Safety: Face slapping, is a very detailed article about the physical dangers of face slapping in BDSM play that both submissives and dominants should read and understand before playing with strong face slapping in their scenes. Face slapping can be dangerous. For instance, the article advises:

Of course, if hitting hard enough, you will break the cheekbone (damaging almost inevitably some nerves), or dislodge or break the jaw articulation, which, even when being very strong, is not designed for receiving a lateral impact. For diminishing the possibility of this damage your sub should close forcefully the mouth.

There are a number of other resources on BDSM safety as well, and I think these will be good to keep all in one place, so I’m going to see if I can blog them all under the BDSM safety label over time.