I actually was tasked recently to research this topic to see how we should be handling it here. I decided to look and see what the three-letter-agencies recommend to their people. In the USA anyway, everyone except the NSA said that the minimum requirement was basically to "overwrite all cells once". If the media contained classified or above at any point in its lifetime, or if it's used for
any purpose at the NSA, it needs to be handled in one of three ways: degauss, incinerate, or shred. (yes, physically shred HDD)
Sledgehammers and bench drills were
not on anyone's approved list for data destruction.
If a wipe was not possible on a normally wipable drive, it got the "classified treatment." So that's the government's answer to your "disposal of a broken hard drive" question.
links reviewed:
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https://wiki.archlinux.org/index.php/Securely_wipe_disk#dd-
http://www.neowin.net/forum/topic/1150550-using-dd-to-securely-erase-a-hard-drive/-
https://en.wikipedia.org/wiki/Gutmann_method-
http://www.linuxquestions.org/questions/linux-security-4/military-grade-disk-wipe-653786/-
http://www.oregon.gov/DAS/OP/docs/policy/state/107-009-005_Exhibit_B.pdf?ga=t-
http://www.killdisk.com/dod.htm-
https://www.nsa.gov/ia/_files/government/MDG/NSA_CSS_Storage_Device_Declassification_Manual.pdf the first link's summary included:
4 Conclusion
The purpose of this paper was a categorical settlement to the controversy surrounding the misconceptions involving the belief that data can be recovered following a wipe procedure. This study has demonstrated that correctly wiped data cannot reasonably be retrieved even if it is of a small size or found only over small parts of the hard drive. Not even with the use of a MFM or other known methods. The belief that a tool can be developed to retrieve gigabytes or terabytes of information from a wiped drive is in error.
I've seen studies done where identical drives had fixed data stored on them, and then one-pass-wiped, and then sent into a mix of places for recovery. NONE of them were able to recover any data. Governments still continue to opt for higher grade security under the assumption that either there is better secret technology available at the nation-state level (which is probably a reasonable bet) or that sensitive data may still be sensitive at some point in the future when more effective recovery techniques are developed. For them (since cost is not a consideration) the stakes are just too high to settle for anything less than "the best available".