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Thread: Burning logs in a pit

  1. #1
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    Burning logs in a pit

    Pit burning is something I never did before I got an excavator. Why do logs and brush seem to burn so much better in a pit?

    I recently burned about 10 dump trailer loads of brush and logs, each about 14x7x6'. I burned in a 20x8x8' pit I dug out in the middle of a field. I like the way the pit confines the fire and minimizes spreading sparks if the wind comes up and the ease of covering the pit with dirt to make sure every ember is out. Far easier to manage than an open brush pile.

    I wasn't prepared for how quickly logs turned to ash. I was afraid the pit would limit getting oxygen to the bottom but that didn't happen. The fire even at the bottom of the pit burned with high intensity. I dump the trailer loads near the pit and use the new excavator to load the piles into the pit, a little at a time until the fire gets going then push in piles at a time, using the bucket as need to distribute the fuel.

    fire_pit.jpg

    The pit fire seems to burn much hotter and far quicker than a brush pile in the open which is what I did for years. With a brush pile I was constantly pushing and turning the pile with the tractor and pushing unburned logs into the hottest places. The entire pit appears to turn into a uniformly raging inferno.

    burning_brush.jpg

    Anyone else burn in a pit?

  2. #2
    If only I had an excavator or backhoe...

  3. #3
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    Quote Originally Posted by Timothy Thorpe Allen View Post
    If only I had an excavator or backhoe...
    I saved up 10 years to pay cash for this one! Makes a great woodturning tool too. (I can hold a 1000 lb log waist high off the ground for chainsawing!)

    I bought the cab model with heat and air since I'm elderly and feeble.

    trackhoe_20190916_190256.jpg

    It also makes it so easy to put logs on the Woodmizer, far better than the tractor or bobcat.

    JKJ

  4. #4
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    I always wondered the same thing about a pit. I should have bought an excavator long ago, but never did. I'm thinking a 50, or 60 series though. I'm keeping my eye open for a low hour one, but haven't seen one with that swiveling blade like yours, which I want now that you brought my attention to it. My rental place stopped renting anything over a 35.

  5. #5
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    My guess is the burning intensity has to do with some basic physics. The rising hot air in the pit draws more fresh air into the pit. An open pile will not accelerate the introduction of air into the fire as completely.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  6. #6
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    Quote Originally Posted by Tom M King View Post
    I always wondered the same thing about a pit. I should have bought an excavator long ago, but never did. I'm thinking a 50, or 60 series though. I'm keeping my eye open for a low hour one, but haven't seen one with that swiveling blade like yours, which I want now that you brought my attention to it. My rental place stopped renting anything over a 35.
    Don't wait another day!

    Mine's a KX033 with hydraulic thumb and angle dozer blade, just over 8000 lbs. The only thing it lacks is rear lights, which I'll add since I like to work well into the dark. I added a radio/stereo system. I decided to buy a new one so I wouldn't be buying someone else's problems and abuse.

    If money was no object I would have bought the KX-040 with the 6-way dozer blade. The tilt function would be so handy at times.

    I bought a hydraulic dump trailer at the same time (at a huge overstock discount), rated at 14000 lbs - they delivered the trackhoe in the trailer. Evidently some people use such a trailer to transport to a job, fill and dump the trailer, then use it to carry the machine back home. But I have other bigger trailers if I need to haul it. Mine will probably never leave my property but I LOVE having the dump trailer - another thing I've wanted for a long time. The pair together have already let me do things that were previously so much effort as to be almost out of the question.

    trackhoe_delivery_trailer.jpg

    JKJ

  7. #7
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    Probably for the same reason a fire in the fireplace will burn hotter if it is constantly pushed to the rear, where the brick soaks up intense heat and radiates it back into the fire.
    NOW you tell me...

  8. #8
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    Quote Originally Posted by Jim Koepke View Post
    My guess is the burning intensity has to do with some basic physics. The rising hot air in the pit draws more fresh air into the pit. An open pile will not accelerate the introduction of air into the fire as completely.

    jtk
    After experiencing the burn that was my theory too. A pile will burn in the center and above and can leave the outsides cold. After using the first pit I dug another one in another spot on the farm.

    Hey, did you ever introduce forced air into a burning brush pile? I have a Shindaiwa backback leaf blower powerful enough to roll 8" rocks across the yard. When directed into a brush file it makes a blast furnace capable of melting aluminum quickly and melting steel if it's not too thick. Ain't no better way to get a whimpy fire roaring hot.

    Of course there is always a little smoke and such involved when getting started and the opportunity to singe a hair or two.

    JKJ_2012-08-27_18-00-27_204.jpg

    JKJ

  9. #9
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    I have started Large burning piles with a 13hp Billygoat blower on wheels, and an Indian pump with kerosene. You get to see close hand how kerosene, and oxygen made a good rocket fuel. Short of a big pit, the 13hp blower will send the fire all the way under a large burning pile, in short order. The seals in the pump don't last but a few months though. I bought sheets of a synthetic rubber to make new seals out of, but don't have a place to burn big piles now, so haven't fixed that pump yet.

    I have a place that I let people dump stumps, and brush, in exchange for doing some work for me. The last pile of that I burned, I waited until a rain storm was just getting here. With the Billygoat, and kerosene pump, I got the fire going just as the pouring rain came. There were flames 30 feet high, in the pouring rain in a little while, but some of the stumps burned for 3 weeks. That was a while back, and is all grown up in trees now. I opened up another place where they are just buried now, in a six acre hole/small valley/big gully.

    Now you've really done it, telling me about a 6-way blade being available! I was looking at John Deere's, and they only offer the blades that swing in one plane.
    Last edited by Tom M King; 01-24-2020 at 7:47 PM.

  10. I burn in a pit when I can. Close to 20 years ago, I picked up a John Deere 210C 4 wd back hoe/loader and it has been a real life saver for work around the farm. I dig trenches for water lines, irrigation lines. animals that take dirt naps, etc. I can load a third of a cord of firewood in the front bucket. I have been reclaiming an old field that had been left fallow for 30 years. Slowly cutting back the trees, saplings, brush etc. I am now at the point where there are two deep gullies at the lower end of the field. I push the brush, tree branches and small stuff into the gullies and mash it down. I have even dropped loads of manure on top to weigh down the brush. The gullies have stopped washing deeper and the brush is catching leaves, chaff and dirt and the gullies are actually filling in now. So for the time being, I am not burning much. But even when camping, my fires are in a pit about 18 inches deep. Easy to put out, burns hotter, less effect of wind and fill the hole back in and replace the sod and it is hard to tell anyone had a fire there.

  11. #11
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    Late this Fall, a guy called me asking if he could dump a few loads of brush in that spot where I've been trading work for dumping, and letting surrounding people dump their leaves in there. I forget how many years that's been going on. Anyway, I knew the guy had a Cat 953, so I told him if he pushed the pile off level, that he could dump his few loads in there.

    He was in the middle of pushing it off, and called me to drive over, and look. He had pushed it down to bare dirt, and the ground was Alive with writhing Very Large earthworms. It was like the ground was alive. I told him if he needed to plant something, to come get some of that dirt, and dump a load of it where I wanted one. He did that while he was there. He took one load, and dumped a load where I wanted one. It's some rich stuff, even blacker than the old horse manure pile.

  12. #12
    A pit fire is insulated, fresh air getting to the fuel must pass thru the heat of the fire to reach it; the air gets superheated, which reduces the oxygen in it-- so the heat of the fire intensifies as the oxidizing fuel is it's looking for more air, which is there, but it further increases in heat and decreases in oxygen, and soon there's still lots of heat but no fuel, at all. Just ashes--

    A ground fire has an unlimited supply of fresh, oxygen-rich cool air. As long as there's plenty of good fuel the oxidation continues, but half-burnt wood isn't good fuel, and soon the heat decreases to the point that the fuel ceases to oxidize...
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  13. #13
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    Around here it's common on road construction where large trees have to be removed for them to burn the trees. They have a blower that is like a very large squirrel cage blower that blows air into the fire. It's surprising how fast large green trees can be reduced to ashes. The air being forced into the fire changes everything. I think as has already been stated the pit creates the same effect. Fresh air is drawn in at the perimeter and the heat rising simply accelerates this process causing a complete burn as fast as the material allows. A chimney effect.

  14. #14
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    Quote Originally Posted by Ronald Blue View Post
    Around here it's common on road construction where large trees have to be removed for them to burn the trees. They have a blower that is like a very large squirrel cage blower that blows air into the fire. It's surprising how fast large green trees can be reduced to ashes. ...
    I've seen that in action at a major construction site - incredible! They used a huge engine-powered fan blowing down a long trench. The heat was amazing.

    Another place I experienced the power of heat was when working on a forest firefighting crew. At one point we had to quickly hunker down behind the top of a ridge when the fire was coming up from a valley on the other side. The superheated wind ahead of the fire was so strong and hot we saw the tops of standing trees burst into flame long before the approaching fire got near them. The sound of the wind and the treetops practically exploding was a bit frightening. Ok, maybe more than a bit. The crew leader called for retreat and no one argued!

    JKJ

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    John, make this your avatar.

    Quote Originally Posted by John K Jordan View Post
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