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According to some conspiracy theory, the explosion that happened last year in Tianjin (China) wasn't caused by sodium cyanide. Can sodium cyanide react with water, and can it cause an explosion if you have 700 tons of it?

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It normally simply dissolves. – Mithoron Jan 6 at 0:18
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Just checking... according to the conspiracy theory, the explosion was, or wasn't caused by NaCN? – orthocresol Jan 6 at 3:28
up vote 10 down vote accepted

Usually, I dislike conspiracy theories.1 However, this one (if it even is one) is true. Looking at the list presented on Wikipedia of the chemicals that were stored in that warehouse, why would you even suspect sodium cyanide as being a cause of the explosion? It is a stable ionic compound that can be put on the shelf, wet with water, dissolved in water, and won’t react with air with any measurable half-life. (Except that you possibly shouldn’t put it on a shelf because it is slightly volatile and highly poisonous.)

What was also in the warehouse and is an explosive was ammonium nitrate. In the 1921 explosion in Oppau (now part of Ludwigshafen), BASF workers tried to use dynamite to loosen a plaster of ammonium nitrate (it is hygroscopic and baked together). Mixtures containing at least $40~\%$ ammonium sulphate were considered stable and the mixture in question was a $50~\%$ mixture of the two according to the production data. After approximately 20,000 uses of dynamite where nothing happened, the entire 4,500 tonne lot exploded killing some 500 or 600 people and leaving thousands injured. The theory $40~\% = \text{safe}$ was later disproven in careful examinations. Apparantly, the explosion could be heard in Munich, some $300~\mathrm{km}$ away.

Another substance stored there and dangerous is calcium carbide $\ce{CaC2}$. When calcium carbide gets wet, it produces acetylene gas (and calcium hydroxide). The acetylene is flammable and can also explode in certain acetylene–oxygen mixtures.2 Luckily, no acetylene or carbide explosions are known enough to make it onto Wikipedia.

So far more likely than sodium cyanide having any primary effect would be one the following theory:

  1. Fire (something must have ignited because the compounds I read there aren’t self-flammable).

  2. Attempts to extinguish fire with water by the fire brigade.

  3. Water reacts with calcium carbide liberating acetylene.

  4. Acetylene burns.

  5. The critical heat is reached, ammonium nitrate explodes.

  6. Toxic sodium cyanide is liberated into the environment causing further severe health risks for man and animal alike.

1: Okay, that was a lie. I love listening to them and making fun of them.

2: A teacher at school talked about his time at uni and mentioned a professor that let a balloon of acetylene explode — he made a fuse long enough to ignite it from outside of the lecture hall (nobody was allowed inside), had the doors closed and my teacher said ‘it was the loudest bang I ever heard.’

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