Fume Hoods, Biosafety Cabinets and Enclosures

Fume cabinets are highly versatile and can be used in biological, medical or pharmaceutical, biochemical and research applications. The main objective of using a fume cabinet is to provide a standardized level of protection against contamination or exposure to unwanted aerosols inside and outside of the hood workspace.

To avoid workers inhaling toxic fumes
In biochemical laboratories, some procedures will call for the use of dangerous chemicals that can omit toxic fumes. Fume cabinets help contain toxic gases and vapor from leaving the workspace. This makes handling such compounds easier, as lab technicians will not have to wear as much protective equipment or gas masks – which can be advantageous when working with toxic fumes for extended periods.

To protect the product or experiment
Laminar flow and biological hoods are designed to protect both products and experimental materials from pathogens and other contamination within the lab space and ambient air. A consistent positive pressure airflow controls this, keeping unfiltered air out with minimal effort while filtering all incoming air into the cabinet. This filtration is accomplished using high-end filters that can trap viruses, bacteria and other microbial contaminants from entering the workspace.

Not only does this help with the efficacy of an experiment, but it also allows for significantly less use of materials as you will not have to account for as high of a failure rate in products like culture plates.

To protect the environment (recirculating fume hoods and other biosafety hoods are fitted with appropriate filters in the exhaust airstream)
Some fume hoods will incorporate recirculating systems for airflow, reducing the exhaust output into the environment. A number of filters can also be applied to the exhaust airstream that will minimize the environmental impact of releasing fumes or foreign compounds into the air outside.

Fume cabinets operate by providing local exhaust ventilation. This process takes contaminated air from the workstation, drawing it through an air filter and trapping chemical and particulate contaminants. The filters are often carbon or HEPA (high-efficiency particulate air) filters. After the air is filtered, it is sent through air ducting to a remote location as exhaust from the system.

Some cabinets work with negative or positive pressure – these techniques control the direction of airflow and exposure to clean or contaminated air. As discussed above, laminar flow is facilitated by positive pressure to protect the contents of the cabinet. Negative pressure, on the other hand, is used to keep contaminated air trapped inside the workspace to avoid exposure outside of the hood. This can be particularly useful if handling toxic compounds or biological hazards.

Based on your laboratory specifications, there are three types of safety cabinets: fume, biosafety and laminar flow benches. Each category offers unique filtration methods with varying degrees of protection and safeguarding for sterility.

Depending on your workflow requirements, these systems also come in varying sizes – you can find both large, free-standing units or smaller bench-top units.

Fume Cabinets
When handling hazardous chemicals in a lab, performing all experiments and reactions inside a fume cabinet is crucial. Their primary function is to protect operators from dangerous fumes in the ambient air of the workspace. Fume cabinets have an array of filters on their exhaust system to avoid possible contamination or toxicity into the air. Otherwise, they do not prevent biological or particulate contamination in the workspace.

Biosafety Hoods
While a fume hood protects the user, a biosafety hood protects the user, the environment and the material. The largest difference in fume and biosafety hoods is that a biosafety hood has more advanced filtration like HEPA filters to protect against biological contamination.

• Class I
  Solely for operator protection. Characterized by outside air infiltration, meaning a sample can get into contact with outside air, but the operator will not be exposed to it. These limitations make the use of Class I cabinets less common in labs.
• Class II
  For operator, product and environmental protection with potential for aerosol transmission, associated with human diseases and primary hazards. These units are used when multidimensional protection is required. They are constructed with an inward airflow, HEPA-filtered particle-free air forced downward and equally clean air going into the exhausting component. These features make Class II cabinets the most widely used model for medicine preparation and research.
• Class III
  For operator, product and environmental protection for specialized laboratory facilities dealing with deadly pathogens. These systems have the maximum leak-tight construction. A fully closed front panel eliminates lab workers’ exposure to materials, along with an air-tight seal to protect the inside workspace. There is also a double door pass to transfer materials from the nonsterile door to the sterile door inside the hood. Class III cabinets are used for hazardous, life-threatening agents only.

Laminar Flow Benches
Similar to a biosafety hood, laminar flow benches provide protection to the lab worker and any specimens or products within the cabinet. However, they do not provide the same filtration protection for the exhaust to the environment. It is not recommended to work with biologically hazardous materials in a laminar flow bench, as contamination is unlikely but possible. Laminar flow is ideal for sensitive biological samples that do not run safety risks in the case of cross-contamination.

Constant Volume
This system operates with a consistent exhaust flow rate or quantity of air pulled through the hood. In this type of configuration, when the sash is lowered and the cross-sectional area of the hood opening decreases, the velocity of airflow through the hood increases proportionally. This causes airflow velocity at the hood's opening to increase as the sash is lowered.

Variable Air Volume (VAV)
In this design, exhaust flow rate through the hood caries as the sash is raised or lowered to maintain a constant face velocity. This allows for a consistent air volume when the sash is lowered or raised.