Mechanical ventilation removes contaminated air and replaces it with clean
outside air. Ideally, each ventilation system should be designed specifically
to match the type of work and the rate of contaminant release at the workplace.
Having the right ventilation system ensures there are acceptable levels of
contaminants in the air as well as a continuous supply of fresh outside air. It
also maintains temperature and humidity at comfortable levels, reduces the risk
of fire or explosion, and removes or dilutes airborne contaminants, depending
on the design. Ventilation is considered an engineering control, and is one of
the preferred ways to control employee exposure to air contaminants.
For added safety, industrial facilities also can implement controls to
eliminate the use of hazardous chemicals or materials altogether, substitute
with less toxic chemicals, or change the work practice or process to reduce
Industrial settings usually require one of two main types of mechanical
ventilation systems: dilution (general) or local exhaust.
Dilution ventilation reduces the concentration of the contaminant by mixing the
contaminated air with clean, uncontaminated air. It supplies and exhausts large
amounts of air to and from an area or building, usually with large exhaust fans
placed in the walls or roof. Dilution ventilation works best if the exhaust fan
is located close to exposed workers and the makeup air is located behind the
worker so that contaminated air is drawn away from the worker's breathing zone.
Dilution should only be used in situations where there are fairly low toxic
levels of pollutants, and where workers do not work in the immediate vicinity
of the source of contamination.
Local exhaust ventilation captures contaminants at or very near the source (a
bit like a household vacuum cleaner, with the vacuum head as close as possible
to the dirt) and exhausts them outside. This is generally a far more effective
way of controlling highly toxic contaminants before they reach a worker's
Use local exhaust ventilation where:
It's important to realize that any ventilation system will have limitations.
The systems deteriorate over the years and require ongoing maintenance and
testing. It takes a qualified professional to make any modifications to a
AplusA-online.de - Source: Canadian Centre for Occupational Health and Safety