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COMMON NAME – ANFO

NAME – Ammonium nitrate/Fuel oil

TYPE – High explosive mixture

DATE FIRST USED AS AN EXPLOSIVE – 1955

COUNTRY OF ORIGIN – USA

COMPOSITION – 94% Ammonium nitrate, 6% Petrolum oil (Fuel oil) by weight

DENSITY – 0.92 g per ml pressed

NORMAL STATE – Spherical grains (prills)

PHYSICAL APPEARANCE/COLOR – White to gray

INITIATION – Not cap sensitive, requires detonator and high explosive booster for proper detonation

SENSITIVITY – Insensitive to friction, impact

STABILITY – Poor, sensitive to water and humidity in the air, often mixed shortly before use.

DETONATION VELOCITY – 5,270 m/s (17,290 fps)

RE FACTOR (BRISANCE) [TNT=1.0] – 0.74

TOXICITY – Toxic if ingested, inhalation of dust is toxic, detonation produces toxic fumes, primarily carbon monoxide and nitrogen oxides

MELTING POINT – 167^o to 169^o C.(332^o to 336^o F.)

IGNITION POINT – 230^o C.(446^o F.) Decomposes

SOLUBILITY – Partially soluble in water

APPLICATIONS – PRINCIPLE USES – General blasting, mining, and earth moving

     Ammonium nitrate-based explosives are the most common commercial explosive materials used in the world. Commonly used in mining, single charges of Ammonium nitrate (AN) -based explosives can be easily measured in hundreds or thousands of pounds. Of these AN formulations, by far the most common one is Ammonium Nitrate-Fuel Oil, commonly called ANFO. Over 4,800,000 tons of ANFO are used each year as a mining explosive just in North America as of 2008. Ammonium nitrate by itself is a rather poor explosive, though a good oxidizer. Mixing it with a fuel greatly increases the explosive usefulness of Ammonium nitrate. Basic ANFO is a mixture of 94% AN and 6% FO (#2 Fuel oil) by weight. The Fuel oil used in the mix can be switched out with a number of other materials, Kerosene, Household fuel oil, Motor oil, even used motor oil, have been tried and tested. All work in a satisfactory manner. Various manufacturers produce their own ANFO mixtures with differing ingredients, but all are basically Ammonium nitrate as the oxidizer and a fuel.

     ANFO has poor water resistance and must be used in a dry environment. Blasting bore holes in rock must be dry and have a sufficient diameter for the detonation wave to propagate through the charge. A minimum bore hole size is considered to be 50mm (2 in). As the size of the bore hole is increased, the velocity of detonation for ANFO also increases, causing the material to be more efficient. One of the other drawbacks of using ANFO is that it is detonator-insensitive. A simple initiator such as a blasting cap will not normally cause ANFO to high-order (explode). A strong primer must be used in addition to the normal detonator. The ANFO explosive must be contained for it to detonate efficiently. A strong container, such as a bore hole in rock, allows the maximum power to come from a very cheap and readily available material.

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