The biological safety cabinet (BSC) is a high-use primary containment device found in microbiology, tissue culture, and toxicology laboratories, among others. Biological safety cabinets employ unidirectional, steady airflow along parallel lines (laminar airflow) and strategically placed high-efficiency particulate air (HEPA) filters to provide varying degrees of protection to the worker, laboratory environment, and material being manipulated (product) in the cabinet.
Engineered for safety and durability, BSCs have become laboratory workhorses. Modern-day BSCs that were manufactured to initial standards of the National Institutes of Health and the National Sanitation Foundation (now called NSF International) have been in use since the early 1970s. Those manufactured from the 1970s to the early 1990s may have been in use for well over 15 years, considered to be the useable lifetime of a BSC. In 1992, the Revision of the NSF Standard 49 became a major driver for the development of improvements in containment performance (safety). Concurrently, manufacturers also improved the ergonomics and energy efficiency of BSCs.
If you are considering the purchase of a BSC for the first time or thinking about replacing your old workhorse, here are some considerations for selecting your new cabinet and for deciding to retire your old one.
The different classes and subtypes of BSCs accommodate specific protection requirements. You need to determine the primary function of the cabinet. Do you need it for sterility, biosafety, or both? If you are working with a microorganism, what is its risk level? Will you also be working with volatile hazardous chemicals or radioactivity? Publications such as the Biosafety in Microbiological and Biomedical Laboratories (BMBL), 5th edition, developed by the U.S. Department of Health and Human Services (HHS), Public Health Service (USPHS), Centers for Disease Control and Prevention (CDC)*, as well as the National Institutes of Health (NIH) are available to help with your decision. In addition, your institution’s safety professional should be consulted.
- HEPA Filters: The control of airborne particles is made possible with HEPA filters. Particles are generated and become airborne with everyday human activity. Bacteria, spores, and viruses are removed from the air by HEPA filters by not allowing penetrating particles of 0.3 μm with a minimum efficiency of 99.97%. It must be noted that the purpose of HEPA filters is to create a sterile environment and/or protect the end user and environment; they do not filter out gases, vapors, or odors.
- Biosafety Cabinet Class: There are three classes of BSCs. Briefly, a Class I BSC uses inflowing air to protect the worker and the environment; but not the product. Unfiltered room air is drawn through the front access opening and is HEPA-filtered at the top of the work zone before entering the exhaust system. The air can be exhausted via hard ducting to the building’s exhaust system or recirculated, depending on the work performed. Class II BSCs feature HEPA filters for both intake and exhaust air to protect the worker, environment, and product. These cabinets were reclassified into four subtypes (A1, A2, B1, and B2) by the NSF in 2002. The classifications are generally based on the amounts of air recirculated and exhausted and how the air is exhausted. The B2 cabinet is a total exhaust cabinet. All Class II BSCs, regardless of the speed of airflow through the front access opening and amount of air recirculated, provide the same degree of protection to the worker and product. Therefore, the selection of cabinet is based on the amount and flammability of volatiles used in your procedures. Some manufacturers offer specific B2 cabinets for the use of dangerous substances. The Class III biosafety cabinet provides maximum protection from high-risk organisms for the worker and environment. It is a gas-tight enclosure that uses HEPA filtration for both the supply and exhaust air. The exhaust air undergoes additional filtration or incineration before discharge to the environment.
- Microorganism: The American Biological Safety Association (ABSA) maintains a database** that provides risk levels for infectious agents. You can write in the genus/species of your organism(s) and the risk level will be provided. You can also find risk-classification criteria specified by the World Health Organization and by various countries. Criteria are also available for recombinant DNA molecules. Note that risk levels do not always have one-to-one correlation with biological safety levels (BSLs). A large volume or high concentration of an organism may need a higher BSL than its risk level would indicate.
Look for a cabinet with a blower/motor system that compensates for normal HEPA filter loading and with alarms for unacceptable changes in airflows. Other safety features include positive-pressure chambers and ducts surrounded by a vacuum or negative pressure relative to the room, larger HEPA filters, prevention of uneven particulate loading over filter surfaces, and single-piece stainless steel construction.
- Performance Requirements (Envelope Testing): The NSF 1992 performance standards challenge a BSC over a range of airflow setpoints. Since various laboratory conditions—including room size, traffic, location, and airflow—can greatly affect the cabinet, a BSC that complies with the 1992 standards can maintain maximum containment throughout a range of real-world conditions.
Ergonomics and Energy Efficiency
Users can spend hours working at the BSC, which can be very tiring. Improved knee/thigh clearance allows better posture. An adjustable base stand with plastic armrest permits better leg and forearm support. Wider work access while maintaining optimal airflow provides forearm comfort and excellent containment. A frameless, polished-edge window allows greater visibility, and improved, energy-efficient fluorescent lighting reduces glare in the work zone. And most important, greatly improved direct-current motors consume 50% less energy and are much quieter with fewer vibrations. In addition, reduced flow modes automatically initiated by window closure reduce energy consumption.
Your BSC must be located a specified distance from lab doors, operable windows, supply diffusers, and other sources of air movement. Manufacturers provide different sizes of cabinets to accommodate space constraints and applications.
When to Replace Your Biological Safety Cabinet
No-brainers for BSC replacement include need for extensive service, repeated failure of the annual exam, and corrosion outside the cabinet or rust on the plenums inside the cabinet. Also keep in mind that older BSCs will become obsolete as replacement parts become unavailable.