Is Ammonia Flammable? (A comprehensive overview)

Is Ammonia Flammable? 

Ammonia (NH3) in its pure form (also called anhydrous ammonia) is considered slightly flammable. Ammonia can react with the oxygen in the air and cause explosions if at high enough temperature.

Anhydrous ammonia is commonly kept in pressurized cylinders, if heated or damaged  they can explode.When in pressurized compartments it poses a higher danger of explosion given the high difference between the pressure inside the cylinder and the ambient pressure.

Ammonia can also be stored in water solutions or under low temperatures. In both these storing methods there is also some danger for explosions because ammonia and air mixtures can cause explosions under high temperatures or sources of ignition.

Main Ammonia Associated Fire Hazards

Since the flash point of pure ammonia is higher than 93 °C, ammonia may be considered non flammable. The higher ammonia associated fire hazard is for explosions, which can affect nearby flammable material.

Ammonia in the air can explode

Although the amount of heat necessary to cause the combustion of ammonia in the air is relatively high, it is possible for ammonia to catch on fire or explode.

The combustion of ammonia with oxygen produces nitrogen gas (N2) and water. Under some circumstances (in the presence of a catalyst) the combustion reaction can be different and produce nitroxide gas (NO) which has a yellowish color.

If ammonia goes in contact with chlorine gas (Cl2) it is immediately oxidized producing a high enough heat to cause ignition. If a large excess of chlorine gas is in contact with ammonia, the highly explosive nitrogen trichloride (NCl3) may be formed.

What Fumes does Ammonia Produces if Exposed to Flames

Ammonia fires can sometimes only produce inert gases like nitrogen gas and water. And sometimes produce nocive gases such as nitroxide gas. If the fire was caused by halogen gases, other substances are released including NCl3.

The adiabatic temperature for the flames produced by burning ammonia is 1800 °C.

Can Ammonia React With Something Other than Air to Produce Fire?

Ammonia gas can react violently with halogen gases, fluorine gas (F2 ), chlorine gas (Cl2) and liquid bromine (Br2).

Flammability Related Properties of Ammonia

Below are represented the flash point of ammonia, which is usually the primary indicator to determine if a given material is flammable or not. When the flash point is under 93 °C, the material is considered flammable. If the flash point is above 93 °C, the material is non flammable.

The autoignition temperature is the temperature in which the material will ignite without any other material present. That is it will spontaneously ignite at the autoignition temperature.

The flammability limits refer to the concentration of a given gas at which it can catch on fire if subjected to an ignition source. In the case of ammonia, it can only catch on fire if it is present in the range of approximately 15 to 26% in volume. 

It is worth nothing that all of the above mentioned values aply to ambient or near ambient conditions. Many times a situation may take place under drastic conditions that differ considerably from the standard conditions.

PropertyValue
Flash point at 1 atm132 °C
Autoignition temperature651 °C
Flammability limits at ambient temperature and pressure15 – 26%  (volume fraction) 

General View of What Ammonia is

Ammonia is the molecule NH3, it has alkaline characteristics, it readily reacts with water to generate NH4+(aq) + OH(aq). When pure or anhydrous ammonia is a colorless gas with a strong odor. Ammonia has been present in the planet for at least 4 billion years.

Ammonia is present in living beings and is essentially the main provider of nitrogen for plants. In the industry of fertilizers in agriculture, it is used to produce explosives, and it is widely used in the synthesis of amines and other nitrogen containing organic substances.

Some Physical Properties of Ammonia

At ambient conditions ammonia is a gas (boiling point of -33 °C) and it freezes into white crystals at -78 °C.

Liquid ammonia does conduct electricity, given its high polarity. This high polarity is mainly attributed to its three hydrogen atoms being capable of performing hydrogen bounds. 

Even though ammonia has a low boiling point, the vaporization heat is relatively high, making it somewhat easy to handle in liquid form.

When in a solution with water the maximum possible concentration of ammonia gives a density for the solution of 0.880 g/cm3. Said solution is sometimes called 880 ammonia.

PropertyValue
molar mass17.03 g/mol
appearancecolorless gas
gas density at 15 °C0.730 g/cm3
liquid density at – 33.3 °C0.681 g/cm3
solubility in water at 25 °C31% mass/mass
solubility in organic solventsethanol, methanol, diethyl ether, chloroform
vapor pressure8.46 atm

Is ammonia Dangerous if Inhaled or Ingested?

Yes! Ammonia is extremely toxic if inhaled or ingested with a very oral low lethal dose of 0.015 ml/Kg in humans. In the gas state ammonia is lethal at 500 ppm or above.

If in Contact with Skin

If in contact with skin or eyes it causes burns.

Some Methods for Detecting Ammonia

In solutions, the Nesslr’s solution can be used to detect ammonia. If ammonia or ammonium salts are present in the solution a yellowish color will appear.

For small quantities in the air burning sulfur sticks may be the method of choice.

Some Ammonia Derivatives and their Related Fire Hazards

There are many derivatives of ammonia, including organic compounds such as amines. Many amines are flammable. Other derivatives of ammonia are salts such as ammonium chloride, ammonium hydroxide and ammonium nitrate. 

Another important ammonia derivative is hydrazine (N2H4).

Below are listed three ammonia derivatives and a brief discussion as to their fire hazards.

Is Ammonium Chloride?

Ammonium chloride (NH4Cl) is considered non flammable.

Is Ammonium Hydroxide?

Ammonium hydroxide (NH4OH) is non flammable, but if it is burned it can release ammonia gas. Ammonia gas may cause the fire to propagate or cause an explosion.

Is Ammonium Nitrate?

Technically, ammonium nitrate (NH4NO3) is not considered flammable, but it can cause explosions. That is because ammonium nitrate is a strong oxidiser. Which means that if ammonium nitrate is in contact with something flammable a fire or explosion will occur if some heat is added.

Ammonium nitrate can also provoque explosions under some conditions through a process called deflagration to detonation transition. That is the believed cause for the Beirut explosions in 2020.

Is Hydrazine Flammable?

Yes, in fact hydrazine is extremely flammable and can even spontaneously ignite ate relatively low temperatures (270 ºC at ambient pressure). The flash point of hydrazine is 52 ºC. Besides, hydrazine is extremely toxic to humans.

How to deal with ammonia leaks?

One of the safer ways to deal with ammonia fires or explosions is by preventing it from happening.

  • Ammonia leaks are easier to happen in higher temperatures, so during warmer seasons more attention should be given.
  • It is important to have a plan of action for the case of an ammonia leak, that includes knowing who to call, be that a neighbor or the firefighters.
  • If ammonia leaking does happen it is important to evaluate the amount of ammonia that is leaking in order to take the proportionate action.
  • Usually the most efficient way to disperse ammonia is using water, as the ammonia will readily be solubilized by the water.

Conclusions

From what was exposed above, it can be concluded that ammonia is not simple to judge in terms of fire hazards. Under the proper conditions ammonia can be safely handled. At the same time the potential risk, especially for compressed ammonia, is high.

Additionally, some information about ammonia toxicity and uses was also provided.

Lastly, some salts derived from ammonia were mildly explored in regards to their fire hazards.

Frequently Asked Questions (FAQ): Is Ammonia Flammable?

Is ammonia corrosive to metals?

Most metals and metal alloys are inert to liquid ammonia. There are a few known to be corroded by ammonia tho, they are zinc, copper, brass and other alloys that contain copper.

Does ammonia react with stainless steel?

All grades of stainless steel are resistant to corrosion by ammonia at least up to 100 ºC.

Is ammonia a fire hazard?

Yes, ammonia is a fire hazard. Ammonia can cause explosions and can react with a series of other materials.

What does ammonia decompose into?

Ammonia decomposes into nitrogen gas (N2) and hydrogen gas (H2). For ammonia to decompose it must be at really high temperatures of above 600 ºC, which does happen within a fire caused by ammonia.

Is ammonia flammable or explosive?

It is both flammable and explosive. However its explosion hazard is more acentuated than its flammability hazard, technically speaking.

How far does ammonia travel in air?

Depending on the conditions ammonia can stay in the air for weeks and travel distances above 500 miles.

References

Safety data sheet for anhydrous ammonia can be found here

Ammonia-Air Mixtures Can Be Explosive. David Tudela. Journal of Chemical Education. 1999 76 (4), 468. DOI: 10.1021/ed076p468.3

King, R. B. Inorganic Chemistry of Main Group Elements, VCH: New York, 1995; p 74.

What was missing from this post which could have made it better?

Leave a Comment