TOF,
Good point, but I submit that you would have to burn the zinc plating (same material as "galvanized" just a different application process) off hundreds if not thousands of screws and purposely inhale the resulting zinc oxide fumes in a very enclosed space to even approach having a problem. And, if you managed to do that, the resulting medical condition is referred to as the "zinc chills", a malady well known to many welders who have either welded a considerable amount of galvanized steel, or torch cut it, in confined spaces. However, the immediately effective antidote for the zinc chills is to drink a glass of milk. Bottom line, while it is theoretically possible to give yourself the temporary condition of zinc chills, you would really have to go out of your way to do it. I would be more worried about handling the torch used to burn the plating off the screws and the fire danger resulting from an open flame.