Don gloves and eye protection prior to dropping the drives into the shredder if your shredder is missing the cover. [1] Ideally buy a shredder that has a protective cover and a slot for hard drives. Use a shop vac with a hepa air filter to get any pieces that don't make it into the bin. There are shredding services that you can safely shred the drive for you for a small fee.
[1] - https://www.youtube.com/watch?v=wb3Xa1h_RqM