A proper paint mask, not a dusk or particle mask, and make sure it fits. One of mine didn't, so from now on I'll be testing any new types out before proper use. Showed up when my mush got close to the piece, and the bounce-back showed up inside of where the mask was... Quality mask, more £s than my normal ones, but the fit was different.
Same thing got a guy on another forum a night in hospital (etch and synth enamel though, not 1k).
2K is the nasty stuff. 1K means no isocynanates, just something you mix with thinners and spray on.
It's still not sensible to breathe it in. I generally go for a filter mask from my local paint supplier with a rubber body and replaceable filters. You can't smell the paint or thinners at all with it on (assuming you've had a recent shave). The smell test is a good test for single pack paint masks. Any hint of thinners and they aren't working.
Thought I'd better check before I got too envolved. Had a quick dabble with the paint yesterday and could smell the thinners through the mask. I've never noticed this before so was a little concerned about going any further.
I find this type quite good - the rubber body fits to my face nicely and it has replaceable filters. I think it was about £35 from the local paint shop. Can't smell the thinners at all.
My old mask looked a little similar but didn't seal properly. It's not even good for dust.