[Stoves] At what temperature are the bad gases from zinc created, vs harmless zinc oxide?

Fri Feb 1 16:10:37 CST 2013

Hey Paul, 

Like Hugh said don't worry about it. If zinc fumes were as toxic as most people think I would have been dead 20 years ago. I have literally welded miles of galvanized duct. I avoid the fumes of course.

It is not good to breath any welding fumes. The best way to vent a welders space is to set up a small fan from one side to the other, not front to back or back to front. The fan should move enough air out of the space without interfering with the welding gas. The flow should be from side to side not from behind you. From behind will create eddies and you will be eating fumes, a little welders jargon. After you have moved the fumes out of the welders space, use an exhaust hood or general room exhaust to purge the fumes out of the room.

You have to be more careful with low ceilings. If you can smell zinc fumes stop until you get the ventilation right. 

I know of 3 kinds of galvanized metal, one is hot dipped another is electroplated and the newest and best one is called "Galvaneal" where the zinc is melted into an bonded with the steel.

Galvaneal will take more heat than galvanized metal and retain the zinc coating. Another benefit to this amazing metal is that it is paintable. The galvaneal that I am using is stiffer than normal galvanize and does not dent as easily, and it is easier to weld. To weld galvanized use trimix gas. You can't beat galvaneal for a stove body and other parts that are not in direct contact with fire.

I have used it in direct contact with fire without burning off the zinc as long as there is an air circulation around the burner. If you use insulation in direct contact with a metal burner it will fail much more quickly.

Lanny

  ----- Original Message ----- 
  From: Paul Anderson 
  To: Hugh McLaughlin 
  Cc: Discussion of biomass cooking stoves 
  Sent: Friday, February 01, 2013 3:26 PM
  Subject: Re: [Stoves] At what temperature are the bad gases from zinc created, vs harmless zinc oxide?

  Stovers,

  I think that Hugh is not on the Stoves Listserv and cannot post messages.   So I am forwarding his reply to all of you.

  In response to Boston's comment, he is correct about the parts of the stoves that are NOT in the direct pyrolysis and combustion pathways.  The galvanizing will remain intact if surfaces are under 200 C.

  Thanks to all for the responses.

  Paul

Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.comOn 2/1/2013 2:08 PM, Hugh McLaughlin wrote:

    My perspective on this is it takes real stupidity to be harmed by galvanized stove parts.

    The core concern is arc welding galvanized material - which vaporizes the zinc metal rapidly enough that it does not oxidize to zinc oxide. Then you have to breath in the zinc-laded smoke - again rather easy to avoid. The same effect happen in spot welding, but in smaller quantities.

    If you are exposed, you get a flu-like response. See http://en.wikipedia.org/wiki/Metal_fume_fever

    The real issue is processes that deal with molten zinc, such as when casting zinc. But even then, the risks of burns outweighs the zinc inhalation concern.

    For stoves, a slow heating of the galvanized surface in the presence of air will oxidize the surface and render it less scary. However, it should be noted, that if you lick the zinc oxide off the ductwork, you will get the same metabolic effect.

    I recommend the same precaution for galvanized materials as I do for any painted materials or recycled tin cans - burn the completed unit first time outside in a well ventilated area - and avoid sucking up excess smoke. Your lungs will tell you when something is disagreeable, and react accordingly.

    Hugh McLaughlin, PE

----------------------------------------------------------------------------
    From: Paul Anderson <psanders at ilstu.edu>
    To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org> 
    Sent: Friday, February 1, 2013 2:38 PM
    Subject: At what temperature are the bad gases from zinc created, vs harmless zinc oxide?

    Stovers,

    Galvanized metal in stoves gets mentioned occasionally.  Do we have a clear answer about what is the temperature at which the zinc makes poisonous gases (such as when welding) versus making zinc oxide (the white stuff that you can by in a tube to put on your nose to prevent sunburn)?  Is it bad if the temperature is at 400 C to 700 C?  Or does it need to get much higher?

    Paul

    -- Paul S. Anderson, PhD  aka "Dr TLUD"
    Email:  psanders at ilstu.edu  Skype: paultlud  Phone: +1-309-452-7072
    Website:  www.drtlud.com

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