Welding produces a complex mixture of fumes and gases that can seriously impact health if not controlled. These include metal oxides, ozone, carbon monoxide, and nitrogen oxides — many of which are toxic or carcinogenic even at low levels.
In the UK, the Health and Safety Executive (HSE) has made it clear: all welding fume, including mild steel, is classed as a carcinogen. This means exposure must be controlled to the lowest level reasonably practicable, not just below workplace exposure limits.
Poor ventilation leads to:
- Short-term risks → headaches, dizziness, nausea, eye/throat irritation
- Long-term risks → occupational asthma, cancer, metal fume fever, neurological effects from manganese
Employers have a legal duty under the Control of Substances Hazardous to Health Regulations 2002 (COSHH) to protect workers by providing effective ventilation, extraction, and respiratory protection where necessary.
This guide explains the standards, airflow requirements, and best practices for welding ventilation, with tables and reference charts to help ensure compliance and worker safety.
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In this guide:
Welding Fume Hazards & Workplace Exposure Limits
Different metals and processes release different fumes. Some are irritating, while others are highly toxic or carcinogenic. The EH40/2005 Workplace Exposure Limits (WELs) from the HSE provide guidance on acceptable airborne concentrations.
Here’s a reference table for the most common welding fume hazards:
| Substance | Main Source in Welding | WEL (8-hr TWA) | Key Health Risks |
|---|---|---|---|
| Iron oxide fume | Mild/carbon steel welding | 5 mg/m³ (inhalable) | Irritation of lungs, “metal fume fever” |
| Manganese | Steel filler metals, fluxes | 0.2 mg/m³ (inhalable) / 0.05 mg/m³ (respirable) | Neurological damage (similar to Parkinson’s) |
| Chromium VI | Stainless steel welding | 0.01 mg/m³ | Potent carcinogen, asthma, skin/eye damage |
| Nickel compounds | Stainless/nickel alloys | 0.05 mg/m³ | Carcinogenic, respiratory disease |
| Aluminium oxide | Aluminium welding | 4 mg/m³ (respirable) / 10 mg/m³ (inhalable) | Lung irritation |
| Ozone | UV arc radiation splitting O₂ | 0.2 ppm (15 min ref) | Chest pain, lung damage |
| Nitrogen oxides (NO/NO₂) | Arc/oxy-fuel processes | 1 ppm (NO₂) | Irritant gas, pulmonary oedema risk |
| Carbon monoxide (CO) | Incomplete combustion (oxy-fuel, confined spaces) | 30 ppm (8-hr TWA) | Headache, nausea, unconsciousness, death at high levels |
⚠️ Key point: Even when fumes are below WELs, COSHH requires reducing exposure to “as low as reasonably practicable” (ALARP).
👉 This is why local exhaust ventilation (LEV) — not just general workshop airflow — is the cornerstone of welding fume control.
Ventilation & Airflow Requirements
Good welding fume control relies on both general ventilation (diluting airborne fumes in the workspace) and local exhaust ventilation (LEV) (capturing fumes at the source). The balance depends on the welding process, the size of the workspace, and how many welders are working.
General Ventilation
General (or dilution) ventilation uses fans and air changes per hour (ACH) to reduce overall fume concentration. It is not a substitute for LEV but provides background protection.
| Workshop Size | Recommended ACH (Air Changes per Hour) | Notes |
|---|---|---|
| Small shops (< 100 m²) | 6–10 ACH | Use in combination with portable extractors |
| Medium workshops (100–500 m²) | 8–12 ACH | Supply fresh air + extraction fans |
| Large fabrication halls (> 500 m²) | 12–15 ACH | Often ducted roof fans with make-up air |
⚠️ General ventilation alone will not adequately control welding fume exposure, especially for stainless or nickel alloys.
Local Exhaust Ventilation (LEV)
LEV is designed to capture and filter fumes directly at the weld point, before they spread into the breathing zone.
| Welding Process | Minimum Capture Velocity | Typical Airflow (CFM) per Station | Notes |
|---|---|---|---|
| TIG (low fume) | 75–100 fpm | 800–1000 CFM | Fume arms or portable units usually sufficient |
| MIG (mild steel) | 100–150 fpm | 1000–1500 CFM | Higher fume volume → stronger airflow required |
| MIG (stainless/duplex) | 150 fpm+ | 1200–1800 CFM | Requires HEPA/activated carbon filters for Cr(VI) |
| Stick (MMA) | 100–150 fpm | 1000–1500 CFM | Portable extractors recommended |
| Flux-cored (FCAW) | 150–200 fpm | 1500–2000 CFM | High fume generation — strong LEV essential |
| Oxy-fuel cutting | 100 fpm | 800–1200 CFM | Extract at tip or cutting table |
| Plasma cutting | 200 fpm | 1800–2500 CFM | Downdraft tables or enclosure extraction |
💡 Rule of Thumb:
- Closer extraction = lower airflow required.
- As distance from source increases, airflow must increase significantly (e.g., doubling capture distance can require 4–6× airflow).
Airflow Distribution
- Supply air should come from behind the welder, pushing fumes towards the extractor.
- Avoid cross-drafts that can blow fumes back into the breathing zone.
- Balanced systems: Ensure extraction does not create negative pressure without adequate make-up air.
Filter Types by Welding Hazard
| Hazard / Process | Main Fume Components | Recommended Filter | Notes |
|---|---|---|---|
| Mild / Carbon Steel (MIG, Stick, FCAW) | Iron oxide, manganese | High-efficiency particulate (HEPA H13/H14 or MERV 15+) | Standard LEV filters handle particles; ensure airflow >1000 CFM per station. |
| Stainless Steel (MIG, TIG, Stick) | Chromium VI, nickel compounds | HEPA H14 + Activated Carbon | Cr(VI) is carcinogenic → HEPA essential. Activated carbon helps capture gas-phase contaminants. |
| Duplex / Super Duplex | Higher Cr/Ni + nitrogen oxides | HEPA H14 + Carbon | Same as stainless, but NOx levels may be higher. |
| Aluminium (MIG, TIG) | Aluminium oxide, ozone | HEPA + Carbon (ozone adsorption) | TIG especially generates ozone → carbon filter required. |
| Flux-Cored Arc Welding (FCAW) | Large particulate, fluorides, manganese | HEPA H13+ | Very high fume generation – frequent filter changes needed. |
| TIG on Stainless / Aluminium | Ozone, fine particulates | Carbon filter + fine particulate prefilter | TIG has relatively low particulates but high ozone. |
| Plasma Cutting | Metal fumes (Fe, Cr, Ni, Al), ozone, NOx | HEPA + Carbon | Strong airflow essential; downdraft tables recommended. |
| Oxy-Fuel Cutting / Heating | CO, CO₂, NOx | Activated Carbon + Pre-filters | More gases than particulates – focus on gas filtration. |
| Welding on Galvanised Steel | Zinc oxide | HEPA H13/H14 | Controls “metal fume fever” risk. |
| Nickel Alloys (Inconel, Monel, Hastelloy) | Nickel oxides, Cr(VI) | HEPA H14 + Carbon | Carcinogenic and sensitising fumes. |
| Titanium / Exotic Metals | Metal oxides, possible reactive gas by-products | HEPA H14 | Check WPS and MSDS – some alloys require additional filtration. |
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Monitoring & Compliance
Even with good ventilation, welding fumes must be regularly monitored to ensure systems are effective and legal obligations are met. Under UK COSHH Regulations, employers must demonstrate that welders’ exposure is as low as reasonably practicable and below workplace exposure limits (WELs).
Welding Fume Exposure Limits (EH40, HSE UK)
| Substance | 8-hr TWA (WEL) | Short-Term Exposure Limit (STEL) | Notes |
|---|---|---|---|
| Welding fume (general, mild steel) | 5 mg/m³ | — | Applies to total inhalable dust |
| Hexavalent chromium [Cr(VI)] | 0.01 mg/m³ | — | Carcinogenic; stainless steel welding |
| Nickel compounds | 0.1 mg/m³ | — | Sensitiser and carcinogenic |
| Manganese | 0.2 mg/m³ | — | Linked to neurological disorders |
| Ozone (from TIG/UV) | 0.2 ppm | 0.4 ppm (15-min) | More common in TIG and plasma cutting |
⚠️ There is no safe level of welding fume – HSE guidance requires extraction and RPE for all welding, regardless of duration.
Airflow & Extraction Testing
- LEV systems must be examined and tested every 14 months under COSHH.
- Measurements should include:
- Capture velocity at hood/tip.
- Airflow volume (CFM/L/s).
- Filter condition (pressure drop across filter).
- Results should be logged in a COSHH inspection report and available to workers.
Personal Exposure Monitoring
- Where there is uncertainty, personal air sampling is recommended.
- Workers wear sampling pumps with filters clipped in the breathing zone.
- Results are compared against WELs to verify compliance.
Record Keeping
- Keep LEV test reports, airflow readings, and maintenance logs for a minimum of 5 years.
- Document any corrective actions taken (e.g., replacing filters, upgrading systems).
- Training records for staff in correct use of fume extraction should also be maintained.
Maintenance & Best Practice for Airflow Systems
Even the best-designed ventilation system will lose effectiveness without proper upkeep. Regular checks, cleaning, and filter replacement are essential to ensure consistent airflow and compliance with standards.
Daily / Weekly Best Practice
- Check airflow visibly – ensure smoke/fumes are being drawn into the hood or extractor.
- Position extraction hoods correctly – keep them as close to the weld point as possible (ideally within 150–300 mm).
- Inspect hoses/ducts – look for kinks, blockages, or damaged seals.
- Clean spark arrestors / pre-filters where fitted.
Scheduled Maintenance
| Frequency | Task | Why It Matters |
|---|---|---|
| Weekly | Wipe down intake grills and duct inlets | Prevent dust/slag buildup reducing capture efficiency |
| Monthly | Inspect filters and check pressure drop gauges | Identifies clogging early, prevents motor strain |
| Quarterly | Check fan belts, bearings, and electrical safety | Maintains airflow and prevents breakdowns |
| Every 14 months (UK law) | Formal LEV test (airflow, capture velocity, filter condition) | COSHH requirement |
| As needed | Replace HEPA/high-MERV filters | Keeps system compliant for fine particles (e.g., Cr(VI)) |
Troubleshooting Common Issues
| Symptom | Likely Cause | Fix |
|---|---|---|
| Weak suction | Clogged filters or blocked duct | Clean or replace filters, clear blockages |
| Excessive noise/vibration | Worn motor bearings or loose duct fixings | Tighten fixings, replace bearings |
| Smoke bypassing extractor | Hood too far from arc | Reposition hood or use on-torch extraction |
| Frequent filter clogs | Wrong filter type for fumes | Upgrade to HEPA/high-MERV or gas-specific filters |
| Airflow meter shows low reading | Fan speed issue or duct leak | Check motor, repair duct leaks |
Extra Tips
- Use airflow indicators – simple visual gauges at the hood reassure welders that extraction is working.
- Train operators – welders should understand correct hood placement and how to spot failing extraction.
- Pair with RPE – even with LEV, HSE requires suitable respirators where exposure risks remain.
Summary & Quick-Reference Tables
Welding ventilation isn’t just about comfort — it’s a legal requirement and a critical health measure. By following airflow standards, maintaining systems, and ensuring regular testing, you can protect workers, stay compliant with COSHH/HSE regulations, and improve productivity in your workshop.
Key Takeaways
- Airflow rates must match welding type (TIG, MIG, Stick, plasma, etc.).
- LEV systems should be tested at least every 14 months under COSHH.
- Hood placement within 150–300 mm of the weld maximises capture efficiency.
- HEPA/high-MERV filters are essential for stainless steel and toxic alloys.
- RPE (respiratory protection) must still be provided where LEV alone cannot meet exposure limits.
Quick Reference: Recommended Airflow Rates
| Process / Fume Source | Typical Airflow Range (Capture at Hood) |
|---|---|
| TIG (light fumes) | 80–100 CFM (2.3–2.8 m³/min) |
| MIG mild steel | 100–150 CFM (2.8–4.2 m³/min) |
| MIG stainless (Cr(VI)) | 150–200 CFM (4.2–5.6 m³/min) + HEPA |
| Stick (MMA) | 100–150 CFM (2.8–4.2 m³/min) |
| Plasma cutting | 200–250 CFM (5.6–7.0 m³/min) |
| Gouging/air arc | 250+ CFM (7.0+ m³/min) |
Quick Reference: Testing & Maintenance
| Task | Frequency | Standard / Requirement |
|---|---|---|
| Daily airflow visual check | Every shift | HSE best practice |
| Filter cleaning/inspection | Weekly/Monthly | Manufacturer guidance |
| LEV inspection | Quarterly | Preventive maintenance |
| COSHH LEV test | At least every 14 months | UK legal requirement |
| Filter replacement | As needed | Based on ΔP (pressure drop) gauges |
Exposure Limits (UK Workplace Exposure Limits – EH40)
| Substance | WEL (8-hr TWA) | Notes |
|---|---|---|
| Welding fume (general) | 5 mg/m³ | Control with LEV + RPE |
| Hexavalent chromium (Cr(VI)) | 0.01 mg/m³ | Carcinogenic – HEPA filters essential |
| Manganese (respirable) | 0.2 mg/m³ | Linked to neurological damage |
| Ozone (from TIG/Plasma) | 0.2 ppm | Requires good ventilation |
✅ Bottom line: Good ventilation = safe welders, legal compliance, and fewer costly health claims.
