How Can Compost Piles Catch Fire? How To Prevent It

How Can Compost Piles Catch Fire? How To Prevent It

Compost can catch fire, but it is less likely to happen in small piles. Composting creates high temperatures, and for it to catch fire, it is because of spontaneous combustion. It is much more likely to happen in larger industrial compost piles.

Although it is less likely to happen if you are composting in your back yard, it’s still possible. For compost to catch fire, it needs to have certain requirements, and there are ways that you can prevent it from happening. How compost can catch fire and how you can prevent it will both be discussed in this article.

For a fire to start and be self-sustaining, it needs to have all three of the fire triangle: HEAT, FUEL, and OXYGEN. Composting creates high temperatures that are aided by the sun (HEAT), it is packed full of decomposing waste like dry grass, etc (FUEL), and it is done outside surrounded by the air (OXYGEN).

Not properly maintaining your compost pile dramatically increases the chances of spontaneous combustion. Keep this and the fire triangle both in mind, because it will make the rest of this article much easier to understand.

If you are here to quickly read how to prevent your compost pile from catching fire, I will explain this first, so you can digest the information and move on. But if you are here for a more in-depth read on why it can catch fire, then carry on reading.

How to prevent a compost pile from catching fire

  1. Don’t build it up too high! If you have a lot of materials that you want to compost, separate them into different piles. This is also a good idea because you will have multiple piles at different stages of the composting process.
  2. Don’t add too many greens! Keep a nice balance within your pile and avoid adding too much green waste, in comparison to brown waste. Green waste is things like fresh lawn clippings, fruit, and vegetable waste, etc. Brown waste is things like dead leaves, twigs, and dry grass, etc.
  3. Don’t allow it to get too dry! Whenever you are adding a fresh layer of waste to the pile, add a bit of water to it, to keep it nice and damp. You don’t need to add too much water, because this is counter-productive and the materials will struggle to break down.
  4. Keep it aerated! Turn your pile weekly to introduce air in the middle and mix it up. Not only will this prevent it from catching fire, but it will also ensure that everything is composting properly and faster.
  5. Don’t allow it to get too hot! If you follow steps 1-4, you will be fine. But you can also monitor the temperature with a thermometer, to be sure that the pile is not getting excessively hot. Monitoring how hot your pile is, is more important in the height of the summer.
  6. Never leave your pile untouched for a long time! Compost that has been left untouched for a long time is the main reason why they catch fire. Never allow this to happen with yours, and follow steps 1-5 with every pile you start.

Now you know how to prevent it from happening, let’s look into more detail on how exactly a compost pile can catch fire.

How can a compost pile catch fire?

  1. The compost pile is too high. If it’s too high, it makes it much more difficult to manage, so it should not be higher than 12 feet. That said, I would rather have two 6 foot, or three 4 foot high, rather than one 12 foot pile. When it’s too large, you can’t be sure that it is not too hot in the middle, it makes it more difficult to keep it aerated and slightly moist.
  2. Too much green waste. Green waste is nitrogen-rich and is essential for a well-balanced compost mix, with carbon-rich browns. But when you have too much of it within the pile, it increases the production of nitrogen gas. This makes the pile much hotter and increases the chances of overheating.
  3. Too many dry materials. This has a higher risk of causing combustion because it is perfect fuel, and if you match it with oxygen and extreme temperatures, the chances of a fire starting are much higher. Having a proper distribution of moisture eliminates this from happening, as well as encouraging organisms to thrive.
  4. Not enough aeration. If you don’t aerate and mix your pile regularly, it doesn’t cool it down enough. The materials underneath stay too hot, and it also slows down the composting process. Also, if you have any pockets within the pile that has no oxygen, and then oxygen makes its way through, it has a higher chance of igniting a fire (when introduced to dry and excessively hot conditions).
  5. The compost is too hot. This increases the chances of combustion and also kills off the organisms within your pile. This is because the excessive temperatures mixed with dry materials and oxygen make it perfect conditions for a fire to start. A good temperature to shoot for is around 150 degrees, but if you notice that it reaches 200 degrees, it is too hot and needs to be cooled down.
  6. It has been left untouched for too long. If you neglect your pile for too long, it is a hazard just waiting to happen. How can you prevent a fire from happening if you don’t do any of the preventatives that are listed above, and you just leave it? You should always monitor it and look out for any of the signs already stated, and be vigilant if you smell anything burning, or notice any smoke.

When you are composting in your back yard, you can easily manage it more efficiently. Preventing your compost from catching fire is eliminated if you follow the steps already stated earlier in this article, and the chances of it happening are slim to none anyway (but still possible). The chances of it happening are much higher for industrial-sized piles.

Why are industrial compost piles more likely to catch fire?

The reason why they are much more likely to catch fire is due to the fact that they are doing it on a much larger scale to you and I. They typically pile up the compost much higher, they tend to leave the piles for longer periods, the materials are often left dry, not aerated often enough and they heat up to more extreme temperatures. These main factors all contribute to the ideal conditions for combustion to take place.


A compost can catch fire if you build it up to high, has too many nitrogen-rich materials, left to get too dry, not enough aeration, the temperatures get too excessive, and when it has been neglected for too long.

You can easily prevent it from happening to yours by keeping your compost pile small and manageable in size, a proper balance of greens and browns (not too many nitrogen-rich greens), never left to get too dry, turned regularly to aerate it, never allowed to get too hot and never left too long.

It is much easier to not allow this to happen when you are composting in your back yard and is more common in industrial-sized piles. Stick to the steps stated in this article, and you will be fine.

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