I have a special storage space for harddisks that died or are removed from discarted pc's.
Properly erasing the drives with software conforming to military wiping standards will cost me many hours.
A couple of years back I saw an article about data recovery, a highly specialized company was able to recover data even from a disk shot with a nail gun. The only real failure in recovery was a computer displayed in the lobby that was mostly melted in a fire.
Now I throw anywhere between 20 and 30 disks a year in a fire after removing the pcb's, they mely to strange artworks.
One time it was too dry to make a fire, removing the platters and putting them in an over at the highest temp for half an hour peeled the magnetic coating (be cairfull with notebook harddisks, those have glass/ceramic platters that are break and shatter with many sharp fragments)