To be effective with throwing the hard drive into the fire, the fire would have to be hot enough to melt the platters into molten metal, which requires an industrial furnance. This requires special facilities. Running powerful magnets over the disk, such as degaussing the disk, may destroy the data, but may also be ineffective. In some cases, the degaussing process for tape and disk may render the disk unusable for use again. (of course throwing the drives into a furnance also guarantee that as well). Formatting the disk multiple times with a low level disk utility is the best way to go, and still beable to re-use the disk for later projects. The keys are "multiple" and "low level". A low level format is typicall a slow, thorough, format that is a wipe. Multiple ?as opposed to once ?is recommended. There is a theory on "how many times", some schools say at least three times. The problem with this answer is that with newer drives, such as ATA and SCSI, low level formats can destroy the volumes as well, and some BIOS may actually ignore the LLF directives. Overwritting the disk with junk data would perform some form of wipe because the old data is wiped out, but still may be recoverd.
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According to some websites:
Physical Methods that will not work to destroy data on a hard drive include:Throwing it in the water (this does not do much)Setting it on fire (the temperature is not going to be high enough at home)Throwing it out of the window. Hard drives can take quite a bit of G force. They are not heavy so the impact of the hard drive on the ground is not likely to destroy the platters.Drive over the hard drive. A car, or even a tank, driving over a hard drive will do nothing, any more than they would driving over a book. Unless the drive is actually flattened, the platters are not going to be destroyed