What's the difference between a fume hood and a biosafety cabinet?
Fume hoods are ventilated enclosures that remove hazardous chemical fumes and volatile vapors from the laboratory, providing personnel protection only. Biological safety cabinets (or biosafety cabinets) utilize HEPA filters to provide environmental, personnel and/or product protection.
They can recirculate or exhaust filtered air, depending on your application, and are suitable for work with hazardous particulates like bacteria and viruses.
Although they're both sometimes referred to as "hoods," biosafety cabinets and fume hoods are two entirely different categories of laboratory equipment. Both are built to safely handle the hazards of the science for which they're particularly designed, but they differ in terms of the precise type(s) of protection provided, airflow and suitable applications.
If tasked with selecting a "hood" for a laboratory, below are some common points for consideration.
Note that improper selection or use of equipment can yield significant consequences for health and safety, so always consult your safety officer for recommendations based on your specific application.
Knowing what type of protection you will require is the first step in selecting the proper laboratory enclosure. Biosafety cabinets provide environmental, personnel and product protection, while fume hoods provide only personnel protection.
Fume hood airflow
Because fume hoods handle hazardous chemicals (see Applications below), air is drawn away from the laboratory worker beginning at the face of the equipment, across the work surface and through ductwork where it is diluted and released into the atmosphere.
Proper and undisrupted airflow is critical within a fume hood; do not store large equipment inside the hood or do anything that could otherwise disrupt the movement of air within the unit. To maintain a safe and efficient work environment, never put your head inside the hood and keep the sash closed as much as possible.
Biosafety cabinet airflow
The three classes of biosafety cabinets (see Variations below) all have one feature in common: HEPA filtration.
In a Class I biosafety cabinet, air is drawn away from the laboratory worker and across the work surface.
In a Class II biosafety cabinet, intake air is drawn safely around the operator, sterile air flows downward onto the work surface and exhaust air is HEPA filtered before it is either recirculated into the laboratory or released into the atmosphere through ductwork or a canopy connection.
Class III biosafety cabinets are gas-tight enclosures, with both intake air and exhaust air passing through HEPA filtration.
Fume hoods: Chemical fume hoods can be used to handle the following: odorous materials, toxic gases, reactive materials, chemicals that can spatter, aerosols, carcinogens, flammables or other toxic and volatile materials.
Biosafety cabinets: Biosafety cabinets provide a safe environment for research involving infectious microorganisms or other hazardous particulates. Depending on the type of cabinet (see below), these enclosures are suitable for use with agents requiring containment in conjunction with Biosafety Level (BSL) 1, 2 or 3. (Note that Class III cabinets can accommodate BSL 4 agents. Class II cabinets can accommodate BSL 4 applications with proper personnel protective equipment.)
Fume hoods: By-pass chemical fume hoods are the most common type, operating at a constant air volume. Auxiliary-air, reduced air volume and high performance fume hoods all fall under the by-pass chemical fume hood umbrella. High performance hoods operating on a variable air volume (VAV) system are the most efficient. Hoods exist for special circumstances as well, such as those particularly suited to handle perchloric acid (constructed of acid resistant materials) and radioactive applications (constructed with extra decontamination features and often require filters in ductwork).
Biosafety cabinets: Class I biosafety cabinets have an open front, operate under negative pressure and do not provide product protection. The most common types of biosafety cabinets, Class II, fall under two main categories—Type A or Type B. Class II, Type A cabinets recirculate air back into the laboratory unless they are canopy connected to the outside as required by the application (work with odorous materials). Class II, Type A1 and A2 cabinets are similar yet separated by the minimum average inflow velocity (fpm) required, and neither type can handle work involving radionuclides or volatile chemicals.
Class II, Type B cabinets, on the other hand, are hard ducted to laboratory exteriors and are suitable for work with only tracer amounts of these more harmful substances if required by the microbiological studies being performed in the interior of the equipment. Class II, Type B1 biosafety cabinets recirculate a percentage of air back into the laboratory while Class II, Type B2 cabinets are entirely hard ducted. Class III biosafety cabinets are completely enclosed and feature attached rubber gloves.
Other types of enclosures: Carefully select the proper enclosure for your intended operation. Using the appropriate equipment helps ensure optimal protection of both the personnel within the laboratory as well as the space itself, and it can also preserve the integrity of your work. Other relevant laboratory equipment can include glove boxes, clean benches and balance enclosures. If your application involves nanoparticulates, there are also enclosure options designed to accommodate your specific needs.
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