On-site testing of Gel Seal HEPA Filters (commonly referred to as PAO/DOP leak testing) is the ultimate and crucial step to verify the installation quality and sealing performance. This task is highly technical and must strictly follow operational procedures. Below are the key points to note when conducting on-site testing.
Pre-Testing Preparations for Gel Seal HEPA Filters
1. Environmental and System Confirmation
- 1.1 All construction, installation, and cleaning work in the cleanroom must be fully completed, and the interior must reach a clean state with no dust-generating operations.
- 1.2 The HVAC purification system must have been running continuously for at least 12 hours to ensure stable system conditions and normal resistance state of the filters.
- 1.3 Notify laboratory or workshop personnel at least 24 hours in advance to prevent any personnel, equipment, or material movement during the testing period, which could interfere with the test results.
2. Equipment Calibration and Inspection
- 2.1 The aerosol photometer and aerosol generator must be within their calibration validity period (usually calibrated once a year). Conduct self-inspection and preheat before use.
- 2.2 Check that the equipment batteries are fully charged, and all connecting hoses are well-sealed without any leaks.
- 2.3 Prepare isopropyl alcohol and lint-free cloths to clean the probes to prevent cross-contamination.
3. Technical Plan Confirmation
- 3.1 Clarify the testing standards (such as ISO 14644-3 or standards specified by the owner).
- 3.2 Determine the pass criteria (typically stipulating that the leakage rate at any point must not exceed 0.01% of the upstream concentration).
- 3.3 Plan the smoke injection points and scanning paths to ensure comprehensive coverage of all filters to be tested.
4. Safety Measures
- 4.1 Testing personnel must wear qualified cleanroom suits, gloves, and masks.
- 4.2 When using PAO liquid, avoid direct contact with the skin, and have an MSDS (Material Safety Data Sheet) on site.
- 4.3 For high-altitude work (such as inside FFU ceilings), sturdy scaffolding or hydraulic lift platforms must be set up, and safety belts must be fastened to ensure safety.
On-Site Testing Operations for Gel Seal HEPA Filters
5. Upstream Concentration Setting
- 5.1 After injecting the aerosol into the system, wait for a while (about 2-5 minutes) until the concentration stabilizes before taking measurements.
- 5.2 The target upstream concentration is usually set between 10-20 μg/L. Too low a concentration results in poor instrument sensitivity, while too high a concentration may lead to overlapping of polydisperse aerosols, inaccurate measurements, and environmental contamination.
6. Scanning Standards (The Most Critical Step)
- 6.1 Scanning Distance: The photometer sampling probe should be 1-2 cm away from the filter surface and sealing joints, without touching the surface to avoid damaging the filter material or disturbing the airflow.
- 6.2 Scanning Speed: The probe movement speed should be slower than 5 cm/s to ensure sufficient time to respond to leakage points.
- 6.3 Scanning Path: Use overlapping back-and-forth or spiral paths to ensure 100% coverage of all areas, including:
- 6.3.1 The filter material itself (to check for any damage).
- 6.3.2 The bonding area between the filter material and the frame (filter’s own manufacturing process).
- 6.3.3 The gel seal joint (the most critical part to check installation sealing).
- 6.3.4 The joints between installation frames.
- 6.3.5 Around the fastening pieces between the frame and the ceiling.
- 6.3.6 Scanning Order: It is recommended to start from one end of the filter or frame and scan in sequence to avoid omissions.
7. Data Recording and Marking
- 7.1 If the photometer alarms (indicating a leakage rate exceeding the standard), pause at that position, confirm the maximum value, and record it.
- 7.2 Immediately mark the leakage point location accurately with non-particulate tape or a label.
- 7.3 It is best to take photos of the leakage points for subsequent analysis and repair.
Post-Testing Processing for Gel Seal HEPA Filters
8. Result Analysis and Repair
- 8.1 Distinguish the cause: Analyze whether the leakage point is due to filter defects, improper gel sealant filling (bubbles/interruptions), uneven frame, or loose mechanical clamps.
- 8.2 On-site Repair:
- 8.2.1 For minor installation leaks: Try to apply special adhesive locally for repair.
- 8.2.2 For severe leaks or product defects: The filter must be replaced. After replacement, retesting of that point is mandatory.
- 8.2.3 Retest: All repaired points must be rescanned until fully qualified.
9. Report and Documentation
- 9.1 Issue a formal test report, including: testing conditions, instrument information, standards, scanning results for each filter, leakage point locations and repair status, and final conclusions.
- 9.2 The report should be signed by the operating and reviewing personnel and archived for future validation and maintenance references.
10. Site Restoration
- 10.1 After the test, turn off the smoke generator.
- 10.2 Allow the HVAC system to continue running for a while to clear residual aerosols.
- 10.3 Clean up the site, remove all marking stickers and testing supplies.
Special Precautions for Gel Seal System During On-Site Testing of Gel Seal HEPA Filters
11.1 Focus Area: The core of the gel seal system testing lies in the contact surface between the knife edge and the gel seal. Carefully scan the entire circumference of this “junction line”.
11.2 Prudent Judgment: Due to the nature of the gel sealant, minor bubbles may sometimes heal themselves after the system has been running for a while. However, if continuous leakage is detected during testing, it must be addressed and not left to chance.
11.3 Tool Prohibition: Avoid using any sharp tools near the gel seal joints during scanning to prevent compromising the integrity of the sealant.
The successful on-site testing of Gel Seal HEPA Filters relies on:
1. Qualified equipment (calibrated photometers).
2. Stable systems (normally operating HVAC systems).
3. Standardized operations (slow, full-coverage scanning).
4. Professional judgment (accurate analysis of leakage causes and effective repair).
5. Detailed records (traceable test reports).
This task is a “hard standard” for cleanroom validation and must be strictly executed by experienced professional teams.
Post time: Sep-11-2025