OKC Federal building compared to West fertilizer company incident (Texas) - not adding up

IDK how many of you have seen the explosion of the fertilizer company in West Texas but it was huge! The reports are that they had 540,000 lbs of ammonium nitrate on site as well as 110,000 lbs anhydrous ammonia - both of these are explosive under the right circumstances. While ammonium nitrate will usually not detonate by itself as it needs a booster (initiator charge/blasting cap) of some type, it will catch fire and there is such a thing as reaching run-away conditions where if there is enough of the fertilizer in one location, it will explode (if on fire or even with minimal ignition sources). The fire was more than enough to reach the run-away point where it detonated the stockpile. This is similar to black powder which will not explode (it actually burns very quickly) if put in a pile and lit, but if the pile is large enough, the run-away conditions are met and it will indeed explode.

As for the anhydrous ammonia, this is a flammable gas that is kept under high pressure and sometimes refrigerated. If the temps rise it could cause rupture of the tank causing a massive explosion which may have been the initiate of the ammonium nitrate stock pile. It really makes no difference which chemical initiated the explosion as it was basically inevitable once the blaze was out of control, but what we need to look at is the damage done to the immediate and surrounding area as well as the effects at a distance (from 1km to 40km).

Now take a look at the damage to the OKC fed building which was supposedly caused by 3 - 3.2 tons of explosive (max 7,000 lbs is reported). They have reported that it was an ammonium nitrate bomb with a fuel added to sensitize it to allow it to be able to detonate. The West explosion had a minimum of 77 times the amount of nitrate. I'm having a difficult time finding the potential energy of the ammonia but it looks like it could be equal to anywhere from about 55,000 to 165,000 of ammonium nitrate which would then give a total of 85 times to 101 times the explosive amount of the OKC bombing.

Now I'd like you to take a look at the reports of the incident and how far

West plant - Notice that there are still silos standing!!

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OKC (they mention a 4m deep crater! The west plant didn't even crator!

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www.createwebquest.com...

media.npr.org...

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(I CAN'T STAND THE PHOTO INSERT OF THIS FORUM - SO UN-INTUITIVE!!!) /rant

Now some people are going to say that the west plant didn't have the material confined like in barrels, well that isn't an issue when you have such a large quantity that reaches run-away velocity - it doesn't need to be confined (much like the gun powder example).

So what I can say from looking at these two explosions that use very similar explosives (both ammonium nitrate, but one had a little extra ingreditent to allow it to be sensitized). Now the thing about explosives is that they have a known rate of detonation called the velocity of detonation. The higher the rate, the more powerful the explosive is, for the most part. These two should have been within 500 meters per second or so but when looking at the OKC I see something that was most likely a MUCH higher VOD explosive. Ammonium nitrate is about 2,700 to 3,000 m/sec VOD while ANFO is about 3,900 to 4,200 m/s VOD. I don't think this difference explains the massive difference in the destruction that we see.

There are many explosives that the military uses that have a VOD of 8,400 m/s to 9,400 m/s (as common explosives) and some over 10,000 m/s (more rare). TNT (the standard by which most explosives are measured) is 6,900m/s and dynamite is 7,700m/s. I think what we are seeing is the effects of a MUCH higher VOD than what we have been told and I would think that it would be very difficult to get these explosives outside of the military or some foreign power.

One of the biggest impacts, still being felt, from this explosion is the effect on small farmers. Ammonium nitrate was one of THE BEST fertilizers you could buy as it was the perfect source of nitrogen, it was incredibly cheap and could be produced out of air! The average price of the replacement fertilizers is about 6-12x the price of pre OKC ammonium nitrate (when looking at available nitrogen per dollar spend). This has caused food prices to increase and many farmers to have to sell their farms and many fertilizer companies are getting rich selling their replacement fertilizers which many believe are no where near as good.

I'm curious of what others think about this, especially those with experience with munitions and have seen the effects of high VOD explosives. To me, the OKC building looks like the buildings after WWII that were shelled or bombed (and they used TNT as a minimum, so a minimum of 6,900m/s in those shells, though they often used stronger explosives then).

I'd post pics if I could figure that out. Sorry about the links, they do go to the pics though..

Oh good times how sideways this whole case study could go!

Dude, it's probably insurance fraud on behalf of the West company, right?

a reply to: DigginFoTroof

From what I can recall, the West, Texas explosion damaged quite a bit of the surrounding area. I remember that a fellow colleague from an office branch in that area lost her home because it was leveled in the blast.

Perhaps the location of the materials involved had an impact on the overall sustained damage.

Otherwise, you make quite a compelling argument.

a reply to: DigginFoTroof

Lots of variables to consider, major one being how much AN actually detonated compared to the volume blown away as dust as it wouldn't be stored in the ideal condition for efficient detonation whereas ANFO is the ideal state for intentional max damage.

Well the thing about a burning pile of this nitrate, is that it won't "blow away" as dust once it reaches "critical mass" and detonates. There may be some (like a few hundred pounds) that might blow away while it was only on fire. Once the explosion happened, it was a chain reaction that detonated ALL of the AN (ammonium nitrate) and I would doubt that any significant amount would have been lost.

When the detonation happens, there is an instant rise in heat that is an uncontrolled thermal run-away which propagates to every surrounding molecule and it goes faster and hotter as it goes, much like a nuclear explosion. Any discussion of a portion, let alone a large amount of the AN being "blown away" in the blast, is either trying to confuse people, mislead them or has no idea of what they are speaking.

As for the ammonia, that is a horse of a different color and depending upon proximity to the flames, this could have been the ignitiator for the explosion. See, ammonia needs heat and O2 to burn and ammonium nitrate is net positive in O2 so they are kind of perfect when mixed (in proper protions and they are actually fairly close in the reported proportions - coincidence??? seems doubtful IMO). What this would do is create the largest fuel/air bomb ever created also known as a Thermobaric bomb. White the AN already hot and in a contained pile on fire, the ammonia is VERY flammable, when the heat weakens the anhydrous ammonia tank enough to rupture, there is a large amount of energy released (as well as LOTS of flammable gases) that then lends massive energy to the burning AN (which has excess O2, which the NH3, ammonia, needs to burn well) and is more then enough for the pile of AN to go critical and we have the fuel-air explosion as well as the standard ammonium nitrate boom.


I'd like people to look at buildings where military explosives are used to destroy a building either by shelling or bombing (ariel or truck). Even if it is jut TNT as the primary explosive. This is when there is most often a crater left at the scene (when there is paved or concrete surface). Lesser explosives can leave craters as well but usually on much softer surfaces like dirt, sand, etc. I've seen videos of 500+ lbs of AN detonated on top of a concrete slab and it scorched the slab, left it cracked but not a crator.

My postulation is that the explosives used in OKC were something of a much higher VOD and probably high brisinance (was there any aluminum or magnesium dust found in the surrounding area??). I still remember hearing that they had found 2 other bombs "bigger" than the original as well as a basement full of military vehicles such as tanks, APC's, helicopters, etc on a level that wasn't supposed to be there (like 3-4 levels down). This was reported by CNN, I know for sure, because that was the only channel we watched in our class back then and some of the military kids were talking about what they might have found and why it might have been there (no-one had a good reason for any of it..)

I am still having a difficult time understanding how some silo's are standing in Texas just 50 ft from the primary blast site (and no amount of shielding would protect that - it was only corregated steel building construction). with 85-100x the explosives, PLEASE tell me how a 50ft metal silo is still standing 50 ft from the main blast? I've seen 50ft concrete silos come down in 100-130 mph winds (and they weren't under-mined/dug or anything). The metal silos that were there are not even like fuel oil tanks with 1/4 - 3/16" steel, these are much less thick and should have been crumpled like a used dixie cup after brushing your teeth.

This guy was asked to blow up the building, but turned it down. He explains all and why the building was targeted by the military in the first place. Fascinating interview.

a reply to: DigginFoTroof

The instability of the ammonium nitrate molecule was something of a late discovery, even later than glyceryl trinitrate. AN was used for making gunpowder as a substitute for potassium nitrate during the Napoleonic wars (Austrians from memory) and using it that way (oxidizer) in cannons and rifles didn't result in detonation so the molecule requires a huge shock to detonate particularly when dry (anhydrous) as it would have to be in a gunpowder mix or stored in pure form. The discovery of its potential for detonation when associated with a liquid fuel like oil plus fire was something of an accident.

Just my thoughts on one of the many variables here.
Was it stored in one huge pile (highly unwise) or lots of smaller locations separated by barriers (smarter) for example.
It's hygroscopic as well so needs special sealed storage to keep it anhydrous.

originally posted by: Pilgrum
a reply to: DigginFoTroof

The instability of the ammonium nitrate molecule was something of a late discovery, even later than glyceryl trinitrate. AN was used for making gunpowder as a substitute for potassium nitrate during the Napoleonic wars (Austrians from memory) and using it that way (oxidizer) in cannons and rifles didn't result in detonation so the molecule requires a huge shock to detonate particularly when dry (anhydrous) as it would have to be in a gunpowder mix or stored in pure form. The discovery of its potential for detonation when associated with a liquid fuel like oil plus fire was something of an accident.

Just my thoughts on one of the many variables here.
Was it stored in one huge pile (highly unwise) or lots of smaller locations separated by barriers (smarter) for example.
It's hygroscopic as well so needs special sealed storage to keep it anhydrous.

Well it was either stored in large piles or it was bagged and stacked in crates. Either way, as soon as the critical mass hit, it didn' t matter how it was stored or bagged (when we are talking about such a large quantity). Even if it wasn't anhydrous (the molecule really doesn't lend itself to hydrate forms like other nitrates but it is hygroscopic so it will attract water - I would suspect the facility to be environmentally controlled with a VERY low humidity level or else they would be dealing with large boulders of AN)