Its other major use is as a component ofexplosive mixtures used in mining, quarrying, and civil construction. It is the major constituent ofANFO, an industrial explosive which accounts for 80% of explosives used in North America; similar formulations have been used inimprovised explosive devices.
Many countries are phasing out its use in consumer applications due to concerns over its potential for misuse.[6]Accidental ammonium nitrate explosions have killed thousands of people since the early 20th century.[6][7] Global production was estimated at 21.6 million tonnes in 2017.[8] By 2021, global production of ammonium nitrate was down to 16.7 million tonnes.[7]
Ammonium nitrate is found as the natural mineralgwihabaite (formerly known as nitrammite)[9] – the ammonium analogue ofsaltpetre (mineralogical name: niter)[10][11] – in the driest regions of theAtacama Desert inChile, often as a crust on the ground or in conjunction with other nitrate,iodate, andhalide minerals. Ammonium nitrate was mined there until theHaber–Bosch process made it possible to synthesize nitrates from atmospheric nitrogen, rendering nitrate mining obsolete.
The ammonia required for this process is obtained by theHaber process from nitrogen and hydrogen. Ammonia produced by the Haber process can be oxidized to nitric acid by theOstwald process. Ammonia is used in itsanhydrous form (a gas) and the nitric acid is concentrated. The reaction is violent owing to its highlyexothermic nature. After the solution is formed, typically at about 83% concentration, the excess water is evaporated off to leave an ammonium nitrate (AN) content of 95% to 99.9% concentration (AN melt), depending on grade. The AN melt is then made into "prills" or small beads in aspray tower, or into granules by spraying and tumbling in a rotating drum. The prills or granules may be further dried, cooled, and then coated to prevent caking. These prills or granules are the typical AN products in commerce.
As ammonium nitrate is asalt, both the cation,NH+4, and the anion,NO−3, may take part in chemical reactions.
Solid ammonium nitrate decomposes on heating. At temperatures below around 300 °C, the decomposition mainly producesnitrous oxide and water:
NH4NO3 → N2O + 2 H2O
At higher temperatures, the following reaction predominates.[13]
2 NH4NO3 → 2 N2 + O2 + 4 H2O
Both decomposition reactions areexothermic and their products are gases. Under certain conditions, this can lead to arunaway reaction, with the decomposition process becoming explosive.[14] See§ Disasters for details. Manyammonium nitrate disasters, with loss of lives, have occurred.
The red–orange colour in an explosion cloud is due tonitrogen dioxide, a secondary reaction product.[14]
The transition between β-rhombic to α-rhombic forms (at 32.3 °C) occurs at ambient temperature in many parts of the world. These forms have a 3.6% difference in density and hence transition between them causes a change in volume. One practical consequence of this is that ammonium nitrate cannot be used as asolid rocket motor propellant, as it develops cracks. Stabilized ammonium nitrate (PSAN) was developed as a solution to this and incorporates metal halides stabilisers, which prevent density fluctuations.[16]
Ammonium nitrate is an important fertilizer withNPK rating 34-0-0 (34% nitrogen).[17] Whilst less concentrated thanurea (46-0-0), ammonium nitrate is more stable and does not rapidly lose nitrogen to the atmosphere.
Ammonium nitrate readily forms explosive mixtures with varying properties when combined with explosives such as TNT or with fuels likealuminium powder or fuel oil. Examples of explosives containing ammonium nitrate include:
ANFO is a mixture of 94% ammonium nitrate ("AN") and 6%fuel oil ("FO") widely used as a bulk industrialexplosive.[18]: 1 It is used incoal mining,quarrying, metalmining, and civil construction in undemanding applications where the advantages of ANFO's low cost, relative safety, and ease of use matter more than the benefits offered by conventional industrial explosives, such as water resistance,oxygen balance, high detonation velocity, and performance in small diameters.[18]: 2
On 14 Nov 2025, 2500 kg Ammonium Nitrate captured from white collar Doctor's Terrorists Network was exploded in Nogaon Police Station in Jammu Kashmir state of India, killing 12 officials[20].
Ammonium nitrate is used in someinstant cold packs, as its dissolution in water is highlyendothermic. In 2021,King Abdullah University of Science and Technology in Saudi Arabia conducted experiments to study the potential for dissolving ammonium nitrate in water foroff-grid cooling systems and as a refrigerant. They suggested that the water could be distilled and reused using solar energy to avoid water wastage in severe environments.[21]
It was once used, in combination with independently explosive "fuels" such asguanidine nitrate,[22][23] as a cheaper (but less stable) alternative to5-aminotetrazole in the inflators ofairbags manufactured byTakata Corporation, which were recalled as unsafe after killing 14 people.[24] The current USA death total is 27.[25]
Numerous safety guidelines are available for storing and handling ammonium nitrate. Health and safety data are shown on thesafety data sheets available from suppliers and from various governments.[26][27][28]
Pure ammonium nitrate does not burn, but as a strong oxidizer, it supports and accelerates the combustion of organic (and some inorganic) material.[26][29][30] It should not be stored near combustible substances.
While ammonium nitrate is stable at ambient temperature and pressure under many conditions, it may detonate from a strong initiation charge. It should not be stored near high explosives or blasting agents.
Molten ammonium nitrate is very sensitive to shock and detonation, particularly if it becomes contaminated with incompatible materials such as combustibles, flammable liquids, acids, chlorates, chlorides, sulfur, metals, charcoal and sawdust.[31][26]
Contact with certain substances such aschlorates,mineral acids andmetal sulfides, can lead to vigorous or even violent decomposition capable of igniting nearby combustible material or detonating.[32][33]
Ammonium nitrate begins decomposition after melting, releasingNOx,HNO3,NH 3 andH2O. It should not be heated in a confined space.[26] The resulting heat and pressure from decomposition increases the sensitivity to detonation and increases the speed of decomposition. Detonation may occur at 80atmospheres. Contamination can reduce this to 20 atmospheres.[31]
Ammonium nitrate has acritical relative humidity of 59.4% at 30 °C. At higher humidity it will absorb moisture from the atmosphere. Therefore, it is important to store ammonium nitrate in a tightly sealed container. Otherwise, it can coalesce into a large, solid mass. Ammonium nitrate can absorb enough moisture to liquefy. Blending ammonium nitrate with certain other fertilizers can lower the critical relative humidity.[34]
The potential for use of the material as an explosive has prompted regulatory measures. For example, in Australia, the Dangerous Goods Regulations came into effect in August 2005 to enforce licensing in dealing with such substances.[35] Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse.[36] Additional uses such as education and research purposes may also be considered, but individual use will not. Employees of those with licenses to deal with the substance are still required to be supervised by authorized personnel and are required to pass a security and national police check before a license may be granted.
Ammonium nitrate can explode through two mechanisms:
Shock induced detonation. An explosive charge within or in contact with a mass of ammonium nitrate causes the ammonium nitrate to detonate. Examples of such disasters areKriewald,Morgan (present-daySayreville, New Jersey),Oppau, andTessenderlo.
Deflagration to detonation transition. The ammonium nitrate explosion results from a fire that spreads into the ammonium nitrate (Texas City, TX;Brest;West, TX;Tianjin;Beirut), or from ammonium nitrate mixing with a combustible material during the fire (Gibbstown, Cherokee,Nadadores). The fire must be confined at least to a degree for successful transition from a fire to an explosion.
^US 4927617, Villard, Alexandre & Cotonea, Yves, "Process of producing concentrated solutions of ammonium nitrate", published 22 May 1990, assigned to Societe Chimique des Charbonnages S.A.
^US 5531941, Poole, Donald R., "Process for preparing azide-free gas generant composition", published 2 July 1996, assigned to Automotive Systems Laboratory
^"Lebanon's president calls for two-week state of emergency in Beirut after blast".Reuters. Beirut. 4 August 2020. Retrieved4 August 2020.Aoun, in remarks published on the Presidency Twitter account, said it was "unacceptable" that 2,750 tonnes of ammonium nitrate was stored in a warehouse for six years without safety measures and vowed that those responsible would face the "harshest punishments".
