Local Ventilation Systems Guide

BioSafety Cabinets

Fume Hoods

Biosafety Cabinet Certification

Owner Requirements

Departments that have biosafety cabinets (BSCs) are responsible for assuring they are calibrated for their intended use. EH&S does not currently perform calibrations. Firms that service BSCs in the Willamette Valley are listed below.

Micro Technology, Inc.   Lake Oswego, OR 
  • Website: None  
  • Phone: 800-356-5999  
  • Fax: 503-635-9164

Asepsis Air Control (ICS)   Seattle, WA  

  • Website: None  
  • Phone: 206-782-5655  
  • Fax: 206-789-7606

Technical Safety Services   Kirkland, WA  

Elliott Bay Laboratory Services, Inc.   Seattle, WA  

ENV Services, Inc.   Albuquerque, NM  

Last update 4/19/2010

Biosafety Cabinet types

BioSafety Cabinet - Class I

Select a Class I BSC when only personnel  protection against particulate materials is required.

Similar in operation to a conventional fume hood. A ventilated cabinet for personnel and environmental protection, having an un-recirculated inward airflow away from the operator that exhausts all air to the atmosphere after filtration through a HEPA filter. Class I cabinets are suitable for work where no product protection is required. It WILL NOT protect users against exposures to gases or vapors.


A. front opening
B. sash
C. exhaust HEPA
D. exhaust plenum

BioSafety Cabinet  - Class II

Select a Class II BSC when both product and personnel protection are required.

Class II Biological Safety Cabinets, regardless of type (i.e. Types: A2, B1, or B2) provide the same level of product and personnel protection from a biological point of view. The National Sanitation Foundation's Listing Program for compliance to NSF Std. No. 49* has subjected each type to the exactly the same testing procedures and exactly the same pass/fail criteria for all Class II cabinets.

What is the difference between the types of biological safety cabinets that affect selection? It is the amount of air that is recirculated within the cabinet.

Studies to determine the dilution within the Class II cabinet of highly volatile liquids have been conducted by the NSF Advisory Committee. Those studies indicated that the total quantity of volatiles designated as flammable which are used in a type A2 cabinet be limited to 25 ml or less. For Type B1 cabinets slightly more is permitted, if the work is carried out in the dedicated exhaust portion (i.e. rear) of the work surface. For the Type B2 total exhaust cabinet, even though there is total exhaust, quantities of volatiles must be limited due to the potential of electrical spark ignition within the cabinet's work zone.

Former Class II, type A/B3 designation has been reclassified to Class II, type A2









BioSafety Cabinet  - Class III

Select a Class III biological safety cabinet when both personnel and product protection are required, and the risk of injury to personnel is imminent with the product at hand.

A totally enclosed, ventilated cabinet of leak-tight construction. Operations in the cabinet are conducted through attached rubber gloves. The cabinet is maintained under negative air pressure of at least 0.50 in w.g. (120 Pa). Downflow air is drawn into the cabinet through HEPA filters. The exhaust air is treated by HEPA filtration or by HEPA filtration and incineration. This cabinet provides the highest level of personal protection of all the BSC’s.

Connection to building exhaust system required.


A. glove ports with O-ring for attaching arm-length gloves to cabinet
B. sash
C. exhaust HEPA filter
D. supply HEPA filter
E. double-ended autoclave or pass-through box

Note: A chemical dunk tank may be installed which would be located beneath the work surface of the BSC with access from above. The cabinet exhaust needs to be connected to the building exhaust system.


Last update 4/19/2010

Biosafety Cabinet Comparison

Comparison of Biosafety Cabinet Characteristics

Airflow Pattern Applications
Nonvolatile Toxic
Chemicals and
Volatile Toxic
Chemicals and
I 75 In at front; exhausted through HEPA to the outside or into the room through HEPA. YES When exhausted outdoors (1,2)
II, A1 75 70% recirculated to the cabinet work area through HEPA; 30% balance can be exhausted through HEPA back into the room or to outside through a canopy unit Yes
II, B1 100 30% recirculated, 70% exhausted. Exhaust cabinet air must pass through a dedicated duct to the outside through a HEPA filter YES Yes
(minute amounts) (1,2)
I, B2 100 No recirculation; total exhaust to the outside through a HEPA filter YES Yes
(small amounts) (1,2)
II, A2
100 Similar to II, A1, but has 100 Ifm intake air velocity and plenums are under negative pressure to room; exhaust air can be ducted to the outside through a canopy unit. FORMERLY “B3”
YES When exhausted outdoors (minute amounts) (1,2)
III N/A Supply air is HELP filtered. Exhaust air passes through two HEPA filters in series and is exhausted to the outside via a hard connection YES Yes
(small amounts) (1,2)

(1) Installation requireS a special duct to the outside, an in-line charcoal filter, and a spark proof (explosion proof) motor and other electrical components in the cabinet. Discharge of a Class I or Class II, Type A2 cabinet into a room should not occur if volatile chemicals are used.

(2) In no circumstances should the chemical concentration approach the lower explosion limits of the compound.


Last update 4/19/2010

Fume Hood Certification

Last update 4/19/2010

Fume Hood Types

Standard Fume Hood

A standard fume hood is a constant air volume (CAV) hood, an older, traditionally less elaborate hood design used for general protection of the worker. Because the amount of exhausted air is constant, the face velocity of a CAV hood is inversely proportional to the sash height. That is, the lower the sash, the higher the face velocity. CAV hoods can be installed with or without a bypass provision which is an additional opening for air supply into the hood.

Standard Hood
standard hood

Bypass Fume Hood

The bypass fume hood is an improved variation on the conventional fume hood. The bypass is located above the sash face opening and protected by a grille which helps to direct air flow. The bypass is intended to address the varying face velocities that create air turbulence leading to air spillage. The bypass limits the increase in face velocity as the sash nears the fully closed position, maintaining a relatively constant volume of exhaust air regardless of sash position.

bypass hood

Auxiliary Air Hood

This fume hood, sometimes referred to as a makeup air fume hood, was developed as a variation on the bypass fume hood and reduces the amount of conditioned room air that is consumed. The auxiliary fume hood is a bypass hood with the addition of directly ducted auxiliary air to provide unconditioned or partially conditioned outside makeup air. Auxiliary air hoods were designed to save heating and cooling energy costs, but increase the mechanical and operational costs due to the additional ductwork, fans, and air tempering facilities. Unless the volume (and therefore velocity) of auxiliary air is carefully adjusted, the air curtain created will affect the hood operation and may pull vapors out of the hood interior. Installation of this type of hood is not permitted at OSU since the disadvantages outweigh the benefits.

Aux Air hood

Last Update 01/04/2006

Fume Hood Design Guidelines

Last update 9/8/2010

Acceptable Hood Models

The following hoods have been shown through institutional experience and laboratory testing to be

Supreme Air

Kewaunee Scientific (available via VWR)
Kirkland, WA
Sales: (425) 823-8070
Fax: (425) 821-7140
Web link

Protector Xstream

Labconco (available via VWR)
Kansas City, Missouri
Sales: (800) 522-7658
Web link

Safeaire II

Hamilton Scientific
De Pere, WI
Sales: 920.793.1121
Web link

Protector XL

Labconco (available via VWR)
Kansas City, Missouri
Sales: (800) 522-7658
Web link

Lyline Airguard

Lyman Associates
Kent, WA
(253) 639-3350
Web link
Now made by Mott Manufacturing

Last update 12/23/2014