What is local exhaust ventilation (LEV)?

LEV in one paragraph

LEV removes harmful airborne substances so workers do not breathe them in. Most systems have five parts: a hood, ducting, an air cleaner, an air mover and a discharge point. The hood takes in contaminated air. Ducting carries it towards discharge, while the air mover powers extraction. An air cleaner removes contamination where needed, and the discharge releases air somewhere safe. Not every system needs air cleaning. Hoods range from tiny fittings inside handheld tools to enclosures large enough to walk into.

The parts of an LEV system

HSE describes these five main components. Machine casings or guards can also form part of the system when they help extraction control emissions. Systems supplying replacement air, known as make-up air, can count too.

• Hood: the entry point for the cloud of contaminated air. It may be built into a tool or surround a much larger process.
• Ducting: the route that carries air and contamination from the hood to the discharge point.
• Air cleaner or arrestor: the part that filters or otherwise cleans extracted air. Some systems do not need this component.
• Air mover: usually a fan, which provides the power for extraction. Its size and type must provide enough suction at the hood.
• Discharge: the outlet where extracted air is released to a safe place.

Types of hood

HSE groups hoods into enclosing, receiving and capturing types. Enclosure is the most effective approach. The more you enclose the process and its source, the more likely control is to succeed.

A full enclosure contains the whole process. A room enclosure contains both the worker and the process. Partial enclosures leave openings for people or materials. For receiving and capturing hoods, HSE says to place the hood as close to the source as possible.

Where LEV is used

HSE names woodworking, welding, paint-spraying, stonemasonry, engineering and foundry work among the industries affected by airborne contaminants. In woodworking, processes include cutting, shaping and sanding. Welding fume can be captured using a conventional hood, a high vacuum nozzle or on-torch extraction.

Other examples include flour dust in bakeries, paint mist from spraying and solvent vapour from painting. Furnaces can produce carbon monoxide gas. Turning, grinding and drilling machines can emit dust and metalworking fluid mist.

Laboratory extraction can include microbiological safety cabinets and external high-efficiency particulate arrester (HEPA) filters. HSE also calls for fume cupboards and microbiological safety cabinets to be tested against appropriate British or European standards.

LEV and the law

COSHH means the Control of Substances Hazardous to Health Regulations. Regulation 7 requires you to prevent exposure or adequately control it where prevention is not reasonably practicable. LEV can help, but you should consider other suitable controls first.

The order matters: control at source, including adequate ventilation, comes before personal protective equipment (PPE). Where other means cannot achieve adequate control, suitable PPE is required alongside those measures.

Under regulation 8, you must take reasonable steps to ensure controls are used properly. Employees must use them fully and properly and report defects immediately. Regulation 9 requires equipment to remain efficient, clean and in good repair.

For LEV controlling hazardous substance exposure, arrange a thorough examination and test at least once every 14 months. Schedule 4 sets shorter intervals for certain processes. Blasting to clean metal castings during manufacture requires testing at intervals no longer than one month. Jute cloth manufacture also has a one-month limit.

The interval is six months for processes producing non-ferrous metal castings that give off dust or fume. Certain powered metal grinding, abrasion and polishing processes also have a six-month limit. That applies to non-wet processes running in any room for more than 12 hours in a week. Articles of gold, platinum and iridium are excluded from that entry.

Keep examination, test and resulting repair records, or suitable summaries, available for at least five years after they are made. These COSHH 2002 provisions cover Great Britain. Northern Ireland has its own COSHH Regulations 2003.

Checking LEV between tests

Your logbook should describe routine checks and set their frequency. HSG258 includes daily, weekly and monthly checks, which a trained employee can carry out. Record maintenance, replacements and repairs, along with who checked the system and whether it was used correctly.

HSE's INDG408 leaflet assigns daily checks and fault reporting to operators. It assigns weekly checks and arranging repairs to supervisors. The works engineer repairs faults, maintains the system and arranges thorough examination. Ask the manufacturer for help if your manual or logbook is missing. If that fails, an LEV specialist can help prepare suitable documents.

Use HSE's pocket card, INDG409, for workers' daily checks. Check the indicator, whether extraction removes contamination and whether you are close enough to the hood. Look for smells or settled dust and listen for unusual noise or vibration. Check that the system has been tested and its tested label is in date. Tell your supervisor about suspected faults.

Maintenance checks should cover moving parts such as fan bearings and filter shakers. Inspect hoods, ductwork and seals too. Filters and flexible ducting can deteriorate with use. Some parts need regular attention, such as filter replacement or sludge removal from wet scrubbers.

Signs your LEV is not working

Airflow can fall because material builds up or ducting is damaged. Control can then become inadequate. Some contaminants are invisible, and fine dust may not be visible in normal lighting.

• Smells or settled dust can indicate a problem. Look for deposits in and around the hood.
• Unusual noise or vibration warrants attention. A noisier fan can also indicate too little replacement air.
• Doors that become hard to open outwards or close inwards can indicate insufficient make-up air. Whistling under doors or around windows is another sign.
• Adding hoods or isolating an unused inlet can seriously unbalance an existing system.
• Do not judge airflow by hand. Paper or plastic tell-tales do not give an effective airflow indication and are easily damaged.

What is not LEV

General ventilation replaces air across the workplace with fresh or cleaned air. Dilution, also called mixing ventilation, and displacement ventilation are forms of general ventilation. LEV extracts contaminated air at or near its source.

Do not assume contamination is evenly spread throughout a room. HSE says that assumption is usually wrong. Local air displacement is also different from LEV because it does not extract air.

LEV may be unsuitable where sources are widely scattered or too large to cover with extraction. It may also be unsuitable where the source moves or produces relatively little contamination.