4.16 Biosafety Cabinets (BSC)
BSCs are specialized pieces of lab equipment designed to safely contain biohazardous agents/ materials and protect sterile items and culture materials from contamination when they are manipulated in the BSC work space. There are several different classes and types of BSCs to meet specific needs. Choosing the right BSC for purchase should be based on a thorough risk assessment of all material (biological and chemical) being handled and the procedures involved with the work.
BSCs must not be confused with chemical fume hoods, which utilize directional air flow to protect lab workers from exposure to toxic chemical fumes or particulates by venting them to the outside. Material in a chemical fume hood is not protected from room air contamination.
Minute amounts of volatile chemicals/ radionuclides may be used ONLY with certain types of BSCs which exhaust them to the outside. However, chemical fume hoods should never be used for protective containment of biologicals. In most cases, BSCs and chemical fume hoods have distinctly different functions and are NOT interchangeable.
The HEPA-filtered directional air flow in a BSC 1) protects the work material from contaminants, 2) protects the worker from exposure to aerosols, and 3) prevents release of aerosolized material into the environment. IMPORTANT: BSC HEPA filters do not entrap or filter chemical vapors or gases; they entrap particulates.
The HEPA filter is the most important feature of the BSC, capturing potentially infectious particles from your work as well as room air contaminants, and contaminants that you may shed. HEPA filters should be replaced every 3-5 years, depending on cumulative hours of operation, the cleanliness of the lab, and the materials being used in the BSC. Changing or cleaning the pre-filter on a regular basis extends the life of a HEPA filter.
The magnehelic gauge on the BSC shows the air pressure difference across the HEPA filter, and indicates whether the air flow system and filter are operating properly. BSC users should know their BSC’s acceptable gauge readings and limits; ask your service provider, or look on the BSC certification label for this information. Before each work session, check the gauge and look for changes higher or lower than this acceptable range. A higher resistance reading indicates the filter is loaded or blocked; a lower resistance reading may indicate a hole or tear in the HEPA filter. In either instance, do not use the BSC; contact a service provider.
Room location is important to the proper functioning of a BSC:
- Ideally, BSCs should occupy lab space that is removed from other work areas, especially high traffic areas.
- Cabinet should be placed 12-14 inches from ceiling and walls.
- Cabinet should be placed away from windows, air supply vents, lab features creating air movement (chemical fume hoods, centrifuges, vacuum pumps), and entry points into lab.
Labconco “C1” BSC
- The Labconco Purifier Axiom Class II, Type C1 biosafety cabinet has recently been introduced to the market. The “C1” designation was generated by the manufacturer and is not currently recognized in the industry by NSF, NIH or CDC although it is designed to protect you, the product and the environment, as with other BSCs.
- This cabinet is marketed to be more flexible than previously available biosafety cabinets because it can be used as a re-circulating Class II Type A cabinet for standard microbiological work, or it can be ducted to the outside (or used with a manifold exhaust system) for working with volatile chemicals and radionuclides, as with a Type B cabinet.
- Special HVAC requirements may be involved with the installation of this type of cabinet and all manufacturer’s recommendations must be followed.
4.16.3 Using Volatile Chemicals/ Radionuclides in a BSC
- Minute amounts can be handled in Class II Type A2 or B1 BSCs vented to outside.
- Small amounts can be handled in Class II Type B2 BSCs vented to outside.
- Check the Safety Data Sheets for volatile chemicals to learn explosion limits, and avoid approaching those concentrations, as chemicals can volatilize and concentrate to hazardous levels in a BSC or after being pulled through HEPA filters.
- Make sure the volatile chemicals you use will not damage HEPA filters.
You have exceeded the quantity of a volatile chemical you can safely use in your BSC if you can smell or otherwise detect chemical fumes out in the lab. In these circumstances, discontinue use of that BSC; instead, locate and use a BSC that exhausts most or all air to the outside.
4.16.4 BSC Certification and Decontamination Requirements
All new BSCs to be used for handling potentially infectious/biohazardous material must be certified before being used; certification involves a standardized check of proper function, performed by a qualified technician.
Yearly certification is required for any BSC which is being used with potentially infectious materials.
Cabinets must be re-certified 1) following a move to a different location; 2) if a HEPA filter is replaced; 3) following any other repair or service to the unit.
Prior to the technician’s arrival, prepare a BSC to be certified by removing all items and disinfecting all work area surfaces.
Work surface decontamination is usually sufficient for certification, in situ repairs and moves within a building.
Decontamination of the entire unit by a qualified contractor is required prior to a major relocation, going to surplus, receiving extensive repairs, or following a high-volume spill.
Disinfecting agents typically used by professionals include formaldehyde gas and vaporized hydrogen peroxide.
If you need assistance in determining whether whole-unit decontamination is needed, or for information on scheduling decontamination service with a contractor, contact EHS.
4.16.5& Guidelines for BSC Use
Cabinet blowers should be operated at least 5 minutes before beginning work to allow the cabinet to purge any unfiltered room air within it. This purge will replace the atmosphere in the cabinet with filtered air.
The work surface, the interior walls (not including the supply filter diffuser), and the interior surface of the window glass should be wiped with a solution of 70% ethanol or other appropriate disinfectant.
The surfaces of all materials and containers placed into the cabinet must be wiped/sprayed with 70% ethanol or other appropriate disinfectant to reduce the introduction of contaminants into the cabinet environment.
Place all necessary materials in the BSC before beginning work. This will serve to minimize disruptions across the air barrier of the cabinet.
Disruption of the air curtain occurs with rapid movement of a worker’s arms into and out of the cabinet, compromising containment provided by the BSC. Move your arms in and out slowly, perpendicular to the face opening of the cabinet, to reduce this risk.
Other personnel activities in the room (e.g., walking back and forth behind someone working at a BSC, entering/exiting lab, opening/closing lab doors, etc.) may also disrupt the cabinet air barrier. For this reason, access to the work area must be restricted when work is in progress.
Before beginning work, adjust stool height so that your face is positioned in front of the BSC glass and is well above the opening below the glass that accesses the BSC work surface.
Manipulation of materials should be delayed for approximately 1 minute after placing the hands/arms inside the cabinet, which allows cabinet’s air flow to stabilize.
When the user’s arms rest flatly across the front grille (partially blocking it), room air may flow directly into the work area, rather than being drawn through the front grille. Raising the arms slightly will alleviate this problem. The front grille must not be blocked with paper notes, discarded plastic wrappers, pipetting devices, etc., and the back grille must not be blocked by supplies, waste containers, pipette tip boxes, racks of tubes, etc.
All operations should be performed on the work surface at least 4 inches from the inside edge of the front grille.
Equipment that causes air turbulence (e.g., centrifuge, vortex, etc.) should be placed in the back 1/3 of the work surface. All other work in the cabinet should stop while equipment is running.
Do not use open flames such as Bunsen burners inside the BSC. Open flames create turbulence that disrupts the BSC protective air flow which could expose personnel to biohazardous material. In addition, if the burner is turned off incompletely, gas can accumulate in the BSC enclosure, creating a risk of explosion. Flame-sterilizing tools in a BSC using a burner and alcohol is very hazardous; if alcohol is ignited, the heat and flame will likely destroy a HEPA filter. Instead of an open flame, use a Bacti-Cinerator, glass bead sterilizer or disposable loops/spreaders.
Separate clean and contaminated items. Minimize movement of contaminated items over clean items (i.e., work from clean to dirty).
Only the materials and equipment required for immediate work must be placed in the BSC. Do not use the BSC as a storage area.
Prior to removal from the cabinet, used pipettes and other contaminated material must be decontaminated or placed into a sealed container which is disinfected on outside surfaces.
All vacuum lines must have in-line HEPA filters and traps containing disinfectant; all vacuum filtering takes place in the biosafety cabinet.
At the end of the work session, all materials and work surfaces must be decontaminated with appropriate disinfectant. The work surface, the interior walls, and the interior surface of the window are again wiped with 70% ethanol or other appropriate disinfectant. A UV light may be turned ON for 30 minutes as an additional precaution, with the understanding that UV radiation is effective upon surfaces only (does not penetrate) and is no substitute for decontaminating the work area with disinfectant. UV lights should be activated in a BSC when personnel are not in the immediate vicinity to avoid eye/skin exposure to UV radiation.