If you are spraying emulsions regularly I suggest you use an air-line respirator. This provides fresh air at a constant rate at a slight positive pressure, so you never breathe in any air from the darkroom itself.

Back in the 70's and 80's I coated thousands of litres of B&W emulsion using a sraygun, we always used air-line respirators fed off the compressor which was housed outside the darkroom and supplied with fresh air from outside the other side of the factory to the darkroom extractor fan. I should add the extractor fan was extremely efficient.

Some of the additions to the emuklsion like hardeners etc would not be good for you to breathe in. We also sprayed all our processing chemicals, again using the air-line respirators.

Ian