If the bottom of the frizzen opens to vertical, 90 degrees to the pan, you will get spit at- a bit. Usually this is just a few specks of 'dirt' (fouling & sparks) to the forehead, but the possibility to catch one in your big shiny eyeball is there.
My wife had a little fragment of copper from an RWS percussion cap in her eyelid for perhaps going on 20 years (tuned green) before one day it simply fell out as she scrubbed her face, as normal. There wasn't even a little cut - one day, she simply said "It's gone". This was from her Seneca .36 - back in the mid 70's when she was shooting conicals, loaded for deer. (no I do not recommend that). The increased pressure used to lift the hammer to 1/2 cock - which was not very high on that lock, but enough to cause cap fragments to fly around. She was not wearing glasses and the frag embedded just above her eye ball.
With round ball loads, she had to pick the spent caps off the nipple.
