Can a pile of fresh wood chips spontaneously combust?

[ning]

My recollection is that paper needs 451°F to spontaneously ignite. I'm not sure for wood, bit it's probably in that vicinity.

To get hot enough, a pile has to have a sufficient amount of nitrogen (sawdust doesn't have much at all - nitrogen is basically from the green stuff) and it can't be very compact, and there needs to be nearly 50% moisture - these are all requirements for the initial composting. Once composting raises the temperature enough (to 70-80 C) chemical processes can take over in some conditions (regardless, composting ceases at these temperatures) and raise it further, but the need the initial conditions.

As far as steaming goes - my 37C lungs emit steam on a 10C day, it's not a good measure of "hot".

 

[rademamj1]

Nitrogen is a stable inert gas, and will never contribute to a fire or spontaneous combustion process. Infact the air we breath is 78% nitrogen. O2 and Methane are explosive when combined.

I used to start paper on fire when I was a kid using a magnifying glass. I seriously doubt I got it any close to 451 degrees F.

 

[KennyG]

Nitrogen is a stable inert gas, and will never contribute to a fire or spontaneous combustion process. Infact the air we breath is 78% nitrogen. O2 and Methane are explosive when combined.

I used to start paper on fire when I was a kid using a magnifying glass. I seriously doubt I got it any close to 451 degrees F.

You probably did, because 451 is close to accurate. Most people don't realize how hot some things are. Did you know that a match is over 1000 degrees F? We don't realize it because the hot part of the flame is so small. Cigarette lighters are several thousand degrees. You could melt steel with a lighter if you could find a way to keep the heat from being conducted away.

 

[ning]

Nitrogen is a stable inert gas, and will never contribute to a fire or spontaneous combustion process. Infact the air we breath is 78% nitrogen. O2 and Methane are explosive when combined.

I used to start paper on fire when I was a kid using a magnifying glass. I seriously doubt I got it any close to 451 degrees F.

The nitrogen is necessary for decomposition which raises the temperature.

Without sufficient nitrogen, you don't get much decomp so the temp stays low.

I have a pile of chips dropped by an arborist (chipdrop) which was oak + pine, wood + leaves/needles; it's a year old now and under 6" it's basically dirt now. I occasionally checked the temperature and it was definitely warm but nothing like ignition temperature (pile was about 6' high, roughly conical and 10' across the base).

 

[ponytug]

Just to clarify @ning's great point, I would point out that it is nitrogen in the form of nitrate/ammonia/nitrite, not the gas that helps speed the decomposition of something like wood chips that are very high in carbon. Oxygen is the prime agent for both for bacterial and fungal decomposition, but also for the creepy crawlies that tunnel through and feed on the bacterial and fungi. That is why commercial composting turns the piles every couple of days to get air in and distribute prime sources of food. Many commercial systems have air blowers in the base to push enough oxygen through.

Fertilizing wood chips with nitrogen fertilizer will accelerate the decomposition as wood chips are very high in carbon, and quite low in available nitrogen, limiting the growth of bacteria and fungi. Nitrogen gas won't do the trick. A pile of would chips solely in pure nitrogen gas would decompose very very slowly, as there would only be anaerobic digestion, which is less complete and at ferments much more slowly than aerobic digestion.

As another example septic tanks are almost always anaerobic, and require pumping every so often, aerobic septic systems digest a much larger fraction of the material (as in ten times the amount), and require pumping much less often. Sand is still sand, and not fermentable... Running an aerobic digestion followed by an anaerobic digestion gets most of the nutrients out of the water, leaving mainly inorganic like phosphate. In some parts of the world, triple tanks (aerobic, anaerobic, and phosphate binding, aka zeolites) are required to limit the ground water contamination.

All the best,

Peter

 

[rademamj1]

Ning was referring to N2 or Nitrogen in the gas phase. Worse yet...if he was referring to nitrogen in Ammonia Nitrates or fertilizer, that's ony 3% Nitrogen by weight....with 45% oxygen and 52% hydrogen. Atmosphere we breathe is 78% Nitrogen 21% oxygen and 1% trace gas...including 0.1% of CO2 the greenhouse gas.

 

[ning]

Ning was referring to N2 or Nitrogen in the gas phase. Worse yet...if he was referring to nitrogen in Ammonia Nitrates or fertilizer, that's ony 3% Nitrogen by weight....with 45% oxygen and 52% hydrogen. Atmosphere we breathe is 78% Nitrogen 21% oxygen and 1% trace gas...including 0.1% of CO2 the greenhouse gas.

I'm glad your omniscience can change my meaning.

I was referring to nitrogen present in some types of organic matter (not gas); this nitrogen is not in significant quantities in basic wood chips but instead is found more in leafy matter.

You're the one who decided to introduce nitrogen as an "inert gas" (it's definitely not an inert gas, thigh it may not significantly contribute to combustion - the presence of NOx in emissions should be an immediate clue to you that it's not inert); I was referring to the non-inert version of nitrogen's presence in compounds that greatly assist composting which can drive temperatures closer to self-ignition.

Why is it "worse" to refer to the nitrogen compounds? They're what makes the composting happen in any reasonable length of time.

 

[Gale Hawkins]

It amazes me how hot horse manure can get in a pile. When dumping it over a steep bank then over time pushing it over the edge it can turn to white ash from the heat but no fire occur.

 

[ning]

It amazes me how hot horse manure can get in a pile. When dumping it over a steep bank then over time pushing it over the edge it can turn to white ash from the heat but no fire occur.

I get a lot of white among the brown in my chip piles after a while but in this case it's fungal/mycorrhizae

 

[Gale Hawkins]

I get a lot of white among the brown in my chip piles after a while but in this case it's fungal/mycorrhizae

Where there's smoke there has to be a little fire they say.