With oil-based stains and finishes, reading SDS safety sheets makes it clear that safely using the products requires nitrile gloves, serious ventilation, and a respirator that can handle VOCs.
With water-based stains & finishes, safety lines are more blurred.
Most SDS safety sheets for water-based stains classify their products as non-hazardous substances (but still say to use gloves/ventilation/respirator).
Some water-based finishes are classified as hazardous substances by their SDS, like Minwax Polycrylic. Other water-based finishes are listed by their SDS as being non-hazardous, like Varethane Water-Based Polyurethane and General Finishes High Performance Water-Based Topcoat
For water-based stains & finishes listed as non-hazardous, what is the real situation with safety? Can I brush this stuff on indoors without a respirator? What about with a respirator, but no/little ventilation? Is an open window considered enough ventilation? If there is practically no odor during or shortly after, am I still inhaling VOCs that are harming me & my family?
*Edit I should specify that this question specifically refers to brush application