PURPOSE
When properly maintained and used in conjunction with good laboratory techniques, Biological Safety Cabinets (BSCs) provide effective primary containment for work with human pathogens. BSCs are used for procedures with the potential to produce infectious aerosols and for high concentrations or large volumes of infectious material.
DEFINITIONS
Hepa Filters – being, using, or containing a filter usually designed to remove 99.97% of airborne particles measuring 0.3 microns or greater in diameter passing through it.
A biosafety cabinet (BSC) — also called a biological safety cabinet or microbiological safety cabinet — is an enclosed, ventilated laboratory workspace for safely working with materials contaminated with (or potentially contaminated with) pathogens requiring a defined biosafety level.
PROCEDURE
* PURPOSE AND USE OF THE BSC
- Biological Safety Cabinets (BSCs) are the primary means of containment for working safely with biohazardous agents. BSCs are designed to reduce the risk of infection by isolating the activities in the BSC from the laboratory environment.
- BSCs provide personnel protection and environmental protection by using a combination of directional airflow and a High Efficiency Particulate Air (HEPA) filter. Bacteria, spores and viruses are removed from the HEPA-filtered air.
* MECHANICAL OPERATION OF A BIOLOGICAL SAFETY CABINET
- Operation Panel and Main Features: The functions of a BSC are controlled through a panel located on the front of the cabinet above the sash (window). Switches on the panel control the lighting, the blower/fan system, the electrical outlets, and the alarm system bypass.
- Magnehelic Gauge: Routinely monitor the pressure on the magnehelic gauge so that you will know what it should be for your cabinet since the normal reading differs from one cabinet to another. The magnehelic gauge provides a "gross" or approximate indication of HEPA filter loading, i.e., the volume of particulate matter the filter has accumulated as the cabinet operates. It provides one indication of how rapidly the filter's capacity is being diminished. This is measured by reading either motor blower suction or pressure.
- Blower: The blower motor should be turned on at least 5 minutes prior to using the BSC. To maintain the proper airflow pattern, the sash (window) should only be opened to the height marked on the front panel (usually a maximum of 10 inches).
- Outlets: Electrical devices can be used inside the BSC by using the plugs and bibs provided.
- Lighting: There are two types of lighting inside the BSC: fluorescent and UV.
1. The fluorescent light should normally be ON while work is being done within the cabinet.
2. UV light direct exposure to UV light (approximately 260 nm wavelength) can reduce the number of pathogenic microorganisms on exposed surfaces and in air. However, it is important to note that (I) UV light has poor penetrating power; (2) the accumulation of dust, dirt, grease or clumps of microorganisms reduce its germicidal effects; (3) UV light is not effective against all organisms; and (4) exposure to UV light is hazardous: it may result in severe eye damage and bums to the skin. Therefore, the routine use of UV lamps to decontaminate a BSC is not recommended. They are useful in certain situations, if properly maintained, such as when using spore-forming bacteria since bacterial spores are resistant to chemical disinfection. UV lamps must be turned off whenever the laboratory is occupied unless the sash can be lowered so that it is completely closed.
PROCEDURES FOR USE OF THE BIOLOGICAL SAFETY CABINET
START UP
- Turn OFF the UV lamp (if it is on) and turn ON the fluorescent light.
- Thoroughly Turn ON the blower (if it is off; many labs leave the blower running all the time) and allow it to run for at least 5 minutes before starting work in the cabinet. Ensure that the alarm has NOT been turned OFF, and that the airflow is sufficient.
- Routinely monitor the pressure on the magnehelic gauge so that you will know what it should be for your cabinet since the normal reading differs from one cabinet to another. If the differential pressure drops by more than 0.2 then do not use the cabinet and call for service.
- Disinfect the work surface with 70% Ethanol (EtOH) or other disinfectant appropriate for the biohazardous agents in use (e.g. Virox, an H2O2 disinfectant). Note that bleach can corrode the stainless steel and make the BSC difficult to decontaminate so it should not be used for routine decontamination. If it is required for spill clean-up then be sure to thoroughly rinse the surface.
- Place the essential items inside the cabinet without obstructing the air grills.
- Wear protective gloves that cover the cuffs of lab coat sleeves to prevent contaminated air from entering the sleeve. Lab coats (or closed front gowns) with fitted cuffs rather than loose sleeves are recommended.
WORK TECHNIQUES
- Movement of arms into and out of the cabinet can disrupt airflow, adversely affecting cabinet performance. Whenever possible, place all materials needed for a procedure inside the cabinet before starting. Move arms slowly and move straight out of the cabinet; do not sweep arms across the front of the cabinet. Do not walk quickly in front of a cabinet when someone else is working.
- Never put anything on the grill at the front opening of the cabinet.
- Do not block the air openings/grill at the back of the cabinet.
- Place supplies, equipment and papers well back from the front of the cabinet, positioned so that air intake or exhaust grills are not obstructed. Avoid bringing non-essential equipment and supplies into the cabinet.
- Work towards the middle of the cabinet, away from the cabinet window.
- Designate separate areas within the cabinet for contaminated and clean materials, place contaminated material at the rear of the work area.
- Discard contaminated waste including contaminated gloves INSIDE the cabinet.
- Clean up spills as soon as they occur. Remove and disinfect the grill if contaminated and remember to clean under the grill.
UPON COMPLETION OF WORK
- Close or cover open containers and leave the blower on for at least five minutes with no activity to purge the cabinet.
- Surface-disinfect objects before removal from the cabinet. Remember that aerosols generated during operations in the cabinet such as pipetting might have contaminated objects in the cabinet, so there does not have to have been a spill for this step to be necessary.
- Remove contaminated gloves and dispose of them as appropriate. Wash hands thoroughly with soap and running water.
- Disinfect cabinet surfaces with 70% Ethanol (EtOH) or other appropriate non-corrosive disinfectant. Periodically remove the work surface and disinfect the area beneath it (including the catch pan) and wipe the surface of the UV light with disinfectant.
- Disinfect or dispose of personal protective equipment appropriately and wash hands.
WARNINGS
- An open flame should not be used in a BSC. Bunsen burners are fire and explosion hazards, contribute to the heat load, generate convection currents that interfere with airflow and have been known to burn holes in the HEPA filters. If necessary, discuss alternatives with the Biosafety Officer (e.g. micro-incinerator for bacterial loops).
- The HEPA filters in the BSCs remove particulates from air, but they are not effective at collecting chemical gases or vapours. If you need to use such material in a BSC, contact the Biosafety Officer for advice.
- Routine use of UV lamps to decontaminate a BSC is not recommended • DO NOT use the BSC if the ALARM sounds or if there are other indications of cabinet malfunction such as no airflow, reduced pressure on magnehelic gauge (drop > 0.2), or unusual noises.
MAINTENANCE/CERTIFICATION OF BIOLOGICAL SAFETY CABINETS
When used for biosafety level 2 containment, biological safety cabinet performance must be tested and certified:
· Upon initial installation in the laboratory
· Annually thereafter
· When moved from one area to another within the same room, or from one room to another
· Whenever maintenance is carried out on internal parts, and whenever filters are changed
For more detailed guidelines and information on biological safety cabinets in clinical laboratories, you can refer to the following resources:
1. Centers for Disease Control and Prevention (CDC) - Biosafety in Microbiological and Biomedical Laboratories (BMBL); World Health Organization (WHO) - Laboratory biosafety manual, 4th edition: Biological safety cabinets and other primary containment devices: https://www.who.int/publications/i/item/9789240011335
2. National Institutes of Health (NIH) - Guidelines for Research Involving Recombinant or Synthetic Nucleic Acid Molecules: https://osp.od.nih.gov/wp-content/uploads/NIH_Guidelines.pdf
3. Occupational Safety and Health Administration (OSHA) - Bloodborne Pathogens Standard: https://www.osha.gov/SLTC/bloodbornepathogens/index.html
These resources provide comprehensive information on the safe use of biological safety cabinets and other biosafety practices in clinical laboratories.