Subject: ANFO
Date: 30 May 90 16:15:12 GMT

>I have not dome any work don sintering/melting explosives.  Does anyone have
>experience with AN/FO mixtures, especially in confinement and initiation?

ANFO must be either very tightly confined or used in big amounts to function
properly. If not confined, the critical diameter for fertilizer (80 % AN) is
about 5 to 7 cm. That means you have to take at least a sphere of 10 to 15 cm
in diameter and place the detonator in the middle. In practice it means only
charges over one kilogram work. And the detonator must be 20 grams of TNT or
some more brisant explosive.

If the ANFO is confined, the critical diameter is smaller and even charges
under 0,5 kg can be detonated completely. Also the grade of the AN affects the
initiation. The best is prilled (spray dried) AN, which has a large surface
area and a lot of pores in the prills. If the AN is ground or dense particles,
it will be much more difficult to ignite - like the fertilizer. 

The sensitivity can be increased with additives, such as nitroglycol, TNT,
aluminum dust, other high explosives. Adding 4 % of EGDN will make any AN cap
sensitive; the excess oxygen released can be used up by adding a solid fuel,
for example carbon black or sugar. However, these mixtures are closer to
dynamites than ANFO.