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Home > Departments > Environment, Health & Safety > EH&S Programs > Laboratory Safety > Fume Hoods

Fume Hoods

Fume hoods are the primary means of control to prevent inhalation of hazardous chemical vapors, gases and dusts. Like any type of equipment, they must be used within their scope of design to be effective. Optimal airflow is between 80-120 feet per minute (fpm). EH&S inspects fume hoods annually, to make sure they are working properly.

Definitions:

  1. Air Foil (sill) – located at front of hood beneath the sash. Minimizes turbulence of air entering the hood by creating a smooth air flow.
  2. Air jambs – vertical sills or side posts at the front of the hood. They assist in making air flow into the hood smooth.
  3. Baffles – moveable panels located on the back wall of the hood through which air is exhausted.
  4. Face velocity – measure of the airflow at the fume hood sash.
  5. Perchloric hood – fume hood with special washdown feature.
  6. Sash – window covering the front of the fume hood. Sashes can be vertical (up and down), horizontal (side to side), or a combination of both.
  7. Sash Stop – device on side of hood limiting how high sash can be raised.

Types of Fume Hoods:

  1. Conventional – air flow at the face of the hood increases as the sash (window) is lowered.
  2. Bypass – relatively constant volume is obtained by a bypass above the sash that limits the increase in velocity as the sash is lowered.
  3. Auxiliary (makeup) – designed to save heating and cooling energy costs, this is a bypass hood with direct auxiliary air connection to provide unconditioned or partially conditioned outside makeup air.
  4. Variable air Volume (VAV) – constant face velocity maintained regardless of sash position.

Maximizing Fume Hood Effectiveness

  1. Air turbulence decreases fume hood efficiency. Designing fume hoods to be located away from doors, areas of high travel and air diffusers will minimize turbulence.
  2. Minimize turbulence by avoiding rapid movements like opening and closing the sash quickly, running by an open fume hood, and reaching in the fume hood quickly.
  3. If there is no gauge, verify that the hood is working by taping a small piece of tissue to the sash; it should be drawn into the hood.
  4. Never turn off alarms.
  5. Minimize the amount of equipment and chemicals stored in the fume hood.
  6. If equipment must be stored or used in the fume hood, elevate it to maintain airflow on the work surface.
  7. Keep equipment and supplies away from the sides, front and back of the fume hood to maximize effectiveness of air jambs, foil and baffles.
  8. Keep the sash as low as possible at all times and close it completely when not working
  9. Use the sash as a shield for your face and upper body.
  10. Be aware that some buildings have on/off or occupied/unoccupied switches on their fume hoods or for their room ventilation. Make sure you have maximized the ventilation before beginning your experiment.
  11. Many fume hoods have cup sinks that drain to building drains. Keep liquid chemicals in secondary containment to prevent spills going into the drain.
  12. Personal protective equipment such as safety glasses or goggles, gloves and lab coats should be worn when working in fume hoods.
  13. Keep papers, paper towels and small objects from being pulled to the back of the fume hood and from entering the baffles.
  14. If you suspect that the fume hood is not working, verify by doing the tissue test in #3. Make sure all room and hood switches are on. If there is still no airflow, do not begin an experiment. Call Facilities Customer Service at “71” to report and get it fixed.
  15. Despite all precautions and good working practices, the capacity of the fume hood can be exceeded.
  16. Do not use the fume hood to dispose of chemicals by pouring them down the drain or evaporating them.