Here is a link to a site that has data on all sorts of chemical hazards. The second one takes you directly to zinc oxide which is what you get when you heat zinc above it's boiling point like in welding or forging. You can then click on metal fume fever in the body of the test to get additonal info. This site "should" be bookmarked in every blacksmith's list of favorite sites and it "should" be consulted before using any chemical. Drinking milk to avoid the effects of metal fume fever is an old wives tale and is totally ineffective, sitting on a popsicle would give you an equal amount of portection. Further, I would direct their attention to my Blueprint on Respiratory Protection which is published on this site.
As bad as Zinc is, there are other materials out there that are worse. Cadmium which can be found in Nickel/Cadmium (NiCad) welding rod and also as a coating on some brands of Grade 8 bolts and nuts. Hydrogen Fluoride is another. Hydrogen Fluoride is the gas given off by heating Fluorite which is found in some welding and braising fluxes. What follows is a direct quote from 29 CFR 1910.146 (OSHA Permit Required Confined Space Regulatons)
"Immediately dangerous to life or health (IDLH) means any condition that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that would interfere with an individual's ability to escape unaided from a permit space.
Note: Some materials – hydrogen fluoride gas and cadmium vapor, for example – may produce immediate transient effects that, even if severe, may pass without medical attention, but are followed by sudden, possibly fatal collapse 12-72 hours after exposure. The victim "feels normal" from recovery from transient effects until collapse. Such materials in hazardous quantities are considered to be "immediately" dangerous to life or health"
http://hazmap.nlm.nih.gov/index.html http://hazmap.nlm.nih.gov/cgi-bin/ha...lAgents&id=679
Woody