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Biological Safety
Cabinets (BSC)
UTHSC-H
BSC Guidance Document
(pdf)
CDC/NIH
Primary Containment for biohazards (pdf)
Please call Biological Safety Program (x4193) for
contact information of local BSC certification companies.
Biological Safety Cabinets (BSC) are engineering controls
which when proper maintained and used offer excellent primary
containment when working with biological agents. There
are three general classes of BSCs (Class I, II, III) each with
there own intended uses and offering a greater level of security
for the environment, product and worker.
Class I - BSCs designated as Class I only provide biological
protection to the user and the environment. Since Class
I BSCs don't provide an adequate means of protection from cross
contamination for product. There is a growing trend
towards the elimination of the Class I BSC. Class I
BSCs operate at a minimum face velocity of 75 lfpm and filter
all exhaust air though a HEPA filter before it is reintroduced
into the laboratory or outside environment. A Class
I BSC is only suitable for low to moderate risk agents.
Class II- BSCs designated as Class II provide not only biological
protection to the user and environment, but also to the product,
creating a safe work environment for BSL 2 and 3 work when
a face velocity of 75-100 lfpm is maintained. All supply air
is filtered via a HEPA. This air is then used to create
a downward laminar air flow to insure product protection.
Within the Class II designation there are many system variations
and add-ons which can adapt a Class II BSC to accommodate specific
work needs.
Type |
Face velocity (lfpm) |
Airflow Pattern |
Radionuclides/ Toxic Chemicals |
Biosafety Level(s) |
Product Protection |
Class I* open front |
75 |
In at front; rear and top through HEPA
filter |
No |
2,3 |
No |
Class II
Type A1 |
75 |
70% recirculated through HEPA; exhaust
through HEPA |
No |
2,3 |
Yes |
Class II
Type A2 |
100 |
Same as IIA, but plena under negative pressure to
room and exhaust air is ducted |
Yes |
2,3 |
Yes |
Class II
Type B1 |
100 |
30% recirculated through HEPA; exhaust via HEPA and
hard ducted |
Yes (Low levels/volatility) |
2,3 |
Yes |
Class II
Type B2 |
100 |
No recirculation; total exhaust via HEPA and hard
ducted |
Yes |
2,3 |
Yes |
Class III |
NA |
Supply air inlets and exhaust through
2 HEPA filters |
Yes |
3,4 |
Yes |
Class III- BSCs designated as Class III offer the highest
level of security and protection to personnel and the environment.
A Class III BSC is a completely enclosed air tight chamber
suitable for BSL 3 and 4 work which completely eliminates the
possibilities for employee exposure to aerosols. Exhaust
air is double HEPA filtered or HEPA filtered and incinerated
before discharge and supply air only makes a single pass through
a HEPA. Class III BSCs must be connected to a double door incubator
or chemical dunk tank to sterile or disinfect all entering
and exiting items. All manipulation of items occurs through
the use of rubber gloves attached to the cabinet.
* Copyright of the CDC-NIH Biosafety in Microbiological and
Biomedical Laboratories, 4 th Ed. 5/99
While BSCs are designed to provide safe work environments
some work habits can greatly affect the security they provide.
Before entry into a BSC the blowers should be turned on and
allowed to run for approximately 5mins in order to allow the
proper pressures to build up. Personnel working within
BSCs should wear lab coats, with appropriate gloves that fit
over the cuffs of the coat. Stools should be adjusted
to a proper height and all materials needed should be gathered
(in order to eliminate the number if entries into the BSC)
and wiped down with 70% ethanol prior to entry. The
area within the BSC should be arranged into clean and contaminated
zones. All aerosol production equipment should be placed
in the rear and proper waste containers considered in the laying
out of the work area so that grilles are not blocked causing
disruptions to the air flow. When work is completed
all exiting materials should be disinfected alone with the
cabinet surface areas with an approved disinfectant.
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