Application Note – Microbiology N.4 – Biological Safety Cabinet Selection
Selecting a Biological Safety Cabinet, it is first of all important to understand the basic difference between a fume hood, an unidirectional (laminar) flow cabinet and a Biological Safety Cabinet.
The “fume hood” is designed to duct corrosive chemicals outside the building but it is not equipped with HEPA filters; therefore the microbiological agents inside a fume hood will be ducted outside, contaminating the environment.
The “unidirectional flow cabinet” provides only product protection by blowing clean sterile air across the work area inside the cabinet toward the operator. Therefore the microbiological agents present in the work area will invest the operator’s body.
The “Biological Safety Cabinet” is designed to protect the operator, the product, the environment by HEPA filtering the inlet and outlet air. The microbiological agents are always contained inside the cabinet.
Biosafety Levels
The “Biological Safety Cabinet” should be selected according to the degree of lethality and medium of transmission of the microbiological agents that are classified under four categories of Biosafety Level (“BSL”).
| LEVEL | DANGER | MEDIUM | TYPE OF AGENT |
| 1 | Safe | Liquid | Bacillus subtilis |
| 2 | Partially Safe | Liquid | HIV |
| 3 | Serious | Bioaerosol | TBC |
| 4 | Extreme serious | Bioerosol | EBOLA |
Biological Safety Cabinet Classification
The BSC are classified in three different classes:
“Class I Biological Safety Cabinet” has inflow that protects the operator, but not the product because the outside air will contact the sample inside the work area. This BSC is therefore not very popular in the microbiological laboratory.
“Class II Biological Safety Cabinet” has inflow to protect the operator, downflow HEPA filter to protect the product in the work area, HEPA filter to filter the exhaust.
“Class III Biological Safety Cabinet” has a completely closed front. The analytical manipulations are performed through integrated gloves. The BSC is hermetically sealed and the material is introduced and taken away from the work area thru a double-door pass box. The product is protected by a stream of HEPA filtered air. The work area is under negative pressure and the air is exhausted passing a HEPA filter. This BSC is indicated for Biosafety Level 4 micro-organisms.
Cytotoxic Safety Cabinet
The Cytotoxic Safety Cabinet (CSC) is required for chemotherapy drug preparation. Such CSC has a third HEPA filter to protect not only the operator during the normal daily activity, but also the servicing people during the exhausted HEPA filter replacement. In fact the cytotoxic drugs are very toxic and cannot be neutralized by formaldehyde or hydrogen peroxide decontamination.
Biosafety Cabinet Certification
The BSCs should be certified by an independent international agency according to standard like NSF 49:2002 or EN 12469:2000 to guarantee their performances.
The requested standard include 3 different tests:
(a) Operator protection
Bacteria are sprayed behind the front window and they should escape through the front opening.
(b) Product protection
Bacteria are sprayed in front of the window and they should not reach the work area.
(c) Absence of Cross contamination
Bacteria are sprayed inside the BSC at one side of the work area and they should not reach the adjacent area, 20 cm apart.
