I don't use masks or respirators. I stand upstream of the action. I've painted real automobiles.
That said, if you get a lungful of catalyzed urethane clear, you're gonna feel it. It'll harden and then you cough it up for a few days.
And if you get a snort of etching primer (with acid) you're gonna feel that too. It's painful.
And btw, i breathe nitromethane fumes in the drag strip pits.
It's not the infrequent experiences that are gonna kill you, it's regular exposure that will do it.