COSHH · Mandatory · Pre-Construction
COSHH Assessment — Welding Fumes
This COSHH assessment addresses welding fume exposure which the HSE reclassified as a carcinogen in 2019. All welding fumes, including mild steel, now require engineering controls such as LEV or on-torch extraction. It covers MIG, TIG, MMA, and oxy-fuel processes, and addresses manganese, chromium, and nickel fume components.
Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. COSHH Regs 2002 / WEL remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.
| 2019 reclassification | ALL welding fume — regardless of process, material or duration — was reclassified as a Group 1 carcinogen (lung cancer and kidney cancer) by IARC. The HSE adopted this classification in January 2019 |
| Specific hazards | Lung cancer, kidney cancer, manganese neurotoxicity (manganism), hexavalent chromium (Cr VI) from stainless steel, nickel compounds, zinc oxide fume fever from galvanised steel |
| Indoor welding | Local exhaust ventilation (LEV) is mandatory for ALL indoor welding. General ventilation (open doors and windows) is not acceptable as a primary control |
| Outdoor welding | RPE is mandatory for ALL outdoor welding — minimum APF 20 (FFP3 or equivalent). The previous exemption for outdoor welding was withdrawn in 2019 |
| Health surveillance | Required for all workers who carry out regular welding. Includes respiratory questionnaire, spirometry and, where stainless steel or chrome-containing alloys are welded, urinary chromium and nickel monitoring |
| Enforcing authority | Health and Safety Executive (HSE) |
1. The 2019 Reclassification and What Changed
In January 2019, the HSE implemented the IARC reclassification of all welding fume as a Group 1 carcinogen — meaning there is sufficient evidence that welding fume causes cancer in humans, specifically lung cancer and kidney cancer. This reclassification applies to all welding processes (MIG/MAG, MMA, TIG, flux-cored, submerged arc and all others), all base metals (mild steel, stainless steel, aluminium, galvanised steel and all alloys), and all durations of exposure. There is no safe threshold and no process-based exemption.
Before 2019, the HSE position was that mild steel welding fume was a lower-risk exposure compared with stainless steel or galvanised welding, and that outdoor welding provided sufficient natural dilution to make additional controls unnecessary in most circumstances. The reclassification overturned both positions. The key changes are:
First, all indoor welding now requires local exhaust ventilation (LEV) as the primary control. General ventilation — opening windows and doors, using portable fans, or relying on natural air movement through the building — is not an acceptable primary control for indoor welding fume. LEV means extraction at the point of fume generation: on-torch extraction, portable extraction arms positioned within 300mm of the arc, or fixed extraction hoods with sufficient capture velocity to draw fume away from the welder’s breathing zone.
Second, all outdoor welding now requires RPE with a minimum assigned protection factor (APF) of 20 — which in practice means an FFP3 disposable mask, a reusable half-mask with P3 filters, or a powered air-purifying respirator. The previous position that outdoor welding did not require RPE has been withdrawn. Natural air movement outdoors reduces fume concentration but does not reduce it to zero, and any exposure to a Group 1 carcinogen requires control.
Third, health surveillance is now required for all workers who carry out regular welding, regardless of the welding process or base metal. This includes respiratory questionnaire, spirometry (lung function testing), and where welding on stainless steel, chromium-containing alloys or nickel alloys, biological monitoring for urinary chromium and nickel.
Opening windows and doors is not adequate ventilation for indoor welding
The HSE has been explicit that general ventilation — including opening windows, doors and roller shutters, and using floor-standing fans — does not constitute adequate control for welding fume indoors. General ventilation dilutes but does not capture fume at source. The welder’s breathing zone remains within the fume plume regardless of general air movement. LEV must be provided to extract fume at the point of generation. This applies to all indoor welding processes including mild steel MIG/MAG, which was previously considered lower risk. A fabrication shop with the roller shutters open is still an indoor space and still requires LEV.
The 2019 change also removed the “sporadic and low intensity” exemption that had previously been applied to occasional welding. Under the old approach, some employers argued that occasional or short-duration welding did not require the same controls as continuous production welding. This argument is no longer tenable. A Group 1 carcinogen has no safe exposure threshold, and the controls (LEV indoors, RPE outdoors) apply to all welding regardless of duration or frequency. A maintenance fitter who welds for 20 minutes a week requires the same controls as a production welder who welds all day.
2. Control Options by Welding Type and Location
The control requirements for welding fume depend on the welding process, the base metal, and whether the work is carried out indoors or outdoors. The following table sets out the minimum control requirements for the most common combinations encountered on construction sites.
| Scenario | LEV requirement | RPE requirement | Additional controls |
|---|---|---|---|
| MIG/MAG indoors (mild steel) | Mandatory. On-torch extraction or portable extraction arm within 300mm of arc. Capture velocity minimum 0.5 m/s at the fume source | Required in addition to LEV where exposure monitoring shows WEL may be exceeded, or during initial set-up before LEV effectiveness is confirmed. Minimum APF 20 (FFP3) | General ventilation as supplementary measure only. Welding screens to protect bystanders. Health surveillance for all regular welders |
| MMA (stick) indoors (mild steel) | Mandatory. MMA generates higher fume concentrations than MIG/MAG. Portable extraction arm is the most practical LEV option for MMA. Position within 300mm of the arc | Required in addition to LEV. MMA fume generation rates are high and variable. Minimum APF 20 (FFP3); consider APF 40 (powered air) for extended tasks | Electrode selection: use low-fume electrodes where available. Restrict access to the welding area. Health surveillance for all regular welders |
| TIG indoors (mild steel) | Mandatory. TIG generates the lowest fume volume of the common arc processes but still produces carcinogenic fume. On-torch extraction or extraction arm required | May not be required if LEV is effective and exposure monitoring confirms WEL compliance. However, RPE must be available and used during any period when LEV is not operational | TIG produces higher levels of ozone and UV radiation than MIG/MAG. Ozone monitoring may be required in poorly ventilated spaces. Health surveillance for all regular welders |
| All welding outdoors (mild steel) | Not normally required outdoors, but should be considered where welding is in a sheltered location (against a wall, under a canopy, in a trench) where fume may accumulate | Mandatory for all outdoor welding. Minimum APF 20 (FFP3). The 2019 reclassification removed the previous exemption for outdoor welding. No outdoor welding without RPE | Position welder upwind where practicable. Welding screens to protect nearby workers. Health surveillance for all regular welders |
| Stainless steel or nickel alloys (any location) | Mandatory indoors. Strongly recommended outdoors in addition to RPE. Stainless steel welding generates hexavalent chromium (Cr VI) and nickel compounds, both Group 1 carcinogens with their own WELs | Mandatory in all locations. Minimum APF 20 (FFP3) with P3 particulate filter. For extended stainless steel welding, powered air-purifying respirator (APF 40) recommended | Biological monitoring: urinary chromium and nickel levels. Cr VI WEL is 0.01 mg/m3 (very low). Nickel compounds WEL is 0.1 mg/m3. Separate COSHH assessment required for Cr VI and nickel exposure. Health surveillance mandatory |
| Galvanised steel (any location) | Mandatory indoors. Strongly recommended outdoors. Welding galvanised steel generates zinc oxide fume which causes metal fume fever (flu-like symptoms within hours of exposure) | Mandatory in all locations. Minimum APF 20 (FFP3). For production welding on galvanised steel, powered air-purifying respirator (APF 40) or supplied-air RPE recommended | Metal fume fever is a reportable disease under RIDDOR. Workers must be briefed to report flu-like symptoms occurring within 4 to 12 hours of welding galvanised steel. Where practicable, remove galvanising from the weld zone by grinding before welding to reduce zinc fume generation. Health surveillance mandatory |
On construction sites, welding frequently takes place in locations that are neither fully indoors nor fully outdoors — partially completed structures, steel frames with cladding partially installed, basements with open access points, and areas under temporary weather protection. These locations must be assessed on their specific ventilation characteristics. As a practical rule, if natural air movement is restricted in any direction, the location should be treated as indoor for the purposes of LEV provision. If in doubt, provide LEV.
On-torch extraction systems are now available for MIG/MAG torches and are the most practical LEV solution for construction site welding because they travel with the welder and maintain extraction at the point of fume generation regardless of the welding position. Portable extraction arms on mobile units are the alternative where on-torch extraction is not available. The extraction arm must be positioned within 300mm of the arc to achieve effective capture. Extraction arms positioned further away lose capture effectiveness rapidly and may provide a false sense of protection.
All LEV systems used for welding fume must be examined and tested by a competent person at least every 14 months under COSHH Regulation 9. The examination must confirm that the system achieves the design capture velocity at the fume source and that filters are functioning correctly. The examination report must be kept on file. Between formal examinations, the user must carry out pre-use checks to confirm that the extraction unit is operating, airflow is adequate, hoses are not damaged or blocked, and filters are not saturated.
3. Common Mistakes
Using general ventilation as the primary control for indoor welding
Opening windows, doors and roller shutters, and using floor-standing or pedestal fans, does not constitute adequate fume control for indoor welding. General ventilation dilutes fume concentration in the wider space but does not reduce the concentration in the welder’s breathing zone, which is within the fume plume rising directly from the arc. The HSE has been explicit since 2019 that local exhaust ventilation — extraction at the point of fume generation — is mandatory for all indoor welding. A workshop with the doors open is still indoor welding. A partially completed building with open window openings is still indoor welding.
Providing P2 dust masks or nuisance dust masks as RPE for welding
P2 (FFP2) disposable masks provide an assigned protection factor of 10, which is below the minimum APF of 20 required for welding fume. Nuisance dust masks (the thin single-strap disposables) have no assigned protection factor at all. For welding fume, the minimum RPE standard is FFP3 (APF 20) or a reusable half-mask with P3 filters. For extended welding, stainless steel welding, or galvanised steel welding, a powered air-purifying respirator (APF 40) or supplied-air RPE is recommended. All tight-fitting RPE must be face-fit tested for the individual wearer — an untested mask provides an unknown protection factor.
No health surveillance for workers welding stainless steel
Welding stainless steel generates hexavalent chromium (Cr VI) and nickel compounds, both of which are Group 1 carcinogens with their own workplace exposure limits (Cr VI: 0.01 mg/m3; nickel: 0.1 mg/m3). In addition to the general welding fume health surveillance requirements (respiratory questionnaire and spirometry), stainless steel welders require biological monitoring — urinary chromium and nickel measurements — to confirm that internal dose remains below action levels. Failure to provide biological monitoring for stainless steel welders is a specific and serious COSHH compliance failure that demonstrates inadequate health risk management for two Group 1 carcinogens.
Not checking that on-torch LEV is functioning before starting work
On-torch extraction systems are the most practical LEV solution for construction site welding, but they require daily pre-use checking. The extraction unit must be running and drawing air, the hose must be connected and undamaged, the capture velocity at the torch tip must be adequate, and the filter must not be saturated. Welders must be trained to carry out these checks and to stop work if the extraction is not functioning. A non-functioning on-torch extraction system that is physically present but switched off or blocked provides zero protection and creates a false record of LEV provision.
Applying the old sporadic and low-intensity exemption
Before 2019, some employers applied an exemption for “sporadic and low-intensity” welding, arguing that occasional or short-duration welding did not require the same controls as continuous production welding. This exemption was withdrawn when all welding fume was reclassified as a Group 1 carcinogen. A Group 1 carcinogen has no safe exposure threshold, and the controls (LEV indoors, RPE outdoors, health surveillance) apply regardless of the duration or frequency of welding. A maintenance fitter who welds for 15 minutes requires the same controls as a coded welder who welds all day. Any COSHH assessment that still references a sporadic-use exemption is non-compliant and must be updated.
5. Frequently Asked Questions
What is the minimum RPE for outdoor welding?▾
The minimum RPE for all outdoor welding is an assigned protection factor (APF) of 20. In practice this means an FFP3 disposable mask, a reusable half-mask with P3 particulate filters, or a powered air-purifying respirator (PAPR). The 2019 reclassification of all welding fume as a Group 1 carcinogen removed the previous exemption for outdoor welding. RPE is now mandatory for every outdoor welding task regardless of process, base metal, or duration. All tight-fitting RPE (FFP3 or half-mask) must be face-fit tested for the individual wearer. Where welding is on stainless steel, galvanised steel, or other hazardous coatings outdoors, a PAPR (APF 40) or higher protection is recommended.
Does the 2019 guidance apply to TIG welding?▾
Yes. The 2019 reclassification applies to ALL welding processes without exception, including TIG (GTAW). While TIG generates the lowest fume volume of the common arc welding processes, the fume it does produce is carcinogenic. Indoor TIG welding requires LEV. Outdoor TIG welding requires RPE with a minimum APF of 20. Health surveillance is required for all regular TIG welders. Additionally, TIG welding generates higher levels of ozone and ultraviolet radiation than MIG/MAG or MMA, which may require separate assessment — particularly in poorly ventilated indoor spaces where ozone concentration can build up.
What defines a restricted-access or confined location for welding?▾
A restricted-access location for welding is any space where the welder's ability to position themselves upwind or away from the fume plume is limited, and where natural ventilation is restricted. This includes working inside steel vessels, tanks, columns, and pipe racks; welding in trenches, pits, basements, and lift shafts; welding inside partially completed structures with limited openings; and welding in any position (overhead, vertical) where the fume plume rises directly past the welder's breathing zone. In these locations, LEV is essential regardless of whether the space technically qualifies as indoor or outdoor, and RPE with a higher APF (40 or above) should be specified because the welder cannot avoid the fume plume.
How often must LEV for welding fume be examined and tested?▾
Under COSHH Regulation 9, all LEV systems used for controlling exposure to substances hazardous to health must be examined and tested by a competent person at intervals not exceeding 14 months. This applies to on-torch extraction units, portable extraction arms, fixed extraction hoods, and any other LEV system used for welding fume control. The examination must verify that the system achieves the design capture velocity at the fume source, that filters are intact and functioning, and that ductwork is undamaged and unobstructed. A written report of the examination must be kept and made available to HSE inspectors on request. Between formal 14-month examinations, the user (welder or supervisor) must carry out daily pre-use checks to confirm the system is operating correctly.
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