Compost piles can and have spontaneously combusted many times over the years I have been gardening. The ignition temperature of paper has nothing to do with the ignition temperature of compost. That compost piles can spontaneously combust is why both the National Fire Protection Association and the US OSHA have writen guidelines on proper storing of these combustibles to prevent that.
There have been several stories in the news of late about manure piles, coal piles, and compost piles self igniting.

I'm also interested in the answer. I build 4'x4' compost piles of fish scrap and ramial wood chips, and routinely have them heat up above 160F.
While it's evident that large piles of wood chips, coal dust, oily rags and similar items have spontaneously combusted, I do wonder how that would extrapolate to a 4'x4'x4' compost pile, particularly if it's kept moist to allow optimal aerobic combustion.
I've decided to watch my piles while they're hot (>160F) keep them moist, and leave them be. I'd love to know what the actual risk of combustion is, and how to tell the pile is getting dangerously close to spontaneously combusting. My instinct tells me it's not a significant danger.

I did a google search on
spontaneous combustion hay
thinking that hay is a prime example of something that you've got to worry about combusting (chiefly if it has been baled wet, if I understand it all right). Got tons of articles, many on official-sounding websites. Not sure if any of those sites would talk through the parameters of when to worry and when not to worry. Wikipedia also has an article (linked below).

One important element for spontaneous combustion is that the conditions not permit heat to escape well. Often, here on GardenWeb, folks say that 4x4x4 is really the smallest you'd want a pile to be, if getting a good hot pile is your goal. And I think folks who say that are thinking of temps well below combustion. I agree with josko that spontaneous combustion in a 4x4x4 pile isn't a significant danger; with the materials most of us compost, I think radiation and convection would be sufficient to move enough heat out of the pile to keep the temps well below the danger zone. Now, if you're composting linseed-soaked cotton rags, all bets are off (my sense on those is that you can get spontaneous combustion with a very small volume of linseed-soaked cotton rag!).

Lloyd, you sometimes make very large piles, right? Not just the fantastic cinderblock-bin piles you show us, but also long windrows? (Or am I mixed up and that's someone else?) I'm curious about the highest temps you've seen in your largest piles, if you've ever measured them.

Here is a link that might be useful: Wikipedia on spontaneous combustion

The cinderblock compost bins would be Jon Hughes, but I understand Lloyd has a fantastic setup, too =:)

I was just reading this article yesterday. Check it out.

Here is a link that might be useful: Composting flower fire

The original poster wondered if a compost pile could self-ignite, given that microbes present would die before the critical temperature was reached. But compost piles do catch fire now & then, usually large ones that contain lots of manure, as well as hay or straw. The implication is that spontaneous ignition does not require living microbes-it requires oxygen, and a concentrated supply of fuel, plus an insulating layer to retain heat. I'm not sure how the fuel supply gets concentrated in a compost pile, but it must be happening.

I think the Lloyd you're thinking of is Pt03 from Manitoba.

Feel free, anyone, to correct me if I'm wrong =:)

My compost never gets hot enough to worry.

Remind me to keep my pile under the size of a small mountain and keep out the sodium. On a more serious note I do keep the pile isolated from buildings etc. But that is a good yard practice for any dry piled matter.

Curt

I was going to stay out of this one....

First, to answer the OP, yes organics can spontaneously ignite.

Jon in Oregon is the dude with the impressive cinderblock bins.

If you can ignore my sniping in this thread, there are two links I posted towards the end that help me to understand a bit about compost fires. Certainly, there are many more threads and links available but those two links are good 'nuff for moi.

I closely monitor the larger piles/windrows for temp and moisture during the thermophilic phase, never met the conditions for spontaneous combustion. 165 is fairly common although I prefer it to be not quite that hot. Even the wire bin got to 162ish but it had cardboard around it and a paper bag cover so convection wasn't as free as it is in the windrows.

Lloyd

If the pile is large enough and heat can build up, reactions between the air, moisture, and any carbonaceous materials can start. Unlike bacterial reactions, chemical reactions go FASTER as they get hotter.

It's often seen in hay barns and piles of wood chips.

My take on that composting "flower pot" fire is that someone dropped a cigarette or smoldering match into the pot, and the plastic of the pot was what did most of the damage, because there's no way a flowerpot that small is going to get hot enough to catch fire.

In these days of everything being pictured and posted on the net, SOMEONE should come up with a picture of a combusting compost....but then we would think it was photoshoped.

dottyinduncan, I'll go even further: how about a competition to see who here (if anyone) can deliberately get a pile to spontaneously combust? Looks like the blueprint should be pretty easy-- find out all the anti-combustion rules and break'em.

The average home sized pile is not large enough to spontaneously combust.

My uncle lost a barn to hay spontaneously combusting, so it does happen.

Hay must be cut, lay where it falls for 3 days to dry then sweep into wind rows to bale. I have never seen a barn burn. My father & future father-in-law would cut hay on half's. I have seen them let hay rot in the field, because they would not put it up a day early to keep it dry from the rain.
Today I would rake it up for compost, but they let new grass grow though it & continue cutting new hay.
I saw manure & wheat straw smoke, that had been dumped near a stable. The stable hand(mucker)said that it would smoke for a few days, if the composter did not come to get it.

Since the ideal way of producing the finished product is to turn the pile over, admit more oxygen and thus speed up decomposition, then the question is moot.
The average home composting pile cannot possibly heat up sufficiently to cause any kind of spontaneous combustion....even if it could....which it cant.

Coal isn't compost.
Its a well known fact that when large areas of what was once garbage dumps heat up, they can, in fact, begin to burn. Such burning can last for days, weeks, months...and local fire departments have had to pour thousands of gallons of water into such grounds. Sometimes, chimneys can be put down...and the gas from the composting ignited on purpose. That is a way to prevent such gas from erupting in a more unmanageable way and possibly exploding.
But that is a rare occurrence....very rare.

Certain materials do heat up and given certain circumstances can self-ignite. But a compost pile.....not a chance!

hmmmm...I had forgotten about my challenge to the senior about finding a quote...never did heve to buy him and his family that steak dinner. ;-)

Lloyd

HEY ! ! !
I can make stuff up......
Can I get in on that Steak Deal and would you mind taking one of those Gargantuan Coffee Sacks and Load me up with some of your awesome compost ;-)

Yeah Babyyyyy ;-)

That's what I'm talking about ! !

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So much back and forth on this. Bet someone could weasel some grant money out of the government to "research" this.
Can you say earmark?

Well.... My Opinion ;-)
There is absolutely NO-WAY a backyard compost pile could ever self combust. I make finished compost in about a month. That is from scratch, it gets hotter than Egypt, but it has never came close to igniting....
These pics are sequential...

February 10 filled Cinderblock cavities with concrete.

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March 20 Found some leaves now I need some greens ;-)

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April 6 I found some greens... YeeHaw ;-)

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April 7 more greens ;-)

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April 14

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April 22nd

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April 30th

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The compost system with the blocks is great.
When I moved into my present home I had several pine trees cut down and chopped up. this included the wood and needles. This was done in the middle of November. The temps would be 45 to 50 day and 25 to 30 at night. The ground up trees were piled about 40 x 15 x 6 foot high.I did not add anything to it. After 4 or 5 days it was steaming like the compost in the photos abve.I reached my arm in and it was too hot to leave it there.Do I think it would spontaniously combust.... no.
The hay thing has been tossed around for years.I worked on a Dairy farm when I was a lot of years younger.My guess is that a couple of things caused hay fires. Birds carrying lit cigerettes into the barn and broken windows near the hay loft that acted as a magnifying glass concentrating suns rays. I know damp hay can get very hot and i cant say there could absolutely not be totally spontaneous ignition but I doubt it. Now how about the idea that the composting process has created methane gas that under certain conditions could ignite?
By the way I did try the trash container and light bulb composter in my garage/ wood shop. Right now the compost is about 91 degrees and the ambient temp is about 20 degrees. I am using a 40 watt bulb.The container is a 30 gallon trash can that i insulated .I am going to put the light bulb on a timer so it will be even more efficient. Happy composting Johnny

There is absolutely NO-WAY a backyard compost pile could ever self combust.

I realize the above is just an opinion however it CAN happen - enough so that precautions are published on how to avoid such an occurrence. And there have been numerous scientific studies on just this topic, so I'm not sure if it is necessary to encourage too many more via government grants :-)) To be realistic, it doesn't happen very often in a backyard compost pile but only because the conditions necessary for spontaneous combustion have not been satisfied:

Recipe for spontaneous combustion in compost --
Key conditions:
�biological activity
�relatively dry materials
�dry pocket
�large, well-insulated piles
�limited air flow
�time for temperature to build up (150-200F optimum for conbustion)
Other factors:
�non-uniform mix of materials
�poor moisture distribution
�difficult to know temperature throughout a pile
�lapse or oversight in monitoring

It was not a compost pile, but I am personally aware of organic matter causing a house fire. It happened to clients of mine who stored an opened bag of alfalfa meal on their front porch. The top of the bag was folded down to limit the amount of air but sufficiently loose to allow moisture to penetrate. The combination of moisture encouraging the biological activity in the decomposing meal to heat up sufficiently to combust combined with a small but adequate source of oxygen to fuel the combustion resulted in a total structural fire.

And dotty, if you do a Google Image search you should be able to turn up a couple of decent photos of a combusting compost pile. In fact, the first one that turns up under "compost fires" is of my own local commercial compost facility burning last summer. True, most of the photos are of large commercial operations undergoing combustion, but not sure too many home composters have the presence of mind to photo theirs going up in flames.......too busy attempting to put them out!! :-)

This is off topic, but Jon Huges is that a Scion xb? How did you add a towing hookup? I have a Scion xa and have been hauling leaves and mulch in containers and I'm sick of the mess after each time, how did you get it attached?Sorry for interupting everyone.

Hey Poaky,
I used that thing to haul everything and more, they are a factory approved item, go to any hitch shop and ask them to put one on....about 150 00

This is my friend Elmer, we are going to fly down the Rogue River Yee Haw ;-)

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I willcheck out and see if I can get a hitch, what kind of cart is it?

I saw your name on a survey game that you won Jon Hughes! I came back on here to make sure it was your name and Grants pass Or. So people do really win something! I Don't mean to freak you out I was taking the survey and recognized the name in the article, and the Grants pass on the scion xb.I just thought that was pretty wild to see you there!

This is a video of a recent compost (possible) combustion in my area. They said it could have been set intentionally (which would not surprise me, especially due to the area). It lasted for a couple days. It is obviously a very large amount, but someone said they wanted to see pictures :)

Here is a link that might be useful: Chino Compost Fire

Hi Poaky,
1. What kind of cart ??? What are you referring too ???
2. Yeah, That was me,it is fun to win stuff ;-)

KissinTazzy: There have been some very large Compost burns, but what most people have never seen was a "backyard" compost pile burn.

Whilst the Chino fire video is interesting, it was stated that, due to the multiple ignition points, it is more than likely not spontaneous combustion.

Lloyd

The cart that is hooked to the scion xb. It looks about 6 ft. I guess that it doesn't matter what kind of cart or trailer it is, when I look for one for my XA I'll ( car) I'll surely find one. I'm just glad to see that a cart for hauling stuff is available for the scion, because I could use a hauling cart.

Hi Poaky,
Yeah ,I was just thinking of different terminology, sorry, my misunderstanding...
I always call them trailers, what I would call a cart would be a something similar to a wagon.
Anyway, any small trailer will be fine.

Friends of mine in California just had their compost combust. It burned down their house.

Holy cripes!!1!

Dayum. Barns burned up and it wasn't a bird carrying a flippin cigarette. Sheesh. It got damned hot from the sun and there wasn't enough air to keep it cooled off. Every time it happened the hay was rather old and had been in storage many years. From this warning we were certain to remove older bales of hay from the barn. Other than that I have no friggin' idea but it happens .. just is rare.

FYI, You can see plenty of images of industrial sized piles by Googling "compost fire." I also Googled "backyard compost fire" and came across at least one incident in which a plastic bin had burned up. Certainly very rare though.

Spontaneous combustion is a strange thing. I suspect it begins on a microscopic level. It only takes a tiny volume of material to start feeding on itself to get it started. An itty bitty spot in the maelstrom where the conditions are just right for a few minutes. You couldn't stick a thermometer in and measure temperatures capable of combustion though.

Yeah, I know a guy who caught his entire backyard on fire when he was out of town and that fire dept spent 3 days trying to put it out. Zeke was always a bit of an Altadena legend, but having a cemetery next door to his giant, smoking compost mountain and the LA Times playing up the juxtaposition every day the fire went on made him a legend. KQED eventually did a documentary about him, "Zeke the Sheik and The Ladder of Matter."

Here is a link that might be useful: Zeke the Sheik and The Ladder of Matter

Thanks for the link, dicot. I remember documentaries about people combusting. They neither proved it or disproved it but left it as "freaky".