Chemical Fume Hoods: Your First and Best Line of Defense  by Brian Anderson
A chemical fume hood (CFH) is an invaluable laboratory engineering control.  They are designed to minimize or eliminate lab personnel’s exposure to hazardous materials by directing gases and vapors away from the breathing zone and by creating a physical barrier between workers and their processes.  CFH’s however, are only as effective as the people using them.  Safe work practices with a CFH include:

  • Lab personnel should not place their upper body in the CFH except during initial setup of equipment inside the hood, before any hazardous materials have been placed inside the hood.
  • Hazardous materials and equipment that could be emission sources should be placed at least 6 inches inside the CFH for proper containment of chemical vapors.
  • CFHs should not be used for permanent storage of hazardous materials.
  • Elevate large pieces of equipment inside the CFH so as to not block airflow through baffle slots in the back of the hood.
  • The hood sash or panels should be set at the lowest (comfortable) working height, usually 12”.  Larger sash openings will reduce the the sash’s effectiveness as a physical barrier to spilled or splashed materials and reduce the hood’s overall capture velocity so that gases and vapors may not be effectively removed. 
  • The hood sash or panels must not be removed except for initial experimental setup and before hazardous chemicals are placed in the hood.

EH&S posts each hood with a sticker showing the date of the last air flow certification check.  If a hood fails its annual performance test because its face velocity is outside of the acceptable 80-120 ft. per minute flow rate range, it is taken out of service until repaired, and posted with a restricted use notice.

Since CFHs exhaust air without recirculating it, they create a large energy burden.  Many CFHs have variable air volume (VAV) controllers which adjust the volume of air that the hood exhausts based on the height of the sash; this allows for less air to be exhausted when the sash is closed.  Keeping the sash closed when the hood is not in use consumes less energy by decreasing the lab’s need for  warm air during winter and cool air during the summer. To find out if you have a VAV hood or if you have other questions relating to work with CFHs, contact the Research Safety Team.    

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