Your respirator needs to have cartriges compatible with the solvent you are spraying.
While the respirator can protect you from the solvent fumes, you also need to have sufficient oxygen content in what you are breathing. Your darkroom's ventilation may not be up to the task.
That's probably the reason for Ian's recommendation that your breathing air come from outside the darkroom, though he might be able to elaborate.
The space should be adequate, I'm using a huge photographic studio (F1 cars got photographed there). I will make sure to get the right cartridge though, thanks!