Spontaneous Combustion in Soil

anna_in_quebec(z4 QC)November 27, 2006

Last night I saw a news clip that featured a local couple that experienced this: a pot of soil they had in their basement had spontaneously combusted and caused a small fire that could have destroyed their home. The lady warned to never keep potting soil in the house - I always do, and have for years. Has anyone experienced this? How likely is it to happen? I have never heard of this in my life!

Thanks,

Anna

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maggiemae_2006

Very unlikely, at my compost facility we had to watch for fire constantly but we had windrows of organic matter 10-12 feet high. You have a anaerobic process and some way for the heat to build up without a way to escape which will happen if there is a heat sink like a piece of metal in the pile. Having this type of situation in a small container will happen about 1 in 500,000 or more. A pile of leaves in a bag or up against a concrete wall or basement floor might create the proper conditions where there is enough moisture in the middle for the composting to keep working and the outside dries out, very hot in the center and dry and very combustible outside.

I wouldn't worry period, but I don't worry about much.

    Bookmark   November 27, 2006 at 10:17AM
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paulns(NS zone 6a)

Anna, we've heard about this happening in NS twice in the past two weeks. The first was a report about a bag of potting soil combusting in somebody's basement, then another lady called in saying the same had happened to her. It's very hard to believe but who am I to contradict them or the fire departments that responded. Maybe it's a problem with particular batches of potting soil? That should be investigated.

    Bookmark   November 27, 2006 at 10:49AM
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bpgreen(5UT)

I had never heard of this happening, but I googled spontaneous combustion potting soil, and apparently it can happen with potting soil stored indoors under certain conditions. A related danger is that people don't realize that potting soil is flammable. They think that since it's dirt, it'll make a good ashtray, and a smoldering ember will ignite the organic matter in the potting soil.

    Bookmark   November 27, 2006 at 10:55AM
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maggiemae_2006

Potting soil is almost never dirt! The 2 main ingredients are pine fines and sphagnum and sometimes a combination of both. There is another product called core which is cocconut shell fibre which is actually quite good as indoor potting "media", a much better word for potting mixes, but a bit more expensive.
Core might be more flamable, don't know, so knowing what the ingredients of said "potting soil" is would help.

Remember potting soil is NOT soil or dirt, rather a combination of things better described as potting media.

    Bookmark   November 27, 2006 at 2:05PM
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hoorayfororganic

Coco Coir, rather than Core

    Bookmark   November 27, 2006 at 9:19PM
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paulns(NS zone 6a)

Typical ingredients of potting mix we find here, like Pro-Mix, are: Sphagnum peat moss, perlite, vermiculite, possibly nutrients, possibly limestone. The surprising thing (to me anyway) about the fires is the relatively small amounts of potting mix involved.

    Bookmark   November 27, 2006 at 10:44PM
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Kimmsr(4a/5b-MI)

For potting soil to spontaneously combust certain conditions need to be present, the right material and just enough moisture. Generally potting soils do not have moisture in the bags, so the homeowner must have added some to that potting soil. So with just enough moisture in a closed bag anaerobic digestion starts and generates enough heat to cause the product to combust. The same thing can happen with slightly damp wool, cotton, flax (linen), or hemp clothing, or any other natural fiber piled up some.

    Bookmark   November 28, 2006 at 7:32AM
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vance8b

I question the "spontaneously combusted" part of the event. Any spark from any source could lead to this "spontaneous" combustion. I find it more likely that some outside source of ignition entered the dry bag of potting soil. I live in Florida, so I have no idea what types of appliences people have in their basement, but any thing with a plug or pilot light is suspect.
When ever I weld in the garage, I refuse to leave the house for like a day, just to assure myself that a stray spark didn't make it into a flammable nook or cranny, and is smoldering slowly, waiting for the right time to flare up. A imagine fire could start hours after suck a spark under the right conditions.

    Bookmark   November 28, 2006 at 9:31AM
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pablo_nh(z4/5 NH)

Agree with Vance. I also think it's less likely that it was heat from composting in just a bag or pot of soil. A more likely scenario is that the potting mix evolved a flamable gas (methane etc.) which was ignited at a distance in a still basement (heater ignitor, etc.).

Still air in a basement is a good place for a vapor to creep across the floor, and a heater sucks air in to support fuel combustion.

    Bookmark   November 28, 2006 at 9:44AM
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hoorayfororganic

The only way I could see it combusting spontaneously is a very dry soil mix and an electrostatic spark. That happens in large grain holders, I thought

    Bookmark   November 28, 2006 at 9:57AM
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gardengal48

I personally know of such a case of "spontaneous" combustion - in fact, I was recently called in to help design their new landscape after the fire that destroyed their home and much of the existing landscape. The culprit was a bag of alfalfa meal, opened and sitting on a covered porch. Moisture entered the bag, the process of decomposition began and sufficient heat was generated to create combustion. Between the OM itself and the paper-based covering of the product, this was enough to ignite wood siding and the rest is history. Confirmed by the fire inspector.

So yes, it can and does happen - may not be the most common phenomenon, but enough to warrant some concerns. Anything that contains unfully decomposed organic matter and suspect moisture is at risk, specially in a restricted environment.

    Bookmark   November 28, 2006 at 9:57AM
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bpgreen(5UT)

From what I read, it does occur from sparks and sources of ignition (especially when people think it would make a good ashtray).

One source I found was in Colorado, and they pointed out that because of the moisture needed for the potting soil to build up enough heat to spontaneuosly combust, it happens less often in Colorado than in more humid climates. If most of the fires were due to sparks landing in dry material, I would expect Colorado to have more problems, not fewer.

    Bookmark   November 28, 2006 at 10:19AM
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paulns(NS zone 6a)

Potting mixes are often pre-moistened.
Here's one of the articles turned up by a google search of potting+soil+fire

Here is a link that might be useful: pei fire

    Bookmark   November 28, 2006 at 10:49AM
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anna_in_quebec(z4 QC)

PaulNS - that is exactly the story I had seen on the news - and what prompted my question, evoking many interesting responses. Thanks everyone.

Ann

    Bookmark   November 28, 2006 at 2:08PM
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maggiemae_2006

If a potting mix does not have moisture naturally then moisture is added unless you are dealing with some specialized mix.

    Bookmark   November 28, 2006 at 2:35PM
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Kimmsr(4a/5b-MI)

Spontaneous Combustion occurs without any outside source of ignition. Any organic material could, potentially during the digestions process, develop sufficent heat to combust spontaneously.

Here is a link that might be useful: Spontaneous conbustion

    Bookmark   November 28, 2006 at 4:09PM
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bpgreen(5UT)

Maggie, if that was directed at my most recent post, I wasn't clear in what I was saying. The reason the potting soil is dry in Colorado is that, although it started out moist, it dried out after the bag was open because of the dry air. I should have been more clear.

    Bookmark   November 28, 2006 at 4:09PM
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maggiemae_2006

bpgreen, I produced and bagged potting mix and other soils and mulch in the millions of bags. I only say what we did which was similar to many other baggers of organic matter. It is very difficult to bag dry material, if it was dry we added water.

    Bookmark   November 28, 2006 at 4:31PM
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hoorayfororganic

i dont see how compost piles, which reach what, 170F, can lead to the temp of combustion (which is what, 400-600F?)

    Bookmark   November 28, 2006 at 4:32PM
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maggiemae_2006

Hooray, search the web there are plenty of detailed explainations.

I apologize in advance of anyone is offended by my tone.

    Bookmark   November 28, 2006 at 5:15PM
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jeannie7

IMPOSSIBLE.....that would be a fairy tale since combustion can only take place when the material itself lends itself to take fire. A drying liquid such as linseed oil is usually a good example when it is soaking in a cloth that is allowed to sit in a crumpled state which the air is excluded. Soaking the cloth in water and laying it out flat then defeats any hint of combustion.

There is hardly enough heat in a compost pile to warn off a mouse from entering....how is that to ever start combustion.

    Bookmark   November 29, 2006 at 5:57PM
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bpgreen(5UT)

Compost piles have been known to generate enough heat to combust. That would be very unlikely to happen in a small pile that somebody would have at home. There was a thread here a year or two ago about a large commercial pile that started burning, and if I remember correctly, there were pictures along with it.

The original topic, though, wasn't about compost piles catching fire, but potting soil. When I first read the post here, I thought it was likely an urban legend, but I googled it and found some credible articles about it.

    Bookmark   November 29, 2006 at 6:29PM
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maggiemae_2006

I had 500 semi loads of mulch stored in an underground quarry. I had an arson fire underground which the fire dept would not fight. It burned for 6 months.

    Bookmark   November 29, 2006 at 6:39PM
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bpgreen(5UT)

Why wouldn't the fire department fight it? Was it too dangerous because it was in a confined space?

It's awful that somebody would do something like that. I hope you had insurance coverage for it.

    Bookmark   November 29, 2006 at 8:05PM
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maggiemae_2006

This was in an underground quarry large enough to run train tracks in and we drove semi's in to load and unload. They were afraid of the fumes in closed quarters, the owner of the quarry told the fire dept that we had all types of dangerous chemicals stored in the quarry.
To the insurance question, 500 semi loads was worth about 1/2 million. I learned a new insurance term called co-insurance, which you should know and understand if you are in business. Bottom line is I got $8,000 and the quarry sued me and got a million.

    Bookmark   November 29, 2006 at 8:15PM
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Kimmsr(4a/5b-MI)

Many years ago when I was in High School, the cotton rags soaked in linsead oil that the wood shop students used had to be put in a closed container and put outside the school at night because of the potential for spontaneous combustion. Many woodworking shops have burned down because that simple precaution was not taken. People that do not believe that this occurs have not taken the time to learn material they should be familiar with, this happens far more often than you hear about and is really so common that it is not news unless you have a very large pile of manure or someone dies in the fire.
Give any form of organic matter the right conditions and it will ignite without an outside ignition source.

    Bookmark   November 30, 2006 at 8:21AM
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jeannie7

Maggiemae, an underground fire is one of those happenings that one cannot be sure to ever extinguish...so they usually, if the area is not in any direct danger, they let it burn.

It is a very common occurrence that community dumps....often will have the trash build up heat....and develop methane from the decomposition of such a large source. Usually they try to chimney away such gas by opening a hole and placing a form of chimney there.
Sometimes, the chimney is not sufficient....and fires do result. To ever hope to put sufficient water down there would involve such amounts that possibly the community wouldn't be able to generate. It may also involve drawing such amounts from nearby wells---which also can affect community wells from which water is drawn for community use.

So....like many fires that involve potential problems afterwards if the fire was put out...they let them burn.

And six months burning....that's a small fire. We had one up here in a Toronto suburb...a former dump location...it was allowed to burn for 3 years.
This is a very good example of why people should not ever consider burning out a rodent....skunk, racoon...etc...
or burn out a stump that has its roots going deep underground. Such fire can last for a very long time....and how would anyone really know how it might show up someplace you wouldn't want it to.

    Bookmark   November 30, 2006 at 6:48PM
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maggiemae_2006

"And six months burning....that's a small fire."

Guess that is true by comparison but it was my life's work including my house which was on the loan.

I apologize in advance if anyone is offended by my tone.

    Bookmark   November 30, 2006 at 7:22PM
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shrubs_n_bulbs(z8/9 UK)

A small pot of soil set on fire? Somebody put their cigarette out in it, or some other spark set it alight. That is not spontaneous combustion.

Spontaneous combustion of compost is relatively well-documented but not widely appreciated. It is caused by a combination of high temperatures generated by the composting and a flammable mixture of organic vapours, also caused by the composting, which can ignite at those temperatures, then setting fire to the solid organic material. It is very likely that the majority of compost fires are actually started by an external spark or flame but the proportion is hard to establish.

    Bookmark   December 3, 2006 at 9:18AM
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maggiemae_2006

Shrubs, compost fire is also caused by the heat of composting which then cannot escape and gets hotter and hotter finally reaching the point where combustion occurs.

    Bookmark   December 3, 2006 at 1:49PM
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heptacodium

I had a neighbor lose his farm after the hay in his loft caught fire...destroyed the barn, his entire milking herd, much of his young stock. The cause was listed as spontaneous combustion, both by the fire marshall and insurance. Somehow, there was just enough moisture in his hay to smolder and smolder and smolder and smolder and eventually ignite.

I believe it was in Missouri last year or so a large pile of manure burned for months and months. Yummy. I'll leave it to others to locate this one on the internet.

I've yet to have a soil mix catch a flame, nor is it one I have heard through the grapvine, although I certainly believe it could happen. All it takes is the right set of circumstances.

    Bookmark   December 6, 2006 at 7:41AM
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