1.Always wear both eye and ear protection when you are shooting any gun. The flame is not going to come back and get you, unless you have some very strange way to hold a flintlock, but bits of flint, or steel, or powder debris can come back and cause you injury.
2.Always ask people to stand back from you and away from the side of the lock so they are not hit with gases blowing out the vent hole when the gun goes off.
3.Ask people not to step up next to you to fire their guns until you have fired yours.
4.Wait for others to finish shooting and step back from the firing line before you step forward to shoot.
These are just common curtesies that are followed by flintlock shooter when they are shooting on a firing line with other people around.
Range rules should require people to wear eye protection and hearing protection if they are on or near the firing line. If they are sitting or standing behind the loading benches, they can make their own decision if they need to be protecting their eyes and ears.
The burning gases, if not the projectiles of these guns, breaks the sound barrier, so there is enough noise to harm your hearing. Over the years, I have been hit in the face with debris from other shooters guns, who stepped up and fired without warning me, or giving me time to step out of the way. They only did that once, because I made sure to let them know what I thought about their carelessness, and thoughtlessness. Because I am Left Handed, shooting a left handed gun, I try to find a spot on the far left end of any firing line to shoot, so I don't pose a danger to other shooters. It also puts me where I am in much less danger from shooters on my right, if they step up and fire without warning me, when my back is towards their position.
BE SAFE- first, and always. When in doubt, Don't Shoot! Find out what is bothering you, and ask! The only stupid question is the one not asked.