I think the main problem is in print developing rather than processing film (where the chemicals are not "open" except when transferring from tank to bottle, etc.) Remember that the presence of "fumes" in your work area depends on the exposed surface area of the liquid in the tray. For this reason you may want to look at getting a slot processor (there is a company called Nova that makes them) to minimize the exposed surface area of the solutions.
There is a book that addresses issues of health and toxicology in the darkroom -- I believe it's called "Post Exposure" or something like that. I can't remember the authors' names.