Welding - Fumes And Gases

Welding fumes are a complex mixture of metals 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). Welding fumes generally contain particles from the electrode and the material being welded.

Yes, the composition of welding fumes is determined by the metals in the material being welded, the composition of the electrode, coatings, and other factors such as:

• 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 can have larger amounts of chromium, including hexavalent 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
• chromates
• vapours from paints and solvents
• lead oxide primer paints
• 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.
• Follow appropriate safety procedures and use the necessary personal protective equipment  during the coating removal process, which will be based on risk assessments, manufacturer’s instructions, and potential exposures.  

• Type of welding process.
• Composition of welding rod.
• Filer metals and base metal used.
• Type of coatings present.
• Location (open area or confined space).
• Type of ventilation controls (mechanical or local).
• Work practices of welder (e.g. remove coatings, clean surfaces, proper positioning to avoid breathing fumes and gases, such as staying upwind when welding in open or outdoor areas).

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.

Source: Tables 1 to 3 are from Work Safe Alberta's Welder's Guide to Hazards of Welding Gases and Fumes, 2009

Hazards from welding gases include:

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

It is important to follow the manufacturer's instructions, safety data sheets (SDSs), and hazard control measures  to minimize the risks and hazards of welding fumes and gases.

• Use substitute materials such as water-based cleaners or high flash point solvents.
• Consider using a lower fume-generating or less toxic process or material
• 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.
• Safely remove coatings before welding.
• Have adequate ventilation in a workplace to prevent the displacement or enrichment of oxygen and to prevent the accumulation of hazardous substances and flammable atmospheres.
• Use local exhaust ventilation systems positioned close to the plume source to remove fumes and gases from the welder’s breathing zone.
• Wear appropriate respiratory protective equipment according to your company’s respiratory protection program. The respiratory protective equipment should not be used to replace the use of mechanical ventilation.
• Following safe work procedures, such as workers positioning themselves to avoid breathing welding fumes and gases
• Risk assessments and occupational hygiene sampling can be performed to determine potential worker exposures and other hazards, and to help identify the control measures that are needed.  See the applicable occupational exposure limits in your jurisdiction.