Understanding Directional Airflow of Ductless Fume Hoods

Horizontal Airflow

With horizontal laminar flow hoods, air enters through the filter(s) at the top of the unit, pushes the air downward and then horizontally across the workbench, and exits through the opening below the sash. Horizontal airflow directly protects the samples by using filtered air to combat particle contamination generated on or above the work surface as the user handles the samples.

Applications using a horizontal laminar flow unit include medical compounding, IV therapy, IVF, small electronic assembly or examination, cell/tissue cultures, media culture preparation, thin film deposition, and more. Exercise caution when using large equipment inside horizontal flow units, as it can disrupt airflow and lead to contamination from unobstructed airflow.

Vertical Airflow

Vertical laminar flow hoods, also called “downflow” hoods, filter air from the top of the unit down toward the work surface, creating a waterfall effect. This downflow of air utilizes high turbulence to reduce cross-contamination from other samples within the hood. It also works well if long, large, or girthy equipment is needed under the hood.

The units that utilize vertical airflow are vertical laminar flow units and PCR hoods. Applications for vertical laminar flow hoods include preventing cross-contamination of powders, microbiological samples, large electronic assembly and examination, and chemical reactions that are considered non-hazardous.

PCR hoods and enclosures can perform similar functions to vertical laminar flow hoods. However, their built-in UV lights decontaminate the worksurface, allowing for DNA and RNA applications and manipulations.

Negative Displacement

In contrast to horizontal and vertical airflow units, negative displacement fume hoods operate based on negative pressure. These negative-pressure fume hoods minimize exposure of harmful airborne pollutants and contaminants to the operator’s breathing area. These hazardous contaminants include airborne contaminants, particles, and chemical fumes.

These units actively draw air through the sash, exposing it to hazardous gases or particles produced by the samples. Subsequently, the fume hood filters the air using a prefilter, HEPA, carbon, and other filter types to purify it. Depending on the unit type, the purified air is reintroduced into the laboratory or recirculated back into the fume hood.

Negative pressure fume hoods are frequently used in various settings, including chemistry laboratories, dental laboratories (particularly for tasks such as denture grinding), and other biological applications where harmful particles, VOCs, and similar substances are a concern.