How dangerous is ammonium nitrate believed to be used in Delhi blast

The devastating explosion that ripped through the vicinity of Delhi’s Red Fort on November 10 has put the spotlight on the chemicals behind some of the world’s most powerful blasts.

The evening car explosion, which claimed at least twelve lives and injured many others, is now under investigation for suspected use of Ammonium Nitrate Fuel Oil (ANFO) — a compound that, while commonly used in mining and construction, has been weaponised in numerous terror incidents around the world.

Just hours before the Delhi tragedy, a joint operation by police from Jammu and Kashmir and Haryana in Faridabad uncovered a cache of 2,500 kilogrammes of explosive materials, including large quantities of ammonium nitrate.

Preliminary links between that seizure and the Red Fort attack have prompted renewed scrutiny of how a readily available industrial chemical — often sold legally as fertiliser — can be turned into a weapon of mass destruction.

While investigators analyse chemical residues from the Red Fort site, experts and law enforcement alike have turned to a familiar question: how does ammonium nitrate, often used in homemade explosives, compare to military-grade RDX, and which of the two is more dangerous?

What is ammonium nitrate and ANFO?

Ammonium nitrate, chemically represented as NH4NO3, is a white, odourless crystalline compound that serves primarily as an agricultural fertiliser.

In its pure form, it is not classified as an explosive but as an oxidising agent — a substance that supplies oxygen to support combustion.

The chemical becomes explosive only when mixed with a fuel source such as diesel, kerosene, or other hydrocarbons, forming what is known as ANFO — Ammonium Nitrate Fuel Oil.

This combination produces a powerful reaction when subjected to a detonating trigger. The ammonium nitrate acts as an oxidiser, while the fuel oil serves as the combustible component.

When ignited, the reaction releases large volumes of high-pressure gas and heat, producing an explosion capable of immense destruction.

Unlike advanced military explosives, ANFO is classified as a “non-ideal” explosive because its chemical reaction is slower and less efficient, meaning it does not produce as rapid or concentrated a shockwave.

However, its relative stability, low cost, and simplicity make it one of the most widely used industrial blasting agents worldwide — particularly in mining, quarrying, and large-scale construction.

According to the National Library of Medicine’s PubMed Central, ANFO remains popular for commercial applications due to its affordability and ease of handling. It requires an external initiation, such as a detonator or booster charge, to trigger an explosion.

Why are terrorists now using ANFO?

Ammonium nitrate and fuel oil are inexpensive, easily sourced, and legally available, making the compound a preferred material for terrorists and insurgent groups.

Ammonium nitrate is easily available in agricultural markets and its transportation would not raise suspicion. Also, the fuels such as petrol and diesel are available and daily-use products everywhere around the world, a 2019 article in Forensic Science International noted.

Together, they form a weapon of mass destruction when combined and confined properly — as evidenced in several major attacks across decades and continents.

This accessibility poses a persistent challenge to security agencies worldwide, as regulating a dual-use material vital to agriculture and industry requires balancing economic necessity with national security.

Have there been past terror incidents involving ammonium nitrate?

India has a tragic history of ammonium nitrate-based bombings. Government records presented in Parliament have identified the compound’s use in several major terror cases.

In the 2010 Pune German Bakery blast, which killed 18 people, investigators found that the explosive device contained a mixture of RDX and ANFO.

A year later, ammonium nitrate was used again in the 2011 Mumbai triple bombings at Opera House, Zaveri Bazaar, and Dadar — which killed more than two dozen people.

Earlier, in the 2006 Mumbai train blasts, seven coordinated explosions ripped through suburban trains during rush hour, killing over 200 commuters. Investigations later showed that the bombs contained both ammonium nitrate and RDX, packed in pressure cookers to amplify the explosion.

Internationally, ANFO has been used in some of the deadliest attacks ever recorded. The 1995 Oklahoma City bombing in the United States remains one of the most catastrophic domestic terror incidents in American history.

Timothy McVeigh and Terry Nichols packed about 2,300 kilogrammes of ANFO into a rented truck parked outside the Alfred P Murrah Federal Building, killing 168 people and injuring more than 900.

The explosion destroyed or damaged over 300 buildings and caused an estimated $652 million in property damage.

In 2011, Norwegian extremist Anders Behring Breivik detonated a 950-kilogramme fertiliser bomb outside the prime minister’s office in Oslo, killing eight people before carrying out a mass shooting on Utoya Island.

Accidents involving improper storage of ammonium nitrate have also caused immense devastation. The 2020 Beirut port explosion — triggered by a fire that ignited 2,750 tonnes of the compound stored for years — killed over 200 people and displaced thousands.

Experts estimated that the blast released energy equivalent to 1.1 kilotonnes of TNT, highlighting how catastrophic ammonium nitrate can be when confined and triggered accidentally.

So then, what is RDX?

In contrast to ANFO, RDX (Research Department Explosive or Royal Demolition Explosive) is a high-energy compound developed specifically for military applications.

Its chemical name, cyclotrimethylenetrinitramine, describes a nitroamine compound with the formula C3H6N6O6.

RDX is a white, odourless, crystalline solid that is far more powerful than ANFO by weight.

First synthesised in Germany by chemist Georg Friedrich Henning in the late 19th century, RDX gained prominence during World War II, when advances in production made it a cornerstone of military explosives.

Known by different names — “Hexogen” in Germany, “Cyclonite” in the United States, and “T4” in Italy — it became one of the most commonly used high explosives in the world.

RDX functions as a secondary explosive, meaning it requires a detonator to initiate an explosion, but once triggered, it produces a supersonic shockwave with enormous brisance (shattering capability).

So which is more dangerous - ANFO or RDX?

RDX’s detonation velocity of roughly 8.0 kilometres per second — about 26,000 feet per second — far exceeds that of ANFO, resulting in greater localised damage.

Because of this concentrated power, RDX is the main component in several military and demolition explosives, including plastic explosives such as C-4 and Semtex.

It is used in warheads, shells, demolition charges, and controlled military demolitions of hardened structures.

Environmentally, RDX can be degraded under certain biological conditions, such as exposure to specific fungi or sewage sludge, making it an area of interest for environmental chemists studying safe disposal of energetic materials.

While RDX is strictly controlled and primarily confined to defence production, its power and compactness make it far more dangerous than ammonium nitrate on a per-kilogramme basis.

While ANFO’s destruction scales with mass — meaning large quantities are required for devastating impact — RDX achieves far greater power from small amounts.

RDX is thus the preferred choice for professional militaries and defence engineers, while ANFO is more common in civilian industries and illicit terror operations that rely on accessibility and quantity.

Is ammonium nitrate easily accessible in India?

India classifies ammonium nitrate and any mixtures containing more than 45 per cent of the compound by weight as “explosives” under the Explosives Act of 1884.

Rules notified in 2012, and further amended in 2021, set strict conditions for manufacture, import, export, transport, and storage.

Under these rules, only licensed manufacturers or handlers can possess or sell ammonium nitrate above certain quantities.

Storage in populated or non-industrial areas is prohibited, and the use of ammonium nitrate in any form requires approval from the Petroleum and Explosives Safety Organisation (PESO).

Despite these regulations, enforcement remains difficult due to the chemical’s widespread industrial and agricultural applications.

Fertiliser-grade ammonium nitrate is sold across the country, and while pure ANFO mixtures are illegal for unlicensed use, components can often be diverted from legitimate supply chains.

Complete bans on ammonium nitrate would cripple agriculture and mining sectors that depend on it, yet unrestricted access increases the risk of misuse.

Authorities in India and elsewhere continue to seek balance through tighter licensing, real-time monitoring, and improved tracking of sales and storage.

The hundreds of kilogrammes of ammonium nitrate recovered from two houses in Faridabad just hours before the Red Fort blast highlight this challenge: even with legal controls in place, small amounts sourced from multiple locations can accumulate into massive stockpiles.

How is RDX regulated in India?

By contrast, RDX’s supply chain is tightly monitored. It is produced primarily in defence manufacturing facilities and used for controlled purposes.

Its superior explosive characteristics — higher detonation velocity, shattering power, and compactness — make it a military staple but also a target for illicit procurement by non-state actors.

When combined with ammonium nitrate, RDX amplifies the destructive potential of ANFO-based bombs, a pattern seen repeatedly in attacks such as the 2006 Mumbai train bombings and 2010 Pune blast.

These hybrid compositions exploit RDX’s brisance to trigger the slower-burning ANFO more efficiently, resulting in explosions of enormous magnitude.

The method of assembly and detonation, as well as the type of explosive used, are now central to the investigation.

Forensic experts have collected residue samples to confirm whether the suspected compound — ANFO — was used.

If confirmed, the Red Fort attack would add to a long list of deadly incidents globally involving ammonium nitrate-based explosives.

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With inputs from agencies