Zinc fumes aren't just dangerous, they're downright deadly. People have died from doing less than cooking zinc off of a few fence posts.
The most I do with galvanized is through 4 inch lag bolts (making wedges for hammer heads, i still prefer un-galvanized), 1 lag bolt in at a time to cook off the coating. Even this little bit kills my fire to the point where forge welding is hopeless.