I found some information that everyone who works with galvanized steel might find useful. I talked to the overseer of several Indiana foundries, and he told me that the only danger that he knew of that was associated with zinc was
something he called the "zinc shakes". I did some research on this, and found the following:
The toxic gas created when you heat galvanized steel (as the zinc burns away) is zinc oxide, and the effects of it, while
unpleasant, are not fatal or cumulative. It causes a syndrome known as the zinc shakes or Metal Fume Fever. The information I could get about this compares it to the flu, and says that it
both goes away in 2 days, and at the same time renders the exposed individual immune to the same efects for 1-2
days afterwards (leading to another name for this, Monday Morning Fever, as foundry workers who had the
weekend off and were not exposed for two days would be susceptible again the following Monday to these effects).
One medical document I found differentiates
between the metal fume fever found in metal workers and a more serious form of the same syndrome (which can be
fatal) that is caused by breathing "military smoke", and warns military physicians to be aware of the differences. It does
not specifically detail the differences between the two forms, or tell what "military smoke" is, or what it contains, that
causes the more serious form.
Another medical document details a study done
on welders of galvanized steel (much more relevant to our work, in my opinion), and notes an increase in white
bloodcell count in the mucus of the lungs after exposure (assuming I translated the medical-ese correctly), but
no TNF (tumor necrosis factor) or significant levels of interleukin-1.
Several "worker's safety" type documents consider metal fumes more serious, but they don't differentiate between zinc
fumes and other metal fumes (chromium, lead, magnesium, etc.), so it's hard to get a good idea as to how serious the
threat from heat-treating galvanized steel might be. All of the documents I found seemed to indicate that the real danger
was from over-exposure rather than trace exposure, and recommended adequate ventilation to prevent problems (as
opposed to respirators, filters, self-contained breathing units, and the other types of protection you'd expect would be
required if these fumes were extremely dangerous).
The most serious problems anyone specifically stated were that long-term exposure to zinc dust can lead to
occupational dermatitis, and zinc dust (not vapor) "may contain small
amounts of materials known to the State of California to cause cancer and reproductive harm".
If anyone has more documentation of serious problems associated with this, please let me know. If this is all that we
have to worry about, though, it's a lot safer than it seemed, before, to heat-treat or case-harden galvanized steel.
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