Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 76
Topic Requirement(s) Commentary
Biological
Safety
Cabinets and
Classifications
(Continued)
Some Class I models used for animal cage changing are designed to allow
recirculation of air into the room after HEPA filtration and may require more
frequent filter replacement due to filter loading and odor from organic materials
captured on the filter. This type of Class I BSC should be certified annually for
sufficient airflow and filter integrity.
CLASS II
As biomedical researchers began to use sterile animal tissue and cell culture
systems, particularly for the propagation of viruses, cabinets were needed that also
provided product protection. In the early 1960s, the “laminar flow” principle
evolved. Unidirectional air moving at a fixed velocity along parallel lines was
demonstrated to reduce turbulence resulting in predictable particle behavior.
Biocontainment technology also incorporated this laminar flow principle with the
use of the HEPA filter to aid in the capture and removal of airborne contaminants
from the air stream.
7 This combination of technologies serves to help protect the
laboratory worker from potentially infectious aerosols
4 generated within the cabinet
and provides necessary product protection, as well. Class II BSCs are partial
barrier systems that rely on the directional movement of air to provide containment.
As the air curtain is disrupted (e.g., movement of materials in and out of a cabinet,
rapid or sweeping movement of the arms) the potential for contaminant release into
the laboratory work environment is increased, as is the risk of product
contamination. The Class II (Types A1, A2, B1 and B2)
8 BSCs provide personnel,
environmental and product protection. Airflow is drawn into the front grille of the
cabinet, providing personnel protection. In addition, the downward flow of HEPA-
filtered air provides product protection by minimizing the chance of cross-
contamination across the work surface of the cabinet. Because cabinet exhaust air
is passed through a certified HEPA filter, it is particulate-free (environmental
protection), and may be recirculated to the laboratory (Type A1 and A2 BSCs) or
discharged from the building via a canopy or “thimble” connected to the building
exhaust. Exhaust air from Types B1 and B2 BSCs must be discharged directly to
the outdoors via a hard connection. HEPA filters are effective at trapping
particulates and thus infectious agents but do not capture volatile chemicals or
gases. Only Type A2-exhausted or Types B1and B2 BSCs exhausting to the
outside should be used when working with volatile, toxic chemicals, but amounts
must be limited. All Class II cabinets are designed for work involving
microorganisms assigned to biosafety levels 1, 2, 3 and 4.
1 Class II BSCs provide
the microbe-free work environment necessary for cell culture propagation and also
may be used for the formulation of nonvolatile antineoplastic or chemotherapeutic
drugs.
9 Class II BSCs may be used with organisms requiring BSL-4 containment in
a BSL-4 suit laboratory by a worker wearing a positive pressure protective suit.
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