Friday, April 19, 2013

Two Reader Comments – 04-19-13 - West Fertilizer Explosion

There have been two comments about to my post from last night about the explosion at the West Fertilizer facility in West, TX (which is actually in the east-central portion of the State between Dallas and San Antonio). Those comments and my replies provide some additional information about the potential cause of the incident.

Ammonium Nitrate Decomposition

Jim avoids giving us a specific chemistry lesson but comments:

“There is not enough space for a chemistry lesson but AN will decompose into oxides of N2 and water when heated. This reaction is very exothermic. In bulk storage situations the heat cannot dissipate faster than it is being produced and a runaway decomposition can occur.”

If you are interested in a brief chemistry lesson on the decomposition see this at
To understand how this impacts storage of ammonium nitrate see this Canadian government site. Three things to note:

• Each mole (80.0 g) of ammonium nitrate produces 3.25 moles of gas. Combined with the exotherm produced by the reaction this provides for a rapidly expanding shell of gas which produces the devastating shock wave.
• The reaction also produces oxygen (O2) that promotes additional combustion of the already existing fire that would have started the heat rise in the first place in this instance.
• Fires frequently cause the collapse of storage tanks. This could provide the confinement to change the burning ammonium nitrate into exploding ammonium nitrate.

Probably not a Bleve

Ed Clarke doesn’t believe that the explosion was caused by an anhydrous ammonia bleve based upon the shock wave seen in various videos. He notes:

“Under intense heat form the fire, in a confined space, the AN in the storage bins pictured in the GE imagery (BTW, Bing birds eye view [here’s a link; click on Birds Eye] provides much better perspective) would have exploded.”

He does have questions about the source of the fire seen in the videos and suggests possible propane storage tanks. I suspect either that or some of the open top transport containers for ammonium nitrate could have been the fuel source, or even some of the other storage tanks that I mentioned in the original post.

A Potential Terrorist Target?

In any case, we will need to watch for the CSB reports on this investigation. Also note that the fire and explosion (and its extensive media coverage) show that an attack on small, out-of-the-way facilities like this could still bring the notoriety that terrorists crave. How much security do you see in the aerial view of the facility? Not even a fence.

ISCD – How many of these facilities have not been reviewed because no Top Screen was submitted? How many facilities like this that did submit Top Screens received a pass because they were in small towns?


Stu Fischbeck said...

Interesting note here: Anhydrous ammonia is not regulated as a flammable/explosive under the Risk Management Program (RMP) rules. Any offsite consequence analysis would therefore have only been performed on ammonia vaporization and the resultant toxic cloud. Ammonium nitrate is not covered by the RMP rule at all, although BATFE and/or DOT rules might address it under explosives.

Toni said...
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