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Improper storage and handling of ammonium nitrate has caused some of the worst chemical explosions in the past century and most recently in West, Texas, where 15 people were killed. To address ammonium nitrate problems, three federal agencies jointly released guidance aimed at improving ammonium nitrate chemical risk management. Today we will look at some lessons learned from past disasters, and tomorrow we will review safe handling and storage practices for ammonium nitrate.
Following the fertilizer factory explosion in West, Texas, this year, President Obama ordered a renewed effort to educate employers, workers, and first responders about the dangers associated with the unsafe storage and handling of ammonium nitrate (AN) in the workplace. In response, the U.S. Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA), and the Bureau of Alcohol, Tobacco and Firearms (ATF) created the Chemical Facility Safety and Security Working Group, which produced the Chemical Advisory: Safe Storage, Handling, and Management of Ammonium Nitrate (Advisory)to assist facilities with AN and reduce the potential for explosion and fires.
According to the Advisory, AN is produced and used in the United States primarily for fertilizer and in explosives and blasting agents. Chemically speaking, AN, by itself, is actually stable at most ambient temperatures and pressures and does not burn. However, because AN is a strong oxidizer, it “supports and accelerates the combustion of organic (and some inorganic) material.” It also may explode under conditions subjecting it to strong shocks and when confined and heated to high temperatures.
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After reviewing several studies and AN-related fires and explosions worldwide, the Chemical Facility Safety and Security Working Group developed several key lessons learned from the accidents. In the past, industry learned from AN disasters as far back as the 1920s when German workers tried to break up large amounts of caked AN and ammonium sulfate mixtures using explosives, initiating a general detonation of the mixture. In 1947, two cargo ships in Texas exploded—the first likely from a fire of wax-coated AN in its hold, and the second from a fire caused by the first ship explosion. Almost 600 people were killed, including almost the entire staff of the responding Texas City Fire Department.
Lessons learned here are simple: do not use explosives to break up caked AN and do not coat AN fertilizer with wax, which is itself a fuel source.
Similarly, based on AN incidents in France and the United States during the past 12 years, the Working Group isolated additional lessons learned. Although the West, Texas, explosion is still under investigation, two accidents in France in 2001 and 2003 described in the Advisory offer additional scenarios of what not to do.
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In the first, 200 to 300 tons of AN stored in bulk at a fertilizer factory hanger exploded killing 30 and injuring 2,500, leveling the factory and heavily damaging another 10,000 buildings. The exact cause is not known, however, storage of incompatible materials is suspected. The second incident in 2003 involved 3 to 5 tons of AN stored in bags at a two-story farm warehouse, which exploded killing 26, including 18 firefighters. Again, improper storage methods are considered the likely culprit.
Lessons learned from these and other similar accidents include:
- “AN will self-compress/self-confine under some conditions, becoming much more likely to explode.
- AN is at risk for explosion when stored near other material that can add fuel to the AN – such as grain, sugar, seeds, sawdust, and most especially petroleum fuels such as diesel.
- AN is a powerful oxidizer and a rich sources of nitrate, which provides energy to an explosion. Thus the presence of fuel and/or heat (and especially both) near an AN is a very high hazard situation.”