One of the main components in manufactured fertilizer is ammonium nitrate. Like we said, nitrogen is one of those macronutrients that plants love, so a lot of fertilizers are nitrogen-based.
Of course, we can't just bottle up some nitrogen and pour it on the ole carrot patch. Atmospheric nitrogen has a really strong chemical bond that plants can't easily break, so fertilizer companies create a nitrogen-based substance that's much easier for plants to take apart. Ammonium nitrate is one such compound. And it's used for good reason: The ammonium part sticks around longer without evaporating, so it's great for hot summer fields, and the nitrate is easily used by plants. Even more compelling in the agricultural industry, it's inexpensive to manufacture. You combine ammonia and nitric acid, and you're done.
But what makes ammonium nitrate capable of such lethal explosions? Surprisingly, not much. Truly, ammonium nitrate is a relatively stable compound, according to the U.S. Environmental Protection Agency. In other words, when it's just sitting quietly somewhere, ammonium nitrate isn't that big of a problem because it needs a relatively high activation energy (the energy needed to cause a chemical reaction) to explode [source: Encyclopaedia Britannica]. However, if an accident where some sort of detonation -- a spark, or some kind of energy -- occurs, you better believe that ammonium nitrate is deadly. The compound essentially makes its own fuel (from the ammonium) and oxidizer (the nitrate), so its reaction is violent and long-lasting [source: Di Justo].
So it makes sense that a fire seems to be the cause -- and not the outcome -- of what happened in West, Texas. If indeed ammonium nitrate proves to be the culprit, it would most likely have gotten very, very hot (probably in an enclosed space) to react the way it did. The explosion could very well have caused the seismic activity (equal to a 2.1 magnitude earthquake) reported at the scene [source: Di Justo].
Author's Note: Why does fertilizer explode?
It's worth noting that although ammonium nitrate and other fertilizer explosions are terrible, they are rare. But we'd be remiss not to mention that some folks have also noted that fertilizer can make a deadly, intentional weapon. Timothy McVeigh, for one, used a fertilizer bomb in the 1995 Oklahoma City bombing.
- Beach, Patrick. "66 years ago, Texas City fertilizer blast killed 600, injured thousands." Austin American-Statesman. April 18, 2013. (April 18, 2013) http://www.statesman.com/news/news/66-years-ago-texas-city-fertilizer-blast-killed-60/nXQLC/
- Di Justo, Patrick. "The fertilizer bomb." The New Yorker. April 18, 2013. (April 18, 2013) http://www.newyorker.com/online/blogs/elements/2013/04/texas-fertilizer-plant- -nitrogen-science.html
- Encyclopaedia Britannica. "Activation energy." Encyclopedia Britannica Online. (April 18, 2013) http://www.britannica.com/EBchecked/topic/4535/activation-energy
- Environmental Protection Agency. "Explosion hazard from ammonium nitrate." United States Government. December 1997. (April 18, 2013) http://www.epa.gov/osweroe1/docs/chem/ammonitr.pdf
- International Fertilizer Industry Association. "Website." International Fertilizer Industry Association. (April 18, 2013) http://www.fertilizer.org/ifa/HomePage/FERTILIZERS-THE-INDUSTRY
- Koerner, Brendan. "Why do we use explosive fertilizer?" Slate.com. April 18, 2013. (April 18, 2013) http://www.slate.com/articles/news_and_politics/explainer/2005/01/why_do_we_use_explosive_fertilizer.html
- Plumer, Brad. "The Texas fertilizer plant explosion is horrific. But how common is this?" The Washington Post. April 18, 2013. (April 18, 2013) http://www.washingtonpost.com/blogs/wonkblog/wp/2013/04/18/the-texas-fertilizer-plant-explosion-is-horrific-but-how-common-is-this/