It has been argued that pyroclastic dust clouds are from volcanoes.

Pyroclastic dust clouds -can- be from volcanoes, but the key is that they are of explosive origin; explosives can clearly be such an origin. This is not something that is recognized by every dictionary- before 9/11, it wasn't something the average person would discuss over breakfast.The American Heritage Science Dictionary does recognize this, however, and you can see this definition from them at dictionary.com:
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pyroclastic: Composed chiefly of rock fragments of explosive origin...
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http://dictionary.reference.com/browse/pyroclastic

It has also been argued that any building collapse will give off a huge dust cloud, citing a 10 story building collapse (a video link of said video link would be appreciated). However, if memory serves, this only happens when the debris hits the earth, not before.