Sciencemadness Discussion Board - ANFO source materials

ANFO source materials

roXefeller - 26-12-2013 at 19:45

I have a friend who studied explosive technology in another country mention a couple odd opinions regarding ANFO. The first thing, he said that the prill density needed for the AN is finicky and detonation won't be supported if incorrect. He also said that common highway diesel fuel isn't pure enough to be used, that a source without the additives is necessary. Any comments on his claims?

Turner - 26-12-2013 at 20:17

I was just going to test this. The prills straight out of a cold pack are dense, and while I know it's AN, I don't know the purity, and how much other wax, anti caking etc. it's got, if it is detonatable in it's stock prill form with Al powder coating the prills.

hyfalcon - 27-12-2013 at 03:34

Should be, I've used a many of them before I found my source for reactive targets.

Hennig Brand - 27-12-2013 at 14:56

From reading, though fertilizer grade and blasting grade AN are the same chemically (different purity?), the densities are different I think. The fertilizer grade is in hard dense prills with a coating on it and the blasting grade is a much less dense, porous prill which easily soaks up the liquid hydrocarbon. There are methods to "activate" fertilizer grade prills and make them more like the blasting grade prills.

The fuel purity thing doesn't make much sense to me, but there is much I don't know.

[Edited on 27-12-2013 by Hennig Brand]

Turner - 27-12-2013 at 15:18

I doubt that diesel straight from the pump at a gas station wouldn't work, it only ends up making 6% of the composition, plus AN by itself is explosive, that's not to say that Fuel Oil used for ANFO in industry is diesel from the gas station though.

Hennig Brand - 27-12-2013 at 15:37

So many different fuels have and can be used in ANFO type compositions that it makes me think any liquid hydrocarbon out of the pump at the gas station could be made to work (including gasoline). That 6% of fuel by weight results in much greater than 6% increase in energy output in comparison to straight AN. The fuel also makes it much easier to initiate.

bobm4360 - 27-12-2013 at 20:54

Fertilizer-grade AN and diesel straight from the pump works. You may need a booster.......

Regards,
Bob

Hennig Brand - 28-12-2013 at 05:28

Didn't bother to calculate it myself, but here is a snip-it from a source that should be accurate. The source is Yarchive and it is from a post made by G.Hurst.

"At ca. 210C decomposes mostly into H2O and N2O. Remember Texas City?

At 210C, yes, but in the texas city explosion it is more likely
that the reaction looked something like this:

8NH4NO3 -> 5N2 + 4NO + 2NO2 + 16H2O

Not counting the loss of nitrogen oxides to fuel impurities.

A trace of organics would have had an enormous effect on the
energy release. Both the above equation and the low temperature
decomposition to N2O yield only about 130 kcal/kg (approximate)
whereas the mixture with 5.7% fuel oil delivers over 1000 kcal/kg.

Like gunpowder, AN does not explode to yield its lowest energy
products. In the presence of fuel oil though, not only the
theoretical maximum energy increases but also the efficiency in
producing the optimum low-energy products (H2O, N2 and CO2)."

The organic fuel present makes a horrendous difference!

I have heard that the fertilizer grade can work, but it is definitely not optimal. It is very dense and non-porous, so it doesn't absorb the optimal quantity of fuel oil unless crushed to a smaller particle size first. It usually has a coating on the prills too which complicates absorption of the fuel oil (unless the prills are crushed or the coating removed). With lots of confinement (borehole) and a big enough booster, it could still be made to work even if it is not optimal (so I have heard).

[Edited on 28-12-2013 by Hennig Brand]

Pard - 31-12-2013 at 17:47

Fert grade AN is working, just ask the poor victims of terror attacks in Oklahoma or Norway.

macckone - 31-12-2013 at 18:05

Fertilizer in the US now contains inhibitors to reduce its explosive potential. I don't know what they are and they are apparently not universally used nor are they used in storage only before sale.
The recent texas explosion is proof that AN will cause a great deal of damage.

Hennig Brand - 1-1-2014 at 07:57

Quote: Originally posted by Pard

Fert grade AN is working, just ask the poor victims of terror attacks in Oklahoma or Norway.

Actually from what I understand the fertilizer (Oklahoma City) was most likely processed in such a way so as to reduce particle size or at least break open the prills. There was also a lot of evidence that a large amount of nitromethane was used along with fuel oil. ANNM is a much different beast than ANFO. Also the charges were massive, which normally means that tolerances are also massive. Also, more than likely a whole stick of dynamite or something similar was used as an initiator. Just because fertilizer was used does not mean that it wasn't processed in some way. I have experimented with ANFO a bit and have found it miserable stuff to work with except in large charge sizes (for the hobbyist) and when prepared properly and initiated with a strong booster. I am not trying to say that fertilizer grade AN won't detonate, and I am not an expert in ANFO blasting either.

ANFO is not a particularly powerful explosive (relatively), but it is cheap and when used in relatively large quantities it definitely can do a lot of damage.

[Edited on 1-1-2014 by Hennig Brand]

testimento - 2-1-2014 at 23:28

AFAIK the critical purity for AN is not actually very high, I cannot give precise estimates, but quite a lot of stabilizers has to be added to render it compatible with combustibles, something even as much as 20-30% of weight.

From the ideal calculations down to practice, the ANFO composition can certainly be detonated with pretty much any combustible, when the amount is large and there is a good enough detonator.

But, as it is said, as long as it contains nitrates, explosives can be made out of it. The effort required may increase a lot, of course.

Pard - 5-1-2014 at 16:27

Quote: Originally posted by Hennig Brand

Quote: Originally posted by Pard

Fert grade AN is working, just ask the poor victims of terror attacks in Oklahoma or Norway.

These thing you say is known. The wikipedia says they used nitromethane. A lot of nitromethane actually ($3,500 is what McVeigh said) I didn't think we were discussing the particulate size of the various AN, but rather the qualities and gradings. I.e blasting grade and fert grade. They used Ammonium nitrate, 630L Nitromethane (wanted to use hydrazine originally), 350lbs of Tovex tubes also shock tubes and detonators. They did use mainly the nitromethane but some diesal was also there.

This last bit was off topic, but just thought if it was being discussed, we should know it truly.

While the article doesn't tell of the particle size, I am stuck in find it hard to believe he crushed so much AN. It would be difficult to crush 20 kgs efficiently, let alone so much more i think.

ScienceSquirrel - 6-1-2014 at 08:31

I believe the IRA who used ANFO on a multi ton scale during the Troubles used to pack it into milk churns. These are aluminium drums with a wall a few milimetres thick.
Their recipe had a few percent of sugar added as well which partly overcame the fact that they were using fertiliser grade and a stick of blasting explosive was used to initiate it.
Typical IRA car bombs were hundreds of kilograms in size and were pretty devastating.