Biological Safety Cabinets
207. Biological Safety Cabinets (BSC)
From the earliest laboratory-acquired typhoid infections to the hazards posed by today’s antibiotic-resistant bacteria and rapidly-mutating viruses, threats to worker safety have stimulated the development and refinement of cabinets in which infectious microorganisms could be handled safely. Work with tissue cultures, the need to maintain sterility of cell lines, and efforts to minimize cross-contamination contributed to concerns regarding product integrity. Biological Safety Cabinets (BSCs) are designed to provide personnel, environmental and product protection when appropriate practices and procedures are followed. Three kinds of biological safety cabinets, designated as Class I, II and III, have been developed to meet varying research and clinical needs. A Properly certified and operational BSC is an effective engineering control that together with the appropriate work practices and procedures reduces the risk of exposure to potentially infectious microorganisms.
- Preparing a checklist of materials necessary for a particular activity and placing those materials in the BSC before beginning work serves to minimize the number of arm-movement disruptions across the fragile air barrier of the cabinet. The rapid movement of a worker’s arms in a sweeping motion into and out of the cabinet will disrupt the air curtain and may compromise the partial barrier containment provided by the BSC. Other personnel activities in the room (e.g., rapid movements near the cabinet opening, open/closing room doors, etc.) may also disrupt the cabinet air barrier and should be kept to a minimum. A sign can be posted on the door of the room stating that the BSC is in use.
- Protective clothing (coats, gowns, aprons, etc.) should be worn over street clothing. A solid front, back-closing lab gown provides better protection of personal clothing than a traditional lab coat. Disposable, single-use latex cloves must be worn while handling any infectious materials. Gloves should be pulled over the knitted wrists of the gown, rather than worn inside. Elasticized sleeves can also be worn to protect the investigator’s wrists. Gloves should be replaced as soon as practical when contaminated or when their ability to function as a barrier is compromised (torn, punctured). Hands should be washed whenever gloves are changed or removed. Disposable, single-use gloves should not be washed or decontaminated for reuse.
- If the work involves human blood, a faceshield, safety glasses or goggles and a mask may be required if there is a potential for splash.
- Before (and after) use, wipe the work surface, the interior walls (not including the supply filter diffuser), and the interior surface of the window of the BSC with a suitable disinfectant, e.g. 70% alcohol (ethanol, isopropanol) or a 1:10 bleach solution or other disinfectant as determined by the investigator to meet the requirements of the particular activity. When bleach is used, a second wiping with sterile water is needed to remove the residual chlorine, which may eventually corrode stainless steel surfaces. Similarly, the surfaces of all materials and containers placed into the cabinet should be wiped with 70 % alcohol to reduce the introduction of contaminants to the cabinet environment. This simple step will reduce introduction of mold spores and thereby minimize contamination of cultures.
- Before beginning work in the BSC, the ultraviolet light should be turned off and the stool height adjusted so that investigator’s face is above the front opening. Manipulation of materials should be delayed for approximately one minute after placing the hands/arms inside the cabinet.
- The front grille must not be blocked with research notes, discarded plastic wrappers, pipetting devices, or user’s arms. These may let room air to flow directly into the work area, rather than being drawn through the front grille.
- All operations should be performed at least four (4) inches from the front grille on the work surface.
- Materials or equipment placed inside the cabinet may cause disruption to the airflow, resulting in turbulence, possible cross-contamination, and/or breach of containment. Extra supplies (e.g. additional gloves, culture plates or flasks, culture media) should be stored outside the cabinet. Only the materials and equipment required for the immediate work should be placed in the BSC.
- BSCs are designed to be operated 24 hours per day, and some investigators find that continuous operation helps to control the laboratory’s level of dust and other airborne particulates. If the cabinet has been shut down, the blowers should be operated at least three to five minutes before beginning work.
- A disinfectant soaked towel can be placed on the work surface (but not on the front or rear grille openings) to contain any spatters or small spills that might occur. All materials and expecially aerosol-generating equipment (e.g. vortex mixers, tabletop centrifuges) should be placed as far back in the cabinet as practical, toward the rear edge of the work surface and away from the front grille of the cabinet. The general workflow should be from clean to contaminated (dirty). Materials and supplies should be placed in such a way as to limit the movement of “dirty” items over “clean” ones.
- Bulky items such as biohazard bags, discard pipette trays and suction collection flasks should be placed to one side of the interior of the cabinet. If placing materials in the cabinet requires opening the sash, it should be made sure that the sash is returned to its original position (usually 8” or 10” above the base of the opening) before initiating work.
- The autoclavable biohazard collection bag should not be taped to the outside of the cabinet.
- Upright pipette collection containers should not be used in BSCs nor placed on the floor outside the cabinet. The frequent inward/outward movement needed to place objects in these containers is disruptive to the integrity of the cabinet air barrier and can compromise both personnel and product protection.
- Only horizontal pipette discard trays containing an appropriate chemical disinfectant should be used within the cabinet. Furthermore, potentially contaminated materials should not be brought out of the cabinet until they have been surface decontaminated or placed into a closable container for transfer e.g. to an incubator or autoclave.
- Good microbiological techniques should always be used when working in a BSC.
- Keeping clean materials at least one foot away from aerosol-generating activities will minimize the potential for cross-contamination.
- Open flames are not required in the near microbe-free environment of a BSC. When deemed absolutely necessary, touch-plate microburners equipped with a pilot light to provide a flame on demand may be used. This will minimize the internal cabinet air disturbance and heat buildup. The burner must be turned off when work is completed. Small electric “furnaces” are available for decontaminating bacteriological loops and needles and are preferable to an open flame inside the BSC. Disposable sterile loops should be used whenever possible.
- Aspirator bottles or suction flasks should be connected to an overflow collection flask containing appropriate disinfectant, and to an in-line HEPA or equivalent filter to protect the vacuum system from aerosolized microorganisms.
- With the cabinet blower running, all containers and equipment should be surface decontaminated and removed from the cabinet when work is completed. At the end of the workday, the final surface decontamination of the cabinet should include a wipe-down of the work surface, the cabinet’s sides and back, and the interior of the glass.
- Investigators should remove their cloves and gowns in a manner that prevents contamination of unprotected skin and aerosol generation and wash their hands as the final step in safe microbiological practices.
- The operational integrity of a BSC must be validated before it is placed into service and after it has been repaired or relocated. Each BSC should be tested and certified at least annually to ensure continued, proper operation. Utilize a certified testing agency to perform periodic certification.
- Individuals using local exhaust ventilation systems should be trained on their proper use. This training should be coordinated by the individual designated by the institution as responsible for safety.
- Certification of the cabinet includes testing of the integrity of the exhaust HEPA filter.