I've always said that welding galvanized steel IS NOT a good engineering practice, although I myself have used it in certain cases in which there wasn't another option. In the old AWS technical forum there was the statement of a welder who was required to weld on galvanized steel for a certain period of time and he began feeling deseases that the doctors attributed to the aspiration of zinc oxyde fumes which weren't properly vented out. Apart from that, galvanized steel welding will present defects due to the zinc which has remained in the steel, no matter how well you've brushed or burnt it.
However, welding top specialists like Mr. Richard LaFave, Head of the AWS A5 Committee, believe that it's possbible to weld galvanized steel taking certain precautions. I must say that I'm not wholly convinced.
Giovanni S. Crisi
Sao Paulo - Brazil