Texas Tech University
Scholarly Messenger
Are You Using Your Fume Hood Correctly?
By Matt Roe

When working with chemicals that can produce toxic or hazardous vapors make sure to closely examine your procedures before use.  Established procedures should include the use of a fume hood or “local exhaust ventilation” as it is typically referred to in material safety data sheets.  Fume hoods are ventilated enclosures designed to contain vapors produced from chemical manipulation and prevent them from affecting the user.  If a fume hood is being used properly there should not be a need for respiratory protection (i.e. a respirator) and there should be no odor of the chemical in the laboratory.  To use a fume hood correctly include the following in your procedures:
  1. Make sure the sash is at the proper working height.  The open sash area determines if the hood is operating within parameters.  If the open sash area is too large then chemical vapors can escape from the enclosure.
  2. Make sure the hood is on and the airflow is directional.  This is most easily accomplished by taping a small piece of light plastic or tissue to the bottom of the sash.  If the hood is operating properly then the piece of plastic/tissue should be drawn inwards into the hood.
  3. Limit storage in the hood.  Storage in the hood should be limited to only actively used chemicals and any necessary equipment.  This will provide for appropriate airflow into the slots along the rear of the hood.  Any large equipment should be elevated to reduce turbulence.
  4. All work in the hood should be done at least six (6) inches inside of the hood face.  This will prevent any fugitive vapors from escaping and provides a safety buffer for the user.
  5. When not actively working in the fume hood the sash must be fully closed.  Most hoods provide an air bypass on the front of the hood to allow the hood to operate properly while the sash is closed.  The sash also provides limited protection and containment in the event of a fire or explosion within the hood.
Fume hoods are considered engineering controls of hazards and are preferred to respirator use or working in short periods to try and reduce exposure.  Even a brief exposure to many chemical vapors, in particular carcinogens, can have negative health effects.  Also, while working in a fume hood you can more easily contain a chemical spill and control the vapors simply by closing the sash.  Fume hoods are verified by Environmental Health and Safety annually and should have a sticker on the front sash to indicate the most recent verification date.  Remember that working in a fume hood is the preferred way of working with any chemicals that produce toxic or hazardous vapors.

Matt Roe is an environmental safety manager in with Environmental Health and Safety at Texas Tech University.