What kind of stuff is it? What is it used for? And how can it lead to such an explosion?
The Lebanese capital Beirut was shaken yesterday afternoon by an enormous explosion in the port area, near the center. The event currently numbers 78 dead and thousands injured. Moreover, the havoc is immense. The enormous blast wave shattered windows, toppled doors and shook buildings to their foundations. Lebanese Prime Minister Hassan Diab said the devastating explosion was caused by an estimated 2,750 tons of ammonium nitrate, which had been dusting in a warehouse for six years. But what kind of stuff is this? And how could things go so badly wrong in Beirut?
Ammonium nitrate (NH4NO3) is a highly water-soluble salt of nitric acid and ammonia and is often used in fertilizers. The pure substance itself has a low sensitivity and is therefore difficult to detonate (although that has sometimes gone wrong in the past). But in combination with gasoline or kerosene, for example, ammonium nitrate can become explosive, which means that the substance is frequently used in mining. “Ammonium nitrate is classified as a hazardous substance,” said associate professor Stewart Walker of Flinders University. “Although it is known as a ‘non-flammable’ substance, it can explode under certain conditions.”
Ammonium nitrate is therefore not flammable on its own, but it can serve as an oxidizing agent to facilitate the combustion of other substances. When ammonium nitrate is heated, the solid passes through a number of phase transitions to eventually decompose into gaseous products. “When it gets hot enough, gases can form, including nitrogen dioxide,” explains Professor Emily Hilder of the University of South Australia. “This increases the risk of explosion, especially in a closed environment. The risk is also increased if pollutants are present. Only a very small amount can make ammonium nitrate unpredictable. ” So if only a little bit of fuel is added – such as oil or organic material – ammonium nitrate can become very dangerous. When combined with heat, such a mixture can easily have catastrophic consequences. The scale in Beirut also suggests that this involved large amounts of dust.
In short, an explosion occurs when a large amount of an energetic substance detonates, creating a large volume of trapped, hot gases that expand and cause a shock wave. “The video footage of the Beirut incident initially shows white-gray smoke, followed by an explosion that created reddish-brown smoke and a large white ‘mushroom cloud’,” says Walker. “This means that the released gases consisted of white ammonium nitrate vapors, toxic nitrous oxide and water.”
Due to the above-mentioned properties, ammonium nitrate is sometimes used in improvised explosives. “The Oklahama bombing in 1995 was carried out using three to four tons of ammonium nitrate,” notes researcher David Caldicott of the Australian National University. In addition, the bombing by Anders Behring Breivik, in the government district of the Norwegian capital Oslo on July 22, 2011, was also caused by explosives based on ammonium nitrate extracted from fertilizers. So if ammonium nitrate falls into the wrong hands, it can have serious consequences. Exactly how the explosion started in Beirut has yet to be revealed. “The cause of such a detonation remains to be investigated, such as whether it was accidental or deliberate,” continues Caldicott.
Although the explosion has already claimed many casualties at this point, it is expected to increase even further. “This is clearly a very large explosion and the reported death toll is likely to be much higher than currently identified,” said Caldicott. The disconcerted Lebanese prime minister has therefore vowed to punish those responsible.