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Local Exhaust Ventilation

103a. Chemical Fume Hoods

A chemical fume hood is the preferred method of reducing or eliminating exposure to airborne substances. Its purpose is to assist in the safe handling of hazardous materials, especially those that produce vapors, gases or dusts. Fume hoods provide ventilation to carry away airborne contaminants and exhaust them outside the building.

BMP

  • Do not use fume hood as a storage cabinet for chemicals. This is not what they are designed for. Excessive storage of chemicals and other items will disrupt the airflow in the hood. In particular, do not store chemicals against the baffle at the back of the hood. This is where the majority of the air is exhausted.
  • If you are using your chemical fume hood for radioactive materials, consult with your Radiation Safety Officer for additional requirements.
  • EH&S inspects chemical fume hoods annually to ensure they are working properly. If you suspect that your fume hood is not working properly or for any other questions regarding fume hoods, call our Hazardous Materials Section at
    2-2185.
  • Do not keep loose papers, paper towels, or Kim wipes in the hood. These materials can get drawn into the blower and adversely affect the performance of the hood.
  • Keep in mind that equipment used inside the hood may create eddies that may impact the face velocity.
  • Make sure exhaust ductwork is maintained under negative pressure.
  • When using, keep chemical containers closed whenever possible.
  • Wear appropriate personal protective equipment.
  • Wear appropriate personal protective equipment when conducting maintenance on any parts of the inside or outside of the hood, including replacing filters and repairing fans.
  • Use secondary containment for chemicals located within the fume hood.
  • Make sure all valves and chemical operations are monitored or shut off when no one is around.
  • Keep hoods operating at all times only when necessary
  • Consider the impact of exhaust air relative to co-mingling of chemicals.
  • Make sure hood exhausts do not negatively affect the air quality of buildings or passersby.
  • Exhaust filters should be tested prior to disposal.
  • If possible, position the fume hood sash so that work is performed by extending the arms under or around the sash, placing the head in front of the sash and keeping the glass between the worker and the chemical source.
  • Avoid opening and closing the sash rapidly.
  • Avoid swift arm and body movements in front of or inside of the hood.
  • Equipment and other materials should be placed at least six inches behind the sash. This will reduce the exposure of personnel to chemical vapors that may escape into the lab due to air turbulence.
  • If large equipment must be kept in a fume hood, raise it 1.5 inches off the work surface to allow air to flow underneath. This dramatically reduces the turbulence within the hood and increases its efficiency.
  • Keep in mind that modifications made to a fume hood system, e.g., adding a snorkel, can render the entire system ineffective.  
  • If a large piece of equipment emits fumes outside a fume hood, have a special purpose hood designed and installed to ventilate that particular device.
  • When evaluating the need for local exhaust ventilation, install capture component of hood as close to the source of the “contaminant” as possible.
  • Minimize the amount of foot traffic immediately in front of a hood. People walking past hoods cause turbulence that can draw contaminants out of the hood and into the room.
  • Consider the use of a visual, flow-monitoring device to ensure function.
  • If using perchloric acid, you must use a hood specifically designed and identified by the manufacturer for use with perchloric acid.
  • These procedures also apply to several types of local exhaust ventilation systems such as canopy and paint spray booths.
  • When the hood is not in use, pull the sash all the way down. While personnel are working at the hood, pull down the sash as far as is practical. The sash is your protection against fires, explosions, chemical splashes, and projectiles.
  • Do not place objects directly in front of a fume hood (such as refrigerators or lab coats hanging on the manual controls) as this can disrupt the airflow and draw contaminants out of the hood.

Training

  • Individuals using chemical fume hoods should have a general understanding of their proper use. This information can be obtained from the Environmental Health and Safety Office.

P2-E2

  • Use low volatility and toxicity materials that do not require the use of hoods.
  • Consider energy efficiency when purchasing and installing equipment.
  • Properly evaluate the need and size of local exhaust ventilation.