Welding Fume COSHH Assessment: What UK Employers Must Do

Why Welding Fume Gets Special Attention

In 2019, the HSE changed its enforcement position on welding fume. Previously, general ventilation was considered acceptable for mild steel welding in some situations. That is no longer the case.

The HSE now treats all welding fume as a potential carcinogen — including mild steel welding fume, which was previously considered lower risk. This follows updated scientific evidence from the International Agency for Research on Cancer (IARC), which classified welding fume as a Group 1 carcinogen (sufficient evidence of causing cancer in humans).

The practical impact: if you carry out any indoor welding without adequate local exhaust ventilation (LEV), you are not compliant with the COSHH Regulations 2002. The HSE has made this a priority inspection area, and enforcement notices have increased significantly since the policy change.

If you are new to COSHH entirely, our plain-English guide to what COSHH covers explains the regulations before you get into the welding-specific detail below.

What Makes Welding Fume Hazardous

Welding fume is a complex mixture of metallic oxides, silicates, and fluorides generated when metals are heated above their melting point. The exact composition depends on the base metal, filler material, flux or shielding gas, and any coatings on the workpiece.

Health Risks by Welding Material

Material welded	Key fume components	Primary health risk
Mild steel	Iron oxide, manganese	Lung cancer, metal fume fever, manganism (neurological damage with chronic exposure)
Stainless steel	Hexavalent chromium (Cr(VI)), nickel compounds	Lung cancer, occupational asthma (Cr(VI) and nickel are both respiratory sensitisers)
Galvanised steel	Zinc oxide	Metal fume fever ("Monday morning fever" — flu-like symptoms within hours of exposure)
Aluminium	Aluminium oxide	Respiratory irritation, potential neurological effects with long-term exposure
Painted/coated surfaces	Lead, cadmium, isocyanates (depending on coating)	Lead poisoning, kidney damage, respiratory sensitisation — remove coatings before welding where possible

Additional Hazards

Shielding gases: Argon and CO₂ are asphyxiants in enclosed spaces. Ensure adequate ventilation beyond just fume extraction.
Ozone: Generated by MIG and TIG welding processes. Irritant to the respiratory tract at low concentrations.
UV radiation and spatter: Not COSHH hazards (covered by PPE regulations), but relevant to your overall risk assessment.

Step-by-Step: Writing a Welding Fume COSHH Assessment

Step 1 — Identify Your Welding Processes and Materials

Document every welding process you carry out and the base metals involved. For each, note:

Process type: MIG, TIG, MMA (stick), gas welding, plasma cutting, brazing, soldering
Base metal: Mild steel, stainless steel, galvanised, aluminium, other alloys
Filler material and flux: Wire type, rod type, flux composition
Coatings on the workpiece: Paint, primer, galvanising, plating — these generate additional hazardous fume when heated
Duration and frequency: How many hours per day/week does each welder spend on this process?
Location: Fixed workshop position, mobile within workshop, outdoor site work

Different combinations require different assessments. MIG welding mild steel in a fixed position with LEV is a very different risk profile from MMA welding stainless steel on a client's site with no extraction available.

Step 2 — Identify the Fume Hazards

For each process/material combination, identify the fume components and their hazard classifications. Sources:

Filler material SDS — your welding wire or rod supplier must provide an SDS. This will list the fume components generated during welding and their occupational exposure limits.
HSE COSHH Essentials sheets — the HSE publishes specific guidance sheets for welding: WL3 (welding fume control) covers the main requirements.
EH40 (Workplace Exposure Limits) — check the current EH40 table for WELs of specific fume components.

Key WELs for welding fume components:

Substance	WEL (8-hr TWA)	WEL (15-min STEL)	Notes
Iron oxide fume (as Fe)	5 mg/m³	10 mg/m³	Main component of mild steel welding fume
Manganese (as Mn)	0.05 mg/m³ (inhalable)	—	Very low limit; exceeded more easily than iron oxide
Chromium (VI) compounds	0.01 mg/m³	—	Stainless steel welding. Carcinogen and respiratory sensitiser
Nickel (insoluble compounds)	0.1 mg/m³ (inhalable)	—	Stainless steel welding. Carcinogen
Zinc oxide fume	4 mg/m³	—	Galvanised steel welding

Note: The manganese WEL (0.05 mg/m³) is very low and is often the limiting factor even for mild steel welding. Effective LEV is essential to stay below this limit.

Step 3 — Assess Who Is Exposed

Think about everyone who could be affected:

The welder — highest exposure. Direct inhalation of fume plume, especially if head position is above or in the fume column.
Welders working nearby — background fume levels in a shared workshop. Fume from one bay drifts to adjacent bays if general ventilation is poor.
Fabrication assistants, grinders, fitters — intermittent exposure from background fume levels and their own grinding/cutting work.
Supervisors and QC inspectors — periodic exposure during inspections and testing.
Office staff in connected buildings — if the workshop has no effective partition and fume migrates to office areas.
Apprentices and young workers — may receive higher relative exposure if given prep/cleaning tasks near active welding.

Step 4 — Apply the COSHH Hierarchy of Controls

The HSE expects you to follow this hierarchy — starting at the top, not jumping straight to RPE.

1. Elimination: Can you avoid welding? Mechanical fastening (bolting, riveting, press-fitting), adhesive bonding, or cold forming may eliminate the need for welding entirely on some assemblies. For most fabrication businesses this is not practical, but consider it for specific joints.

2. Substitution: Can you use a less hazardous process? Some options generate less fume than others:

TIG generates less fume than MIG or MMA for the same joint
Pulsed MIG generates less fume than conventional MIG
Low-fume welding wires are available for some applications

3. Engineering controls — Local Exhaust Ventilation (LEV):

This is the critical control for most welding operations. The HSE's current position:

All indoor welding must have effective LEV. This is non-negotiable since the 2019 enforcement change.
LEV options: on-torch extraction, flexible arm extraction, downdraft tables, extraction hoods, or push-pull ventilation systems.
On-torch extraction captures fume closest to the source and is the most effective option where practical.
Fixed arm extraction must be repositioned for each weld — check that welders actually move it, not leave it pointing at the ceiling.
LEV must be tested at least every 14 months by a competent person (COSHH Regulation 9). Keep records for at least 5 years.

4. Administrative controls:

Segregate welding from other activities where possible (separate bays, curtains, enclosures)
Schedule high-fume work when fewer workers are present
Ensure welders position themselves to avoid breathing the fume plume (upwind, or to the side of the extraction)
Training on correct use and positioning of LEV

5. Respiratory Protective Equipment (RPE):

RPE is the last line of defence — not the first. Use it alongside LEV, not instead of it.

Indoor welding: RPE as backup when LEV alone cannot control exposure (e.g., confined spaces, awkward positions where extraction cannot be positioned effectively).
Outdoor welding: RPE is required. The HSE expects at least RPE with an Assigned Protection Factor (APF) of 20. A powered air-purifying respirator (PAPR) or supplied-air respirator is preferred for extended outdoor welding.
Stainless steel or galvanised welding: Higher protection may be needed. Consider a PAPR with APF 20+ as standard.
All RPE must be fit-tested (face-fit test for tight-fitting masks) and the test records retained.

Step 5 — Determine Health Surveillance Requirements

For mild steel welding: Health surveillance is recommended but not always legally required, depending on your risk assessment. If exposure is well-controlled (effective LEV, below WELs), the risk assessment may conclude that health surveillance is not necessary. However, given the carcinogenic classification, many employers are now providing it as good practice.

For stainless steel welding: Health surveillance is required — Cr(VI) and nickel are respiratory sensitisers. You must provide:

Baseline lung function test (spirometry) before first exposure
Annual lung function testing
Respiratory symptom questionnaire
Referral to occupational health if any abnormalities
Records retained for 40 years

For any welding where workers report symptoms (coughing, wheezing, breathlessness, skin irritation): health surveillance should be implemented regardless of the material being welded.

Step 6 — Record, Communicate, and Review

Write up the assessment in a structured format. Our free COSHH assessment template provides the framework, and our worked example with wood dust shows the same structure applied to a different process-generated substance.

Share the assessment with every welder and anyone else who could be exposed.
Pin a summary near the welding bay — especially the PPE requirements and emergency procedures.
Set a review date. Review annually, or sooner if you change processes, materials, extraction equipment, or receive health surveillance results that raise concerns.

The LEV Testing Requirement

This catches many small fabrication businesses. Under COSHH Regulation 9:

Every LEV system must be examined and tested at least every 14 months by a competent person (not just a visual check — an actual performance test).
The competent person must provide a written report confirming the system is in efficient working order and in good repair.
You must keep these reports for at least 5 years.
If the report identifies deficiencies, you must act on them.

The 14-month interval is specific to LEV. It is not 12 months — the extra 2 months provide flexibility for scheduling. But if you miss the 14-month window, you are non-compliant.

Daily and weekly user checks (is the extraction running? Is the airflow strong enough to deflect a piece of tissue paper at the extraction point?) are good practice and help you spot problems before the formal test.

Sporadic vs Regular Welding

The HSE distinguishes between regular and sporadic welding:

Regular welding (most shifts, significant duration): full LEV, RPE backup, health surveillance — no exceptions.
Sporadic welding (less than once per week, under 1 hour each time): engineered fume controls may not be required, but you must provide RPE and ensure good general ventilation.

Document which category each welder falls into. If someone "occasionally" welds but it amounts to 3-4 hours per week, they are a regular welder for COSHH purposes.

Site Work and Mobile Welding

Fabrication shops have fixed LEV. But if your welders also work on client sites, you need a COSHH assessment for site work too — and the controls will be different.

Outdoor site welding: RPE is required (minimum APF 20). Position upwind of the fume plume where possible. Consider the exposure of other workers nearby.
Indoor site welding (in client buildings, confined spaces): You need to provide portable LEV or on-torch extraction. If neither is available, the task may need to be reorganised — welding in a confined space without extraction is extremely high risk.
Hot work permits: Site work involving welding typically requires a hot work permit from the site controller. This is separate from your COSHH assessment but often reviewed alongside it.

Emergency Procedures

Your COSHH assessment should include:

Acute fume exposure (metal fume fever): Symptoms typically appear 3-10 hours after exposure — fever, chills, muscle aches, headache. Move the affected person to fresh air. Symptoms usually resolve within 24-48 hours, but seek medical attention if breathing difficulty occurs. Record the incident and investigate why controls failed.
Confined space emergency: If a welder collapses in a confined space, do not enter without breathing apparatus. Call emergency services. This scenario should be covered by a separate confined space risk assessment and rescue plan.
Fire: Welding fume is not flammable, but the welding process is a major ignition source. Fire extinguishers appropriate for the materials in the workshop. Hot work procedures for site work.

Pre-Publish Checklist for Your Assessment

Before you sign off your welding fume COSHH assessment, check:

Every process/material combination is covered (not just "we do welding")
LEV arrangements documented for each welding position
LEV test reports up to date (within 14 months)
RPE specified by type and APF, fit-testing records current
Health surveillance arrangements in place for stainless steel and sensitiser exposure
Review date set (annually or sooner if processes change)
Assessment shared with all exposed workers and posted near welding bays

Keeping On Top of It

Welding fume assessments are not a one-time exercise. Product changes, new contracts, staff turnover, and equipment wear all affect your risk profile. The HSE expects active, ongoing management — not a ring binder that gets looked at once a year.

COSHHmate is being built to handle exactly this kind of complexity. You will get a guided assessment builder, a chemical register for every substance and process across your workshop, and email reminders before review dates. Flat monthly pricing — no per-user fees.

If you want to get your welding fume COSHH compliance properly organised, join the waitlist to be first to know when COSHHmate launches.