Is Fertilizer Flammable? All You Need To Know

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Manufacturers design fertilizers to provide the nutrients to help plants flourish, and they are an essential ingredient in our gardens and farms-but fertilizers have a downside. If not used correctly, fertilizers also pose serious threats to humans, animals, and the environment. With this in mind, you may wonder: Is fertilizer flammable?

Most fertilizer is not flammable, but there are some exceptions. Ammonium nitrate, for example, is a type of fertilizer that is highly flammable due to its high nitrogen content. If ammonium nitrate is not stored or used correctly, it can pose a serious fire hazard.

If you’re interested in learning more about this common gardening product and want to keep yourself and your family safe from accidental fires and explosions, read on: I’ll start with a quick overview of what kinds of fertilizers are flammable, followed by details about their use, storage, and safe handling.

What Kind of Fertilizer Is Flammable?

Fertilizers that contain Ammonium nitrate, or NH4-NO3, are highly flammable. When these fertilizers reach 210℃(410℉), it creates gasses such as nitrogen, nitrous oxide, and water vapor that can lead to explosions. Urea nitrogen fertilizers are also flammable due to their high ammonia content. 

It’s essential to know that there are different types of fertilizer when it comes to understanding fertilizers’ potential flammability. The two main types are Organic and Inorganic Fertilizers.

Organic Fertilizers

Organic fertilizers contain natural materials, such as manure, compost, and bone meal. The natural decay of these materials produces nitrogen, phosphorus, and potassium, essential nutrients for plant growth.

Organic fertilizer is less likely to catch fire because it contains a minimal amount of nitrogen. However, if you store organic fertilizer in an enclosed space, the build-up of methane gas can create a fire hazard.

Inorganic Fertilizer

Inorganic fertilizers are made from synthetic materials and are highly concentrated. They are typically cheaper than organic options but can also be harsher on the environment. 

You can find inorganic fertilizers in both granular and liquid forms. They include nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer.

Nitrogen Fertilizers

Nitrogen is essential for plant growth as it helps develop leaves and stems. It also helps with photosynthesis, which is how plants create their food. I’ve written an article just about nitrogen fertilizers here.

Ammonium nitrogen fertilizer, nitrate-nitrogen fertilizer, and urea nitrogen fertilizer are all nitrogen fertilizers. 

Ammonium nitrate is one of the most common types of fertilizer. This chemical contains two nitrogen atoms and one oxygen atom (NO3). This composition makes it a very effective fertilizer, as it can release a large amount of nitrogen when mixed with water.

Ammonium nitrate is not flammable, but it is a potent oxidizing agent that can cause fires if not handled correctly. When it burns, solid ammonium nitrate decomposes into nitrous oxide and water vapor which has the potential to generate a powerful explosion.

Nitrate nitrogen fertilizer is another type used in agriculture and gardening. It comprises calcium nitrate, sodium nitrate, and potassium nitrate. Furthermore, this white crystalline solid is highly soluble in water. 

Nitrate nitrogen fertilizer is less flammable than ammonium nitrate fertilizer but can still catch fire if exposed to heat or spark. It contains a relatively high amount of nitrogen which can make it explosive.

Urea nitrogen fertilizer has a high nitrogen content, which makes it a very effective fertilizer. It comprises two ammonia molecules (NH3) joined by a carbonyl group (-CO-NH2). When mixed with water, urea breaks down into ammonia and carbon dioxide. 

Urea nitrogen fertilizer is highly flammable because of its high ammonia content. When urea fertilizer mixes with water, the ammonia molecules escape from the area and rise into the air. This reaction makes the urea-ammonia mixture very flammable.

Phosphorus Fertilizers

Phosphorus is another essential element for plant growth. It helps with the development of roots, flowers, and fruits. It also helps with the process of photosynthesis.

The two most common phosphorus fertilizers are superphosphate and triple superphosphate. These fertilizers are a combination of phosphoric acid and limestone.

Superphosphate is about 20% phosphorus, while triple superphosphate is approximately 40-45% phosphorus. Both fertilizers are water-soluble so that plants can easily absorb them.

Phosphorus fertilizer can be flammable. When phosphorus comes into contact with oxygen, it produces a highly flammable substance called phosphorus pentoxide. For a phosphorus fertilizer to be flammable, it must have a high phosphorus concentration.

Potassium Fertilizer

Potassium is an essential nutrient for plants, and many gardeners add it to the soil as a potassium fertilizer. It involves many plant processes, such as photosynthesis and water uptake.

Potassium sulfate (SOP) and muriate of potash (MOP) are two common types of potassium fertilizer. 

Potassium fertilizer is not flammable, but it is an oxidizer that can create a fire when mixed with other combustible materials, such as ammonium nitrate. If you want to know more about potassium fertilizers, check out my article here.

Can Fertilizer Explode?

Some fertilizers are highly combustible and often used as an ingredient in homemade explosives. When mixed with other flammable materials such as fuel or charcoal, they cause a chemical reaction that produces large amounts of heat and pressure and may create a powerful explosion.

Ammonium nitrate is not in itself explosive as it is a salt. But when mixed with certain hydrocarbons such as fuel oil, diesel, aluminum powder, sulfur, nitrates, acids, alkalis, etc., ammonium nitrate fertilizer can become flammable and create an explosive mixture since ammonium nitrate is an oxidizer.

That is why the construction and mining industries use ammonium nitrate as a blasting agent. 

There are three mechanisms by which ammonium nitrate fertilizer can cause an explosion:

  • Heating in Confinement. If you heat ammonium nitrate fertilizer in an enclosed space, it will decompose and release a large volume of gas. This increase in pressure can cause the container to rupture, leading to an explosion.
  • Detonation. When combined with a detonator, ammonium nitrate fertilizer can create a powerful explosion. The resulting shock wave can cause extensive damage to buildings and other structures.
  • Runaway Reaction. If ammonium nitrate fertilizer mixes with fuel, it can create a self-sustaining chemical reaction that will continue until it consumes all the material. This type of reaction can lead to a powerful explosion.

The United Nations’ Globally Harmonized System of Classification and Labeling of Chemicals classifies ammonium nitrate fertilizer as a Class 5.1 oxidizer. The Department of Transportation classifies it as a Division 5.1 explosive. This designation means that it can cause or accelerate combustion, causing serious fires and explosions.

Major accidents involving ammonium nitrate fertilizer have occurred, the most notable being the following incidents:

  • Texas City disaster of 1947. In this incident, a ship carrying 2,300 tons (about 2,100 metric tons) of ammonium nitrate fertilizer caught fire and exploded, killing 581 people and injuring nearly 4,000 others. The explosion caused extensive damage to the surrounding area and was one of the most significant industrial accidents in U.S. history and one of history’s largest non-nuclear explosions.
  • The West Fertilizer Company explosion. In n 2013, an ammonium nitrate fertilizer plant in the town of West, Texas, caught fire and exploded, resulting in 15 deaths and over 160 injuries. The blast caused extensive damage to the town, with over 150 destroyed or damaged buildings.
  • Port of Beirut, Lebanon Explosion. In 2020. 2,750 tons of ammonium nitrate stored in a warehouse for six years were the cause of the explosions. The resulting blasts killed over 200 people and injured over 6,000 others. The blast caused extensive damage to the surrounding area, with over 300,000 people left homeless. It was felt as far away as Cyprus and was the largest non-nuclear explosion in history.

Urea nitrogen fertilizer is another fertilizer used to make improvised explosive devices. As I stated earlier, it comprises two types of nitrogen, ammonium, and carbonate. When mixed with gasoline, urea can create a powerful explosion.

Urea is classified as a Class 5.2 oxidizer by The United Nations’ Globally Harmonized System of Classification and Labeling of Chemicals classify urea as a Class 5.2 oxidizer. It can readily cause or accelerate combustion but is not as reactive as an ammonium nitrate fertilizer.

Urea has been behind several terrorist attacks, including the following:

  • 1993 World Trade Center bombing. A truck bomb was detonated in the garage of the World Trade Center, resulting in the deaths of six people and the injury of over 1,000 others. The bombers used a mixture of urea and nitrate, and the resulting explosion caused extensive damage to the garage and the surrounding area.
  • 2010 Times Square bombing attempt. A vendor foiled this bombing attempt when he alerted authorities to a suspicious vehicle. The vehicle, parked in an area evacuated due to the fear of a bomb, contained urea-based explosives.

Potassium nitrate can also cause explosions as it contains potassium, nitrogen, and oxygen, which can combine with fuel such as gasoline to form a powerful explosive.

It is classified as a Class 5.1 oxidizer by the United Nations’ Globally Harmonized System of Classification and Labeling of Chemicals. 

How To Handle Fertilizers Safely

While the risk of a fire or explosion is always present when working fertilizers, taking the following precautions can help you avoid accidents and injuries when handling fertilizers:

  • Read the label carefully before using any fertilizer. Be sure to follow the instructions for safe use.
  • When handling fertilizer, wear appropriate protective gear, such as gloves, goggles, and a dust mask. As a general rule, the more dust produced, the greater the risk of an accident.
  • Wash your hands thoroughly after handling fertilizer products, even if you are wearing gloves.
  • Wet down fertilizer products before handling them to reduce the risk of dust exposure.
  • Never mix fertilizer products unless the manufacturer’s instructions say it is safe.
  • If you accidentally spill fertilizer, immediately take measures to clean it up. Be sure to wear the appropriate protective gear while doing so.
  • Keep fertilizer products in their original containers and stored in a cool, dry place.
  • Never smoke while handling fertilizer products. Smoking near fertilizer is hazardous because the sparks from a cigarette can easily ignite the flammable chemicals in fertilizer.

How To Store Fertilizer Safely

Fertilizer is a necessary gardening product, but it can be dangerous if not stored properly. Here are some tips for storing fertilizer safely:

  • Keep fertilizer in a cool, dry place. Fertilizers are more likely to catch fire if stored in a hot, humid environment. Heat and humidity can cause the fertilizer to break down and release highly combustible nitrogen gas. Choose a cool, dry place for storage to eliminate the causative conditions for potential combustion. 
  • Store fertilizer in a metal container. Fertilizers should be stored in a metal container with a lid to prevent moisture from getting in. Moisture can cause the fertilizer to break down and release nitrogen gas which may cause a fire.
  • Keep fertilizer away from heat sources. You must keep fertilizers away from heat sources, such as stoves, heaters, and sunlamps. Heat can cause the fertilizer to break down and release nitrogen gas which may cause a fire.
  • Do not store fertilizer near combustible materials. You should keep fertilizer from combustible materials, such as gasoline, kerosene, and oil. These materials can easily ignite the flammable chemicals in fertilizer if placed in close proximity.
  • Fertilizers should be stored in a well-ventilated area to prevent the build-up of nitrogen gas. The build-up of nitrogen gas is a health hazard and may cause headaches, dizziness, and nausea. If you must store fertilizer in an enclosed space, open the windows and doors to ventilate the area to prevent potential health implications. 
  • Do not store fertilizers in your garage, basement, attic, or kitchen. These areas are hot and damp, which can cause the fertilizer to deteriorate faster than usual, causing it to release nitrogen gas.
  • Dispose of unused fertilizer properly. Unused or expired fertilizer should be disposed of properly to prevent it from becoming a fire hazard. The best way to dispose of fertilizer is to contact your local hazardous waste disposal facility to remove the product. 


Fertilizer is a great way to promote plant growth, but it can be dangerous if not handled properly. Be sure to read the instructions on the fertilizer container, wear protective clothing when handling fertilizer, and always store fertilizer in a safe place away from children and pets.

With these tips and tricks, you can safely use fertilizer and promote plant growth while avoiding fertilizer fires.


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