I always always use a cartridge respirator. I just bought it at Home Depot. Just make sure it has cartridges that you can replace and then replace them as recommended. Anytime you pour lead or plastic you need to be wearing a cartridge respirator. The long term effects of not doing so is not good.
My old respirator had a lot of less than admirable qualities to it.... wearing glasses with it was a joke and it never really fit all that well. The elastic strapping finally got so loose that I bought a new one. The new one is a 3M mask with replaceable cartridges and filters, not the most expensive but better than halfway. Its pretty much an industrial model so it should cover the airbrush paint too. Spraying powder paint puts a lot of paint dust in the air and regular air brush painting will also put a ton of fine particles in the air. The new mask is also capable of trapping solvent vapor so while working the plastic I should stay protected.
I did some plastics not long ago, not a super long project, and got headachy afterwards. The day after I did some airbrushing and the same occurred. I checked that old mask and wasn't too sure it was offering any protection anymore so I bought the new one. The new one fits way better and seals very well.
Way back in the Caney Creek days when I got started with plastics, I did not wear a mask to begin with. I assumed a fan or an open window was sufficient. After a couple months I began to read up on the issues plastic injection could bring with it and bought the respirator and made certain I used it, especially if I decided to do an extended session. Within the last ten years I have been doing more and more airbrushing and early on did not mask up. After a few sessions of spraying paint and having my nose stuffed up afterward I found quite a lot of color when I blew my nose. SO.... the mask is worn when I do any spraying, either with airbrush paint or powder and regardless of how long I am going to paint.
