Laboratory hoods serve a number of critical purposes in the modern lab environment.
Such hoods, often called laminar flow workstations or clean benches, use a flow of micro-filtered air to prevent influx of particles into the enclosure and to sweep away any contaminants generated by the work process.
For fume containment, laboratory fume hoods use a ducted ventilation system that maintains negative pressure. Where ducting is impractical, ductless hoods are also available for removal of non-hazardous contaminants (fumes or particles), using either HEPA or activated carbon filters.
Biological safety cabinets combine aspects of both hood types: a laminar flow of micro-filtered air and negative-pressure containment of hazardous fumes.
Laminar flow hoods (also called clean benches) force air through a HEPA or ULPA filter to create a clean work area free of nearly all contaminating particulates, including bacteria, mold spores and many viruses. These hoods use a vertical or horizontal airflow design. Both provide excellent protection of products from particulates and cross-contamination, but do not protect the operator or environment.
So why choose one over the other? Vertical laminar flow (VLF) hoods require less floor space, but more overhead clearance. In addition, a sash at the front of the VLF hood provides a barrier between air exiting the hood and the operator’s face. VLF hoods create turbulent air flow when air strikes the work surface, requiring sterile work to be performed above the work surface.
HLF hoods minimize air turbulence (and particle backflow) on the work surface except where equipment disrupts the horizontal airflow. However, they direct the airflow directly at the operator’s face and require more depth to accommodate placement of the fan filter unit at the rear of the hood.
Laboratory fume hoods draw air from the environment into the opening of the hood, allowing environmental contaminants into the work area. Thus, fume hoods do not offer a sterile environment or product protection. Instead, fume hoods are designed to protect the operator from dangerous or irritating fumes and powders generated from work done inside the hood.
In ducted fume hoods, air passes out of the hood through a duct leading to in-house ventilation system that contains and/or neutralizes hazardous materials.
In ductless fume hoods, fans draw exhaust through a series of filters that remove irritating substances and then release it back into the room. Since these filters are not 100% efficient in removing all substances, ductless fume hoods are not advised in the presence of biohazards; however, they provide a convenient, cost-effective solution for operations involving irritating but non-hazardous fumes in facilities where an in-house HVAC system cannot be accessed.
Biosafety cabinets combine aspects of both laminar flow and fume hoods. Filtered air is directed downward onto the work surface and then travels into a plenum through openings on the front and sides of the hood. Depending on the classification of the biosafety cabinet, some percentage of air is recirculated and the rest is directed out of the hood through an exhaust system. Thus, biosafety cabinets offer both operator and product protection.
These hoods are ideal when working with sterile substances such as chemotherapeutic agents that may pose a risk to the operator.