A respirator is not the answer, it's asking for trouble.

I used to be a research chemist and toxicologist until I went commercial. Here are a couple of old incidents from my time as the hot-line guy for Eastman Chemicals:

A darkroom worker complains of headaches, dizziness, and general malaise while working in a well ventilated darkroom. He blames the "fumes" from the "chemicals".
When I check his work space I find that the guy is doing 5 hour darkroom sessions while wearing a double cartridge (dust and vapour) face mask. He's got a deep fear of chemicals but what's getting him is ordinary anoxia and re-breathed carbon dioxide because he's not ventilating adequately.

An urgent call comes through from someone with metol allergy. The stuff is literally eating his hands even though he is wearing surgical gloves. It turns out that the victim has latex allergy from the gloves and the metol is innocent. But the story has spread to every darkroom in town and it takes ages to hose it all down.

Sometimes fear of chemicals can lead people into danger. Sometimes chemical sensitivity is so extreme that only an actively inflated positive pressure biohazard suit is mandatory . Any darkroom design, any chemical process, that requires respirators and gloves for worker survival is absolutely not worth going into at any price. There is an unbreakable principle of workplace safety at stake here.