Welding fume and ventilation
Welding fume is condensed metal vapour with a particle size in the sub-micron range, which means it goes to the deepest part of the lung. Since 2017 all of it is classified as a Group 1 carcinogen.
What is in it
Fume is not smoke from burning. It is metal that vaporised in the arc and condensed into extremely fine particles, plus gases created by the arc from the surrounding air and from any coating on the metal.
| Source | What it produces | Effect |
|---|---|---|
| Mild steel | Iron oxide, manganese | Lung damage; manganese affects the nervous system |
| Stainless steel | Chromium(VI), nickel | Both carcinogenic; the worst common case |
| Galvanised steel | Zinc oxide | Metal fume fever |
| Painted or primed steel | Isocyanates, lead, organic products | Sensitisation, poisoning |
| Degreased surfaces | Phosgene from chlorinated solvents | Acutely toxic. Never weld near trichloroethylene |
| The arc itself | Ozone, nitrogen oxides | Airway irritation; ozone is worst in TIG on aluminium |
The order of controls
1. Eliminate. Grind galvanising and paint back 25 mm from the joint before welding — this also improves the weld, since those coatings cause porosity.
2. Substitute. A lower-fume process or consumable where the job allows. TIG produces far less fume than flux-cored wire; a low-fume electrode produces less than a standard one.
3. Extract at source. A fume arm positioned within about 300 mm of the arc, or an on-torch extraction system. This is the control that actually works, and its effectiveness collapses with distance — at 600 mm a fume arm captures a fraction of what it captures at 300.
4. General ventilation. Dilutes what escapes the extraction. Not a substitute for it.
5. Respiratory protection. FFP3 or a powered respirator, as the last layer rather than the first.
Where you stand
The plume rises. Standing directly over the joint puts your face in it, and no amount of general ventilation changes that. Keep your head to one side of the plume, and use the extraction arm to pull the fume away from you rather than past you.
On a bench, position the extraction on the far side of the joint so the flow is away from your face. It sounds obvious and it is routinely done the other way round.
Confined spaces
Inside a tank, a vessel or a duct, everything changes. Fume accumulates instead of dispersing, shielding gas displaces oxygen, and argon is heavier than air so it collects in the bottom — which is where the welder is.
Forced ventilation, continuous atmosphere monitoring, a permit, and someone outside watching. This is not an area for judgement calls; it is the scenario that kills welders who were entirely competent at welding.
Frequently asked questions
Is welding fume really classified as carcinogenic?
Yes. In 2017 the IARC reclassified all welding fume as a Group 1 carcinogen — carcinogenic to humans — not only the stainless-steel fraction. That reclassification is why enforcement of extraction requirements tightened across Europe afterwards.
Is an open door enough ventilation?
No, and the reason is where the fume goes. The plume rises straight past your face on its way to the roof. General ventilation dilutes the workshop air; it does nothing about the concentrated plume in your breathing zone. That needs local extraction at the arc.
What is metal fume fever?
Flu-like symptoms — fever, aching, chills — starting a few hours after welding galvanised steel, from inhaling zinc oxide. It passes in a day or two and it is a warning, not a rite of passage: it means you inhaled a substantial dose of something you should not have.
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