Filtech Testing Division - Inflow Velocity

Inflow Velocity Test

The Inflow Velocity Test is a crucial component of ensuring the safety and effectiveness of biological safety cabinets (BSCs). This test is designed to measure the airflow entering the BSC's work access opening, helping to maintain a safe and sterile environment. It is particularly important for personnel protection and preventing contaminants from escaping the hood.

Why Inflow Velocity Matters:

Inflow velocity ensures that a steady flow of air is directed into the BSC, providing personnel protection and maintaining the integrity of the workspace. Here's how it works:

Air is drawn in through the cabinet's grates.
Approximately 70% of this air is directed through the supply HEPA filter, creating downward flows over the work surface.
The remaining 30% is exhausted through the exhaust HEPA filter.
The instrument used for this test is a Shortridge DIM (Direct Inflow Measurement) device, which is securely affixed to the BSC. The openings around the device are sealed with boards and duct tape to ensure accurate measurements.

Test Procedure:

1. Purpose: The Inflow Velocity Test determines the inflow velocity through the work access opening.

2. Apparatus: Various devices may be used for this test, including:

Direct Inflow Measurement (DIM) Instrument: Accuracy of ±3% of reading ±7 ft³/min (±12 m³/h) or as specified in Annex N-2.
Thermal Anemometer: Accuracy of ±3 ft/min (±0.015 m/s) or 3% of indicated velocity, whichever is larger.
Pitot Tube: Constructed according to the dimensions outlined in the Industrial Ventilation Manual.Freestanding Fixture: Allows for precise positioning of the thermal anemometer probe without disrupting airflow (e.g., ring-stand and clamp).

3. Methods: The specific testing method is validated for each cabinet model by the manufacturer and must be approved by the testing organization. The validation process includes a minimum of ten replicate tests, with approval granted based on data review and successful result replication. The validated alternative method is indicated on the manufacturer's data plate.

4. General Procedure:

Once the nominal set point is established for a cabinet model and size using a DIM device, an approved alternative method can be employed to determine the set point in the field.
For the Direct Inflow Measurement Method: a) Secure the DIM device at the center of the front opening of the BSC, sealing open areas around the capture hood as needed. b) Ensure all cabinet and exhaust blowers are operational. Take a minimum of five non-back-pressure compensated readings and calculate their average to determine inflow volume rate. Maintain unrestricted airflow through the instrument intake area. c) Calculate the average inflow velocity in ft/min (m/s) by dividing the average inflow volume rate in ft³/min (m³/s) by the work access opening area in ft² (m²). d) Reported data should include individual inflow volume rate readings, average inflow volume rate, work access opening dimensions and area, directly measured average inflow velocity, and the methods used for measurement. e) Reported values should encompass individual volume readings, overall average volume, calculated inflow volume, work access opening area, view screen opening height, correction factor (if used), acceptance criteria for average airflow volume, acceptance criteria for calculated inflow velocity, inflow velocity test method, and the name of the test (inflow velocity test).

These procedures ensure that inflow velocity through the work access opening is accurately measured and documented, aligning with the requirements specified in NSF/ANSI 49-2020. Your safety and the integrity of your work environment are our top priorities.