Iron filings produced as a result of hack-sawing, grinding, or filing iron or steel could pose a hazard to people or pets.  It's easy to pick them up with a permanent magnet, but then the magnet is hard to clean.

Wrap the magnet in a paper towel.  Once the filings are trapped by the magnet, carefully unwrap the magnet, and enfold the filings in the towel for easy disposal.