HEPA Filters play a critical role in various industries where the clean air environment is essential. To ensure the optimal functioning of these systems, testing is carried out as per standard guidelines. One such standard is ISO14644-3:2019, which specifies procedures for the leakage test of installed HEPA filters. This article provides an in-depth look into the procedures and considerations for these tests.

Purpose of the Tests

These tests are primarily conducted to confirm that installed HEPA filters are installed correctly by checking for bypass leakage in the installation. They also verify that the filters are free from defects, including small holes and other damages in the filter media, frame, seal, and leaks in the filter bank framework.

Importantly, these tests do not aim to determine the efficiency of the filter media.

Adaptation from Other Standards

Portions of the test methods have been adapted from IEST-RP-CC034.4.

Procedures and Specifications

1. Installed Filter System Leakage Scan Test with an Aerosol Photometer

This procedure is applicable for Ceiling, Wall, or Cabinet applications and involves the following methodical steps:

a. Measuring Aerosol Concentration Upstream: This will be used as a 100% reference point, and the downstream measurements are displayed as a percentage of this concentration.

b. Scanning the Downstream Side: The scanning should be done at a rate no more than 5 cm/s using the photometer’s probe. It must be held 3 cm or less from the filter face or frame, with overlapping strokes of 1 cm recommended.

c. Thoroughly Scanning the Entire Downstream Face: This includes the entire downstream face of each filter, the perimeter, the seal between the filter frame, and the grid structure, including its joints.

d. Repeating Measurements Upstream: This is done at reasonable intervals to confirm the stability of the challenge aerosol concentration. This methodical approach ensures accurate detection of any leaks in the system.

The rest of the specifications and criteria follow as described earlier:

• Probe Size: 1 cm x 8 cm, with a scan rate of approximately 5 cm/s.
• Leakage Criteria: H13 Filter Class (with MPPS efficiency greater than or equal to 99.95% and less than 99.995%) The maximum allowable penetration is 0.1%. If the upstream mass concentration exceeds 0.1%, then there is leakage.
• Leakage Criteria: H14 Filter Class(with MPPS efficiency equal or greater than 99.995%) Maximum allowable penetration is 0.01%. If the upstream mass concentration exceeds 0.01%, then there is leakage.
• Particle Diameter for Testing: Ranges from 0.3 µm to 0.7 µm, with a geometric standard deviation of up to 1.7.
• Aerosol Concentration: Should be within 1 mg/m³ to 100 mg/m³.
• Testing at Highest Air Velocity: The filter should be tested at the highest air velocity at which it will be operated.

This comprehensive and systematic approach ensures that the filters are meticulously examined for any signs of defects or leakage, reinforcing the quality and performance of the installed filter systems.

2. Overall Leak Test of HEPA Filters for Ducts or Air-Handling Units (AHUs)

This method can be applied to assess the complete leakage in duct-mounted filters, and it can further be utilized to gauge the entire leakage in multi-stage filter arrays, even without testing each individual stage. It’s crucial to understand that this method is not as sensitive as a scanning test. Therefore, it is suitable for less critical areas where duct-mounted filters are used, and where scanning tests of these filter installations are not feasible. If a critical analysis is needed, the scanning method should be adopted instead. The examination is conducted by placing the challenge aerosol before the filters, located away from the cleanroom or clean zone. Initially, the upstream particle concentration is recorded. Following that, the concentration of the particles in the filtered air is measured, then compared to the upstream concentration to find out the total leakage or penetration of the filter setup.
The measurement of downstream aerosol concentration must be done at places where the mixing is uniform. If uniform mixing doesn’t happen, measurements must be taken at evenly spaced points on a predetermined plane, ranging from 30 cm to 100 cm downstream from the filter. This approach is known as grid sampling, and the location and quantity of measurements must be settled upon by both the customer and supplier.

Test Documentation

Test Documentation An agreement between the client and the provider stipulates that the ensuing details and data must be documented;

• The selected testing approach: either an aerosol photometer or a light-scattering airborne-particle counter (LSAPC);
• The specific labels of each piece of measuring equipment utilized, along with its calibration status;
• A detailed description of the filter;
• Any unique conditions or deviations, or both, from this testing technique, as well as any custom procedures decided upon between the client and the provider;
• The noted upstream aerosol concentrations at specific sample points, together with the precise times they were measured;
• The sample’s flow rate, and in the case of LSAPC measurements, the range of particle sizes;
• A computed average for upstream aerosol concentration and its dispersion; h) The calculated criteria for accepting downstream measurements;
• The outcome of the downstream measurement for every distinctly identified filter, segment of the area, or measuring point;
• The conclusive result of the test for every designated location;
• A pass if there are no leaks. If leaks are found, the report should include the location of the leak, the remedial measures taken, and the results of retesting the area.

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