Chemistry Sep 03, 2020

We’ve all grown up having learnt at some point or the other about the Bhopal Gas Tragedy and the Chernobyl disaster. Moreover, every so often, we see social media blowing up talking about another chemical catastrophe. Two such recent incidents that have left us all troubled and are no doubt still on our minds are – the Beirut blast on 4th August and Vizag Gas Leak on 7th May. Today, we are here to explain to you the “chemistry behind these chemical disasters.”

The Beirut explosion was caused by 2,700 tonnes of ammonium nitrate (NH4NO3) stored for six years without preventive measures. Ammonium nitrate is a crystal-like white solid that absorbs moisture and eventually turns into an enormous rock, making it dangerous. In this instance, there was a fire, which caused the ammonium nitrate that had been stockpiled to combust, and when it’s in a confined space, it releases a lot of hot gas. Because the gas takes up a higher volume than the solid, there’s a build-up of pressure, and you get to the point that when it’s confined, it will explode and release that pressure in a shockwave. At the time of the explosion, there was a large column of red-orange-brown smoke and a large white ‘mushroom cloud,’ which was the shockwave. The red-orange-brown smoke is nitrous oxide, a toxic gas released from the ammonium nitrate.

So how should ammonium nitrate be stored? It is a valuable inorganic compound, commonly used as a source of nitrogen for agricultural fertilizers. Safe storage would mean keeping the ammonium nitrate away from any ignition source, keeping it away from anything combustible, and keeping it in small enough containers, far enough away from one another, that if one were to ignite it would not spread to the others.

The Vizag gas leak was caused in a plant using a styrene monomer (C8H8) to produce expandable plastics. Styrene monomer must be stored at temperatures strictly below 17°C. There was a temporary partial shutdown of the plant owing to the Covid-19 pandemic. Since styrene was not being stored at the appropriate temperature, there was a pressure build-up in the storage chamber, which caused the valve to break, resulting in leakage of 3 tonnes of the toxic gas.

Styrene is an organic compound used in the manufacture of polymers, plastics, and resins. It is manufactured in petrochemical refineries. It can enter the body through respiration, skin, and eyes. It is classified as a ‘hazardous and toxic chemical,’ It has also been named a possible carcinogen. It combines with oxygen to form styrene oxide, which is more lethal. After the catastrophic leak incident, a crucial chemical called PTBC – para‐tertiary butyl catechol was used to neutralize the impact of the gas leak and contain the spread. It is a retarder of the polymerization reaction.

So, that was the chemistry behind these two recent blasts, what exactly made them as huge as they were. It isn’t too tough then to figure out why they, unfortunately, caused so much damage, so many fatalities, and injuries and left countless more homeless and unemployed. It is the need of the hour to have more stringent regulations for such plants, and also ensure that they are enforced so that these calamities don’t strike again.

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Alchemy - The Chemistry Association; BPHC

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