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Can Compost Catch Fire? How To Prevent Compost Fires

Compost is a great way to improve your garden soil and create a sustainable environment by using everyday scraps you get from food and yard clippings you would otherwise throw away. However, there are two major risks associated with compost: spontaneous compost heap combustion and compost fires.

Although it is a rare occurrence, compost can catch fire, and heaps have combusted when the materials reach temperatures between 300°F to 400°F and have very little to no moisture. Poor aeration is also a factor, which is why it is important to tumble your compost intermittently.

The process of creating compost can take several months, and there’s nothing more frustrating or frightening than to watch all of that hard work and dedicated time literally go up in flames. Compost fires are a very real risk when creating this eco-friendly material, which is why we’re going to discuss how this can happen and, more importantly, how you can prevent it.

Can Compost Catch Fire?

Compost is a combination of organic matter like leaves, grass clippings, and kitchen scraps that are mixed together and then allowed to decompose naturally until it becomes a soil-like material.

Because compost is comprised solely of organic material, it is extremely flammable and can catch fire easily, especially when there is minimal to no moisture present.

In addition to the material itself is flammable, the activity of the microorganisms within compost breaking down the organic material removes oxygen from the materials. As a result, a significant amount of heat is emitted, contributing to compost catching fire under the right circumstances.

In fact, studies have shown (source) that enough heat is generated during the process of composting that it could be used as a source of renewable energy, rendering it a valid example of bioenergy.

At What Temperature Does Compost Catch Fire

Although it is expected for compost heaps to create heat that will dry out its organic material, the risk of fire and spontaneous combustion is usually minimal because the heap must reach extreme temperatures to achieve this.

Compost heaps catching fire or spontaneously combusting can only occur when the material within the heap reaches temperatures of at least 300°F to 400°F.

Typically, compost is maintained at temperatures of 150°F to175°F for a short period before cooling to ambient temperatures. Therefore, the heap has to reach temperatures twice as hot as optimal composting temperatures, which is highly unlikely to occur as long as someone is maintaining it properly.

Of course, the heat generated during composting isn’t the only factor at play here. While a majority of spontaneous combustion cases are caused by spontaneous heating, where the slow oxidation of its compounds increases their temperature element without the addition of an external heat source, we can’t disregard external factors completely in this case.

External heat from the sun can also increase the compost’s internal and external temperatures significantly, raising them to dangerous levels where spontaneous combustion can occur when the combustion process alone would not have made this possible.

Can Compost Heaps Combust?

Considering compost itself is incredibly flammable, it’s already one ingredient in a recipe for disaster when considering the possibility of spontaneous combustion.

Although compost heap combustion is rare, it is possible because the organic material is inherently highly combustible, meaning it can catch fire easily under the right conditions, and the process of composting generates heat naturally.

Compost fires can occur when the compost heap gets too hot from a lack of air and moisture, usually caused by improper ventilation. This causes the organic material to dry out, producing heat that may cause it to spontaneously combust.

Fortunately, cases of compost fires and combustion are rare because they are easily avoidable, and we’ll show you how.

Here’s a quick news clip showing a case where a compost pile did combust on its own causing a large fire:

How to Keep Compost from Catching on Fire

Apart from the occasional lightning strike, most compost fires are ultimately caused by human negligence during the composting process. Therefore, only you can prevent compost fires, and here’s how.

Before we delve too deeply into ways you can prevent compost fires and combustion, let’s cover the most common causes.

There are two predominant reasons why your compost heap might catch fire.

  1. The heap is too dry: This can happen to compost piles that are not covered or are left to sit in the sun for too long without being watered down and turned over. The lack of water will cause your organic matter to heat up quickly, which leads us right into reason number two.
  2. Lack of sufficient oxygen:  When organic matter is too tightly packed and not mixed with air, it will start to decompose without oxygen. If this process happens for a long enough period of time, the reaction can get out of hand and lead to combustion.

The ultimate key to preventing either of these common causes is regular maintenance of your compost heap throughout the months necessary to complete the composting process.

Ensure There Are Appropriate Levels of Oxygen in Your Compost

Firstly, you should prepare your compost heap for the ensuing process by layering it with organic material. This will allow for oxygen to seep through the compost heap, preventing a lack of sufficient oxygen from occurring in your pile and therefore reducing the risk of combustion.

You can also introduce oxygen back into the compost heap by turning it regularly, as this encourages the pile to heat up, which will, in turn, lead to a faster decomposition process and reduction of potential risk factors for combustion.

Most people will turn their compost heaps with a simple shovel and generally follow the rule that compost tumblers should be turned every three to four days and compost piles should be turned every three to seven days (source).

Regular turning also helps ingredients mix together more efficiently so that you can get more out of your compost heap with less effort when you’re finally ready to use it in your garden.

Maintain Optimal Levels of Moisture

Secondly, you should monitor the moisture level throughout this process because excessively dry compost material ignites easily.

The best way to wet your compost pile is simply by adding water. However, if you are using an irrigation or sprinkler system, it should be set on a timer to ensure that the compost heap is always wet enough and never dry during this process.

The amount of moisture you should have in your compost heap will vary depending on your climate. If you live in a dry area, the moisture content should be about 50% to 60% (source) by weight, whereas heaps located in more humid regions can maintain a content of 40%.

You’ll want to test the moisture content of your compost heap intermittently to ensure it isn’t too low or too high.

If the heap is too dry, your risk the material catching fire, but if the percentage is too high (above 60%), it will develop a foul odor and enter anaerobic conditions.

Covering your compost heap is a good preventative measure to take as well because it helps to retain moisture and insulates the pile while keeping out excessive amounts of water, such as heavy rain. However, you’ll want to ensure covering your heap doesn’t inhibit airflow, as this can cause the heap to sour.

Keep Your Compost Away from Fire Sources

Finally, to prevent any risk of combustion from occurring at all in your compost pile, make sure that there are no open flames or fire sources anywhere near your heap. The smallest spark could easily ignite the entire pile and lead to a serious fire.

While it is still incredibly rare for a home compost heap to catch fire or spontaneously combust, there have been cases of these eco-friendly soil enrichers reaping havoc on facilities and nature with this destructive reaction.

For example, in 2018, a commercial composting facility in Albuquerque (source) experienced a large fire from spontaneous combustion that was so serious it degraded air quality in the city and adjoining counties. Local firefighting crews and helicopters were required to put out the seemingly endless flames.

This demonstrates that compost fires are a very real hazard and can have serious repercussions if neglected or maintained improperly. So, when you are finding a location for your new compost heat, make sure it is far from anything that could potentially ignite the pile.

Final Thoughts

While it is comforting to know that compost fires and combustion rarely occur, it is still important to be aware of this risk and how you can prevent such instances from occurring. Luckily, this is easily done through routine maintenance of your compost heap through regular turning and keeping the compost at optimal moisture content.

These steps alone will prevent the material from becoming excessively dry and overheating, which are the two elements that make combustion possible.

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