Glove boxes, pharmaceutical isolators, sand-blast cabinets — the source is fully or mostly contained, with extraction maintaining inward airflow through openings. The most reliable capture, used wherever the COSHH risk justifies the engineering cost. Fume cupboards in laboratories are the canonical partial enclosure.
01
Total and partial enclosures
02
Booths and walk-in enclosures
Paint spray booths, weighing booths, sample preparation booths. The operator works inside the booth; airflow is drawn past them and away from their breathing zone. Sized so that face velocity at the open face is 0.5–1.0 m/s typically.
03
Captor hoods
Slot hoods on solder benches; flexible extraction arms on welding stations; downdraft tables for grinding. The hood reaches into the contaminant cloud and captures it. Performance is sensitive to operator behaviour — capture distance must be maintained, which is a training and supervision issue as well as an engineering one.
04
Receptor hoods (canopies)
Canopy hoods over kettles, ovens, heat-treatment baths — they catch buoyant plumes from hot processes. They do not work for cold or low-buoyancy emissions; the rising plume must do most of the work. Misapplied receptor hoods are a common cause of LEV test failure.
05
On-tool extraction
Integrated into power tools used in construction and joinery — circular saws, grinders, drills, planers. Mandatory for HSE's hierarchy of dust control on UK construction sites since the introduction of the workplace exposure limit for respirable crystalline silica.
06
Choosing the right type
Start with the COSHH risk assessment: what is released, how much, how often, and how close is the operator? Total enclosure is the default for high-toxicity substances. Captor hoods are workable for moderate-risk processes where the source location is fixed. Receptor hoods only suit buoyant releases. Every choice must then pass COSHH Regulation 9 testing.
07
Frequently asked questions
What are the main types of LEV?
Total enclosures (glove boxes, isolators), partial enclosures (fume cupboards, spray booths), captor hoods (welding fume arms, slot hoods), receptor hoods (hot-process canopies), downdraft tables, and on-tool extraction. Choice depends on the contaminant, the process and the operator's working position.
Which LEV type is most effective?
Total enclosure — it captures the contaminant before it can escape into the room. Effectiveness declines as the operator's access to the source increases: partial enclosures, captor hoods, then receptor hoods are progressively less reliable.
What is a captor hood?
A hood that draws air across the source from a distance, capturing the contaminant in the airflow before it can disperse. Capture velocity must be sufficient at the furthest emission point — typically 0.5–1.0 m/s for dust and fume, higher for buoyant or projected releases.
Is on-tool extraction LEV?
Yes. On-tool extraction — common in construction (cutting, drilling, grinding) — is a form of captor hood integrated into the tool body. It still requires COSHH Regulation 9 testing and a competent-person record.