By Shahrul Nizam Ahmad
Ammonium nitrate (AN) has become the prime focus recently as it has been alleged to be the cause of the deadly explosion in Beirut, Lebanon. I used the word ‘alleged’ here as the investigation is still ongoing and according to law, AN is innocent until it is proven guilty.
That being said, this very article is not in any way trying to make an attempt in rebutting the allegation. In fact, there is a strong basis to it as AN has been reported to be engendering explosion in numerous cases such as in Oppau (1921), Texas (1947, 2013) and Tianjin (2015).
But was AN the only culprit here? Was AN likely colluding with other crime partner/s?
Hence, this article aims at giving a basic explanation about AN and its behaviours so we will get to know it better and take necessary precautionary measures.
AN, also known as nitric acid ammonium salt, is a salt with a chemical formula of NH4NO3, consisting of cation (NH4+) and anion (NO3–). It is normally found as white crystalline solid. It is mainly used to make fertilizers. It can be synthesized by reacting ammonia (NH3) with nitric acid (HNO3).
Regardless of your academic background, we must all be very familiar with the term salt. However, AN is not like your table salt as it is classified as dangerous goods under certain circumstances. You can refer to its Safety Data Sheet (SDS) where it clearly forewarns about the hazards that AN may cause.
But is AN explosive?
Yes, it can be. That is why it has been mainly used to make explosives like ANFO (ammonium nitrate/fuel oil) since the early years of the 19th century. This is clear evidence that AN cannot be acting alone – it is safe and tame on its own but it would become violently wild when partnered with other chemicals/substances. ‘AN is a bringer of life while ANFO is a bringer of death (Hambling, 2020)’ perhaps is the best quote to describe the distinctive properties of these two chemicals apart.
AN can be thermally decomposed at as low as 120 oC and as high as 180 oC but there is no agreeable consensus range of decomposition temperature reported so far. The decomposition of AN will give rise to nitrogen, oxygen and water vapour which are harmless but the energy to produce these products is high especially so when a huge amount (reportedly tons) of AN is present. Heat (and pressure) in the confined space where AN is hoarded could be one of the contributing factors of the explosion.
The possible occurrence of contaminants such as acids, metals, or even fuels (or other combustibles) may also lead to the explosion. This is very likely as AN has been improperly stored and carefully handled for 6 years. Although AN is not flammable under normal circumstances, it can support the combustion by producing oxygen and this is self-explanatory. The emergence of red smoke aftermath the blast is a clear indication of nitrogen dioxide (NO2) – a common pollutant – produced upon the decomposition or combustion of AN. The gas can pose a significant health risk to those in the area.
We can always learn something from this tragedy. This is not the first and I am afraid if there are no precautionary measures taken in handling chemicals – this will not be the last. Get to know your chemicals, read their SDS, and follow SOP religiously – you may save a lot of lives in the future. Or would you rather have blood on your hands?
Shahrul Nizam Ahmad is Senior Lecturer at the School of Chemistry and Environment, Faculty of Applied Sciences, UiTM Shah Alam. He is a passionate science communicator who loves reading, writing, researching and above all educating.
* This is the personal opinion of the writer or publication and does not necessarily represent the views of Science Media Centre Malaysia