of the pile to begin a plume of smoke that is rapidly rising and sucking in fresh air from the edges. After awhile, you get to know how much heat that feels like and once you get there, the pile will quickly engulf the rest of the pile. Sometimes you need to start several spots of the pile to get that sufficient critical mass of heat needed to assure a clean burn.
It only takes maybe an hour or two to have the piles safely burned past their highest flame point. Once this has been completed you have a burned safe zone around the fire. At this point you can safely work on other piles or take a break away from the fire if needed without much chance of anything getting away from you. At this point the fires are still too hot to comfortable gather the surrounding fuel back into the center. I find it best not to try messing with the fire at this point but rather let it burn another 4-8 hours at which point you can regather all the surrounding fuel into the center of the file area. I usually use a large rake to push the smaller fuel in. This creates an even more safe zone around the edge of the fire with almost no fuel available for escape of the fire.
Here the piles have lost enough heat to regather the fuel into the center. Once this is done, you can safely leave the fire overnight.
One very dangerous thing to keep in mind is that stumps, especially rotten ones, are often the source of a root fire. I like to burn the stumps up as well as I can but before I let it go overnight I will completely douse the stump in water and make sure no smoke is rising from it. This will reduce the probability of a root fire significantly. For this reason, it is not a good idea to build a burn pile next to a stump or a large tree. If you want to burn up a stump build the pile directly over it and make a nice wide safe area around the pile to reduce the odds of a root fire.
Another good idea is to try to burn your piles just before it rains. A nice hard rain is a great way to greatly reduce the odds of root fires or otherwise have surprises.