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Chemical Fume Hoods

Chemical fume hoods are the primary containment device in the laboratory used to control airborne contaminants generated by experimental procedures. Chemical fume hoods provide personnel protection by means of directional airflow from the laboratory into the hood through the face opening. This airflow reduces the potential for escape of airborne contaminants into the laboratory. Procedures involving volatile chemicals and those involving solids or liquids that may result in the generation of toxic vapors should be conducted in a chemical fume hood rather than on the open bench. Placing a reacting chemical system within a hood, especially with the hood sash closed, places a physical barrier between the workers in the laboratory and the chemical reaction. This barrier can afford laboratory workers protection from chemical splash, sprays, fires, and minor explosions. Hoods should be evaluated before use to ensure adequate face velocities. Hoods are checked annually by the Safety & Risk Management Office to determine the face velocity. An adequate face velocity for most applications is 100 feet per minute + / - 10%. Hoods with a low face velocity <75 feet per minute are posted as "low toxic only" use. Although chemical fume hoods do protect laboratory personnel from exposures to hazardous materials, they must be used properly in order to maximize their effectiveness. The following practices should therefore be observed when using fume hoods:

  • Hood work areas should be clear of unnecessary equipment and materials which can disrupt airflow and block vents.
  • Hoods should not be used for the storage of chemicals.
  • Work should be carried out as far back in the hood as possible. Moving apparatus 6 inches back from the front edge can improve performance by 90%.
  • Experiments should be planned so that, as much as possible, all of the materials needed for a procedure are present in the hood to eliminate disruption of airflow by carrying equipment in and out during a procedure.
  • Disruptive room air currents should be minimized by avoiding traffic near fume hoods and opening and closing doors near fume hoods while experiments are in progress.
  • Keep the sash as low as possible.
  • Use equipment with legs, if possible.
  • Adjust the inside baffle at the back of the hood so the bottom slot is wide open and the one at the top is closed or partially closed. This will favor airflow across the workbench where heavier than air solvent vapors congregate.


Most laboratories handle hazardous materials, whether radioactive or chemical, which can generate harmful concentrations of aerosols, fumes, and vapors within fume hood exhaust air and which can contaminate the surfaces of laboratory equipment. It is essential for the safety of those required to repair fume hoods, fans, and motorized equipment that appropriate precautions be taken to prevent exposure to air and surface contaminants. Whenever work is performed on roof vent fans, within fume hood enclosures, or on laboratory equipment the following procedures must be followed:

  • Roof Fans: Prior to starting maintenance work the laboratory personnel must certify that all sources of harmful aerosols, fumes, or vapors are contained or removed from the hood being serviced as well as hoods with roof fans that are adjacent to the one being serviced.
  • All work within the duct air stream enclosure shall be performed with appropriate PPE (i.e. neoprene gloves, safety glasses).
  • Switches operating the hood fan shall be tagged by the maintenance employee during work.
  • Hood Enclosures: Prior to starting work all materials must be removed from the hood enclosure and contaminated surfaces cleaned by laboratory personnel.
  • Laboratory Equipment: Prior to starting work all containers of hazardous materials must be removed and all potentially contaminated surfaces cleaned by laboratory personnel. A radiation survey is to be done for equipment which has been used with radioactive materials.

For a variety of reasons whether it's an electrical problem, mechanical problem, or routine maintenance a fume hood malfunction can occur. In the event that a low airflow alarm should signal or if the personnel recognizes there is low or no airflow from the fume hood; these outlined procedures should be followed:

  • Immediately stop all work inside the fume hood.
  • If safe to do so, secure or isolate reactions and turn off all equipment being used (ie. hot plates, burners etc.)
  • If safe to do so, close all open chemical containers.
  • Close the sash completely.
  • If processes or reactions that could create a hazard to the lab or building occupants cannot be stopped or contained, the lab(s) or possibly the building should be evacuated until the hazard is eliminated. Activate the Fire Alarm. Evacuate the building and wait for emergency personnel to arrive. Inform emergency personnel of the situation.
  • During a power outage turn off or unplug other electrical equipment that could turn on once power is restored.
  • Report the problem immediately to your lab manager or to the Safety and Risk Management Office 828-227-7443
  • Notify others in the area or anybody who could use the fume hood at a later time.
  • Hood(s) that have malfunctioned should have a sign posted to inform that the hood is not functioning correctly and may not be used until repairs have been made. Signs posted should state FUME HOOD OUT OF SERVICE - DO NOT USE. Sign(s) will be installed by either the personnel who discovers the fume hood problem or by the Safety and Risk Management Office.
  • Only the Safety and Risk Management Office will remove any posted sign. Do not use the fume hood until the posted sign has been removed.
  • Once the sign has been removed the department or lab manager will then be notified of completed repairs.


Fume Hood Out Of Service Sign 

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