Fume Hoods and Biological Safety Cabinets

Fume Hoods

Use the following safe practices for all laboratory fume hoods:

  • Conduct all operations which may generate air-borne contaminants inside a hood.
  • Always wear appropriate eye protection, gloves, and a lab coat when working around a fume hood.
  • Do not raise the sash higher than the labelled height. This will reduce hood efficiency.
  • Keep apparatus at least 15 cm from the face of the hood.
  • If the hood is used for semi-permanent experiments, post the name of the person in charge, experiment title, and possible hazards.
  • Do not store chemicals inside the hood. Hazardous chemicals should be stored in an appropriate safety cabinet.
  • Keep your face outside the plane of the hood opening.
  • Avoid cross drafts at the face of the hood. Minimize foot traffic past the hood and position windows and supply air diffusers to direct air flow away from the hood.
  • 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.
  • Avoid blocking the rear ventilation slot. Material stored at the back of the hood should be stored on an elevated shelf so that the slot air flow is not impeded.
  • Leave the sash lowered when the hood is unattended.
  • Keep the bypass grille clean and unblocked at all times.

Biological Safety Cabinets (BSC)

The most common error made by new people to a lab is the confusion of fume hoods with biological safety cabinets (BSC). Before using these devices, ask some one to clarify the difference. A fume hood removes fumes which are then ducted to the outside of the building. A BSCs’ airflow is ducted through a HEPA filter before entering the work area or outside of the building depending on the type of BSC. A BSC which is vented back into the room will not protect you from noxious fumes used inside the BSC.

Exposure to infectious aerosols is believed to be responsible for approximately 85% of laboratory acquired infections. The biological safety cabinet was developed to prevent exposure of laboratory personnel to the aerosols created during the normal manipulation of infectious agents. Class II cabinets are common in many research and hospital labs and are designed for work involving low to moderate risk biological agents.

Class II Biological Safety Cabinets

The essential components of Class II biological safety cabinets are:

  • High Efficiency Particulate Air (HEPA) filtered supply and exhaust airflow.
  • Open front access with inward airflow.
  • Laminar downward filtered airflow.
  • Air “curtain” at access opening to prevent product contamination and aerosol escape.

Class II cabinets provide:

  • Protection of the user from exposure to aerosols
  • Protection of the product from possible contamination
  • Protection of the environment from aerosol release

For more information about the different types of BSC’s please refer to the UBC Department of Health Safety and Environment Laboratory Biosafety Reference Manual

Cabinet Certification

All biological safety cabinets must be certified annually to assure the integrity of the HEPA filters and the maintenance of adequate and balanced airflow. All new cabinets must be certified before being used and all cabinets must be recertified after changing the HEPA filter or being moved.

Proper Use of a Biological Safety Cabinet

  • No cabinet can replace good aseptic and experimental technique. The proper use and limitations of the BSC must be clearly understood by all users before they begin their work.
  • Turn on the BSC for 15 min before use to purge non-sterile air.
  • Wearing gloves, wipe down the work surface with 70% ethanol before (and after) use (ethanol does not disinfect unless it is kept wet for 20 min.)
  • Gather your supplies and anticipate your needs BEFORE beginning your work in the BSC. Add equipment slowly to BSC, wiping each item with 70% ethanol. Do not overload the work surface, and be careful not to block either the front or the rear grilles. Wait 2min before beginning experiment.
  • Perform work.
  • Do not move hands in and out of BSC while flasks or media bottles are open.
  • When finished, wipe all items with 70% ethanol before removing from the BSC. Spray BSC surface with 70% ethanol and let evaporate. When your work is completed, allow the BSC to run for at least 10 min to remove any aerosols which may have been generated.

Additional Safety Precautions

  • Unprotected hands may be contaminated by aerosols generated within the BSC. Therefore, disposable nitrile gloves should be worn when working with biohazards.
  • A back closing gown should also be worn. The yellow gowns that are available at St. Paul’s are perfect for this. Be sure to remove the gown before leaving the room.
  • Never wear the gown or gloves outside of the laboratory.
  • When working with viruses, used gowns, gloves and any other materials that come in contact with the virus must be autoclaved.
  • Procedures that generate aerosols should be performed towards the rear of the BSC where the air is being pulled away from the operator’s arms and into the back air removal grill. Air in the front half of the cabinet is being pulled towards the front air removal grill. Remember this when planning the placement of your supplies and equipment.
  • Do not use a large flame Bunsen burner in the BSC. The heat it produces disrupts the laminar air flow and may damage the HEPA filter. Use a micro-burner, an electric incinerator, or disposable loops instead.
  • If it is necessary to use equipment that generates air turbulence, such as a centrifuge, no other manipulations should be performed in the BSC while that equipment is running, and time should be allowed for the airflow to re-establish before work resumes.
  • Employ aseptic technique and be aware of other possible methods of pathogen transmission that could occur in a BSC including direct contact and the risks of using sharps.