The explosion of the West Fertilizer Company plant in the town of West, Texas, has devastated the small community of twenty-eight hundred, killing at least five people and injuring more than a hundred and fifty. At least fifty to sixty homes have been damaged.
This is not the first fertilizer explosion to devastate an entire community: in 1947, Texas City, Texas, was the site of what has been called “the worst industrial accident in U.S. history,” in which a ship carrying twenty-three hundred tons of ammonium nitrate fertilizer caught fire and exploded, setting off a chain reaction that killed nearly six hundred people. More recently, Timothy McVeigh used a bomb primarily composed of fertilizer to destroy Oklahoma City’s Alfred P. Murrah Federal Building in 1995.
Why are fertilizers so explosive?
Plants need nitrogen to build proteins, and it is difficult to get that nitrogen from the atmosphere (which may seem odd, since our atmosphere is nearly eighty per cent nitrogen). The N2 molecule consists of two nitrogen atoms joined by a triple atomic bond; that triple bond makes atmospheric nitrogen so stable that, for years, scientists thought it was an inert gas. It takes a lot of energy to break apart the N2 molecule, energy most plants do not have, so they get nitrogen in other ways: either through nitrogen-fixing bacteria (bacteria equipped with special nitrogen-busting enzymes, which combine atmospheric nitrogen with hydrogen to make ammonia), or fertilizers like animal manure, whose composition can be nearly five per cent nitrogen.
Ammonium nitrate is probably the world’s most widely used artificial fertilizer. It is made of nitrogen, hydrogen, and oxygen. The bonds between these elements are less stable than atmospheric N2 bonds, so plants can more readily get at the nitrogen. The nitrate portion of the fertilizer (NO3) is already in the form plants can use; the ammonium portion (NH4) is slowly converted to usable nitrate by soil bacteria, and thus remains available to the plant for a longer time.
Now, think back to the very stable N2 molecule. If a lot of energy is needed to split the two nitrogen atoms and break those bonds, then, conversely, a lot of energy is given off when two nitrogen atoms come together to make the bond. The nitrogen atoms go from a less stable, high-energy state (such as in NO3 or NH4), to a very stable, low-energy state (such as in N2), with the excess energy being released very rapidly, even explosively. It’s not a coincidence that many of the most famous bomb-making chemicals—nitroglycerin, nitrocellulose, trinitrotoluene (TNT), and C4 plastic—are nitrogen compounds.
Video From The New Yorker
Thank You For Your Service: Healing From the Trauma of War
Another concern is the gas that was stored at the plant. Ammonium nitrate is most commonly made from anhydrous ammonia gas; the Dallas News reports that fifty-four thousand pounds of the gas were stored at the plant. When anhydrous (which means “without water”) ammonia meets with water, the reaction gives off heat and forms caustic ammonium hydroxide. When this happens in the body, the reaction can cause fluid to accumulate in the lungs, irritation of the large airways (bronchitis), inflammatory lung disease, and severe corrosive damage or burns to the mouth, throat, and stomach.
So why doesn’t ammonium nitrate explode spontaneously? Because of something called activation energy, which is defined as the minimum energy necessary to start a chemical reaction. Ammonium nitrate’s activation energy is just high enough that it will not explode in everyday use. But provide it with a source of energy, like a flame, spark, or even mechanical impact, and the results can be explosive. “The ammonium nitrate has its own fuel, the ammonium, and its own oxidizer, the nitrate,” making the process self-sustained, explained Jimmie Oxley, chemistry professor at the University of Rhode Island. It’s because of ammonium nitrate’s explosive potential that the Department of Homeland Security proposed an ammonium nitrate registration program in 2011, to regulate transactions involving the sale or transfer of ammonium nitrate at the point of sale.
Amateur video shows that the West Fertilizer Company plant was on fire—the town’s mayor described it as fully engulfed in flames—just before the explosion. The combination of unstable nitrogen bonds in the fertilizer, plus heat from the fire, resulted in an explosion as powerful as a 2.1 magnitude earthquake.
Photograph, of a vehicle near the remains of the fertilizer plant in West, Texas, by Mike Stone/Reuters.
