The laminar flow hood provides an aseptic work area while allowing the containment of infectious splashes or aerosols generated by many microbiological procedures.  Three kinds of laminar flow hoods, designated as Class I, II and III, have been developed to meet varying research and clinical needs.

Classes of Laminar Flow Hoods

Class I laminar flow hoods offer significant levels of protection to laboratory personnel and to the environment when used with good microbiological techniques, but they do not provide cultures protection from contamination.  They are similar in design and air flow characteristics to chemical fume hoods.
Class II laminar flow hoods are designed for work involving BSL-1, 2, and 3 materials, and they also provide an aseptic environment necessary for cell culture experiments.  A Class II biosafety cabinet should be used for handling potentially hazardous materials (e.g., primate-derived cultures, virally infected cultures, radioisotopes, carcinogenic or toxic reagents).
Class III biosafety cabinets are gas-tight, and they provide the highest attainable level of protection to personnel and the environment.  A Class III biosafety cabinet is required for work involving known human pathogens and other BSL-4 materials.

Air-Flow Characteristics of Cell Culture Hoods

Laminar flow hoods protect the working environment from dust and other airborn contaminants by maintaining a constant, unidirectional flow of HEPA-filtered air over the work area.  The flow can be horizontal, blowing parallel to the work surface, or it can be vertical, blowing from the top of the cabinet onto the work surface.  

Depending on its design, a horizontal flow hood provides protection to the culture (if the air flowing towards the user) or to the user (if the air is drawn in through the front of the cabinet by negative air pressure inside).  Vertical flow hoods, on the other hand, provide significant protection to the user and the cell culture.

Clean Benches

Horizontal laminar flow or vertical laminar flow “clean benches” are not biosafety cabinets; these pieces of equipment discharge HEPA-filtered air from the back of the cabinet across the work surface toward the user, and they may expose the user to potentially hazardous materials. These devices only provide product protection.  Clean benches can be used for certain clean activities, such as the dust-free assembly of sterile equipment or electronic devices, and they should never be used when handling cell culture materials or drug formulations, or when manipulating potentially infectious materials.

Cell Culture Hood Layout

A cell culture hood should be large enough to be used by one person at a time, be easily cleaned inside and outside, have adequate lighting, and be comfortable to use without requiring awkward positions.  Keep the work space in the cell culture hood clean and uncluttered, and keep everything in your direct line of sight.  Disinfect each item placed in the cell culture hood by spraying it with 70% ethanol and wiping clean.

The arrangement of items within the cell culture hood usually adheres to the following right-handed convention, which can be modified to include additional items used in specific applications.  

  • A wide, clear work space in the center with your cell culture vessels
  • Pipettor in the front right, where it can be reached easily
  • Reagents and media in the rear right to allow easy pipetting
  • Tube rack in the rear middle holding additional reagents
  • Small container in the rear left to hold liquid waste

Figure 2.1:  The basic layout of a cell culture hood for right-handed workers.  Left-handed workers may switch the positions of the items laid out on the work surface.