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Re: [TCML] DC Coil progress.
On 11/22/13 5:32 AM, Futuret wrote:
I've heard that vaporized zinc (from the galvanizing) is
extremely toxic. Whenever I've tried using brass
electrodes they eroded away very quickly. I've had
much better results with copper electrodes. Others
may have had different results, but I thought I'd
mention it.
I don't know about "extremely". It's zinc oxide, which is non-toxic,
but it does cause "tinner's tummy" or "zinc fume fever" and welders who
have to work with galvanized iron often call in sick the next day,
although the mechanism is unclear. There are some theories that there
is zinc chloride involved, or that it is a general reaction to a foreign
material/heavy metal.
It's not in the Hydrogen Cyanide, Hydrogen Sulfide sort of class. The
IDLH (Immediately dangerous to life and health) for H2S is 100 ppm (150
mg/m3). The ACGIH recommendation for H2S is 1 ppm (1.4 mg/m3) TWA. HCN
is similar (IDLH of 50ppm, typically tolerated by humans for 30min,
100-130 ppm is fatal after 0.5-1 hr)
As it happens, the OSHA Permissible Exposure limit for Zinc Oxide Fumes
is quite low: 5mg/m3 total weighted average (TWA) over 8 hour day. but
there's no IDLH level, and it's not clear that you can die (immediately)
from it. CDC says:"Studies in the workplace have shown that welders
exposed to zinc oxide fume at concentrations of 320 to 580 mg/m3
reported nausea, with the development of chills, shortness of breath,
and severe chest pains 2 to 12 hours later." And some guinea pigs gave
up the ghost: "The animals in the high-exposure group (2500 mg/m3 for
three to four hours) died after exposure."
But the 2.5 GRAMS/cubic meter that caused the rodent demise is a LOT of
fumes. It would be an exceedingly dense cloud at that level. You could
probably see the particulate fumes at 10mg/m3.
pubmed has
http://www.ncbi.nlm.nih.gov/pubmed/11094787
The OSHA(etc) limit is 5mg/m3 total weighted average (TWA) over 8 hour day.
Zinc oxide fume is a respiratory irritant that causes metal fume fever
and can temporarily decrease lung function for up to 48 hours after
exposure (ACGIH 2003).
The effects of metal fume fever may be delayed a few hours after initial
exposure (NIOSH/IPCS 2004).
The inhalation of zinc oxide at the PEL concentration for two hours by
naïve subjects was reported to trigger an inflammatory response
involving the release of cytokines, thought to mediate the symptoms of
metal fume fever (chills, elevated body temperature, myalgia, cough,
fatigue, chest pain, nausea, and vomiting) that peaked about nine hours
after exposure. Prior zinc oxide exposure resulted in the development of
some tolerance (desensitization) to these inflammatory effects (Fine et
al. 2000; Kuschner et al. 1997).
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