Ammonium nitrate may have caused last week’s Beirut explosion, Deutsche Welle reported. When it suddenly exploded on August 4th, 2,750 metric tons of the volatile substance had been sitting in port for seven years. The compound is just part of our history with explosives.
According to Deutsche Welle, Lebanese officials are narrowing down the potential causes of the explosion in Beirut on August 4. One of the explanations is a popular—but controversial—chemical compound: ammonium nitrate, commonly used in fertilizer.
“The ammonium nitrate in question was said to have been brought to the Lebanese capital on a freight ship that was impounded for safety reasons in 2013,” the article said. “Ammonium nitrate is a white crystalline salt that can be fairly cheaply produced from ammonium and nitric acid. At 32.2 degrees Celsius (89.96 degrees Fahrenheit), ammonium nitrate changes its atomic structure, which in turn changes its chemical properties.”
Unfortunately, its potential for being volatile has led to several deadly disasters around the world—some of which were intentional. Timothy McVeigh used ammonium nitrate to bomb a federal building in Oklahoma City in 1995, while a Norwegian extremist in Oslo used it for similar purposes in 2011. Humanity’s history with explosives dates back 2,000 years.
Gunpowder: The First Man-Made Explosive
It’s believed that China discovered gunpowder as early as the 1st century CE. What makes it explosive? There are three components: a kind of fuel, like pure hydrogen; a form of ignition, such as a flame; and an oxidizer, like oxygen.
“The chemical reaction that drives gunpowder explosions, specifically black powder explosions, is this one: It’s carbon with potassium nitrate and a little bit of sulfur to alter the reaction a bit to lower the energy needed to get it to go,” said Dr. Ron B. Davis Jr., Associate Teaching Professor of Chemistry at Georgetown University.
Dr. Davis said that gunpowder explosions release high amounts of energy very quickly, and all of gunpowder’s solid ingredients react to form carbon dioxide and nitrogen gases, which cause expansion.
Considering this, “you have one very hot, very forceful expansion as a result of this reaction,” he said. “This force is adequate to propel rockets across the sky or musket balls across a battlefield. It remained the method of choice for this purpose from the time of its invention until the late 1800s.”
The First Fully Self-Oxidizing Compound
An Italian chemist named Ascanio Sobrero discovered the world’s first fully self-oxidizing explosive. It began with soap.
“Sobrero used glycerin, a readily available material that’s a by-product of the soap-making process,” Dr. Davis said. “He added some nitric acid to his glycerin to create a very familiar compound to us all—nitroglycerin. In this particular reaction, the glycerin molecule reacts with nitric acid and a condensation reaction to form water [and create nitroglycerin].” There’s so much oxygen in the compound that it self-oxidizes.
When mixed properly, nitroglycerin leaves no carbon dioxide leftovers; in fact, it leaves a bit of oxygen after its combustion. Dr. Davis said nitroglycerin has all it needs to release the potential chemical energy stored inside it. “This is what makes nitroglycerin such an effective and potent explosive,” he said.
According to Dr. Davis, Sobrero found nitroglycerin to be so unstable that he became his own strongest critic. Soon, Alfred Nobel discovered him and sought to stabilize nitroglycerin, eventually inventing not only the blasting cap but also one of the most popular explosives of modern times: dynamite.
Dr. Ron B. Davis, Jr. contributed to this article. Dr. Davis is an Associate Teaching Professor of Chemistry at Georgetown University, where he has been teaching introductory organic chemistry laboratories since 2008. He earned his PhD in Chemistry from the Pennsylvania State University.