I use only Macs, and I've had more than one hard drive corrupted by hot swapping firewire devices. My advice: don't do it.
If there is a desktop icon, throw it in the trash to unmount. Then, power down the device before physically disconnecting it. Hard drives have desktop icons, so this would apply to those.
If it's something like an audio interface that doesn't have a desktop icon, power it down before disconnecting it. If you have a hard drive chained to the firewire audio interface, unmount the drive first, power down the interface, and only then disconnect it.
I do believe that hot swapping can mess up other drives on the same buss, and in my experience, drives on a different firewire buss as well. I can't explain it technically and it's not *supposed* to happen, but it has.
I'm an experienced Mac user of going on twenty years, so I do know Macs pretty well. My advice once again: don't hot swap.