Local exhaust ventilation (LEV) is an engineering control that captures dust, fumes, vapors and gases at their source before workers breathe them in.
Local exhaust ventilation (LEV) is an engineering control that captures airborne contaminants such as dust, fumes, mists, vapors and gases at or near the point where they are released, before they spread into the work area and are breathed in by workers. The captured air is carried through ducting to a filter or air cleaner and then discharged safely.
LEV differs from general or dilution ventilation, which brings in clean air to dilute contaminants across a whole room. Because LEV removes contaminants at the source, it is usually much more effective for toxic or high-volume emissions, and it often uses less energy than ventilating an entire building.
LEV is common in welding, grinding, woodworking, stone and concrete cutting, spray painting, laboratories, foundries, pharmaceutical production and food processing. In the UK, the COSHH Regulations require LEV systems to be thoroughly examined and tested at least every 14 months. In the United States, OSHA standards for substances such as silica, lead and certain chemicals require engineering controls like LEV where feasible, and ACGIH's Industrial Ventilation manual provides design guidance.
The hood should enclose the source as much as possible, and capture hoods should sit as close to the source as practical. Capture velocity drops sharply with distance, so a hood that is twice as far away may capture far less contaminant. The hood should also be placed so contaminated air is drawn away from the worker's breathing zone, not across it.
New systems should be commissioned to confirm they control exposure as intended. Systems should then be examined and tested regularly, including air velocity, pressure readings and a visual check of hoods, ducts, filters and fans. Air monitoring can confirm whether worker exposures stay below the relevant occupational exposure limit (OEL).
LEV sits above respiratory protection in the hierarchy of controls. Respirators may still be needed where LEV alone cannot reduce exposure enough.
A stone countertop fabricator cut and polished engineered stone, which can release high levels of respirable crystalline silica. Silica exposure monitoring showed that workers using handheld grinders were well above the exposure limit, even with water suppression on some tools.
The company installed tool-mounted shrouds connected to HEPA-filtered vacuums for handheld work and a downdraft table with integrated extraction for edge polishing. A ventilation engineer commissioned the system, and the shop added daily airflow checks and quarterly testing. Follow-up monitoring showed silica exposures dropped below the action level, and respirators became a backup rather than the main control.
LEV captures contaminants at the source before they spread. General ventilation dilutes contaminants that are already in the room by bringing in clean air.
It depends on the regulations and the system. In the UK, COSHH requires a thorough examination and test at least every 14 months, and more often for some processes. Many companies also do simple daily or weekly checks.
Yes. Fume extractors, welding fume arms, dust collectors on tools and fume cupboards are all types of local exhaust ventilation.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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