THE MAGAZINE

Chemical Facilities Tackle an Explosive Problem

By Megan Gates

Ammonium Nitrate

The executive order expressly calls for the working group to examine how ammonium nitrate is handled and for the Secretary of Homeland Security, the Secretary of Labor, and the Secretary of Agriculture to “develop a list of potential regulatory and legislative proposals to improve the safe and secure storage, handling, and sale of ammonium nitrate and identify ways in which ammonium nitrate safety and security can be enhanced under existing authorities.”

Millions of tons of ammonium nitrate are produced each year in the United States and are used for fertilizer and other chemicals, including nitrous oxide. It is also used to produce explosives, and to make blasting agents. The list the secretaries compiled has not been made available to the public yet, but the EPA, OSHA, and the ATF released a chemical advisory about the safe storage, handling, and management of the chemical in August of 2013, using previous incidents, including the West, Texas, disaster, to make initial recommendations about the use of the chemical.

The working group noted that, when ammonium nitrate isn’t properly stored, it can have devastating effects like those seen in September 2001 in France. At the Azote de France fertilizer factory in Toulouse, 200 to 300 tons of ammonium nitrate that was stored in bulk in a hangar exploded, killing 30 people, causing 2,500 injuries, and heavily damaging 10,000 buildings. The exact cause of the explosion is unknown, but it is believed to have been the result of storage with incompatible material.

“Pure ammonium nitrate is stable and will explode only under extraordinary circumstances,” the advisory said. “However, the addition of combustible materials, such as sugar, grain dust, seed husks, or other organic containments, even in fairly low percentages, creates a dangerous combination and the ammonium nitrate mixture becomes far more susceptible to detonation,” warned the advisory.

In the case of the West explosion, the warehouse was filled with seeds that fed the fire and may have aided its spread. “Not only were the warehouse and bins combustible, but the building also contained significant amounts of combustible seeds, which likely contributed to the intensity of the fire,” according to the findings of the U.S. Chemical Safety Board, which investigated the disaster alongside several other federal agencies.

The advisory board noted that ammonium nitrate is particularly dangerous because it is its own oxidizer, meaning “it provides its own oxygen and once combustion begins, it cannot be smothered,” according to the advisory. “Moreover, the combination of heat and confinement will accelerate combustion, perhaps to the point of detonation.”

Because of this, the advisory recommends storage and process conditions to avoid, including avoiding heating ammonium nitrate in a confined space, ensuring that it’s not exposed to strong shock waves from explosives, avoiding contamination with combustible materials or organic substances, avoiding contamination with some metals—aluminum powder, chromium, copper, cobalt, and nickel—and chlorides, and keeping molten or solid ammonium nitrate out of confined spaces, such as sewers or drains.
 

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