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 Ducts that carry corrosive vapors, gases, and mists require materials
that are corrosion resistant. Ducts that carry dust laden air should have
cleanouts located near elbows, junctions, and vertical runs.
Air leakage into industrial ventilation system should be maintained at
less than 1 percent. Any leaks that appear should be repaired immediately.
In many operating systems, poor performance can be traced to cleanouts that
have been opened and not properly closed.
4.5 FANS. The fans used in an industrial ventilation system depend upon the
function of the system. Items considered in the selection of the fan are:
volume of air required; fan static pressure; type of material being handled
through the fan such as fibrous, explosive, or inflammable; space
limitations; noise; operating temperature; efficiency; and corrosive
applications.
The types of fans used in industrial ventilation systems may be axial,
centrifugal, or special design such as an air foil type. However, the work-
horse for most exhaust systems is the centrifugal straight or radial blade
design as shown in Figure 2-10. This type of fan is used to reduce dirt
buildup in the blades.
4.6 TESTING OF VENTILATION SYSTEMS. Airflow measurements are often needed
to determine if the industrial ventilation system is operating properly.
Measurements can be done following the procedures outlined in the current
volume of the Industrial Ventilation Handbook by the American Conference of
Governmental Industrial Hygienists. Measurements are made using the
equipment and techniques outlined in Chapter 2.
4-5
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