Huh? My compost get over 150 (below 160) without any problems. It's only 105 here. I doubt the extra air temperature will make a difference.

Heat helps it go poof, but unless it is in a dry area, it just makes it decompose very quickly.

I once put what I thought were mostly cold ashes on the leaf-compost pile on a very, very foggy evening. The type of fog where headlights at forty feet are just dots.

I walked out to the garage and noticed an orange glow in the garden, all the drys leaves on top were burned up and it was the glowing coals of what was left on top of the wet bottom.

Spontaneous combustion of organic materials can, and has happened, although there are those that do not believe it can. Organic material piled up with limited air flow, moisture levels in the 25 to 40 percent range, and internal temperatures in excess of 200 degrees F can cause spontaneous combustion of that compost pile. If a small quantity of cotton rags soaked in Linseed Oil and put in an airless container can spontaneously combust so can any other organic matter, given the right conditions.

Here is a link that might be useful: About Composting

Got that right!

It's so hot, my compost pile is whistling at the dogs. :-p

I guess it would be awful if it caught fire and burned the house down.

Don't worry about it unless your compost gets a lot hotter than the 160 most of us can manage on a good day.

Yes, many various items can spontaneously combust, but a properly maintained, moist compost pile that is within the size recommendations for home composting (1-2 cubic yards) is not one of them.

The bigger the pile, the hotter they can get. If you have a commercial compost facility or a farm with a huge pile the size of a small building, then you would need to be more concerned about combustion. Otherwise it's nothing but an urban legend.

In this thread,
http://forums2.gardenweb.com/forums/load/soil/msg0900524023752.html
poster "Zasu" stated in March of this year that friends in CA had their compost catch fire and burn down their house. No details on the size of the pile or whether the combustion was actually spontaneous, though. Someone could have dropped a lit cigarette for all we know.

I think it is rare at the very least for a home compost pile to spontaneously combust. I personally called in a smoldering mountain of mulch once, though, while dropping off yard waste at a public mulch site. Given the conditions I suspect it was spontaneous. The firemen said it had happened before.

I am sure if you keep it well watered it won't explode, but it is something to keep in mind. I keep my bins as far from the house as possible anyway.

Someday you'll have to see how hot freshly chipped branches get. If you chip a bunch of green twigs from a tree, especially in spring, the pile of chipped mulch gets burning hot. Mix in a few dried leaves or the right kind of bark and I can easily believe that it will ignite.

subk3, if about 20 percent of the people living in the USA believe the sun moves around the earth do you really question that there are those that do not believe in spontaneous combustion? I have even found people that do not believe smoking a cigarette while filling thier vehicle with gasoline is dangerous because they have not yet erupted in a ball of fire.

Hahaha. Well said kimmsr.

Hey wait a minute. Are you saying the sun doesn't move around the Earth? :-o

Here's my question:
Does the air temperature impact the temperature of a compost pile? I understand that if it's really cold out it could impact a smaller pile but we're talking excessive heat. If my pile is at 150 and it's 90 degrees out will my pile move to 160 if it hits 100+ degrees? I could see if the outside temp hit 180 or so then there would be a problem but do normal temperatures really cause excessive heat to build up in the compost pile?

Ambient air temp does affect core compost temp, but I don't think its a one to one relationship. My core temp never goes above 160 or 165F regardless of how hot the temp is.

Of course with a high temp of 108F expected, I'm not going to measure the pile today. My 'hot' piles are either in the sprig or the fall, when leaves and fresh grass are available.

PS Of course the earth is flat...

I'm thinking the compost is more affected by the ambient temp when the pile is not heating much or at all and is near the ambient temp (this is assuming summer weather, not cold temps). As you move up the scale, heat from the compost is more responsible for the temp than ambient. At the top end the compost can only go so far regardless of the ambient temp, and I suspect the curve is a lot flatter up there, or as robertz6 said put it, it's not a 1 to 1 relationship.

This scares me! I live in a suburban area and the other day I turned my like and a small amount of steam came out of the center.... Don't wanna burn the whole area down! It's only about 3 foot by 2 foot by 1.5 foot tall!

If even one home is saved by reading this, that is a good thing. Take precautions!

The relative humidity and wind probably affect pile temperatures more than ambient air temperatures.

Lloyd

Nobody here has said they don't believe in spontaneous combustion. Sheesh. If you think I have said that, you need to read a bit more carefully or stop trying to put up a straw man argument.

Various items, organic and not, can certainly combust on their own. Very large compost piles can combust. But no one here has presented an example of a home-sized, maintained compost pile spontaneously igniting, and I have never seen that documented anywhere else, either. The maximum temperature of such a pile is approximately 165F, which is several hundred degrees below the temp needed to ignite damp yard waste materials, so it is physically impossible. Hay stacks, oily rags, bags of fertilizer, piles of debris, gasoline and other random things that are not compost piles are not relevant to a discussion of home compost piles.

A properly maintained compost pile is damp and damp materials just don't ignite that easily. And if a compost pile isn't damp, it won't heat up. A dry compost pile could burn, but it would have to be lit by an outside source because it won't be generating much, if any, heat. That is not what is meant by a properly maintained compost pile.

Just because X and Y are similar doesn't mean X will do everything that Y does.

I tend base my beliefs on relevant proof; it's the scientist in me. Like any good scientist, I am open to changing my mind, but only with a sound reason to do so. I'll gladly believe a home compost pile can spontaneously combust when I read a report of it documented, preferably in a controlled setting and replicable. Sorry, anecdotes or approximations will not do. I prefer to live in a world of science, facts, and reality but plenty of people do not. So don't let me spoil your fun. If you want to change the topic or stubbornly believe in folk tales or your own imagination over facts, feel free.

If you think because there is steam in your compost bin it might catch on fire I don't even know where to begin to address that. Are you also afraid that your cup of coffee might start a fire? Just get a soil thermometer and let me know if your compost ever gets above 165F.

This topic has been discussed repeatedly on this forum. Frankly, in the absence of any new evidence, I don't see any point in going over it all again.

But, who wants to be the first to have their house burn down?

"No documented cases of spontaneous combustion have been reported for compost piles smaller than seven feet. Most reported fires occurring in compost piles are the result of external sources such as matches or the addition of hot ashes. In short, a well maintained compost pile with temperatures less than 150 degrees F will not spontaneously combust."

That is from the link that kimmsr provided, above.

"But, who wants to be the first to have their house burn down?"
I don't compost inside

Well, I'm new so I didn't know and it's been a concern to me. In my logic water boils at like 212 F or whatever so idk was just wondering if that meant anything bad. :)

"A properly maintained compost pile is damp and damp materials just don't ignite that easily."

For what it is worth, hay that has been put up without properly drying out is hay that is more likely to combust. Dampness IS the culprit and a trigger in spontaneous combusting hay. So you might want to think twice becore you comfort yourself that something won't blow simply because it is damp.

Just because some people come here and might only have weenie sized compost piles doesn't mean there aren't some here with bigger piles at home that could use the reminder. *cough* *cough*

karchita - And if a compost pile isn't damp, it won't heat up.

Arrant nonsense. Bull manure. You don't know what you are talking about.

I can chip the green branches from an apple tree, completely dry, pile the chips into a pile, and make compost hotter than anybody here has ever seen.

Stay tuned. I might just do this on Sunday just to prove the point.

Karchita, you don't know what you're talking about.

Green branches are no where near "completely dry".

Moisture is absolutely necessary for the heat generating bacteria. As well as an appropriate C:N ratio and some oxygen. Take any of those parameters away and you will not get sustainable organically generated thermophilic heat.

Karchita's post was very accurate. The only thing she might have also mentioned is that it is dry pockets of material within a larger pile that actually begin the actual combustion. The wet stuff won't catch fire, it is the dry materials nearby that actually begin the ignition.

Lloyd

A 5 gallon pail of linseed oil soaked cotton rags will, if all other conditions are right, spontaneously ignite.
I have been on barn fires that were ignited from improperly cured hay, and have seen a single hay bale reach internal temperatures of 195 degrees F when we tested that in Fire Investigation School. I have also been to structure (house, garage, barn, or other outbuilding) fires that did start from compost piles smaller then those the University of Minnesota people found would ignite. I agree with most of what they wrote, which is one reason I posted that, but they also do not have enough data to make a statement that no "documented" fires started in compost piles smaller than 7 feet.
Moisture levels of 25 to 40 percent, sufficient levels of Nitrogen to feed the bacteria which can cause the internal temperatures to aproach 200 degrees would be enough to cause a compost pile to spontaneously combust. Much the same has been found in woodworking shops with sawdust collectors that have caught fire. Much the same thing has been found in landscape supply yards where wood chips and shredded wood materials are improperly stored until sold and that is why the National Fire Protection Association and the Occupational Health and Safety People have established guidelines for proper storage of such organic materials to prevent this spontaneous combustion.

Lloyd,

It seems like we're talking semantics here. Karchita said "damp". The dictionary defines 'damp' as slightly wet.

I can take un-wetted green branches and make a pile of decomposing organic material that will likely be over 170 degrees in less than 36 hours. Just ramial chipped wood.

Paul

Green tree branches, for what its worth, can have upwards of 55 percent moisture. Just like piles of coal that need constant turning to lower the possibility of spontaneous combustion piles of wood chips shole be constantly turned for the same reason.
"Damp" would be enough moisture to allow enough heat to build up in a pile of organic material to allow spontaneous combustion to occur.

As stated, even chipped up "un-wetted green branches" still contain enough moisture to obtain thermophilic temperatures. One does not have to add water to reach the dampness required. Logically, if there was not enough moisture present, there would be no heat.

Lloyd

Lawdy, I need another coffee to keep up with this thread! Seems we have the whole gamut here: the seasoned intellectuals debating semantics, the grumpy gardener who had too much caffeine already, Henny Penny announcing the sky is falling, and the innocent newcomer who wandered into the chipper shredder. LOL

If you were not home and it caught fire the house could burn down before anyone called the fire department. But, I compost in big plastic bins, so I don't think the fire would spread, due to lack of air available in those bins for a fire. Fires need oxygen.

I was microwaving some vegetation to kill insect eggs and it caught fire. But, it was several tiny little sparks not a big fire.

Everyone please take note: Do not insert your compost pile into the microwave due to the danger of fire. This has been a Public Service Announcement.

:-)

The newest issue of FARM SHOW has an article about how in Europe they use compost bins to heat the house in the winter.

Larger wood chips and not more than fifteen percent pine as more kill the green slime that digests the chips.

Good for up to two years. (Also used for hot water heating.)

I read something in Mother Earth News way back in the 70s about using a huge wood chip pile to preheat water coming into the house. I think they had hot water even when there was snow on top of the pile.

Most farmer & rancher who cut & bale their own hay, know that the green hay can burn a barn to the ground.
You cut the hay, let it lay in the sunny field for 3 days, the windrow it & bale it.
If you bale it too early it can burn. But that is like a tight bound compost pile of ALL greens, that is 12 feet high, 24 feet long & 12 feet wide.
Most of us will not have a problem.

The reason for this heat wave is kimmsr's piles :)
Isn't that how the Midwest fires got started?
Every year we hear about kimmsr's hot piles ;)

As a side note if/when it gets to 180 outside - my compost will provide the cooling effect.

I agree - indoor composting should be banned. Or there goes another for the gene pool.

Lmao I've been reading posts in this forum for 3 days and this is by far the funniest yet! I'm just getting started with composing so my pile was only 140 today. It's in a soil saver bin and has been cooking for a week with one turn of the pile a day or 2 ago. I can't wait until I'm good enough to build some exploding piles! Hahaha.

Shhh, Homeland Security reads this forum. I know because I saw them putting their coffee grounds into a black stealth-bin behind their office. They don't think anyone can see it, but I can, even at night, with my infrared binocs. It's heating up so nicely I had to sneak over there to see if it was going to catch fire. Turns out they have a perfect mix - coffee grounds and shredded paper. I bet they have a lot of shredded paper. :-D

Anyway, I just don't want you to get in trouble for attempting to make Compost of Mass Destruction.

One January day, when the ambient air temperature was minus 5 degrees F, we were called to a fire in a pile of wood chips. We found an extremely hot and blazing fire that required a dozer to spread it out so we could extinguish it since the water we tried pouring on that fire would not get down into the base of the fire. The wind that night was from the north at 30 mph and was fanning the fire in the pile.
If all of the conditions necessary for spontaneous combustion are present the ambient air temperature will not have any affect.

Compost of mass destruction I love it! Lol I'm using a black soilsaver so hopefully they will think I'm one of them Hahaha

That's the way, blend in, and if they ask questions, refer them to Col. Flagg.

Sounds like a doozy there, kimmsr.