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Fume Hoods and Workplace Safety : Decommissioned/Removed from Service

In your lab or place of  business by law you must Annually verify the presence of each hood and that the proper signage is posted, but will not test any such listed hood unless notified by the manager or department supervisor of a change in its status.  In addition, during the annual testing, the company will be notified about any hoods that don’t appear to be in use, and senior company staff will work with the department to determine if the fume hood should be decommissioned or marked as removed from service.

Fume hoods provide primary confinement in a chemical laboratory. They exhaust toxic, flammable, noxious, or hazardous fumes and vapors by capturing, diluting, and removing these materials. Fume hoods also provide physical protection against fire, spills, and explosion. Fume hoods provide the best protection when the fume hood sash is in the closed position. All chemical fume hoods must be ducted to the outside of the building.

Types of Chemical Fume Hoods

There are three basic types of general purpose fume hoods: (1) standard, (2) bypass, and (3) auxiliary air.

 

When using a fume hood, REMEMBER:

  • Keep everything at least six (6) inchesinside the fume hood.
    • Why? Drafts and eddy currents within this zone can pull vapors out of the hood.
  • Run electrical cords under, not over,the front airfoil.
    • Why? Cords create further air turbulence and prevent the sash from closing fully.
  • Do not block the rear exhaust slots.Raise bulky equipment off the work surface.
    • Why? Blocked slots disrupt air flow, creating turbulence and allowing exposure to users.
  • Close the sashwhen the fume hood is not in use.
    • Why? The sash can work as a blast barrier or fire containment for experiments gone awry. Additionally, each hood uses as much energy as a house. Closing the sash can save energy and money.

Fume Hood Safety Considerations

The potential for glass breakage, spills, fires, and explosions is great within a fume hood. Due to the chance for fires or explosions, fume hoods should be located towards the back of a laboratory, away from primary and secondary exits. Practice safe work habits when working with fume hoods, including the following:

  • Air Flow and Ventilation:
    • Employee traffic in front of a fume hoods or opening/closing laboratory doors can interfere with hood performance. Ensure that there is sufficient aisle space in front of fume hoods.
  • Fume Hood Type:
    • All fume hoods are not appropriate for all types of work.
    • Ensure that hazardous chemicals are used in the proper type of hood.  For example, use perchloric acid only in fume hoods specifically designed for perchloric acid.

Fume Hood Use and Care

To ensure safety and proper fume hood performance, follow these guidelines:

  • Use a fume hood when working with chemicals or procedures that may produce hazardous fumes or vapors.
  • Know how to properly operate a fume hood before beginning work. Inspect the fume hood before starting each operation to ensure it is working.
  • Place equipment and chemicals at least six inches behind the fume hood sash.  This practice reduces the chance of exposure to hazardous vapors.
  • Do not allow paper or other debris to enter the exhaust duct of the hood.
  • Do not store excess chemicals or equipment in fume hoods.
  • Do not block the baffle area of the fume hood.
  • Elevate any large equipment within the hood at least three inches to allow proper ventilation around the equipment.
  • When working in a fume hood, set the sash at the height indicated by the arrow on the inspection sticker.  The only time the sash should be completely open is while setting up equipment.
  • Wear personal protective equipment, as appropriate.
  • Do not alter/modify the fume hood or associated duct work.
  • Clean up spills in the hood immediately.

IMPORTANT!
If a power failure or other emergency occurs (e.g., building fire or fire within the fume hood), close the fume hood sash and call for emergency assistance.

Fume Hood Inspections

Fume hoods should be tested at least annually. Fume hoods should also be tested in the following circumstances:

  • When an employee requests an inspection
  • When a procedural change requires a hood classification upgrade
  • After major repair work
  • After a fume hood is moved

Lab staff and Certified Safety Persons performs fume hood inspections and testing monthly. The test includes an inspection of the hood system, airflow measurements, and an assessment of the use of the fume hood.

Confirm the fume hood is operational before each use (check the magnahelic gauge, indicator ribbon or the visual face velocity display).

  • Work with the sash at the proper operating level as indicated by the sash arrows.
  • When the hood is not in use, the sash should be completely closed.
  • Set up apparatus as close to the back of the hood as possible. Apparatus should not be closer than 15 cm (6 inches) from the front of the hood.
  • Do not block airflow. Raise large objects 5 cm (2 inches) off the counter by placing them on blocks.
  • Avoid filling the hood with excessive equipment and do not store chemicals in the fume hood. Excess clutter and chemicals can impede airflow.
  • Limit foot traffic around the fume hood. People walking by the hood face will disrupt the airflow in the hood.
  • Keep lab doors and windows closed at all times to ensure maximum hood performance and to maintain negative pressure in the room.
  • Avoid rapid removal of objects or arms from the hood and never place your head inside the hood.
  • Ground all electrical equipment.
  • Radioisotopes and Perchloric acid should only be used in designated fume hoods.
  • If the alarm soundsimmediately stop work, turn off all equipment and close the sash. Evacuate the area if highly volatile or toxic chemicals are being used.

 

Exhaust Fan Maintenance

The exhaust fans that operate to pull air through the fume hoods receive maintenance twice a year.

Terry Penney

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