The magnetic pulser will induce a back EMF in the metal.
This will cause the coil and the metal to repel each other.
To visualize this, imagine putting two opposing magnets near each other that is what will happen. It will push the metal away.
This would be painful, and could be dangerous. You do not want loose pieces of metal floating around your body.
Now the force might not be enough to be a problem depending on the situation.
If itís being used to hold together broken bones, thatís a bad idea.
If its life or death, I would hold the coil one ft away from the area, and slowly move closer with each pulse. The magnetic field gets weaker with distance. By slowly moving it in, hopefully you can feel if there is going to be a problem.