According to the Health and Safety Authority, Local Exhaust ventilation (LEV) is an engineering system designed to reduce employee exposure to airborne contaminants (dust, mist, fume, vapor, gas) in the workplace by capturing the emission at the source and transporting it to a safe emission point or a filter/scrubber.
It is vital that the correct LEV is chosen for a particular task and kept correctly maintained. If a process or activity with which the LEV is associated is changed then the suitability and specification of the LEV system must be re-assessed.
Components of the Local Exhaust Ventilation
A local exhaust system has five basic elements;
-
The “hood” or opening that captures the contaminant at the source.
This captures, contains, or receives contaminants generated at an emission source. It converts duct static pressure to velocity pressure and hood entry losses (e.g., slot and duct entry losses).
Hood entry loss (He) is calculated according to the following equation:
He = (K)(VP) = |SPh| = VP
where:
K = loss factor
VP = velocity pressure in the duct
|SPh| = absolute static pressure about 5 duct diameters down the duct from the hood.
2. Ducts:
That transports the airborne chemicals through the system (exhaust air) and the air that is re-circulated.
3. An air-cleaning device
This removes the contaminant from the moving air in the system (not always required).
4. Fans
This moves the air through the system and discharges the exhaust air outdoors.
5. An exhaust stack
It is the component through which the contaminated air is discharged
Advantages of Local Exhaust System (LEV)
- Captures the contaminant at the source and removes it from the workplace.
- Handles many types of contaminants including dust and metal fumes.
- Requires a smaller amount of makeup space, since a smaller amount of air is being exhausted.
- Less energy costs since there is less makeup air to heat or cool.
Disadvantages of Local Exhaust Ventilation
- Higher cost for design, installation, and equipment.
- Requires regular cleaning, inspection, and maintenance.
Some documents will help you to understand more about the local exhaust ventilation and also help you maximize its use. These documents include:
- Guideline on Occupational Safety and Health for Design, Inspection, Testing and Examination of Local Exhaust Ventilation System. Check document
- Local exhaust ventilation checklist. See document
Concise video on reducing workplace contaminants with local exhaust ventilation. Watch Now
Local Exhaust Ventilation Price
Here are some LEV with their prices from Alibaba;
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