So, Is Fertilizer Flammable?

Accidental, dangerous fires are a threat that pretty much everyone will ace at some point. It could be an accident in the kitchen, a mishap in the garage or workshop or, potentially, even one getting started out on the farm or in the fields.

There are lots of materials that can contribute to contribute to or start fires, and knowing what they are and how to manage them is an important part of fire safety. Let’s look at fertilizer, for instance. Is fertilizer flammable?

No, most fertilizers aren’t flammable but some are combustible, particularly synthetic variations and any fertilizer that contains lots of ammonium nitrate.

Contrary to what lots of folks think, fertilizer is not inherently flammable. Quite the opposite, most of it is actually exceedingly difficult to ignite if it can be ignited at all.

But there are a few types out there that can be a special hazard, and you’ll definitely need to know about them if you’re going to stay safe around the homestead.

Even if you just work in a garden, this is need-to-know stuff! Keep reading and I’ll tell you all about it…

What Ingredients are in Fertilizer?

Fertilizer is primarily made of three major ingredients: nitrogen, phosphorus and potassium. This composition is often referred to as the NPK ratio which is commonly seen in literature on the subject, and on packaging.

These ingredients all play various roles directly in plant health, but from a fire safety perspective, it is nitrogen that can be potentially hazardous.

Many fertilizers also contain other minor or additive ingredients, which can vary greatly based on the specific type of fertilizer and the manufacturer. These may include elements like calcium, magnesium, and sulfur, among others.

A comprehensive overview of these blends for flammability is way beyond the confines of this article, but for now, just know that added ingredients might significantly alter the flammability of a “straight” fertilizer blend.

Is Fertilizer Combustible?

Yes, some are. The combustibility of fertilizer is contingent on its specific ingredients and their respective ratios. Certain types of fertilizers, particularly those with high nitrogen content, can pose a substantial combustion risk.

But it’s important to differentiate between flammable and combustible substances. Flammable materials catch fire and burn easily at normal temperatures, while combustible materials need higher temperatures to ignite.

As such, while some fertilizers might not be inherently flammable, they could be combustible under specific conditions, meaning intense heat or open flames that could serve as ignition sources.

Does Fertilizer Ignite at Any Temperature?

Yes, various types of fertilizer can ignite based on their composition and the temperature they’re exposed to.

For instance, ammonium nitrate, a common and highly combustible ingredient in many fertilizers, begins to melt around 337 °F (170 °C). As it melts, it starts to break down, and can shortly thereafter ignite.

Similarly, urea, another common component of fertilizers melts at a temperature of 534 °F (278 °C). Although it’s not a significant combustion hazard itself, it can contribute to the flammability of other compounds and elements.

At temperatures higher than that, it can undergo reactions that might lead to direct ignition.

Does Fertilizer React with High Temperature?

Yes. If you couldn’t tell already, fertilizers do react with high temperatures. When subjected to elevated temperatures, certain fertilizers may produce toxic gases.

For example, ammonium nitrate produces harmful gases when its temperature exceeds 400 °F (204 °C).

It’s also important to note that other fertilizers may become more sensitive to ignition generally when kept at a sustained high temperature for an extended period of time, even if the temp is well below the nominal ignition point.

Worse yet, some fertilizers can release nitrogen when exposed to elevated temperatures if impurities are present.

These reactions necessitate careful storage and handling of fertilizers to prevent severe potential fire hazards.

Warning: Ammonium Nitrate Is Very Combustible!

Among all the fertilizers and their ingredients, it is ammonium nitrate that poses the most significant fire hazard. Its likelihood of ignition under high heat conditions makes it a major concern.

When ammonium nitrate is exposed to temperatures around 337°F, it creates conditions conducive to ignition. This makes fertilizers containing ammonium nitrate particularly risky if mishandled or improperly stored.

You probably already know that there have been many disasters caused by ammonium nitrate combustion.

The Texas City disaster and A.W. Higgins Plant incident of 1947, Port Neal disaster of 1994 and Bryan, Texas incident of 2009 are just a few of the many, many catastrophes directly attributed to the dangerous nature of ammonium nitrate.

Caution: Even All-Natural Fertilizers Can Emit Combustible Gasses

Don’t get complacent if you stick to all-natural, old-fashioned fertilizers: even the all-natural stuff can pose a real fire hazard!

While synthetic fertilizers and those rich in ammonium nitrate are most often associated with catastrophe, natural fertilizers like manure aren’t entirely safe either; these organic materials undergo normal decomposition processes that can release flammable gases like methane and more.

If these gases accumulate in a confined space and there is an ignition source- sparks, fire, hot surface, cigarette, etc.- they may ignite in a devastating fireball and subsequent fire.

Be on the lookout for foam appearing on the surface of mass manure and other natural fertilizers: you cannot always count on it being present, but if it is, it’s usually a sign of methane accumulation.

Regardless, you must ensure proper ventilation when dealing with all types of fertilizers, including the all-natural ones.

Will Fertilizer Make a Fire Worse?

Yes, depending on its composition. Fertilizer can potentially worsen or start a serious fire. Fertilizers that are prone to combustion can intensify an existing fire and particularly those rich in nitrogen such as ammonium nitrate, can pose significant risks.

In large quantities, these fertilizers can generate intense heat and swiftly spread flames, making any bad situation considerably worse.

Is Fertilizer Reactive with Other Substances?

Fertilizers can potentially react with other substances, although most of these reactions do not pose significant health hazards or increase fire risks most of the time.

However, certain combinations can be potentially dangerous. For instance, when ammonium nitrate comes into contact with organic materials, or certain chemicals, it can become even more sensitive to ignition.

Similarly, mixing different types of fertilizers without proper knowledge can lead to unexpected reactions. I advise you to only handle and use fertilizers according to package or manufacturer instructions unless you’re sure of the consequences.

How Should You Deal with Fertilizer Exposed to Fire?

Handling a fire involving fertilizer, particularly in large quantities, can be extremely dangerous and requires specific fire extinguishing agents.

For fires involving ammonium nitrate-based fertilizers, using water is often the most effective approach as it helps cool down the material and prevent further decomposition.

However, you’ll need to use tons of water, as small quantities might not be enough to lower the temperature effectively. For other types of fertilizers, dry chemical fire extinguishers, foam, or carbon dioxide may be used.

If you have any doubts about the situation or your ability to control it, you must get as far away from the fire as fast as you can!

Due to its drastic combustive properties in some instances, fertilizer fires should ideally be handled by the fire dept. due to the potential risks involved. Always prioritize evacuation and alerting emergency services in such situations.