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Last week on August 4, 2020, the city of Beirut, Lebanon, suffered a tragic, massive explosion at its seaport, killing hundreds, wounding thousands, and rendering hundreds of thousands homeless. (bbc.com) The explosion resulted from the ignition, apparently by a fire in an adjacent building, of 2,750 tons of ammonium nitrate stored in a dockside warehouse. Ammonium nitrate serves as a widely used agricultural fertilizer and as an explosive.
The chemical formula NH4+NO3- for ammonium nitrate contains two nitrogen, three oxygen, and four hydrogen atoms. Many people would recognize the distinctive smell of ammonia from window washing liquid such as original Windex. The ammonium salt, like table salt, consists of two chemicals held together by electromagnetic forces just as the positive and negative poles of a magnet attract each other, the positive ammonium ion attracts the negative nitrate. Together, the charges balance each other out, allowing the chemical to remain stable at average temperatures. The general stability of ammonium nitrate and its being soluble in water make it a convenient source of nitrogen for farming.
Although stable under general environmental conditions, ammonium nitrate decomposes at higher temperatures around 575 degrees Fahrenheit (300° C), around the same temperature that wood catches fire. When ammonium nitrate decomposes, it makes nitrogen, oxygen, water, and nitrous oxide. The decomposition of ammonium nitrate generates heat. The combination of the expanding gasses with heat generation makes it an ideal explosive that gets used around the world in mining and construction as well as for improvised explosives.
The explosive quality of ammonium nitrate has resulted in many deadly explosions over the years. A massive ammonium nitrate explosion in Texas City near Galveston, Texas, in 1947 made local residents think that the Russians had dropped an atomic bomb on their port city. (washingtonpost.com) Since the year 2000, other ammonium nitrate explosions have taken lives around the world. Sixty tons of ammonium nitrate exploded in Toulouse, France in 2001, taking thirty lives, and in 2015, a massive explosion of illegally stored ammonium nitrate exploded in Tianjin, China, killing 165 people.
All living things from plants to animals absolutely require nitrogen to survive and grow because nitrogen forms an essential building block in vital cellular processes from the production of protein to the replication of DNA. Although much of the earth’s atmosphere consists of nitrogen gas (78%), most plants and animals cannot convert nitrogen gas directly into forms of nitrogen that cells can use. Plants need nitrogen in a fixed form such as ammonium. The kind of nitrates that plants need get produced by microorganisms that pull the nitrogen from the air and convert it to a kind of nitrogen plants can use. Legumes such as alfalfa, clover, and soybeans have a special symbiotic relationship with these microorganisms. These plants are called nitrogen-fixing plants because they are useful for giving farm soil the kind of nitrogen that plants need. Nitrogen-fixing plants provide over half of the nitrogen need in agriculture, but that isn’t enough to feed the whole world. To grow enough food, farmers also rely on nitrogen-based fertilizers like ammonium nitrate to help make up for the rest of the needed nitrogen. (ourworldindata.org) Even though it is dangerous when stored incorrectly, ammonium nitrate remains a valuable fertilizer for feeding the Earth.
The dual applications of ammonium nitrate for fertilizer and explosives have led to a long history of this chemical providing an essential compound that helps to feed a growing world population that would starve without such synthetic fertilizers and a checkered history of deadly explosions. The tragedy of Beirut should never have happened. It turns out that the ammonium nitrate had been sitting in that warehouse for there for over six years. According to the BBC, this particular shipment of ammonium nitrate was destined for explosives manufacturing by Fábrica de Explosivos Moçambique (FEM), a Mozambican explosives manufacturing company. (cnn.com) According to multiple news sources, this shipment of ammonium nitrate had been sitting in storage for six years due to a dispute over shipping fees. After years of neglect, the shipment caught the heat from a fire next door, causing the explosive reaction that destroyed about half the city.
The explosive quality of ammonium nitrate has moved governments, including the United States, to push for alternative fertilizers for agriculture. One alternative, urea, provides a non-explosive option. However, it evaporates when applied to crops making it less efficient. According to researchers at the University of Missouri, up to 40% of urea applied to a crop can evaporate away without rainfall within 48 hours. The need for fertilizers to feed our growing population will not diminish, but the dangers of ammonium nitrate indicate the need for cost-effective alternatives. Until that time comes, the safe handling and storage of ammonium nitrate require our closest attention.
Dr. Smith’s career in scientific and information research spans the areas of bioinformatics, artificial intelligence, toxicology, and chemistry. He has published a number of peer-reviewed scientific papers. He has worked over the past seventeen years developing advanced analytics, machine learning, and knowledge management tools to enable research and support high level decision making. Tim completed his Ph.D. in Toxicology at Cornell University and a Bachelor of Science in chemistry from the University of Washington.
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