Comment by cmatteri

I believe it contains on the order of twice as much flux, but I can't find a source for that at the moment. So I don't think flux fumes are much more of a concern than with leaded solder (for which you should have good ventilation or a fan). I did have a ball of solder shoot towards me when I was first getting a feel for it, so you definitely need safety glasses, though I understand this can occur with leaded solder as well, and you want to wear glasses anyways to keep clipped leads out of your eyes.