This is why we have welding respirators, it doesn't have to be a fresh air, though that would be much better. I have been protecting myself welding for years and I can smell it RIGHT NOW when I walk into the shop. It kills me when I see some of the guys not wearing protection, I can only suggest it so many times.
On the rot, the Zinc is a "sacrificial" metal. That is all zinc is, it doesn't so much "block out" moisture from getting to the metal. It sacrifices it's self instead of the metal under it, well that can only happen so long before the zinc is gone and the metal rusts.
If you will notice rust on cars is very localized now, right next to the rusted hole the metal is solid, where in the old days the whole area would be rusting.