Even with good torch-mounted extraction, fabrication shops often see a build-up of background weld fume. This affects air quality away from the arc, drives complaints about haze, and can push exposures towards COSHH limits for metals in fume. The answer is a planned approach to ambient air control that complements local exhaust ventilation (LEV).

Plan the airflow and zones

Start by mapping hot work areas, walkways, and clean zones. Aim to move air from clean to dirty and then out or through filtration, avoiding cross-draughts that push fume across workstations. Keep make-up air consistent; sudden door opening can short-circuit your pattern.

Positioning and direction

Weld fume rises with heat, then cools and drifts. Place air scrubber intakes higher to intercept buoyant plumes and return filtered air lower to promote a gentle downward sweep. Avoid placing units so they blow across the welding arc or past the welder’s breathing zone.

Recirculation vs exhaust

Recirculating air scrubbers with high-efficiency filtration reduce particulate without heat loss. Where processes generate hazardous metals (e.g. stainless), consider negative air machines exhausting outside, balanced with adequate make-up air. If recirculating, use HEPA to H14 where fine or carcinogenic particulates are present.

Choose and maintain the right equipment

Specify airflow under load, not free-air ratings. Use prefilters to catch larger debris and extend HEPA life, and check for a sealed housing so air cannot bypass the filter. Monitor filter loading and set a change schedule; falling airflow means falling control. In larger bays, equipment such as large-scale MAXVAC Dustblockers can run continuously to reduce background particulate between welds.

LEV remains the first line: keep hoods close, extraction arms correctly balanced, and capture speeds verified. Effective source capture cuts the burden on ambient control and lowers whole-shop concentrations.

Housekeeping and shift tactics

Avoid sweeping and compressed air, which re-suspend particulates. Use industrial vacuums with high-efficiency filtration for floors and benches. Sequence high-fume tasks when additional air scrubbers or negative air can be operated, and keep adjacent processes upwind where possible.

Measurement and adjustment

Use a particulate monitor to track PM1/PM2.5 trends through a shift and adjust fan positions accordingly. Simple smoke tests help visualise dead spots. Log checks, especially after layout changes or when new welding procedures are introduced.

Compliance in brief

Under COSHH, engineering controls take priority over PPE. HSE expects effective LEV for welding and suitable filtration (H14 where fine or carcinogenic aerosols are present). Keep records of maintenance, airflow checks, and filter changes.

Practical takeaways

• Design a clean-to-dirty airflow pattern and avoid cross-draughts.
• Intercept buoyant fume high; return filtered air low.
• Use LEV first, then ambient air scrubbers or negative air to reduce background.
• Choose HEPA H14 for fine/carcinogenic fume; track airflow under load.
• Vacuum, don’t sweep; verify with a particulate monitor and adjust.

With a planned airflow, suitable air filtration, and disciplined housekeeping, fabrication shops can materially cut background fume, protect workers, and keep productivity steady.