Therefore the intention is to sanitise them of data before they get chucked as well.
To that end, I have looked at erasure software such Darik's Boot and Nuke (DBAN), which seems to be a defacto for this job. Unfortunately, and unsurprisingly, it seems to require potentially many hours to do the job - perhaps 10 hrs per drive. It appears that although it will handle all the drives visible (so 4 IDE on a standard PC), it does them sequentially, so very protracted, and I have some 30 drives to do.
Therefore physical means seems to appeal.
There is the obvious one of bashing some 100mm nails through the case, but I rather like the idea of fire - I have always been attracted by any excuse for some pyrotechnics.
Thermite would appeal, but I can't be bothered to organise the ingredients and environment to do it, so a blowtorch seems like a good alternative.
I found this video, where the guy does the job using a Mapp gas torch and it seems to be an effective solution.
He mentions that it's hotter and faster than propane. I already have a propane torch and cylinder so would need to go and buy a Mapp gas handheld one - they seem not to be that expensive.
Has anybody done a disk destruction exercise, and more to the point has anyone used Mapp gas? Is it significantly hotter than propane? What other applications would it have?