Stainless steel welding fume: chromium VI and nickel
Fume from stainless differs from ordinary fume not in quantity but in composition. It carries two carcinogens — hexavalent chromium and nickel — and the permitted concentration of chromium VI is so low that it is reached sooner than common sense suggests.
Short answer
In 2017 IARC placed welding fume in Group 1: agents with proven carcinogenic effect in humans. That applies to fume as such. On stainless steel two further components appear, each with a classification of its own — hexavalent chromium and nickel with its compounds.
Chromium VI attacks the airways and the lungs; nickel also sensitises, and an allergy once acquired stays for life and closes off further work with the material.
What the fume holds, by material
| Material | What is in the fume | Main hazard |
|---|---|---|
| Non-alloy steel | Fe₂O₃, MnO, SiO₂ | Dust bronchitis and pneumoconiosis; manganese attacks the nervous system |
| Stainless steel | Cr(VI), Ni, Fe₂O₃ | Hexavalent chromium and nickel — carcinogens |
| Galvanised steel | ZnO, Fe₂O₃ | Metal fume fever, hours after the job |
| Aluminium | Al₂O₃, O₃ | Ozone is created by the arc radiation and irritates the lungs |
| Coatings and paint | CO, NOₓ | Thermal breakdown of coatings: toxic gases, not just fume |
Where hexavalent chromium comes from
There is no chromium VI in the steel itself — there is metallic chromium, harmless to breathe in that form. It is created in the arc: the heat oxidises the chromium, and whether the oxidation stops at the trivalent state or goes on to the hexavalent one depends on the chemistry around the pool.
That is the crux: alkali compounds from electrode coatings and from flux-cored wire stabilise the hexavalent form. So on one and the same steel:
- MMA and FCAW give the most chromium VI — the coating and the flux contain sodium and potassium;
- MIG with solid wire — markedly less, as there is no flux;
- TIG — least of all, because there is least fume altogether.
The practical conclusion is inconvenient but simple: for long work on stainless, the choice of process cuts exposure more effectively than any addition to the kit.
How much is allowed
In the EU chromium VI falls under the carcinogens directive and carries a binding limit value of 0.005 mg/m³ measured as chromium. A transitional period with a laxer figure applied to welding and plasma cutting, but it ended in January 2025, and the base value now applies to all work.
The directive sets a floor, and member states may adopt stricter values — several have. What binds you is always the figure in your national regulations, not the EU one. Workplace concentration measurements are arranged by the employer, and the result is what the choice of protective measures rests on.
What actually reduces exposure
The choice of process — see above; the difference runs in multiples, not percentages.
Extraction at source, not a fan blowing sideways. A fan spreads the fume around the shop and hands it to your neighbours instead of removing it. On-torch extraction or an extraction arm is set a hand's width from the arc, on the side away from the incoming air.
Powered air instead of a half mask for a full shift: equipment you do not want to take off protects in reality, not on paper. Details — respiratory protection.
Hygiene afterwards. Dust is not blown off with compressed air — that scatters it through the whole room. Workwear from stainless jobs does not go home to be washed: the exposure is then handed to the family, and no mask covers that.
What next
What fume contains and how a bay is ventilated — welding fume. Choosing a mask or a powered hood — respiratory protection. The welding of stainless itself — welding stainless steel.
Frequently asked questions
Is welding fume carcinogenic?
Yes. In 2017 the International Agency for Research on Cancer (IARC) classified welding fumes in Group 1 — carcinogenic to humans — and that applies to fume in general, not only to stainless. On stainless, hexavalent chromium and nickel are added on top, so the risk is markedly higher.
Which process produces the most chromium VI?
Covered electrodes and flux-cored wire. Alkali compounds from the coating and the flux stabilise chromium in its hexavalent state, so MMA and FCAW produce several times more of it than MIG with solid wire, and TIG the least of all. Choosing the process can do more than any mask.
Is extraction enough on stainless?
Not on its own. Extraction at source takes most of the fume and remains the first step, but with chromium VI what is left over matters: the exposure limits are so low that the remainder still counts. For long work on stainless you also need respiratory protection, preferably powered.
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