Adaptec's CDR mailing list posted some quite interesting ways to entirely destroy a CD:
"...Put the CD-R between the pages of a newspaper, with at least 30 pages on each side. (This prevents anyone's being hurt by sharp or flying pieces.) and then bend until it breaks.
- I have found that obsolete CDs make excellent targets for "plinking" [target practice], which renders them fairly unusable. But for the "I don't ever want this read by anyone" CDs, the office shredder works very well!
- The easiest and most effective way to destroy a CD completely is to put it into a plastic bag, wrap it further in newspaper and pulverize it with a hammer on a concrete floor. Here, you have safety and efficiency (unless you hit your finger with the hammer). The resulting polycarbonate dust and CD shards would be impossible to reconstruct.
- Use propane torch or an oxygen-acetylene torch. It's not too dangerous an operation provided you wear protective gear, keep a fire extinguisher handy, and don't try it on the 20th floor of an office building..."