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.