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Clearances to Combustibles Theory

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by wkpoor, Dec 31, 2012.

  1. wkpoor

    wkpoor Minister of Fire

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    I've read on here many times about combustibles too close to a stove causing a fire. And maintaining good clearance is indeed a good practice. But I have often thought about the wooden handles on my stove. Both are very close and the primary handle is about 1" in the close position. After 3yrs that handle looks exactly like it did new. And I just measured the temp with an IR gun at 220 degrees on the side nearest to the glass. Now I know what has been said before about "not yet". Well 30+ yrs , 7000+ stoves and no handles have caught fire yet. This why I'm slightly skeptical when I hear something sitting too close to a stove is what caused the fire.

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  2. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Houses burn down by the dozens every year from combustible materials being too close to wood stoves. If you are looking for somebody to prove it too you, search Google News every week of the month during heating season.

    Fire investigators these days make CSI techs look like a bunch of rookies when it comes to determining the source of ignition.
  3. Smokey

    Smokey New Member

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    As I scan the combustibles around my stove with an IR gun, I am trying to remember the minimum temperature at which a very dry piece of wood will spontaniously combust? I would think it would have to be well over 200 f, and in most cases 2 times that.
  4. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    180 degrees over ambient is the temp used to determine if exposure over time will lower the combustion threshold. Pyrolosis over time from the exposure to heat lowers the ignition temperature of a combustible material.

    Ain't a guess. Just science.
    Smokey and Hearth Mistress like this.
  5. fossil

    fossil Accidental Moderator Staff Member

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    Happened to me, some 5 years ago. Had loaded up the old Lopi 520 that came with our house, got it burnin' good and turned in for the night. Had a copper tub full of wood sitting right next to the stove...pushed it close to the stove to get it out of the hallway. It was overfull, so there were splits sitting sideways on top of the ends of all the vertical splits filling the tub. The ends of those sideways splits were just about 3" from the side of the stove. As I lay in bed in the next room drifting off to sleep, I had this vague sensation of smelling something burning. Woke up, got up, went to look, and found the ends of those sideways splits smoking and charring. They weren't far at all from burning. Scared the bejeezuz outta me, and I've always been very careful about CTC since that night. I've got no reason whatever to store combustibles close to either of my woodstoves...in fact, I've got every reason not to. Rick
  6. Hearth Mistress

    Hearth Mistress Minister of Fire

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    I just don't understand why anyone would question this. If it can catch on fire, don't leave it near the stove, it's a no brainer. I don't need an IR gun to tell me what the temperature is, when my stove is at full blast for awhile, I run my hand around the things closest (but not necessarily right near) my stove. Anything warmer than "right out of the dryer" gets moved. I love my stove and my home and just don't want to chance losing either, period. You don't need a scientist to prove theories or explain combustion, just use commom sense ;)
  7. wkpoor

    wkpoor Minister of Fire

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    A buddy of mine said "well what about roof sheeting boards under a black roof in the hot summer sun". Guarantee they are over the temp you guys say should ignite. I've got 5000bdft of lumber stored under a dark green metal roof on racks. Top boards are nearly in contact with the roof. 10yrs now no fire. Just saying there has to be more to the story. Not saying it doesn't happen just whens the last time you heard of a house burning down cause the roof got too hot from the sun.
  8. Cross Cut Saw

    Cross Cut Saw Feeling the Heat

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    I think a lot of times it's not just wood spontaneously igniting next to the stove but rather things like small embers that fly out when you stir the coals and land on a piece of folded paper and just smolder for a few hours before POOF.

    I was burning some wood earlier in the season that shot embers all over the place when I stirred the coals. Had I had a paper bag full of paper sitting next to the stove and even one of those embers bounces in there I'm sure it could have caught fire, so I think it has a lot to do with other sources of ignition than spontaneous combustion.
  9. wkpoor

    wkpoor Minister of Fire

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    I guess we could approach this in a different way. Anyone ever hear of wooden handles catching fire on a wood stove.
  10. Cross Cut Saw

    Cross Cut Saw Feeling the Heat

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    rideau and ditchrider like this.
  11. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Look guys, the chit can happen. When we moved from the house in Texas in 1985 I went up in the attic to move down junk we had stored up there. While I was up there I crawled over to where the chimney came up through the ceiling to the roof. The 2X8 ceiling joists on all sides of the chimney pipe were charred. I laid down on the joists because my knees got weak thinking about how many nights I went to bed with the stove kicking.

    That install was done by "pros". All after that have been done by me.
    ScotO and Trilifter7 like this.
  12. KaptJaq

    KaptJaq Minister of Fire

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    Friend lost his workshop and all of his tools to a load a ceder shakes that were delivered and stacked too close to the stove. He told them to stack along the wall and they went a couple of rows deep instead of high. He did not even think to check how they had been stacked. Locked up and went home. They caught and carried the fire to the wall.

    If it can burn it is not near the stove.

    KaptJaq
    ScotO likes this.
  13. stoveguy2esw

    stoveguy2esw Minister of Fire

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    im assuming it has to do with surface area and dissipation, ambient air is moving around the handle , its rounded it is able to depart heat gained into the surrounding air. surface areas in a wall are different somehow, maybe being flat , maybe being only able to dissipate heat in one direction while allowing absorption in the inner surfaces behind the wall. anyway, these calculations were made by people much better educated than i was, they really should be adhered to rather than ignored. there are plenty of examples where fires have happened so we should learn from these examples and take proper precautions, the house that doesn't burn down can be yours.
    firefighterjake likes this.
  14. fox9988

    fox9988 Minister of Fire

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    No. I have seen a lot of them blackened on the side that faces the stove. I don't know how they survive the heat.
  15. FyreBug

    FyreBug Minister of Fire

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    Wooden handle on stoves may have less to do with cosmetics than how a particular lab or lab tech decides to interpret the UL safety test. There's some room for interpretation there and some tech choose to a bit 'tight' in how they view it.

    For some reason they consider a coil handle 'not valid' as part of the handle and put the temp sensor on the handle shaft itself. Obviously the safety test will fail since no one opens the door bare handed on the shaft itself since they will have severe burns. But for some reasons some tech will refuse to put the sensor on the coil itself.

    However, in the views of some techs a wood handle is perfectly acceptable and will then put the sensor on the wood part and the safety test is then passed.

    Some MFG's get fed up with all the variances and interpretations between labs and techs and if they can afford it build their own labs.

    As to why a wood handle is acceptable for clearances it's a good question and i'll ask our lab guys.
  16. Seasoned Oak

    Seasoned Oak Minister of Fire

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    I think a lot of those house fires are caused by people placing combustibles too close or even ON the stove. Visitors ,children and others not used to having a wood stove in their living room. Im sure Mfgs take into consideration that stroves do overheat from time to time and thats when that clearance is most important.
  17. wkpoor

    wkpoor Minister of Fire

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    When I first moved out I lived in a story and a half duplex. My room was upstairs and the design was such that most of the wall area was actually roof line. No insulation and on a hot summer day the temps in the room would easily top 110. The plaster got so hot you couldn't old your hand on it for long. I never really thought about how hot the sheeting boards must have been. The place was built in 36 and as far as I'm aware it and the all the rest of the neighborhood is still standing. According to what I'm told on here it should have burnt down.
  18. Leftyinthewoods

    Leftyinthewoods New Member

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    Let's see if I can put my physics and engineering training to use here, although I'm by no means an expert and don't even own a wood stove yet...

    As I see it, the enemy here is radiant energy, the infrared radiation given off by the stove striking all exposed surfaces. Radiant energy can increase surface temperatures far above the ambient air temperature (think sand or asphalt on a sunny summer day). The ultimate surface temperature is a function of the amount of radiant energy striking the surface and the ability of the surface to shed energy to adjacent matter through conduction and natural convection. To the first part, the closer the surface to the radiant source, the more radiation strikes and the more energy is transferred to the surface. To the second part, the more matter is in contact with the exposed surface molecules, the lower their temperatures. I figure combustion occurs at a molecular level, when a molecule becomes energetic enough to break down into simpler molecules or react with an oxygen molecule, releasing heat into adjacent molecules and escalating the combustion process. With a smooth surface, few molecules are warm/energetic enough to react, and those that are can't impart enough energy on their neighbors to continue the process. On the other hand, something like a dried split presents a very rough surface with many thermally isolated surfaces that can be made to break down and combust. I think size also matters, a large smooth wood surface is likely to crack as it dries, increasing the surface area and creating areas with poor thermal conduction to the rest of the wood. Wood species matters too I bet, a dense wood should be less combustible due to the tighter packing of its molecules and resultant improved conduction. A small smooth surface of dense wood (like a door handle) will be better at conducting the heat away from the surface to non-exposed surfaces, reducing surface temps.

    The conditions under a hot roof are very different. First, the air is humid, preventing extreme drying of the combustibles. Perhaps more importantly, the combustibles are shielded from the source of radiant heat (the sun), and no matter how rough the surface, no portion can reach temperatures sufficient for combustion. I don't think it makes sense to apply the 180 F over ambient rule when the surface temperatures aren't the result of direct exposure to radiant energy.

    Hope this helps.

    -Stephen
  19. wishlist

    wishlist Minister of Fire

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    What he said. ^ :eek:
  20. HotCoals

    HotCoals Minister of Fire

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    Now I wonder if the stoves with the farthest clearance requirements may also have the best heat transfer.
    But yeah..keep crap away from your stoves!
  21. tfdchief

    tfdchief Minister of Fire

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    BB,
    I thought it was 100 degrees plus ambient.
    HollowHill likes this.
  22. Lumber-Jack

    Lumber-Jack Minister of Fire

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    I've never seen them on fire before, but I had an old Blaze King with wooden handles, they both eventually charred black and fell off.
    There is no doubt that the clearances stove manufacturer's recommend exceed absolute minimum clearances you could get away with, but obviously they recommend farther clearances to try and build in a safety buffer in case several other things go wrong. For instance, the handles on my Blaze King probably burned off because I exceeded the manufacture's max stove temperature too many times, and yet the walls around the stove didn't catch fire and burn the house down. Likely the stove manufacturer's knew that users like me would probably exceed their recommended max stove temp, and that the handles might eventually char and fall off, but they obviously knew that wouldn't be a life threatening situation, no worse really then a hot coal rolling out the front of the stove, providing I maintained proper clearances around the stove.
    Point is, the fact that the handles charred from the excessive heat, but the walls didn't, shows that those extra clearances actually worked.
    Dune likes this.
  23. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    I will check tomorrow but I think UL uses 180 over. Pretty much where you can't hold your hand on it for long.

    Would't be the first time I was wrong this week.
  24. begreen

    begreen Mooderator Staff Member

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    I think it is around 170F as the top temp, or 100F over ambient. The problem with using ambient temp as a baseline is that some folks here call 90F ambient :eek:! I have seen some shots of water pipes carrying 180F hot water that charred wood over time. That startled me. I didn't think it was possible.

    http://www.doctorfire.com/low_temp_wood1.pdf
  25. soupy1957

    soupy1957 Minister of Fire

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    I seem to recall a discussion about this topic b4, and I believe that someone said that spontaneous combustion takes place at 450 degrees. I seriously doubt any of your household items will get that hot from normal burn situations.

    That said, the other side of this discussion would be how careful you are to keep combustible materials away from spark potential, when opening the firebox.

    -soupy1957

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