Welding
Chemical hazards when welding
Welding is a complex process involving high temperatures and/or pressures as well as chemicals to fuse pieces of metal together. The base metal is melted and a filler material is often added to form a pool of molten material that cools to form a joint that can be as strong as the base material. As a result of the high temperatures, a range of hazardous components can be released from the base metal, the filler and from any surface coating/paint left on the metal piece. When not adequately protected, not only the welder, but also workers in the surrounding area will inhale these components in the welding fumes. Inhalation of particles, gases and vapour from the welding process can lead to airway irritations. Over time, chronic lung diseases such as asthma, bronchitis and emphysema may result from this type of work. Particular care should be taken when welding on stainless steel where the welding fumes contain the carcinogens nickel and hexavalent chromium. Welding on pre-coated metals also causes serious concerns when the paints involved contain hazardous agents such as lead pigments or isocyanates.
It is of great importance to know which chemical compounds are being emitted during welding in order to take the correct precautions for avoiding or minimizing any adverse health effects. There are a number of different welding methods in use, including Metal inert gas (MIG), active gas (MAG), Manual metal arc (MMA) (stick) and Tungsten inert gas (TIG) welding. The relative importance of emissions and exposure to hazardous compounds varies with the method used as well as with many other factors, including the base metal, the filler material and the coating on the metal surface.
Welders with and without respiratory protection. © M. Bråtveit and Jessy Zgambo
The table below gives an overview of some chemical hazards released during welding and the acute and chronic health effects related to such exposure.
| Chemical hazard | Health effect |
|---|---|
| Aluminium; Welding and grinding aluminium alloys | Irritation of airways, asthma |
| Lead; Welding and grinding materials coated with lead-containing paint | Effects on blood and nervous system. Lead colic and kidney damage. Fetus damage and abortion |
| Epoxy; Welding and grinding surfaces coated with epoxy | Airway allergy and allergic dermatitis. Welding on epoxy can produce toxic decomposition products. |
| Phosgene; Welding on material cleaned by chlorinated organic solvents, e.g. trichloroethene | Acute toxic and corrosive. Causes irritation at low levels (ca. 5 – 10 ppm). High concentrations (> ca. 90ppm) is corrosive on lung tissue and are ultimately fatal due to suffocation. |
| Isocyanates; Welding and grinding on and close to polyurethane foam | Asthma and bronchitis. Eczema |
| Iron/iron oxide; Welding and grinding iron and steel | Connective tissue proliferation in lung tissue, siderosis (iron lung) with increased cough. |
| Carbon-monoxide (CO); Can occur when CO2 is used as shielding gas, e.g. in confined spaces | Binds to hemoglobin. Can lead to oxygen deficit. Acute symptoms vary with the concentration and duration of exposure, from tiredness and reduced concentration, through headache, dizziness and heart arrhythmia to unconsciousness and death |
| Chromium; Welding and grinding on stainless steel | Irritation of the airways, allergic dermatitis, bronchitis, lung cancer (hexavalent chromium) |
| Manganese; Welding and grinding on most types of steel | Symptoms of Parkinsons disease (tremor). |
| Nickel; Welding and grinding on stainless steel | Irritation of airways, allergic contact dermatitis, chronic airway infections, cancer in lungs, nose and larynx |
| Nitrous gases (NO and NO2); Produced at high temperatures. NO is often converted to NO2 | Acute irritation of the airways and reduced lung function. NO2 can lead to lung edema after short, but high levels of exposure |
| Organic solvents; Evaporate after cleaning/degreasing of workpieces | Eczema, chronic encephalopathy, polynevropathy |
| Ozone; Formed particularly in TIG-welding, but also some at MIG and MAG. | Low levels: Pungent/burning feeling in the throat, chest pain, breathing problems. Lung edema at high levels |
| Zinc/zinc oxide; Welding and grinding on galvanized materials | Acute irritation in nose and throat. Metal fume fever with symptoms similar to flu, but usually lasts only 24h |
© University of Bergen/Author: M. Bråtveit
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