FUME HOODS AND SAFETY CABINETS
Fume Hood Vs Biological Safety Cabinet?
Fume hoods are ventilated enclosures that remove volatile vapors and hazardous chemical fumes from the laboratory, providing personnel protection only.
Biological safety cabinets (or biosafety cabinets) utilize HEPA filters to provide personnel environmental 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.
Biosafety cabinets and fume hoods are both sometimes referred to as "hoods," but are two completely different categories of laboratory equipment. Both are laboratory equipment built to safely handle the hazards for which they're particularly designed, but they differ in terms of the precise type(s) of protection provided, airflow and suitable applications.
When selecting a "hood" for a laboratory, below are some key 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.
Protection
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.
Airflow
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 impact the circulation of air within the hood. 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 cabinets
Three classes of biosafety cabinets (see Variations below) all have one feature in common: HEPA filtration.
Class I biosafety cabinet, air is drawn away from the laboratory worker and across the work surface.
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 ducting.
Class III biosafety cabinets are gas-tight enclosures, with both intake air and exhaust air passing through HEPA filtration.
Applications
Fume hoods: Chemical fume hoods can handle the following: toxic gases, odorous materials, 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.)
Variations
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 these are constructed of acid resistant materials and radioactive applications come with extra decontamination features and often require filters in the ducting.
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 and expel all air. Class III biosafety cabinets are completely enclosed and feature attached rubber gloves.
