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New Delhi: Preliminary forensic reports into the deadly explosion near Delhi’s Red Fort indicate the device used ammonium nitrate fuel oil (ANFO) together with a detonator. The blast killed and injured several people and has prompted a nationwide investigation by security agencies. ([Reuters][1])

What exactly is ANFO?

ANFO is a simple, bulk explosive made by mixing two common components: ammonium nitrate (an oxidiser often sold as fertiliser) and a liquid fuel such as diesel. Practical ANFO mixtures are typically about 94% ammonium nitrate and 6% fuel oil by weight. In normal conditions the components are stable — but when properly confined and initiated they detonate violently. ([Wikipedia][2])

How ANFO works — why it is so destructive

Ammonium nitrate supplies oxygen while the fuel supplies hydrocarbons. When a high‑energy initiating device (a booster or detonator) sets off the reaction, a supersonic shock wave propagates through the material, converting the mixture into very hot gases (mainly nitrogen, carbon dioxide and steam) almost instantaneously. That rapid gas expansion and shock front cause the blast pressure and fragmentation that produce large-scale damage. Large, poorly confined ANFO charges also generate toxic gases such as carbon monoxide and nitrogen oxides. ([Wikipedia][2])

Why terrorists have used ANFO

ANFO is attractive to attackers because its ingredients are cheap, widely available and easy to mix and transport in bulk. It is relatively insensitive to accidental ignition (so easy to handle), but once properly primed with a detonator it can produce devastating explosions — especially in heavily populated or confined urban locations. Security analysts have noted ANFO’s use in several past terrorist incidents for these reasons. ([ScienceDirect][3])

Key technical point: ANFO needs a detonator/booster

ANFO is not reliably set off by a simple blasting cap; it requires a higher‑energy booster (a secondary explosive) or a strong detonator to initiate full detonation. That is why investigators focus not only on the bulk material but also on recovered detonators, timers or other initiating devices at blast scenes. ([Wikipedia][2])

Legal and regulatory context in India

India tightly regulates ammonium nitrate. Under Indian rules and the Explosives Act, mixtures containing more than 45% ammonium nitrate by weight are treated and regulated as explosives; manufacture, storage, transport and sale are subject to licensing and strict controls. The Petroleum & Explosives Safety Organisation (PESO) and subsequent Ammonium Nitrate Rules govern these activities to limit diversion for malicious use. Large, unaccounted stockpiles in populated areas are illegal and treated as a major security risk. ([Drishti IAS][4])

What investigators are doing now

Police and national agencies are collecting residue, fragments and device components to confirm the exact composition of the explosive, the presence and make of any detonator or booster, and the sequence of events. Early media and official reports say ANFO and a detonator were identified in initial forensic reads; investigators are also tracing supply chains, storage locations and possible handlers linked to the seizure of large quantities of explosive material in nearby Faridabad. The probe remains active and is being led by national agencies. ([www.ndtv.com][5])

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