Ammonium nitrate-fuel oil

Ammonium nitrate-fuel oil (ANFO) is a general term for a class of high explosives that are prepared at or near the point of use, by mixing solid ammonium nitrate with a hydrocarbon such as diesel oil. It has legitimate industrial applications, especially in earthmoving and mining, because, in a semisolid slurry form, it can be pumped into a hole drilled into rock or earth. It is also widely used in improvised explosive devices, although optimal mixing, detonation, and effects are more complex than many amateur bomb-makers realize.

While a high explosive, the rate of propagation of the detonation wave is slower than, for example, trinitrotoluene (TNT). This is actually advantageous for earthmoving, as it tends to push rather than shatter the ground.

The rate can be increased with additives, such as nitromethane or aluminum powder, although these can make the mixture more unstable.

ANFO is relatively insensitive to shock, considerably less so than TNT, which rarely would detonate when hit by a rifle bullet but will go off with a suitable blasting cap. In general, ANFO is detonated indirectly, with a blasting cap encircled by a more sensitive booster, such as tetryl.

It is bulkier than other explosives, but, in large quantities as in a truck bomb, can be devastating. The Oklahoma City bombing used approximately 4000 pounds/1800 kg of ANFO, and wrecked a large office building with an explosion in front of it.