Appendix B: Laboratory Ventilation and Containment for Biosafety

Last updated on June 29, 2016 6 min read Biosafety Manual - Appendix B: Laboratory Ventilation and Containment for Biosafety

Laboratory-ventilated containment equipment fall into three (3) major categories:

Laboratory Chemical (Fume) Hoods

Traditional laboratory chemical (or fume) hoods are designed to capture and control chemical vapors and pull them away from the worker. Although the inward flow of air protects the user, chemical hoods do not protect the product (the desired organism being manipulated).

Other Local Exhaust Ventilation (LEV) Systems

Horizontal Laminar Flow Clean Bench

With horizontal laminar flow clean benches, HEPA-filtered air flows horizontally across the workspace directly toward the user. These clean benches provide product protection and were originally designed to provide a particulate-free environment for the manufacture of semiconductor components.

Clean benches provide product protection against microbial contamination, but they do not provide personal or environmental protection. In fact, the horizontal flow of air will blow biological agents directly toward the user and into the laboratory. Clean benches are not a biological safety cabinet, and they should not be used with any materials (biological, chemical, or radiological) requiring containment for protection of personnel or the environment.

Clean benches are acceptable for use with materials that do not present risks to the laboratory workers (including immunocompromised individuals who may frequent the lab). Human cell lines and nonhuman primate cell lines are generally considered to be BSL2 agents and would not be suitable for use in a clean bench.

Biological Safety Cabinets

Biological safety cabinets (BSCs) are divided into Class I, II, and III (see schematic below). Class II BSCs are subdivided into type A and type B. All BSCs provide personnel and environmental protection, with Class II BSCs also providing product protection.

Personnel protection is achieved by inward airflow through the front of the cabinet.
Product protection is achieved by downward HEPA-filtered airflow from the top of the cabinet.
Environmental protection is achieved by HEPA filtration of exhaust air.

New NSF Classification (Adopted 2002)	Previous NSF Classification	General Description
A1	Class II, 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 that is a portion of the mixed downflow and inflow air from a common plenum (i.e., a plenum from which a portion of the air is exhausted from the cabinet and the remainder supplied to the total work area; may exhaust HEPA/ULPA filtered air back into the laboratory or to the environment through an external exhaust system connected to the cabinet with a canopy connection; and have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums. If using chemicals with toxic vapors, the unit shall be connected to an external exhaust system. Type A1 cabinets may be used for work with volatile chemicals if deemed appropriate by a chemical risk assessment NOTE — Type A1 BSCs manufactured prior to 2010 are not suitable for work with volatile chemicals due to the contaminated positive pressured plenums that are not surrounded by negative pressure plenums.
A2	Class II, Type (formally Class II A/B3) When exhausted to the environment were formally designated Type B3	Maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the work access opening; have HEPA/ULPA filtered downflow air that is a portion of the mixed downflow and inflow air from a common exhaust plenum; may exhaust HEPA/ULPA filtered air back into the laboratory or to the environment through an external exhaust system connected to the cabinet with a canopy connection; and have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums. If using chemicals with toxic vapors, the unit shall be connected to an external exhaust system. Type A2 cabinets may be used for work with volatile chemicals if deemed appropriate by a chemical risk assessment.
B1	Class II, Type B1 3	Maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the work access opening; have HEPA/ULPA filtered downflow air composed largely of uncontaminated recirculated inflow air; exhaust contaminated downflow air from a region of the total work area via an internal dedicated exhaust plenum and through HEPA/ULPA filter(s) to a dedicated external exhaust system for BSCs with a direct connection and exhausted to the atmosphere; recirculate the balance of the downflow and inflow air through a supply HEPA/ULPA filter(s); and have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums. Type B1 cabinets may be used for work with volatile chemicals if permitted by a chemical risk assessment
B2	Class II, Type B2	Maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the work access opening; have HEPA/ULPA filtered downflow air drawn from the laboratory or the outside air (i.e., downflow air is not recirculated from the cabinet exhaust air); exhaust all inflow and downflow air to the atmosphere through a dedicated external exhaust system for BSCs connected to the cabinet with a direct connection after filtration through a HEPA/ULPA filter without recirculation in the cabinet or return to the laboratory; and have all contaminated ducts and plenums under negative pressure or surrounded by directly exhausted (non-recirculated through the total work area) negative pressure ducts and plenums. Type B2 cabinets may be used for work with volatile chemicals if permitted by a chemical risk assessment
C1	Class II, Type C1	Maintain a minimum average inflow velocity of 100 ft/min (0.51 m/s) through the work access opening; have HEPA/ULPA filtered down-flow air composed largely of uncontaminated recirculated inflow air; exhaust contaminated down-flow air from a region of the total work area via an internal dedicated exhaust plenum and blower, and then through HEPA/ULPA filter(s); recirculate the balance of the down-flow and inflow air through a supply HEPA/ULPA filter(s); have all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums; and may exhaust HEPA/ULPA filtered air either back into the laboratory or via a canopy connection to an external system that exhausts to the atmosphere. If working with volatile chemicals, the unit must be connected to an external exhaust system. Type C1 cabinets may be used for work with volatile chemicals if permitted by a chemical risk assessment.

Certification of BSCs

Generally, BSCs are tested by the cabinet manufacturer in accordance with National Sanitation Foundation (NSF) criteria. Cabinets that meet the NSF 49 criteria for performance characteristics, including biological containment, ventilation, cabinet leakage, and HEPA filter leakage, are NSF certified.

Field certification of BSCs is also required to ensure that the cabinet still performs as it did when it obtained NSF certification at the factory. NIH requires field certification under the following circumstances:

upon installation of a new BSC;
annually thereafter;
after repair or maintenance is performed;
and after the BSC is moved and relocated.

CDC recommends that BSCs be recertified annually to ensure for proper function. They will also be recertified after being moved to ensure that they have not been damaged. Laboratories are responsible for ensuring that the BSCs are recertified in a timely manner. Laboratories at CRC will contact EHS at (617) 353-4094. Laboratories at BUMC will contact the certification contractor directly. The contact information to reach the contractor is indicated on the certification sticker affixed on the front of the BSC.

NSF standard 49 provides criteria for construction of BSCs, testing by manufacturers (including biological containment testing), and field certification. NSF has also established a certification program for field certifiers to ensure a minimum level of competency and professionalism. It is recommended that NSF field certifiers be used for field certification of BSCs. Field certification tests include:

Primary tests (BSC performance)

Inflow test
Down-flow test
Smoke pattern test
HEPA filter leakage
Cabinet leakage (when BSC is newly installed, relocated, or maintenance has been performed that involved removal of access panels)