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Tianjin chemistry
18 August 2015 - Chemical disasters

tianjin calcium carbide.PNGThe death toll of the 2015 Tianjin explosions currently stands over a hundred. As expected the media debate the cause. Everyone agrees the following chemicals were present in the explosive mix: calcium carbide, potassium nitrate and sodium cyanide (BBC News, Der Spiegel). A dozen Youtube clips demonstrate how any combination of calcium carbide, water and an open-flame will set of an ignition (example here). The local fire department is blamed for using water to fight the fire. The release of the gas phosphine (from phosphorus contaminations) may present a longer-term problem (cdc.gov). The media also report that the ammonium nitrate could have been the source of the secondary explosion. See this clip for a very stark example of ammonium nitrate combustion.

The sodium cyanide is a current concern, but how? It does not just form hydrogen cyanide, the lethal gas, just like that. It requires an acid. The website cdc.gov is helpful (here) with the information that carbon dioxide from the air is sufficiently acidic to help liberate it. The NYT by the way is certain hydrogen cyanide is a liquid (here). More details: a molten wheel hub here to give an indication of the heat developed in the explosion.

Update: The Guardian in 16 August reports the amount of sodium cyanide originally stored at the disaster site may be several hundreds of tons (Link). It also reports fear that potential rain will react with remaining calcium carbide. It is unclear what the report means with "and creating a potentially toxic airborne gas". Acetylene as flammable but toxic or does it refer to the phosphine gas?