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
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Asepsis Air Control (ICS) Seattle, WA
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Technical Safety Services Kirkland, WA
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Elliott Bay Laboratory Services, Inc. Seattle, WA
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ENV Services, Inc. Albuquerque, NM
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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
| BSC Class |
Face Velocity |
Airflow Pattern | Applications | |
| Nonvolatile Toxic Chemicals and Radionuclides |
Volatile Toxic Chemicals and Radionuclides |
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| 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 (minute amounts) |
NO |
| 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
- Fumehoods are inspected and certified on an annual basis by EH&S.
- Optimum certificaiton guideline: average face velocity = 100 FPM with sash at 18 inches above counter-top or airfoil.
- Minimum acceptable certification: average face velocity = 100 FPM with sash at 15 inches above counter-top or airfoil.
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.
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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.
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.
Last Update 01/04/2006
Fume Hood Design Guidelines
- OSU policy on local exhaust systems
- OSU's constrcution standards/design criteria contain a policy listing of several factors to consider when purchasing, installing, or upgrading fume hoods. These criteria address installing filters, stack height, acceptable flow rates, flow monitors, duct pressurization, and other topics. Some of those criteria:
- Ductless hoods are not to be used for protection against volatile chemical or radioactive materials.
- Filters are typically not installed within hood exhaust systems.
- Hood fans are placed external to the building whenever possible.
- Fume hood stacks will extend sixteen feet above any accessible working surfaces within 50 feet of the stack.
- Exhaust capacity of the system is designed for 120 fpm face velocity at 18 inch sash height for each hood.
- Fume hood exhaust is adjusted to 100 fpm average face velocity at 18 inch sash height for each hood.
- Vertical sashes are preferred over horizontal sliding sashes.
- Variable volume systems will typically be used in new construction.
- Electronic flow monitors with digital airflow readout and two-point real-time calibration will be installed on all new or upgraded hoods.
- Hood purchasess are limited to known manufactureres and models.
Last update 9/8/2010
Acceptable Hood Models
The following hoods have been shown through institutional experience and laboratory testing to be
- well constructed
- capable of providing good containment hof hazardous materials
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Supreme Air Kewaunee Scientific (available via VWR) |
Protector Xstream Labconco (available via VWR) |
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Safeaire II Thermo Scientific |
Protector XL Labconco (available via VWR) |
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Lyline Airguard Lyman Associates |
Last update 04/19/2010