The ammonium nitrate/fuel oil compound typically comes in pellet form (Image via Wikimedia)
What began as a small factory fire outside Waco, Texas turned into a disaster of historic proportions in less than an hour on Wednesday night. And there's one very specific reason for that pivot: the factory on fire was filled with fertilizer that was likely laced with ammonium nitrate, an inexpensive yet highly explosive chemical compound that boosts soil productivity. "Highly explosive" is almost understating the facts. The blast in the tiny town of West, Texas sent a hundred-foot-wide fireball into the air and registered as a 2.1-magnitude earthquake on nearby seismographs. The explosion killed as many as 15 people and injured over 160.
Before digging too deep into the question of explosive fertilizer, it's important to point out that scientists do not yet know what caused the blast. Most people suspect it's ammonium nitrate-related. We know that the West Fertilizer Co., the Texas plant that's now in ruins, stored large quantities of ammonia, a key ingredient in ammonium nitrate, and it was fined $2,300 by the Environmental Protection Agency in 2006 for insufficient risk management practices including, evidently, not taking care of its storage tanks. Experts say that the details of the incident — notably the explosion occurring between 30 minutes and an hour after the fire broke out — are consistent with tanks of ammonium nitrate heating up to the point of combustion.
This ammonium nitrate stuff sounds pretty dangerous because it can be. However, when properly stored, it's perfectly safe. Ammonium nitrate on its own won't explode unless it comes into contact with a hydrocarbon-based fuel like oil and a detonator. The stuff that's used in mining and (God forbid) improvised explosive devices is typically an ammonium nitrate/fuel oil compound known as NFO. But again, pure ammonium nitrate is safe as long as you keep it cool. As it heats up, the chemical compound starts to oxidize, producing nitrus oxide and water, and it does't take much of a combustion to set off an explosive chain-reaction.
Accidents like what we saw in West Texas are not common, but they're not unheard of, either. In fact, the deadliest industrial accident in American history was caused by 2,300 tons of ammonium nitrate that had been loaded onto a French ship called the Grandcamp in the port of Texas City, Texas back in 1947. The parallels with the West, Texas disaster are unmistakeable.
After being turned away from the port of Houston due to its ammonium nitrate cargo, the Grandcamp docked at Texas City. While at port the Grandcamp somehow caught fire—much like the fertilizer plant in West, Texas—and the resulting explosion was unprecedented. The blast killed 581 people, including nearly all of the town's fire department who had rushed to the scene of the initial fire—just like the West, Texas fire department did. Over 5,000 people were injured, and the surrounding area was leveled. One of the Grandcamp's anchors was found a mile-and-a-half away from the blast.
All in all, there are 17 major explosions involving ammonium nitrate on record worldwide since 1921. So these disasters aren't as common as, say, a car accident, but they are persistent. Why don't we find a new fertilizer? Slate's Explainer asked the same question back in 2005 and the answer he suggests is rather capitalistic: "Because ammonium nitrate is in many ways one of the best (and certainly one of the cheapest) sources of crop-nourishing nitrogen available. For starters, ammonium nitrate is inexpensive to manufacture."
Ammonium nitrate also works really well as a fertilizer. (Plants love nitrogen!) So in order to strike a compromise between the very appealing side of ammonium nitrate and the more dangerous side, many countries around the world have regulations in place that require stores of ammonium nitrate to be cut with other chemicals to keep the nitrogren levels low. In the European Union, the limit is 28 percent nitrogen; in the United States, such a regulation doesn't exist. Another trick is to require the compound to be stored in large pellets that don't oxidize as quickly or soak up fuel oil as easily. The United States does not.
There's bound to be a new conversation about ammonium nitrate regulation after this blast. Whether it's newly minted experts on the topic rapping about how the government should fix the danger or the government themselves actually looking at laws remains to be seen. The proximity of the disaster in Texas and the terror attack at the Boston Marathon is not insignificant either, especially since the Oklahoma City bombing was caused by a fertilizer bomb.
One thing's for sure, though. The town of West, Texas needs help. Click here to find out how.