Hesh and others are right, spraying nitro, but for that matter, anything can be dangerous. One must have all the necessary equipment, and take the proper precautions. I assumed when said ventilation, all would know I meant that. I forgot the assume rule.
I was also looking at it on a economic basis also.
Spraying nitro, if doing all the above is no more dangerous to people, environment, or anything else at home in a nieghborhood, in commercial area, out in the country wherever. Tony and others spray somewhere, they just do what it takes to do it right and safe as possible.
I think it depends on what one is doing. If building a few a year, and want to spend the money to sub it, that is up to them. Same if a person wants to do it at home and save those funds for other things. Same for business builders, they may upcharge the client for the service, or work it out some other way.
To me if building 5-15 guitars a year, and not selling them, but donating, giving to relatives, keeping them, whatever, and this is a hobby,that turns out to be a lot of money. This is just based on the $400.00 I have seen as a standard fee (this may be higher or lower, just based on hearsay, and what seen) for subbing out, and no return on the money. If one can afford that, great, go for it. For that money though, one could build a really, really good booth with the proper equipment and precautions. Point is what are your goals in the long term, and what are you willing to spend on finish work.
As far as spraying in home, I can only go by my experience. Over the last bunch of years, the shop I am at now (not been there all the years) there have been several hundred guitars built, repaired and other things sprayed in our booth. Nitro is what is sprayed on instruments. The boss and myself, are in the camp that thinks it is the best of finish, for various reasons. The booth has the proper ventilation equpiment, fire precausions the whole thing. Time and money was put in doing it right. But less money than would have been spent subbing it out. Do the math. Hardly ever if at all is the smell outside the booth. We may at times open a window, but we do that for lots of reasons anyway. the nieghbors have been told and asked if ever a problem, let the boss know. Not one nieghbor has complained and when asked never knew when sparying was going on. We have most of the time 5-10 guitars in the booth. Like said, wherever, or whatever one sprays or finishes, the fumes go somewhere and then dissipated in envionment.
There is the issue also, some just don't know how to spray and don't want to learn, or they are not good at it and don't want to get better. I am in the camp that says learn and do it and learn to do it well. If then for health or other issues ensue while learning no matter what materials are used, then sub it out. Most can do some sort of finish without health issues though.