COSHH Assessment for Welding Fumes: Complete UK Guide for Fabricators
Since 2019, HSE reclassified all welding fume as a carcinogen. LEV or RPE is now required for ALL welding, including mild steel in open-air environments. This guide covers writing a COSHH assessment for welding fumes, including substance-specific WELs, extraction requirements, and health surveillance.
The 2019 Rule Change: All Welding Fume is Now Carcinogenic
In February 2019, the Health and Safety Executive issued Safety Alert STSU1, fundamentally changing the way every fabrication shop, site welder, and maintenance team must handle welding fume. The International Agency for Research on Cancer (IARC) confirmed that exposure to mild steel welding fume causes lung cancer. HSE acted immediately.
ALL welding fume, including mild steel, is now classified as a carcinogen.
Before 2019, the guidance allowed mild steel welding outdoors or in large, well-ventilated spaces without RPE. That is no longer acceptable. HSE inspectors will issue enforcement notices if they find welders working without adequate extraction or respiratory protection, regardless of the material being welded.
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The bottom line: LEV (local exhaust ventilation) or RPE (respiratory protective equipment) is required for every welding task, with no exceptions. If your COSHH assessment was written before February 2019, it needs updating now.
Substances in Welding Fume
Welding fume is not a single substance. It is a complex mixture of metallic oxides, gases, and particulates. The exact composition depends on the base metal, consumables, welding process, and any coatings on the material. Your COSHH assessment must identify the specific substances present.
Mild steel welding produces iron oxide fume and manganese. Manganese is a neurotoxin. Prolonged exposure can cause symptoms similar to Parkinson's disease.
Stainless steel welding generates chromium VI and nickel compounds. Both are confirmed human carcinogens. Stainless steel welding carries the highest fume risk and demands the strictest controls.
Galvanised steel welding releases zinc oxide fume, which causes metal fume fever. This is discussed in detail later in this guide.
Flux-cored and MMA (stick) welding can produce fluoride compounds from the flux coating. These are respiratory irritants and can cause long-term damage.
Key Workplace Exposure Limits (WELs) from EH40:
- Manganese: 0.5 mg/m³ (8-hour TWA)
- Chromium VI: 0.01 mg/m³ (8-hour TWA)
- Nickel: 0.1 mg/m³ (8-hour TWA)
- Iron oxide fume: 5 mg/m³ (8-hour TWA)
- Zinc oxide: 4 mg/m³ (8-hour TWA)
Note that the chromium VI limit of 0.01 mg/m³ is extremely low. It is very easy to exceed this when welding stainless steel without effective extraction.
Writing the COSHH Assessment
A COSHH assessment for welding fume must be specific to your workplace. Generic assessments downloaded from the internet will not satisfy HSE inspectors. Here is the step-by-step process.
Step 1: Identify the Welding Process
Different welding processes produce different levels and types of fume. MIG (GMAW) welding generally produces more fume than TIG (GTAW). MMA (stick) welding produces the most fume overall. Flux-cored arc welding (FCAW) generates high levels of particulate. Record every welding process used on site.
Step 2: Identify the Base Metals and Consumables
Check the material safety data sheets (SDS) for your welding consumables. Identify the base metals being welded: mild steel, stainless steel, galvanised steel, aluminium, or other alloys. Note any coatings, paints, primers, or galvanising on the workpiece. These coatings produce additional hazardous fume when burned off during welding.
Step 3: Assess Exposure
Consider how long each welder is exposed per shift and how often welding takes place. Assess the working environment: is the welding done in a fabrication shop, outdoors on a construction site, or in a confined space? Confined space welding dramatically increases exposure because fume cannot disperse. Document the number of welders working simultaneously, as multiple welders in the same space creates collective exposure for everyone nearby.
Step 4: Control Measures
COSHH requires you to apply the hierarchy of controls. For welding fume, the practical controls are:
Local Exhaust Ventilation (LEV) is the primary control. On-torch extraction is the most effective option, capturing fume at the source before it enters the welder's breathing zone. Fixed extraction hoods work well in fabrication shops where the workpiece can be positioned under the hood. Mobile extraction units with flexible arms are suitable for site work and larger fabrications that cannot be moved.
Respiratory Protective Equipment (RPE) should be used in addition to LEV, not as a replacement. For regular welders, a powered air purifying respirator (PAPR) with a P3 filter provides the best protection and comfort for extended wear. For occasional or short-duration welding, an FFP3 disposable mask is the minimum acceptable standard. All RPE must be face-fit tested for the individual wearer.
Important: natural ventilation alone is NOT sufficient. Since the 2019 reclassification, opening doors and windows does not constitute adequate control for welding fume. This applies to outdoor welding as well. You must provide LEV, RPE, or both.
Train welders to position themselves so their head is out of the fume plume. This simple practice significantly reduces exposure, though it does not replace the need for LEV and RPE.
Step 5: Health Surveillance
Following the 2019 reclassification, health surveillance is required for all workers who are regularly exposed to welding fume. This is not optional.
Health surveillance for welders must include:
- Lung function testing (spirometry) at baseline before starting welding work, then annually
- A respiratory health questionnaire at each assessment
- Biological monitoring for stainless steel welders, including urinary chromium testing to check for chromium VI absorption
Keep all health surveillance records for at least 40 years. If any results show deterioration, review your controls and refer the individual for further medical assessment.
Step 6: LEV Maintenance
LEV that is not maintained will not protect your workers. Under COSHH Regulation 9, you must:
- Have LEV thoroughly examined and tested at least every 14 months
- Carry out daily user checks (filter condition, airflow indicator, hose integrity)
- Keep examination and test records for at least 5 years
If the extraction unit is not working, welding must stop until it is repaired or suitable RPE is provided.
Metal Fume Fever: The Friday Afternoon Problem
Metal fume fever is an acute illness caused by inhaling zinc oxide fume, most commonly from welding or cutting galvanised steel. It is one of the most under-reported occupational illnesses in the UK.
Symptoms appear 4 to 12 hours after exposure and mimic a bad dose of flu: fever, chills, muscle aches, nausea, and a metallic taste in the mouth. Many welders dismiss it as a cold or virus, which means it goes unreported.
The condition is sometimes called "Monday morning fever" because workers develop a short-term tolerance during the week that fades over the weekend. When they return on Monday and start welding galvanised material again, the symptoms hit hardest.
Prevention is straightforward: use LEV and RPE for all galvanised welding, and never burn off the galvanised coating as a shortcut before welding. If the galvanising must be removed, use mechanical methods (grinding) rather than thermal methods.
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Related Guides
Welding Fume Composition by Process and Material
MIG welding mild steel produces fumes that are primarily iron oxide and manganese. The typical fume generation rate is around 0.3 to 0.6 g/min. While considered the lowest risk welding process for mild steel, it still requires controls since the 2019 reclassification.
MIG welding stainless steel generates fumes containing iron oxide, chromium VI, nickel, and manganese. The presence of chromium VI makes this significantly more hazardous. Chromium VI is a known human carcinogen with a workplace exposure limit (WEL) of just 0.01 mg/m3. Stainless steel welding demands the most rigorous controls and health surveillance.
MMA (stick) welding fume composition depends heavily on the rod coating. Basic rods produce fluoride fumes, which can cause irritation to the eyes, nose, and throat. Rutile rods produce titanium dioxide particles. MMA welding generally has a moderate fume generation rate, higher than MIG but lower than flux-cored processes.
TIG welding has the lowest fume generation rate of any arc welding process, typically around 0.01 to 0.05 g/min. However, the fumes still contain metal particles from the base material and filler wire. There is also a risk of tungsten inclusion if the electrode contacts the weld pool, producing tungsten oxide fumes. Despite the lower fume rate, TIG welding on stainless steel still produces chromium VI.
Flux-cored wire welding produces the highest fume generation rate among common arc welding processes, typically 1 to 2 g/min. The fumes contain fluorides and manganese from the flux core. Effective local exhaust ventilation is essential for this process, and on-torch extraction is strongly recommended.
Oxy-fuel cutting produces metal oxide fumes along with carbon monoxide from incomplete combustion. When cutting coated or painted metals, additional toxic fumes may be released from the coating material. Adequate ventilation and RPE are required, particularly in enclosed or semi-enclosed spaces.
The critical point to remember: the 2019 HSE reclassification means that ALL welding fume is now classified as a carcinogen. Every process listed above requires adequate controls, including mild steel MIG welding in open air. The previous guidance that allowed outdoor mild steel welding without controls is no longer valid.
Choosing the Right Extraction System
Selecting the correct extraction system is one of the most important decisions in your welding fume COSHH assessment. The right choice depends on the welding process, workshop layout, and whether work is fixed-position or mobile.
On-torch extraction captures fumes directly at the source and is over 90% effective when properly maintained. It is the best option for fixed-position welding. The main drawback is that it adds approximately 1 to 2 kg to the torch weight, which can cause fatigue during extended use. Despite this, it remains the preferred solution because it captures fume before it enters the welder's breathing zone.
High-vacuum extraction arms use a flexible arm that can be positioned near the weld. These are effective when kept within 150 to 200 mm of the arc, which is their main limitation. In busy fabrication shops, welders sometimes push the arm aside if it obstructs their work, reducing effectiveness. Regular supervision and training are needed to ensure correct positioning.
Mobile extraction units are portable and designed for site welding where fixed systems are not practical. They must have a HEPA filter to capture fine particles effectively. Position the inlet within 300 mm of the fume source for adequate capture. Check filters regularly and replace according to the manufacturer's schedule.
General ventilation alone is NOT sufficient as a sole control measure since the 2019 reclassification. It is only acceptable as a supplement to local exhaust ventilation (LEV). General ventilation can help reduce background fume levels in the workshop but does not protect the welder at the point of exposure.
Downdraft tables draw air downward through a perforated table surface, pulling fumes away from the welder's breathing zone. They work well for small fabrication work and bench-level welding tasks. They are less effective for large assemblies that cover most of the table surface and block airflow.
Push-pull ventilation systems are designed for large fabrication bays where fixed extraction at each workstation is impractical. Clean air is pushed across the workspace from one side and extracted from the other, creating a controlled airflow pattern that moves fume away from welders. These systems require careful design and commissioning by a ventilation engineer.
Biological Monitoring for Stainless Steel Welders
For workers who regularly weld stainless steel, biological monitoring is an essential part of health surveillance. This involves testing urine samples to measure the levels of hazardous metals absorbed into the body.
Urinary chromium testing is recommended for all regular stainless steel welders. The Biological Monitoring Guidance Value (BMGV) for urinary chromium is 10 μmol/mol creatinine. Samples should be collected at the end of the shift, at the end of the working week, to capture peak exposure levels.
You should also consider urinary nickel monitoring with a BMGV of 30 μmol/mol creatinine. Results that exceed the BMGV indicate that current control measures are inadequate and must be reviewed and improved. Biological monitoring does not replace exposure controls. It serves as a check that your controls are working effectively.
Frequently Asked Questions
Can I weld mild steel outdoors without RPE?
No, not since February 2019. HSE Safety Alert STSU1 reclassified all welding fume as carcinogenic. Even mild steel welding in open air requires either LEV or RPE. The previous guidance allowing outdoor mild steel welding without controls is no longer valid.
What RPE should a welder use?
For occasional welding, a minimum FFP3 disposable mask under the welding helmet can be used, though this combination is difficult to fit test properly. For regular welders, a powered air purifying respirator (PAPR) with a P3 filter integrated into the welding helmet is the best option. This provides an Assigned Protection Factor (APF) of 40 and does not rely on a face seal, making it far more practical for extended welding work.
Do I need health surveillance for welders?
Yes. All workers who are regularly exposed to welding fumes should be under health surveillance. This includes baseline lung function testing (spirometry) before starting welding work, then at least annually. For stainless steel welders, add biological monitoring for urinary chromium and nickel as described in the section above.
What about welding in a confined space?
Welding in a confined space is extremely high risk. Fume concentrations build rapidly, and there is a risk of oxygen depletion and toxic gas accumulation. You need a separate confined space RAMS, forced mechanical ventilation, continuous gas monitoring, supplied-air respiratory equipment, and a rescue plan. An FFP3 mask is NOT sufficient in a confined space.
Authority Sources and Further Reading
The following external resources provide authoritative guidance on welding fume hazards and control measures:
- HSE Safety Alert STSU1: Welding Fume and Lung Cancer/COPD - the official HSE safety bulletin on the reclassification of mild steel welding fume
- HSE EH40 Workplace Exposure Limits - contains the legally binding workplace exposure limits for all welding fume constituents
- TWI (The Welding Institute) - provides technical guidance on welding health and safety, fume composition, and control strategies
- BS EN ISO 15012-1 - the standard covering health and safety in welding, specifically requirements for testing and marking of equipment for air filtration
For related guidance from Swift, see the following articles:
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