On August 4, a major fire broke out in a Port of Beirut warehouse and spread to 2,750 tons of stored ammonium nitrate. In the past, many incidents have occurred with ammonium nitrate: quite a few of them with disastrous consequences, often developing in a similar pattern to what we saw in Beirut. How could this happen? Was it an unlucky chain of events, or the result of a deliberate malicious act? Can we consider this as an incidental ‘freak’ accident?
The explosion caused at least 200 deaths with many thousand injured. An estimated 300,000 people have been left homeless and large parts of the Lebanese capital are now flattened. Some reports say the shock wave was so intense that it was felt in Cyprus, an island about 250 kilometers north-west of Lebanon. A giant orange cloud of combustibles was seen following the detonation, suggesting the vast release of nitrogen dioxides.
It is too early to draw conclusions as to the immediate causes of the accident and an independent investigation will need to be conducted. But one thing is already sure: this accident is not a one-off.
The ammonium nitrate that caused the explosion appears to have been impounded and stored for six years after it was seized from a cargo vessel in 2014. Ammonium nitrate is a white crystalline solid consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic (i.e. tending to absorb moisture) as a solid. It is predominantly used in agriculture as a high-nitrogen fertilizer, with an estimated global production of more than 20 million tonnes. Thus, it is hardly an exotic material, rather than a household product.
If ammonium nitrate’s primary use is as a fertilizer, how can it cause so much mayhem? Ammonium nitrate can decompose – non-explosively and non-violently – in temperatures above 210 °C into nitrous oxide gas and water vapor when heated. However, under certain conditions it can be induced to decompose explosively. Explosions are not uncommon. Many relatively minor incidents are recorded every year, and several large and devastating explosions have occurred. Historical data reveals that industrial accidents involving ammonium nitrate explosions have killed hundreds of people since the early twentieth century. Accordingly, the explosion hazards of ammonium nitrate are well understood. It is also known that large stockpiles of the material can be a major fire risk as ammonium nitrate acts as oxidizer.