Local exhaust ventilation systems 

What is a Local exhaust ventilation system?

Local exhaust ventilation (LEV) is an engineering system designed to reduce employee exposure to airborne contaminants such as dust, mist, fume, vapour, and gas in the workplace. It does so by capturing the pollution at source and transporting it to a cyclone / prefilter / filter. LEV is the option highest in the hierarchy of control after elimination and substitution of the hazard, which is often not practical. LEV systems may include:

• Welding fume extraction systems 
• Spray booths 
• Wood dust extraction systems 
• Grinding dust extraction systems 
• Laboratory fume cupboards 
• Soldering fume extraction systems 

What are the basic types of ventilation systems?

There are two types of mechanical ventilation systems used in industrial settings; General Industrial Ventilation (GIV) & Local Exhaust Ventilation (LEV). GIV systems reduce the concentration of the air contaminants or controls the amount of heat that accumulates in hot industrial environments, by mixing (diluting) the contaminated air with fresh, clean, uncontaminated air. This ventilation system is also known as Dilution Ventilation. LEV systems capture contaminants at, or very near, the source and exhaust them outside. 

Which airborne contaminants are produced in workplaces that need Local exhaust ventilation systems?

Typically, the most common workplaces that require a LEV System, have processes that can potentially produce the following airborne contaminants:

Mineral Dusts: Usually a result of extracting and processing minerals such as quartz, coal or cement (mineral dusts often contain silica, which is particularly dangerous).

Welding Fumes: Such as aluminium, arsenic, beryllium, lead and manganese.

Metallic Dusts: such as lead and cadmium, nickel, beryllium and their compounds.

Chemical Dusts: such as ammonia, detergents and pesticides.

Gases: Such as carbon monoxide, chlorine, nitrogen dioxide and phosgene

Vegetable Dusts: From wood, flour, cotton, tea, and pollens usually found in manufacturing plants.

Fibres: From wool, ceramic, nylon and carbon.

Moulds and Spores: Can usually exist in damp, poorly ventilated environments.

How does a Local exhaust ventilation system work?

A LEV System works by:

• Sucking in air and collecting the airborne contaminants.
• Carrying the airborne contaminants away from the workplace.
• Cleaning the air and removing or discharging the contaminants.

The primary elements of a LEV system are:

A hood: This is where the airborne contaminants enter the system.

Ducting: This safely transports the contaminants to a filter/cleaner/exhaust point.

Air cleaner, filter or scrubber: This filters and cleans the extracted air and removes the contaminants, leaving only clean air.

Air mover: This is a fan that powers the entire extraction system.

Discharge: This releases the extracted air and contaminants into a safe place away from workers.

What are the technical aspects of a Local exhaust ventilation system?

For modern technical equipment, during the operation of which harmful substances are released, it is necessary to design and install local exhaust ventilation devices (local exhausts), either built into this equipment, or as close as possible to the zone of release of harmful substances. When removing air from industrial premises containing harmful substances or substances with an unpleasant odour, it is also necessary to install specialized cleaning filters. In addition, the exhaust air discharge pipe must have a certain diameter and height in order to disperse residual emissions in the atmosphere to an acceptable level of harmful substances that are required for the surface layer of atmospheric air in populated areas, in accordance with current sanitary standards.

When is a Local exhaust ventilation system the preferred control method? 

In a general way, a local exhaust system operates similar to a household vacuum cleaner with the hose as close as possible to the place where dirt would be created. An LEV system is usually the preferred control method if:

• Air contaminants pose a serious health risk.
• Large amounts of dust or fumes are generated.
• Increased heating costs from ventilation in cold weather are a concern.
• Emission sources are few in number.
• Emission sources are near the workers’ breathing zones.

Is it mandatory to test a Local exhaust ventilation system?

It’s a legal obligation of an employer who uses local exhaust ventilation to control dust or fume, vapour, to ensure that it is operating effectively and is in good repair. A thorough examination of equipment including hoods, filters and ducts is performed during an LEV test. This is a Thorough Examination and Test (TExT) of a system. We benchmark the results recorded against Commissioning or previous TExT data. This is a mandatory statutory assessment undertaken at least once in a period of 14 months. Measurements of the technical performance is conducted using the appropriate equipment and assessment of the effectiveness of the LEV System. A new installed system should be thoroughly tested and examined as to ensure that the design specifications are met and airflow through each of the hood is sufficient to extract contaminant effectively away from the workroom. 

How frequent should the Local exhaust ventilation system be tested?

According to the Health and Safety Executive (HSE), an employer ‘must maintain LEV system performance’. In addition, COSHH ‘Regulation 9 – Maintenance’, states that a thorough examination and test must be conducted at least every 14 months*. However, it is possible to establish exact frequency of testing according to the outcome of the risk assessment, as detailed in ‘Regulation 6 – Risk Assessment’. Maintenance regimes can be evaluated by observing evidence of poor repair such as holes in ducting or blocked and dirty extraction systems. COSHH is the law that requires employers to control substances that are hazardous to health and includes nanomaterials. 

What are your responsibilities as an employer?

The responsibilities of the employer that runs a business which utilizes LEV systems are as follows: 

• Maintain LEV system performance 
• Arrange a thorough examination and test every 14 months 
• Know whether or not an examination has been done or when it is due (and so must supervisors and operators) 
• Ensure the examination and test is conducted by a qualified person (minimum qualification required is P601) 
• Keep a record of testing for at least 5 years 
• Ensure all information about testing and examination is kept on the installed LEV system for the life of the system

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