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].