Extraction Systems
Extraction Systems · Extraction Systems overview
Workplace extraction systems are engineered ventilation systems that capture airborne contaminants — dust, fume, mist, vapour or smoke — at or close to the point they are generated and remove them from the working environment before they can enter operators' breathing zones. Industrial extraction is the practical engineering answer to the COSHH duty to control exposure at source rather than relying on respiratory protective equipment alone.
What workplace extraction systems are
An extraction system is a powered air-moving installation built to draw contaminated air away from a specific process, transport it through ductwork, clean it through a filter or collector, and discharge the cleaned air to a safe location. The terms 'extraction system', 'industrial extraction system' and 'local exhaust ventilation (LEV)' overlap in everyday use and are essentially the same thing in regulatory terms under HSE guidance HSG258.
Extraction is contrasted with general or dilution ventilation, which lowers room-average concentrations by mixing fresh air through the whole space. Extraction at source is more effective for hazardous substances because it removes the contaminant before it can spread, rather than waiting for it to disperse.
General ventilation vs extraction at source
General ventilation has a role in workplace comfort, odour control and managing low-toxicity nuisance contaminants. It is not, however, an adequate primary control for substances with workplace exposure limits or for processes that release significant quantities of airborne contamination. Dilution alone cannot guarantee that any one operator's exposure stays below the limit, because concentrations near a process are always higher than the room average.
Source-capture extraction targets the contaminant where it is produced. Provided the capture velocity at the source is sufficient to overcome surrounding air currents, the contaminant is drawn into the hood before it can drift into the breathing zone. This is why extraction sits high in the COSHH hierarchy of control, above administrative measures and PPE.
Main components of an extraction system
Every workplace extraction system, regardless of scale, is built from the same functional components. A weakness in any single component compromises the whole system even if everything else is in good order.
- Capture hood or enclosure — the inlet that draws contaminated air in. Hoods range from simple receiving hoods over hot processes, through capturing hoods close to the source, to fully enclosing booths.
- Ductwork — the network that transports captured air to the air-cleaning stage. Duct sizing, transport velocity, run length and bend geometry all influence whether contaminants stay airborne or settle out and accumulate inside the system.
- Air cleaner or filter — bag filters, cartridge collectors, cyclones, scrubbers or electrostatic precipitators that remove contaminants from the airstream before discharge.
- Fan — the powered air mover that generates the system airflow. Fan selection, drive condition and operating point determine the system's capacity and resilience to filter loading.
- Discharge — the exhaust point where cleaned air is released. Discharge location must avoid re-entrainment back into the workplace through doors, windows or fresh-air intakes.
How extraction performance is assessed
Extraction performance is assessed against the system's original design intent — where commissioning data exists — and against HSE benchmarks in HSG258. A competent assessment combines documented system understanding with instrument measurement and direct observation of the system while it is in use.
Typical measurements include capture or face velocity at the hood, duct transport velocity, static pressure across the fan and filter, total extracted volume and discharge airflow. Smoke and dust-lamp observations confirm whether the visible contaminant cloud is being drawn into the hood rather than escaping into the room.
A defensible assessment also records the condition of ductwork, fans, filters, dampers and instrumentation, and notes any modification, damage or accumulated dust that affects performance. This is the same methodology used during a statutory Thorough Examination and Test (TExT) under COSHH Regulation 9.
Common extraction system failures
Most workplace extraction systems do not fail catastrophically. They drift — quietly losing capture performance over months and years until they no longer adequately control the exposure they were installed to manage.
- Hoods relocated, removed or partially blocked by stored materials, putting the source outside the effective capture envelope.
- Ductwork extended, re-routed or partially blocked by accumulated dust, changing system balance and reducing transport velocity.
- Filters left unchanged beyond their service life, raising resistance and starving the system of airflow.
- Fans operating off their original duty point because of belt slippage, impeller wear, damper movement or motor degradation.
- Discharge points placed where prevailing wind or proximity to fresh-air intakes allows re-entry of contaminated air.
- Operator practice that defeats the system — working outside the booth, leaning past the hood, or running the process with extraction switched off to reduce noise.
Why user practice and process layout matter
An extraction system is only as effective as the way it is used. Capture velocity falls off rapidly with distance from a hood — a plain unflanged hood often loses most of its capture performance within one hood diameter of the face. If operators routinely work beyond that envelope, even a well-maintained system will not control exposure.
Process layout, workpiece size, operator posture, draughts from doors and roller shutters, and competing air movement from cooling fans all affect capture in practice. A good assessment looks at how the process is actually carried out, not just how the system was specified, and identifies practical changes — hood repositioning, flanging, partial enclosure, screening of draughts, brief operator instruction — that can dramatically improve real-world control.
When to review or upgrade an extraction system
An independent review is sensible whenever the process changes, when the system has been altered or extended, when operators report symptoms or visible escape of dust or fume, when statutory test dates are approaching, or when an HSE inspection or insurance audit is anticipated.
A review is not the same as the statutory test — it is a broader engineering and exposure-control judgement that helps decide whether the existing extraction is the right answer for the current process at all, or whether targeted upgrades or replacement would be more proportionate.
Frequently asked questions
What is the difference between an extraction system and LEV?
In UK regulatory terms there is no meaningful difference. 'Local exhaust ventilation (LEV)' is the HSE's preferred phrase, used throughout HSG258 and COSHH guidance; 'extraction system' is the more common phrase on the shop floor. Both describe a powered system that captures contaminants at source and removes them from the workplace.
Does every industrial extraction system need statutory testing?
Where the extraction system is provided to control exposure to a substance covered by COSHH, Regulation 9 applies and the system must be examined and tested at suitable intervals — at least every 14 months for most applications, and more frequently for some substances.
Can general ventilation replace an extraction system?
Only in limited cases. For hazardous substances, dilution alone cannot reliably keep individual operator exposures below the workplace exposure limit because concentrations near the source are always higher than the room average. Source-capture extraction is normally required where reasonably practicable.
How long should an industrial extraction system last?
Well-designed and maintained extraction systems can serve for many years, but performance drift is inevitable. Component life depends on contaminant loading, duty cycle and maintenance regime; filters and fan drives are typically the first elements to need attention, with ductwork and hoods lasting considerably longer.
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