Workplace Contaminant Extraction
Strategy & Controls · Strategy & Controls overview
Workplace contaminant extraction is the engineered removal of airborne hazards — dust, fume, vapour, mist, odour and process emissions — from the point of generation, before they can reach the worker breathing zone or spread through the wider building. Done well, it is the single most effective ventilation response to occupational exposure risk.
What workplace contaminant extraction covers
Contaminant extraction spans the full range of source-based ventilation controls: LEV hoods at machines, booths and partial enclosures, on-tool extraction for hand processes, downdraught benches, extracted weighing stations, fume cupboards, slot extract on tanks, and dedicated process exhausts on reactors, ovens and dryers. The common thread is intent — extraction is sized and located to capture a specific contaminant at a specific source.
This focus is what distinguishes contaminant extraction from general ventilation. Where general ventilation reduces average concentrations across a space, contaminant extraction prevents the contaminant from entering that space in the first place.
Types of airborne contaminants
Effective extraction depends on understanding what is being captured. Different contaminants behave very differently in air and demand different design choices.
- Dust — particulate solids from grinding, cutting, sanding, weighing and handling. Requires higher transport velocities to prevent settlement in ductwork.
- Fume — very fine particulates from welding, soldering, hot processes and condensation of vapours. Often invisible at low concentrations but high in toxicity.
- Vapours — gaseous emissions from solvents, coatings and chemical processes. Generally captured with lower transport velocities but may require carbon or scrubber treatment.
- Mists — fine liquid droplets from machining coolants, spraying and electroplating. Require mist eliminators or coalescing filtration.
- Odours — low-concentration nuisance or process emissions, often controlled with activated carbon or biofiltration.
- Process emissions — bulk gas or particulate releases from reactors, kilns, ovens and combustion plant, typically handled by dedicated process exhaust.
Why at-source extraction is preferable
Capturing a contaminant at source is more effective and more energy-efficient than allowing it to disperse and then trying to clean it from a much larger volume of air. At the source, the cloud is small, concentrated and predictable. A few seconds later it has mixed into thousands of times more air, becoming impossible to remove without enormous and largely wasted extraction volumes.
Source capture also protects the workers closest to the process — the people at highest exposure risk. Dilution-only strategies inevitably leave operators standing in the undiluted cloud during the seconds it takes for mixing to occur.
How capture, transport, filtration, discharge and make-up air interact
Contaminant extraction is a connected chain. Capture velocity at the hood face must be sufficient to draw the cloud against any cross-draughts. Transport velocity in the duct must keep the material moving without settling or condensing. Filtration must match the contaminant — fabric, cartridge, HEPA, mist eliminator, carbon, wet scrubber — and must be maintained as it loads. Discharge must be at a location and height that prevents re-entry through inlets or openings. Make-up air must replace the extracted volume so the building does not become depressurised.
A weakness in any link compromises the whole. A perfectly specified hood will not protect workers if the fan is undersized, the filter is blocked, the building is starved of make-up air or the discharge is being drawn back in through a nearby door.
Common extraction problems and evidence gaps
Most contaminant extraction problems are gradual and only become visible when exposure or compliance issues surface.
- Hood positioning has drifted from the original design as the process or operator has changed.
- Filters have loaded beyond their useful range, dropping system volume well below specification.
- Duct velocity has fallen below the transport minimum for the material, allowing accumulation and partial blockage.
- Make-up air is insufficient, leaving the building depressurised and pulling contaminants from adjacent areas.
- Discharge re-entry is contaminating supply inlets, undoing the work of the extraction system.
- No commissioning record exists, so there is no baseline against which to judge current performance.
When contaminant extraction should be reviewed
Statutory LEV systems require thorough examination and test at least every 14 months under COSHH Regulation 9. Beyond that minimum, contaminant extraction should be reviewed whenever the substance or process changes, when the building layout or fabric is altered, when exposure monitoring or health surveillance suggests a problem, when workers report visible emissions or odour escape, and as part of a planned ventilation improvement programme.
Proactive review almost always costs less than reacting to enforcement, exposure incidents or production disruption. Where extraction is found to be underperforming, the most cost-effective improvements are usually identified through measured assessment before any capital is committed.
Frequently asked questions
Is contaminant extraction the same as LEV?
LEV is the regulated form of contaminant extraction at source under COSHH Regulation 9. Workplace contaminant extraction is a broader concept that includes LEV alongside related controls such as process exhaust, fume cupboards and extracted enclosures.
Does extraction remove the need for PPE?
Often, but not always. Where engineered extraction reliably reduces exposure below the relevant workplace exposure limit and the COSHH risk assessment supports it, respiratory PPE may not be required. Where residual risk remains, PPE supplements but does not replace the engineering control.
Can one extraction system serve multiple processes?
Sometimes, but only where the substances are compatible, the transport velocities required are similar, and the duct routing supports balanced flow at every branch. Combining incompatible processes onto a single system is a common cause of underperformance.
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