Blog 5: Local Exhaust Ventilation
Local Exhaust Ventilation or LEV is a control system used to
reduce one’s exposure to Particulate Matter like dust, harmful fumes or gasses
in an area. In laymen terms it takes an airborne contaminant out of the area
and prevents a build-up of flammable gases or vapors
The main parts of an LEV:
A hood of some kind, where the contaminants enter the system
Duct, transports the contaminants to a
filter/cleaner/exhaust point
Air cleaner/filter/scrubber
Air mover, like a fan to power the system
Discharge, a safe point of air exhaust
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“There are two types of mechanical ventilation systems used
in industrial settings: Dilution (or general) ventilation reduces the
concentration of the contaminant by mixing the contaminated air with clean,
uncontaminated air.
Local exhaust ventilation captures contaminates at or very
near the source and exhausts them outside.”
A dilution ventilation does not completely remove contaminants.
Should not be used for highly toxic chemical, since it’s not effective for
dusts or metal fumes or large amounts of gases or vapors. It also needs large
amounts of makeup air to be heated or cooled to be considered efficient. Finally
it is not effective for handling a surge of gas, vapor or irregular emissions.
Normal fans are usually ineffective as they typically blow
the contaminant around the work area without effectively removing it from the
immediate area. Opening a door or windows can be used as a form of dilution
ventilation, however this is not reliable because the air movement is not
controlled.
A Local exhaust system traps particulate matter near the
source. It is generally much more effective in controlling the flow of
particulate matter. Generally, local exhaust system operates similar to a vacuum
cleaner. This type of system is preferred control method when:
The particulate matter being emitted can pose serious health
risk.
Large amounts of particulate matter is being generated.
There is an increased heating costs from ventilation in cold
weather.
The emission sources are near a person’s breathing zones.
The limitations of an LEV system include but are not limited
to:
The LEV systems will deteriorate over because of particulate
matter build-up within the LEV system, especially in the filters.
LEV systems need ongoing maintenance.
There must be regular testing to ensure the system is
working and effective.
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