VENTILATION & FUME HOODS

 

Ventilation controls are those controls intended to minimize employee exposure to hazardous chemicals by removing air contaminants from the work site. There are three main types of ventilation controls:

  1. General (Dilution) Exhaust - a room or building-wide system which brings in air from outside and ventilates within. Laboratory air must be continually replaced, preventing the increase of air concentration of toxic substances during the work day. General exhaust systems are not recommended for the use of most hazardous chemicals.
  2. Local Exhaust - a ventilated, enclosed work space intended to capture, contain and exhaust harmful or dangerous fumes, vapors and particulate matter generated by procedures conducted with hazardous chemicals.
  3. Ductless, or Portable Fume Hoods – an enclosed work space which employs filtration media, may be an option to conventional local exhaust hoods.

To determine ventilation requirements, assess the MSDS. Some MSDS terminology, as listed below, may indicate a need for special ventilation considerations beyond general exhaust:

    • use with adequate ventilation
    • avoid vapor inhalation
    • use in a fume hood
    • provide local exhaust ventilation

Local exhaust ventilation is the one of the best engineering methods available to reduce the health hazard risk associated with the use of hazardous chemicals in the laboratory. Laboratory fume hoods are the most common local exhaust ventilation devices found in the laboratory. Fume hoods are used to prevent hazardous, offensive, or flammable gases and vapors from mixing with the general room air. A hood, especially with the sash down, acts as a physical barrier between the laboratory workers and chemical reactions. The hood can also contain accidental spills of chemicals

 

Inspection of Local Ventilation Systems

 

Laboratory fume hoods should be inspected annually. Hoods are passed or failed for use based on the following criteria:

  1. The face velocity of air being drawn into the hood at maximum sash height is measured quantitatively in feet per minute (fpm) by a thermoAnemometer (a hot wire). One measurement is taken per square foot of face space and averaged. Hoods must have an average face velocity of 60-150 fpm, depending on their design, with 100 fpm being the ideal average face velocity.

  2. The turbulence of the air is measured qualitatively by releasing smoke from a smoke tube. The smoke must be captured by the hood, with a minimum of turbulence.

Proper Use of Local Ventilation Systems

 

No large, open-face hood with a low face velocity can provide worker protection against all events that may occur in the hood. The hood may not adequately protect the worker from volatile or airborne contaminants with a low exposure limit (part per billion range). For typical exposures, a well designed hood in a properly ventilated room can provide adequate protection. However, certain work practices are necessary in order for the hood to perform adequately. The following work practices are generally required; however, more stringent practices may be necessary in some circumstances.

    Recommended Work Practices for Laboratory Fume Hoods

     

    1. Conduct all operations that may generate irritating and/or hazardous air contaminants inside a hood.

    2. Keep all apparatus and chemicals at least 6 inches back from the face of the hood.

    3. Do not lean into the hood or put your head in the hood when contaminants are being generated.

    4. Do not use the hood as a waste disposal method (i.e., volatilize chemicals).

    5. Do not store chemicals or apparatus in the hood. Store hazardous chemicals in an approved safety cabinet.

    6. Maintain the hood sash closed as much as possible.

    7. Keep the slots in the hood baffle free of obstruction by apparatus or containers.

    8. Use equipment with legs or otherwise raise it off the work surface to allow even airflow under equipment as well as around and over it.

    9. Minimize sources of turbulence at the hood face (e.g., foot traffic, equipment, fans, moving arms in and out of the hood).

    10. Keep laboratory doors closed whenever possible.

    11. Do not remove hood sash or panels except when necessary for apparatus set-up. Replace sash or panels before operating hood.

    12. Do not place electrical receptacles or other ignition sources inside the hood when flammable liquids or gases are present. No permanent electrical receptacles are permitted in the hood.

    13. Use an appropriate barricade or shield, if there is the possibility of explosion or eruption.

    14. Periodically check the air flow in the hood using a continuous monitoring device or another source of visible air flow indicator. If air flow has changed, contact Supervision.

    15. Unlabeled chemicals, unused equipment, materials, etc., are subject to removal and/or disposal.