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Biological Safety Cabinets
Biological safety cabinets (BSCs), often referred to as tissue
culture hoods, are the primary method of laboratory containment for
working with infectious microorganisms. When used appropriately and
in combination with good microbiological practices, they provide
worker, environmental and product protection.
The Centers for Disease Control and Prevention (CDC) and the
National Institutes of Health (NIH) have categorized three classes
of BSCs: Class I, II, and III - all which offer different degrees of
protection to handle the hazards imposed within each biosafety
level. One of the main components of each class is one or more high
efficiency particulate air (HEPA) filters, which removes microscopic
contaminants equal to and greater than 0.3 μm with an efficiency of
99.97%.
Class II Biological Safety Cabinets are the most commonly used
BSCs. Their open front design with inward airflow protects the
researcher; downward, laminar HEPA filtration protects the product;
and HEPA filtered exhaust protects the environment.
The subtypes typically found in Vanderbilt research laboratories
include:
- Class II A1 - recirculates 70% of the HEPA-filtered
air back into the laboratory and should never be used for work
involving volatiles or radio-nucleotides. Airflow is a minimum
of 75 lfpm.
- Class II A2 - also recirculates 70% of the HEPA-filtered air
but can be ducted or unducted back into the cabinet. For minimal
use with toxic chemicals, it can be operated safely. Airflow is
100 lfpm.
- Class II B - is designed for use with BSL2 or BSL3 agents
and minute quantities of volatile chemicals. Airflow is 100 lfpm
and 70% of air is HEPA-filtered to the outdoors while 30% is
HEPA-filtered and recirculated back into the cabinet. For
maximum performance, experiments should be conducted as
centrally located into the cabinet as possible.
Proper use of a Class II Biological Safety Cabinet
- The cabinet should be certified yearly to ensure
proper function (Contact VEHS for names of accredited field
certifiers).
- If not already running, turn on the blowers in the cabinet
and let them run for 15 minutes before starting work.
- Wear appropriate personal protective equipment (typically
gloves and buttoned lab coat) while working at the cabinet.
- After loading the cabinet with your research materials, let
the blowers circulate the air for at least 5 minutes to remove
contaminants that could be on the outside of the materials.
- When first placing hands and arms into cabinet, pause
briefly so that airflow can stabilize.
- Limit movements into and out of the cabinet to reduce the
possibility of bringing-in or letting-out contaminants.
- Avoid blocking airflow slots, or grills, with research
materials such as pipette aids, biowaste bags, flasks, etc.
- Keep all materials at least four inches inside the sash
opening. This will provide the most product protection.
- Conduct research in a ‘clean to dirty’ (left to right) work
pattern.
- Keep head out of the work area.
- Do not use an open flame in the cabinet as it disrupts
airflow and could damage the HEPA filter.
- The use of UV lights in BSCs is not recommended by safety
professionals due to their limited effectiveness and potential
harm to those exposed.
- Clean and decontaminate all visible surfaces and front sash
before and after each use. A disinfectant more stringent than
70% ethanol is necessary if conducting research with human cell
lines, viral vectors, and other pathogenic microorganisms.
- Chemical fume hoods and clean air benches are NOT the same
as a BSC, and they should not be used as a substitute for a BSC!
Neither should a non-ducted BSC be used with large quantities of
volatile chemicals.
For more detailed information on BSCs and their application,
please refer to the following texts:
Appendix A. Biosafety for Microbiological and Biomedical
Laboratories, 5th edition. U.S. Department of Health and Human
Services, Public Health Service, Centers for Disease Control and
Prevention, and National Institutes of Health, February 2007.
Fleming, D.O. and D.L. Hunt. 2006. Biological Safety: principles
and practices. 4th edition. ASM Press: pgs.303-323.
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