For the often time-consuming and labor-intensive process of HEPA filter leak detection, a more efficient and practical alternative can be adopted. This method, frequently used by the author during engineering construction and testing, is outlined as follows:
If the HEPA filters have passed factory leak testing, are properly packaged, handled according to standards, delivered to the site by dedicated vehicles, and stored under compliant conditions—in other words, if the filters are confirmed to be leak-free prior to installation—then they can be directly installed (ensuring that installation procedures are strictly followed). After installation, only the “installation frame” of the filter needs to be inspected for leakage.
However, if the filters were not leak-tested at the factory, or if there is uncertainty about transportation, unloading, or storage practices, then each HEPA filter must be tested on-site prior to installation. To do this, a designated leak-testing area can be set up on the construction site where filters are tested one by one. In this setting, it is easy to introduce a high particle concentration airflow on the upstream side. Once tested and confirmed to be leak-free, the filters can be immediately installed. This approach is far more scientific than scanning for leaks after the filters are installed.
Once installation is complete, only the installation frame needs to be leak-checked. In practice, when inspecting the frame, there is no need to introduce ultra-high particle concentrations (such as 10⁷ particles/m³ or more) into the upstream airflow. Frame leakage is typically due to poor sealing, and only a modest level of particles in the upstream airflow (e.g., filtered outdoor air that has passed through prefilters or medium-efficiency filters) is sufficient for detection. If a frame leak is present, the downstream side will clearly show increased particle counts, which can be easily detected by a particle counter.
Key Features of This Method:
This method breaks down the standard leak testing process into two more manageable steps:
-
Pre-installation HEPA filter leak test
Simple and easy to perform
No need for high-level work or scaffolding
Upstream high particle concentration is easy to introduce
No risk of contamination to the clean air duct system -
Post-installation installation frame scan
Requires brief high-level access
Inspection is fast and efficient
If sealing gaskets are properly cut and adhered, leaks are rare
For gel-seal filters, no frame scan is needed if gel and frame pass inspection
The author often uses outdoor air filtered through prefilters and medium filters for this frame leak test, which has proven effective. This approach also avoids contaminating the air supply system with artificially generated high-concentration aerosols.
During frame scanning, open the fresh air valve wide (the air handler should only have coarse filters installed at this stage), fully open the exhaust valve, and partially close the return air valve. This creates the conditions necessary to conduct a scan of the installation frame area only.
Conclusion:
Leak testing at the filter manufacturing stage is fundamental; proper handling, transportation, and storage are essential safeguards; and real-time supervision of installation is the key to ensuring cleanroom construction quality. In cleanroom projects where on-site leak testing is required, filters that have passed on-site testing can be installed using scientific methods and dynamic supervision. Only the installation frame area needs to be scanned, significantly saving time and labor while maintaining reliability and operational feasibility.
