Laminar flow is defined as airflow in which the entire body of air within a designated space is uniform in both velocity and direction.
Clean benches and biological safety cabinets are common examples of laminar flow hoods. They are laboratory enclosures designed to carefully direct HEPA filtered air. Some of these hoods protect items placed on the work surface from contamination. Others prevent exposing the user to contaminants in the work area. Laminar flow hoods are often used to work with biological samples, semiconductors or other sensitive materials.
According to the CDC, the laminar air flow principle was first developed in the early 1960s. It's still incredibly relevant for modern labs, having literally shaped the way air safely moves in many generations of laboratory enclosures. Today, many categories of laminar flow hoods exist. Although they differ depending on the science performed within, there is one common denominator: all use this type of unidirectional airflow to aid in maintaining sterility, preventing cross-contamination and reducing turbulence.
Just what exactly is laminar air flow, why is it effective and what does it look like in labs today? Let's explore.
How is laminar air flow utilized in different types of equipment?
Class II Biosafety Cabinets, sometimes referred to as laminar flow hoods, maintain product protection through HEPA-filtered laminar downflow over the work zone. Per the NSF definition, these ventilated cabinets also feature inward airflow at the open front to protect operators and HEPA filtered exhaust air for environmental protection.
(Note that some categories of laboratory equipment, like Class I enclosures with perforated baffles or certain high performance fume hoods, employ laminar-like flow. Watch: Airflow in a Class I Enclosure.)
Video demonstration, laminar flow in action:
Zoned airflow is not truly laminar. Zoned airflow is used when equipment cannot achieve all of the protection required of a Class II biosafety cabinet with standard laminar airflow. Each zone, or column, of airflow is defined and has its own range in airspeed. This allows for higher speed barrier air columns to be utilized as an engineering solution to equipment that otherwise would have poor containment or product protection ratings.
Dilution flow is not the same as laminar air flow. The dilution flow principle is used in equipment such as filtered glove boxes. In these instances, HEPA-filtered air mixes with and dilutes interior airborne contaminants inside the glove box, and those contaminants are removed via a filtered exhaust system. After the contamination source has been sealed, the dilution rate—or air changes per minute—will determine how much time must lapse before materials can be removed from the main chamber.
While laminar air flow helps to reduce turbulence, turbulent flow encourages it by creating unintentional swirls of air that place particles randomly on surfaces within an enclosure. Turbulent flow can be disruptive to work that requires a dust-free environment and can lead to contamination. Obstructions, like items left inside enclosures, can create this unwanted turbulence.
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