• Marks & Listings: UL, ULC
Laboratory hoods serve a number of critical purposes in the lab environment.
Such hoods, often called laminar flow workstations or clean benches, use a flow of HEPA-filtered air to prevent influx of viable and non-viable 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 bio-hazard fumes.
Laminar flow hoods (also called laminar flow 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 hoods (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 through the opening of the hood, allowing environmental contaminants into the work area. Thus, lab fume hoods do not offer a sterile environment or product protection. Instead, chemical fume hoods are designed to protect the operator from dangerous or irritating fumes and powders generated from work performed inside the hood.
In ducted fume hoods and canopy fume hoods, air passes out of the hood through a duct leading to an in-house ventilation system that contains and/or neutralizes hazardous materials.
In ductless fume hoods, fans draw exhaust air through a series of filters that remove irritating substances before release 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.
Biological Safety cabinets combine design 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 hood, some percentage of air is recirculated through a HEPA filter while the rest is directed out of the hood through an exhaust system. Thus, biosafety cabinets offer operator, environmental and product protection.
These laboratory safety cabinets (sometimes called IV hoods or compounding hoods) are ideal when preparing sterile medications such as chemotherapeutic agents that may pose a risk to the operator.
When it comes to working with hazardous or potentially infectious material, protecting personnel must be the primary concern. However, offering personnel protection does not have to come at the cost of risking product integrity. Class II BSCs provide protection to both personnel and product simultaneously. They maintain an ISO class 5 clean work area for product manipulation, while ensuring that exhaust air is filtered and ducted out of the environment. Thus, a class II BSC is the ideal solution when working with moderately hazardous material and both personnel and product safety are required.
Activated charcoal, the most common purification filtration medium, adsorbs chemicals with a molecular weight above 30 and a boiling point above 60°C. Carbon filters are also effective with many other chemicals because of their particular molecular structure.
Adsorption takes place in the active filter zone, the small cross-section of the filter bed in which the material to be removed comes in contact with the filtering medium. This active filter zone moves upward as the filter becomes saturated (see illustration). When it reaches the filter's top surface, there is an initial breakthrough by the contaminant gas; thereafter the percentage of contaminant gas that escapes filtration increases until total saturation of the filter is reached.
Ductless fume hoods manufactured by Terra use activated carbon filters to eliminate most nuisance fumes and can be used in conjunction with HEPA filtration. For more hazardous chemicals like strong acids and bases, specialized Labconco filtered fume hoods can be equipped with a wider range of filters and include an array of safety sensors for breakthrough detection.
To optimize filtration efficiency, any ductless exhaust fume system must ensure that the exhaust stream is exposed to the purification medium for an adequate time. Terra exhaust purification systems satisfy this condition in several ways.
First, our specially selected impeller ventilators are designed to ensure the optimal linear velocity of the airstream—sufficient to maintain a negative pressure in the work area that prevents backflow, but low enough to allow adequate adsorption of fumes by the filtering medium. Our pre-filters also extend exposure time by reducing the airflow through the filter.
A ductless exhaust fume system needs to be monitored in two areas. The user must detect the period between initial contaminant breakthrough and the point at which the contaminant gas reaches the Threshold Limit Value (TLV) for that substance. The velocity of the airstream must also be monitored to ensure an adequate negative pressure and to detect ventilator failure.
Through periodic testing of the exhaust airstream, you can determine the useful filter life in your particular application and gauge filter effectiveness with an elapsed time meter.
An electronic airflow velocity monitor also helps users ensure safe, effective operation and provides an alarm when velocity falls below a user-defined threshold.
Avoid filter use in applications involving very toxic substances, very high volumes of contaminants, and unknown or highly volatile chemical reactions. Always make sure that filters are promptly changed when the Threshold Limit Value (TLV) has been reached for any contaminant gases present.