work done on the basis of lab training. credits: Hema latha Muthu and Sindhuja Natarajan.

1. Biosafety levels
BSL 1:
 Practices safety equipment and facilities appropriate for
work with defined and characterized strains of viable
microbes not known to cause disease in healthy adult
humans.
 The laboratory is not necessarily separated from the
general building.
 Work is generally conducted on open bench tops using
standard microbiological practices.
 Special containments equipment or facility design is
neither required nor generally used.
 Laboratory personal should have specific training in
procedure conducted.
 Eating and drinking must be avoided.
 Organisms- E.coli, B.subtilis, Saccharomyces cerevisiae.
BSL 2:
• Practices, safety equipment and facilities appropriate for
work done with a broad spectrum of indigenous
moderate-risk agents present in the community and
associated with human disease in varying severity.
• Differs from BSL 1 in that:

2. a) Laboratory personal have specific training in handling
pathogenic agents and/or directed by competant scientist.
b) Access to the lab is limited when work is being
conducted.
c) Extreme precautions are taken with contaminated sharp
items.
d) Certain procedures in which infectious aerosols maybe
created are conducted in BSC.
e) Class I & II BSC are used.
f) Eg. HAV, HIV, HBV, HCV, pathogenic E.coli,
staphylococcus aureus, salmonella, P. falciparum and
Toxoplasma gondii.
BSL 3:
• Practices, safety equipment and facilities appropriate for
work done with indigenous or exotic agents with a
potential for respiratory transmission which may cause
serious and potentially lethal infection.
• More emphasis is placed on primary and secondary
barriers to protect personal in the contagious area, the
community, and the environment from exposure to
potentially infecious aerosols.
• A class I or class II BSC is required for work involving
these agents.
• Eg. M. tuberculosis, Francisella tularensis, Chlamydia
psittaci, Venezuelan equine encephalitis virus, SARS
corona virus, Coxiella burnetti, Ricketsia rickettsi.

3. BSL 4:
• Practices, safety equipment and facilities appropriate for
work done with dangerous and exotic agents which pose
a high risk of life threatening disease.
• Materials leaving the cabinet must be decontaminated
and the cabinet must also be disinfected.
• Workers must pass through a chemical shower.
• Entry is strictly restricted.
• The entrance is air locked.
• Eg. Viruses that cause viral haemorrhagic fever, lassa
virus, crimean-congo haemorrahagic fever. Pathogens
like hendra virus, nipoh virus, flavi virus, variola virus.

4. Biosafety cabinets
Biosafety cabinets are used as the primary means of
containment for working safely with infectious
microorganisms.
Biosafety cabinets are designed to prevent biological exposure
to personnel and the environment and may also protect
experimental material from being contaminated when
appropriate practices and procedures are followed.
Biological safety cabinets use high efficiency particulate air
(HEPA) filters in their exhaust and/or supply systems. These
filtered cabinets are primarily designed to protect against
exposure to particulates, including biological agents used in
the cabinet.
The Class I Biosafety Cabinet
Provides personnel and environmental protection, but no
product protection.
It has a negative pressure ventilated cabinet.
It has similar turbulent air flow as a chemical fume hood,
but has a HEPA filter in the exhaust system to provide
containment and environmental protection with front
opening.
This older class of biosafety cabinet is rarely seen in
MUSC's biomedical and microbiological laboratories.
Low and moderate risk agents can be handled using this
type.
All the air from the cabinet is exhausted through HEPA
filter into the lab or outside

5. The Class II Biosafety Cabinet
A1 type:
It is designed with inward air flow to provide protection
to the user, the experimental material and the
environment.
The Class II biological safety cabinet is the type most
commonly used in MUSC's biomedical and
microbiological laboratories.
It provides product, environmental and personal
protection.
The air is mostly filtered.
All the air from the cabinet is exhausted through HEPA
filter into the lab or outside
It has a positive pressured plenum
No toxic chemical is handled in this type.
70% of the air is recirculated and 30% of the air is
exhausted through HEPA filter.
A2 type:
It has both positive and negative pressured plenum. In
case of the air leaking out of positive pressured plenum,
it is trapped by negative pressured plenum.
70% of the air is recirculated and 30% of the air is
exhausted through HEPA filter.
Exhaust air is hard ducted.
B1 type:
30% of the air is recirculated and 70% of the air is
exhausted through HEPA filter.
Products of BSL 2 and 3 are used in this type.

6. The cabinet exhaust system is connected to the building
exhaust system and the air is ventilated out.
B2 type:
There is no recirculation in this type and so 100% of the
air is exhausted.
Radio nucleotides and toxic chemicals can be handled in
this type.
Exhaust hard ducted out.
Products of BSL 2 and 3 are used in this type.
The Class III Biosafety Cabinet
The Class III biological safety cabinet is most suitable
for work with biohazardous agents requiring high contain
(biosafety level 3 or 4).
The Class III cabinet is completely enclosed, HEPA
filter-ventilated cabinet fitted with glove ports and
decontamination capabilities for entry and exit of
material.
It offers the highest degree of personnel and
environmental protection from infectious aerosols.