Cell culture equipment: the laminar-flow hood

infographic comparing laminar flow hoods and biosafety cabinets showing horizontal and vertical airflow and different levels of protection in cell culture laboratories — Figure 1. Comparison between horizontal laminar flow hoods (clean benches) and vertical biosafety cabinets. While horizontal systems ensure product protection only, biosafety cabinets provide protection for the sample, the operator, and the environment.

Working in a cell culture laboratory requires strict aseptic conditions. For this reason, the use of a laminar flow hood is essential.

In theory, aseptic procedures could also be performed in a sufficiently isolated and clean environment with restricted access. However, such ideal conditions are rarely achievable in real laboratory settings. Therefore, the laminar flow hood remains the most reliable tool for maintaining sterility during cell culture work.

Because design and performance vary significantly, selecting the appropriate cabinet requires careful evaluation of experimental needs.

Types of laminar flow hoods

Both horizontal-flow and vertical-flow hoods can be used to maintain aseptic conditions, although their applications and safety profiles differ significantly.

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HORIZONTAL FLOW HOOD

The horizontal-flow hood (also known as a clean bench) draws air from the laboratory environment and passes it through a pre-filter and a high-efficiency particulate air (HEPA) filter.

The filtered air flows horizontally from the back of the hood toward the operator, creating a clean working surface by preventing airborne contamination from reaching the samples.

These hoods are generally less expensive and provide excellent product protection. However, they do not offer protection to the operator or the environment.

For this reason, horizontal-flow hoods should not be used when working with hazardous materials, including human or primate cell lines, virus-producing cultures, or toxic or carcinogenic substances (for example, trypan blue).

Their use is therefore limited to the preparation of sterile media and reagents, or to work with non-hazardous cell types.

VERTICAL FLOW HOOD

Vertical laminar flow hoods, commonly integrated into biological safety cabinets, direct filtered air from top to bottom over the working area.

Although more expensive, these systems provide a higher level of safety, as they protect not only the sample but also the operator and the surrounding environment.

However, airflow in vertical systems can be more easily disrupted by incorrect operator movements or overcrowding of the working surface, leading to turbulence and reduced sterility.

Despite these limitations, vertical laminar flow hoods are essential when handling hazardous biological materials.

Class II microbiological safety cabinet

Class II biosafety cabinets are the most widely used systems in modern cell culture laboratories.

They are designed to provide triple protection:

product protection (sterility of the sample)
personnel protection (operator safety)
environmental protection

These cabinets are characterized by:

inward airflow from the front opening
HEPA-filtered laminar airflow within the work area
HEPA-filtered exhaust air released either into the room or through a dedicated system

Here is the NSF actual classification for Class II vertical flow hood:
http://www.nsf.org/services/by-industry/pharma-biotech/biosafety-cabinetry/nsf-ansi-49-biosafety-cabinetry-certification

It is important to understand differences in cabinet type in order to select the best fitted to your purpose, the NSF_49-2016_Annex_E is a very useful document to make the right hood choice, anyway here is a semplificative table.

NSF CLASSIFICATION	DIAGRAM	GENERAL DESCRIPTION
A1	http://www.nsf.org/newsroom_pdf/NSF_49-2016_Annex_E.pdf	70% air recirculated; 30% exhausted from a common plenum to the room; 0,38 m/s intake; Offers product, personnel and environmental protection. Biologically contaminated ducts and plenums under positive pressure to the room
A2	Same as above	70% air recirculated; 30% exhausted from a common plenum to the room; 0,51 m/s intake; Biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure
B1	http://www.nsf.org/newsroom_pdf/NSF_49-2016_Annex_E.pdf	Less then 50% air recirculated exhaust air expelled through dedicated exhaust duct into lab exhaust system; 0,51m/s intake All biologically contaminated ducts and plenums are under negative pressure or surrounded by negative pressure ducts and plenums. Type B1 cabinets must be hard connected to an exhaust system. Offers products, personnel and environmental protection.
B2	http://www.nsf.org/newsroom_pdf/NSF_49-2016_Annex_E.pdf	There is no recirculation within the work area. exhaust air pulled through dedicated exhaust duct into facility exhaust system; 0,51 m/s intake all contaminated ducts are under negative pressure or surrounded by directly exhausted negative pressure ducts or plenums Type B2 cabinets must be hard-connected to an exhaust system. widely used in toxicology laboratories and similar applications where chemical effluent is present and clean air is essential
C1

Class III Total Containment Cabinets

Class III biosafety cabinets are completely enclosed, gas-tight systems designed for work with highly hazardous biological agents.

They provide the highest level of protection for personnel, product, and environment and are used in specialized high-containment laboratories.

Practical considerations

Regardless of the type of hood used, correct handling is essential to maintain sterile conditions.

Airflow must not be obstructed, excessive movements should be avoided, and materials must be positioned properly to prevent disruption of the laminar air stream.

Regular maintenance, including filter integrity checks and proper cleaning, is also crucial to ensure long-term performance.