Figure 16-7
Left: The horizontal laminar flow “clean bench” (A) front opening; (B) supply grille; (C) supply HEPA filter; (D) supply plenum; (E) blower.
Right: The vertical laminar flow “clean bench” (A) front opening; (B) sash; (C) supply HEPA filter; (D) blower. Note: Some vertical flow clean benches have recirculated air through front and/or rear perforated grilles.

Horizontal and vertical laminar flow clean benches are sometimes mistaken for biological safety cabinets. Clean benches provide product protection but no personnel protection. The horizontal flow clean bench discharges HEPA filtered air across the work surface onto the operator. The less common vertical flow clean bench discharges air downward from a HEPA filter above the work surface. The airflow leaves the work area through the front opening where the operator is located. With both versions of the clean bench, work performed on the work surface could expose the operator to contaminants. Researchers often use clean benches for assembly of sterile apparatus. Do not use clean benches for handling cell cultures, drug formulations, radionuclides, biological hazards, or chemicals. Exposure to some of these materials from manipulation on a clean bench can cause hypersensitivity. Clean benches are to be posted with a label from the EHS Safety Labels webpage or similar.

Table 16-1. Comparison of Biological Safety Cabinet Characteristics and Applications

Class,
Type
Work
Opening
Inflow
Velocity
(fpm)
%
Recirc.
Air
%
Exhausted
Air
Exhaust
Vol. (cfm)
(approx.)
Exhaust
Req.
Application
Class I Fixed 75 0% 100% 4 ft – 200
6 ft – 300
Exhausted to the outside (remote fan) or to the room through a HEPA filter (integral fan) Biosafety Level 1-3; small amounts of toxic chemicals or radionuclides (if exhausted to outside)
Class II,
type A1
fixed, sliding, or hinged 75-100 70% 30% 4 ft – 300
6 ft – 400
Exhausted to room through HEPA filter or to the environment through an exhaust canopy Biosafety Level 1-3
Class II,
type B1
Sliding 100 30% 70% 4 ft – 250
6 ft – 400
Exhausted to outside, with remote fan; duct is hard connected Biosafety Level 1-3; small amounts of toxic chemicals or radionuclides
Class II,
type B2
sliding,
hinged
100 0% 100% 4 ft – 600
6 ft – 1000
Exhausted to outside, with remote fan; duct is hard connected Biosafety Level 1-3; small amounts of toxic chemicals or radionuclides
Class II,
type A2
sliding,
hinged
100 70% 30% 4 ft – 300
6 ft – 400
Exhausted to room through HEPA filter or exhausted to outside, with remote fan, utilizing canopy connection Biosafety Level 1-3; small amounts of toxic chemicals or radionuclides
Class III Glove ports N/A 0% 100% a Exhausted to outside, through 2 HEPA filters, with remote fan; duct is hard connected Biosafety Level 1-4; small amounts of toxic chemicals or radionuclides

a Class III cabinets should have approximately 20 air changes per hour or enough ventilation to accommodate the heat load. The cabinet must maintain a negative pressure of 0.5 in. w.g. and should maintain 100 fpm through a glove port, if a glove is accidentally removed.