"Petter says the shredding machines were under such strain they eventually burned out... Panic-stricken, the Stasi's agents resorted to ripping up files with their bare hands."
> After the Iranian Revolution and the takeover of the U.S. embassy in Tehran in 1979, Iranians enlisted local carpet weavers who reconstructed the pieces by hand. The recovered documents would be later released by the Iranian regime in a series of books called "Documents from the US espionage Den".[8] The US government subsequently improved its shredding techniques by adding pulverizing, pulping, and chemical decomposition protocols.
It looks like the US people locked themselves in the vault in order to destroy the documents. After they were done, they left. There might not be the oxygen in the vault to burn all of the documents. But that's conjectural.
According to http://en.wikipedia.org/Burn_bag , burning isn't so common due to environmental concerns and the high value of recycled paper, though some places have burn bags with built-in thermite charges, in case of emergency.
It's a good addition to any suite of destruction, but creating any kind of fire is a higher amount of risk for collateral damage than the other methods. Plus, unless the combustion is thorough, you may still be able to discern information off the paper.
http://www.npr.org/2012/10/08/162369606/piecing-together-the...
Why such regular pieces?
"Petter says the shredding machines were under such strain they eventually burned out... Panic-stricken, the Stasi's agents resorted to ripping up files with their bare hands."