Class I – provides personnel and environmental protection but not product protection. Personnel protection is provided as a minimum velocity of 75 lfpm (0.38 m/s) of unfiltered room air is drawn through the front opening and across the work surface. The environmental protection is provided once air is then passed through a HEPA/ULPA (High Efficiency Particulate Air/Ultra Low Penetrating Air) filter in the exhaust plenum.
Class II – contains partial barrier systems that rely on the movement of air to provide personnel, environmental, and product protection. In these biosafety cabinets, the combination of inward and downward airflow captured by the front grille of the cabinet grants their level of protection.
Class III – designed for work with highly infectious microbiological agents and other hazardous operations. Being a gas-tight pressure water enclosure with a viewing window that remains secured with locks or requires the use of tools to open, with passage of materials into the cabinet only being conducted through certain means (such as a double-door pass-through box that can be decontaminated between uses), Class III BSCs provide maximum protection for the environment and the worker. Both supply and exhaust air are HEPA/ULPA filtered.
Class II biosafety cabinets can be further designated into types. According to NSF/ANSI 49-2016 - Biosafety Cabinetry: Design, Construction, Performance and Field Certification, these are:
Type A1 Cabinets (formerly Type A) - maintain minimum average inflow velocity of 75 ft/min (0.38 m/s) through the work access opening, have HEPA/ULPA filtered downflow air, may exhaust filtered air back into the environment through an external exhaust system, and have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums.
Type A2 Cabinets (formerly Type B3) - maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the work access opening, and have HEPA/ULPA filtration and plenum pressure conditions identical to those of Type A1 cabinets.
Type B1 Cabinets – have a minimum average inflow velocity of 100 ft/min (0.51 m/s), have HEPA/ULPA filtered downflow air, exhaust contaminated downflow air to an external exhaust system with a direct connection and exhausted to the atmosphere, and recirculate the balance of the downflow and inflow air through a supply HEPA/ULPA filter(s).
Type B2 Cabinets – maintain the same minimum average inflow velocity as B1, have HEPA/ULPA filtered downflow air drawn from the laboratory or the outside air, exhaust all inflow and downflow air to the atmosphere through an external exhaust system connected to the cabinet, and have all contaminated ducts and plenums under negative pressure or surrounded by directly exhausted (nonrecirculated through the work area) negative pressure ducts and plenums.
Type C1 Cabinets – maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s), HEPA/ULPA filtered downflow air is composed largely of recirculated inflow air, exhaust contaminated downflow air via an internal dedicated exhaust plenum and blower and then through HEPA/ULPA filter(s), recirculate the balance of the downflow and inflow air through a supply HEPA/ULPA filter(s), have all biologically contaminated ducts and plenums under negative, and may exhaust HEPA/ULPA filtered air back into the laboratory.
In general, biosafety cabinetry, of any class or, with Class II cabinets, type, may be designed for use with activities involving infectious microorganisms within the different biosafety levels. These vary in severity as the numbers increase, with biosafety level 1 being suitable for work involving well-characterized agents not known to consistently cause disease and present minimal potential hazard to laboratory personnel and the environment, and level 4 being assigned to work with agents that pose a high risk of life-threatening disease, aerosol transmission, or related agent with unknown risk of transmission.
All Class II cabinets are designed for work involving procedures assigned to biosafety levels 1, 2 and 3. However, class II BSCs may be used with procedures requiring BSL-4 containment if used in a BSL-4 suit laboratory by a worker wearing a positive pressure protective suit.
NSF/ANSI 49-2016 covers basic guidelines for the design, construction, and performance of biosafety cabinets that are used for protecting personnel, products, and the surrounding environment, as well as providing reliable operation, durability and structural stability, cleanability, limitations on noise level, illumination, vibration, and motor/blower performance.
These different qualities are assured by meeting the testing procedures defined in NSF/ANSI 49-2016. The standard applies to Class II BSCs, Type A1, A2, B1, B2, and C1, which can work with agents assigned to biosafety levels 1, 2, 3, and 4.
NSF/ANSI 49-2016 - Biosafety Cabinetry: Design, Construction, Performance and Field Certification is available on the ANSI Webstore.