Filtech Testing Division - Downflow Velocity

Downflow Velocity Certification: Ensuring Safe and Sterile Workspaces

At Filtech, we are dedicated to maintaining the highest standards of safety and sterility in controlled environments like biological safety cabinets (BSCs) and clean benches. Our Downflow Velocity Certification process, in accordance with NSF Standard 49, specifically section N-1.8, is designed to verify and ensure the proper downflow velocity of HEPA/ULPA-filtered air within these critical workspaces.

The Purpose of Downflow Velocity Certification

Downflow Velocity Certification focuses on one key parameter: the velocity of HEPA/ULPA-filtered air as it flows downward through the total work area. This certification process ensures that the downflow velocity falls within the specified range and maintains uniform distribution. By doing so, it upholds the containment, uniformity, and prevention of product contamination as established by the validation procedures of the Primary Engineering Containment (PEC). The specific velocity requirements can be determined by the manufacturer's guidelines or NSF standards.

Measurement Process

Our experienced technicians employ a rigorous measurement process:

Grid Measurements: We use a calibrated thermal anemometer securely fixed on a ringstand. Velocity measurements are taken on a grid defined by the manufacturer's specifications. If the manufacturer does not specify a grid, we utilize the NSF grid guidelines.
Multiple Measurement Points: Air velocity is measured at multiple points across the workspace or zones as defined by the manufacturer. These measurements are taken in the horizontal plane, precisely 4 inches (100 mm) above the bottom edge of the sash frame, which is the certified height. For Cabinets manufactured before 2001, measurements are taken at sash level.
NSF Grid Requirements: The downflow grid or zone must meet specific criteria, including:
A uniform rectangular equidistant grid with spacings between 4 inches (100 mm) and 8 inches (200 mm).
Minimum three rows or as defined by the zone(s).
For cabinets with a nominal width of 3 feet (0.9 m) or greater, a minimum of seven readings per row or zone.
For cabinets with a nominal width less than 3 feet (0.9 m), a minimum of four readings per row or zone.
Ensuring that the area defined by the perimeter of the test points equals at least 30% of the total area of the measurement plane.
Proper Placement: Perimeter or zone air velocity readings are taken at least 6 inches (150 mm) away from the walls and sash enclosing the total work area.
Adaptation for Cabinet Size: In cases where meeting the grid requirements is not possible due to the cabinet's size, grid spacing shall start 6 inches (150 mm) away from the walls and sash. Equidistant spacing may be used with a minimum of four readings per row or zone.
Sloped Sash: Cabinets with a sloped sash and multiple access opening heights may have different downflow grids or zones, meeting the specified requirements.

Certification Accuracy

During the certification process, we calculate the average velocity and ensure that the high and low readings meet a strict 15% or less standard deviation. This rigorous approach guarantees that your controlled environment complies with safety and quality standards and displays uniformity across the work surface, providing you with peace of mind and confidence in your workspace's integrity.