From what I know, experts disagree on what is a safe level of formaldehyde. I agree with this site that says "pick your poison and research it." I did a lot of research which made me comfortable with my decision. Each individual has to do his or her own.
I am unsure about the FDA safe levels because I think they do it by ppm which is different from % in aqueous solution.
This site makes reference to the FDA regulations being 37% at least at some point in time for food additives, but it is quite possible that it is different for cosmetics.
ETA: To keep the fumes away, I have a fan that blows directly in my face. I wear a mask and gloves and I keep my windows open. The windows are quite large and let a lot of air in. It does irritate my eyes though if I turn away from the fan for too long so I am sure there some bad stuff happening there lol.