Trouble shooting of various types of ventilation systems

If an existing ventilation system appears to not be functioning properly, the following simple checks can be made without extensive measurements or expert help:
• Is the fan belt broken or slipping?
• Is the fan wired backward (reversed polarity)?
• Is ductwork clogged with dust?
• Is there holes, cracks or openings in the ducting?
• Is the air cleaner clogged?
• Are any dampers in the ductwork closed?
• Is there insufficient makeup air?
• Has ductwork been changed to include more length, more or sharper bends, or abrupt diameter changes?
• Have additional hoods and ductwork been added? Without proper airflow balancing, some hoods in a multiple system may have inadequate flow. Or the fan may be too small to handle the additional resistance.
• Has the contaminant source been moved further away from the hood opening?
• Is more contaminant being generated at the source?
• Are cooling fans causing cross-drafts?
• Have employees modified the hood because it interferes with their job tasks?