Welding fumes are a complex mixture of metallic oxides, silicates and fluorides. Fumes are formed when a metal is heated above its boiling point and its vapours condense into very fine, particles (solid particulates).

Yes, welding fumes contain oxides of the metals in the materaal being welded.

• Fluxes containing silica or fluoride produce amorphous silica, metallic silicates and fluoride fumes.
• Fumes from mild steel welding contain mostly iron with small amounts of additive metals (chromium, nickel, manganese, molybdenum, vanadium, titanium, cobalt, copper etc.).
• Stainless steels have larger amounts of chromium or nickel in the fume and lesser amounts of iron.
• Nickel alloys have much more nickel in the fume and very little iron.
  

Vapours or fumes can come from coatings and residues on metal being welded. Some ingredients in coatings can have toxic effects. These ingredients include:

• Metal working fluids, oils and rust inhibitors.
• Zinc on galvanized steel (vaporizes to produce zinc oxide fume)
• Cadmium plating
• Vapours from paints and solvents
• Lead oxide primer paints
• Some plastic coatings
  

Metal Coatings - A Source of Hazardous Fumes

• Remove coatings from the weld area to minimize the fume. The removal of coating will also improve weld quality.
• Use stripping products to remove coatings. Make sure to remove any residues before welding.
• Use wet slurry vacuum removal techniques for removing very toxic coatings.
• Do not grind coatings. Grinding dust may be toxic.
  

Welding gases are gases used or produced during welding and cutting processes like shielding gases or gases produced by the decomposition of fluxes or from the interaction of ultraviolet light or high temperatures with gases or vapours in the air.

Gases used in welding and cutting processes include:

• shielding gases such as carbon dioxide, argon, helium, etc.
• fuel gases such as acetylene, propane, butane, etc.
• oxygen, used with fuel gases and also in small amounts in some shielding gas mixtures
  

Gases produced from welding and cutting processes include:

• carbon dioxide from the decomposition of fluxes
• carbon monoxide from the breakdown of carbon dioxide shielding gas in arc welding
• ozone from the interaction of electric arc with atmospheric oxygen
• nitrogen oxides from the heating of atmospheric oxygen and nitrogen
• hydrogen chloride and phosgene produced by the reaction between ultraviolet light and the vapours from chlorinated hydrocarbon degreasing solvents (e.g., trichloroethylene, TCE).
  

Gases are also produced from the thermal breakdown of coatings:

• Polyurethane coatings can produce hydrogen cyanide, formaldehyde, carbon dioxide, carbon monoxide, oxides of nitrogen, and isocyanate vapours.
• Epoxy coatings can produce carbon dioxide and carbon monoxide.
• Vinyl paints can produce hydrogen chloride.
• Phosphate rust-inhibiting paints can release phosphine during welding processes.
• Minimizing exposure to degreasing solvent vapours.
  

Hazards from gases include:

• asphyxiation (lack of oxygen).
• fire or explosion.
• toxicity.

It is important to follow manufacturer's instructions, MSDSs, and safety protocols to minimize the hazards of welding gases.

• Use substitute materials such as water-based cleaners or high flash point solvents.
• Cover the degreaser baths or containers.
• Do not weld on surfaces that are still wet with a degreasing solvent.
• Do not weld near degreasing baths.
• Do not use chlorinated hydrocarbon degreasers.
• Have adequate ventilation in a workplace to prevent the displacement or enrichment of oxygen and to prevent the accumulation of flammable atmospheres.