Having been an AFSC 30670 (Electronic and Cryptographic Equipment Systems Technician), and been assigned in hazardous areas you use document destroyers on paper stuff - glass vials with grenade fuses). Equipment destroyers were 35 lb thermite charges, designed to sit on top of a standard piece of equipment in a 19 inch relay rack. I had orders to Iran but got diverted when the Shah fell. The liquid in the document destroyers was clear, and we got to set one off for demo purposes twice a year (never did get to set off thermite, though). Had a one acre room half filled with crypto, thermite would have brought the roof and lots of airconditioners down. All the key cards were treated with lead acetate, they would burn without leaving anything but a greasy wisp of ash.