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Table 8.1 - Comparison of Ventilation Systems

Comparison of Ventilation Systems
Dilution Ventilation Local Exhaust Ventilation
Advantages Disadvantages Advantages Disadvantages
Usually lower Does not completely Captures Higher cost for
equipment and remove contaminant at design, installation
installation costs contaminants. source and removes and equipment
it from the
workplace
Requires less Cannot be used for Only choice for Requires regular
maintenance highly toxic highly toxic airborne cleaning,
chemicals chemicals inspection and
maintenance
Effective control Ineffective for dusts Can handle many
for small amounts or metal fumes or types of
of low toxicity large amounts of contaminants
chemicals gases or vapours including dusts and
metal fumes
Effective control Requires large Requires smaller
for flammable or amounts of heated or amount of makeup
combustible cooled makeup air air since smaller
gases or vapours amounts of air are
being exhausted
Best ventilation Ineffective for Less energy costs
for mobile or handling surges of since there is less
dispersed gases or vapours or makeup air to heat
contaminant irregular emissions or cool
sources

The following is an example of changes that can affect how a system works
(Figure 8.5):

Figure 8.5 - Adding a duct branch

A hood and branch are added to an existing duct. The local exhaust ventilation
pulls air into the system from the new location, which will reduce the airflow from
other locations that are further away from the exhaust fan. Again, airflow will all be

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