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Any ventilation system will have slight performance fluctuations. As with any piece of machinery, a ventilation system is subject to wear, misalignment and breakdowns. Only through regular and thorough maintenance can it remain in effective operating condition.

The following are a few of the more common problems to be aware of:

Hood System

  • Adjustable slots have been altered

  • Resistance has been changed (i.e., the hood has been modified or more fume hoods have been inappropriately added, so the velocity and flow rate of air are less than specified)

  • Holes in the enclosure resulting in air entering the hood in other locations

  • Inspection doors left open or removed, allowing air to enter

Duct Work

  • Duct partially plugged, increasing the resistance of air flow and decreasing the flow rate

  • Damper settings changed which lessens the amount of air flowing through (some duct have fused dampers, designed to close in case of fire, and occasionally, fuses will melt, causing damper to close inadvertently)

  • Additional ducts added since last inspection

  • Too many corrugated ducts (high static pressure)

  • Corrosion, leaks, holes, bent, crushed, dust

  • Inspection doors left open

  • Ducts joints have worked loose or become separated

  • Hangers missing and/or damaged

  • Blast gates/dampers

  • Incorrect position (causing system to become unbalanced)

Collecting Devices

  • Bags missing, blocked, overloaded

  • Cleaning mechanism not working

  • Hopper full of dust

  • Filters clogged


  • Duct or corrosion on fan blades

  • Incorrect rotation of blades (with flow axial fans, air flow may be reversed; with centrifugal fans, rate of flow may be reduced, making detection more difficult)

  • Fan blade assembly incorrectly mounted (turned around)

  • Incorrect fan size for system

  • Incorrect speed

  • Field modification to fan wheel or casing

  • Broken fan belt

  • Belt slippage/pulley sizes changed

  • Motors not lubricated, drives belts and other parts worn out

  • Poor fan inlet connections causing uneven air flow into fan (can reduce fan capacity by 20%)


This checklist is a sample only. Modify it to suit your own particular needs and operations. Although intended primarily as a maintenance or department check, it may be useful as a pre-shift check as well.

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