HEPA FILTER INTEGRITY TEST SOLUTION

High-efficiency filter (HEPA) generally refers to a filter with a capture efficiency of more than 99.97% for particles with a particle size greater than or equal to 0.3um. It is usually used as the terminal filter device in the clean workshop of pharmaceutical companies to provide clean air. Whether the clean room can achieve and maintain the designed cleanliness level is related to the performance of the high-efficiency filter and its installation to a certain extent. Therefore, it is one of the important means to ensure the clean environment of the workshop to conduct a leak test on the high-efficiency filter of the clean workshop to ensure that it meets the requirements. The FDA also pointed out in the sterile drug production guidelines that a leak test should be performed after the high-efficiency filter is installed to check the tightness of the filter gasket, frame and filter material. Leak testing of high efficiency filters.

1. Purpose of Leak Detection of HEPA

The filtration efficiency of the high-efficiency filter itself is generally tested by the manufacturer, and the filter filtration efficiency report and qualification certificate are attached when leaving the factory. For pharmaceutical companies, high-efficiency filter leak detection refers to the on-site leak detection of high-efficiency filters and their systems after installation, mainly to check for small pinholes and other damage in filter media, such as frame seals, gasket seals, and filtration. Slots in the frame of the device, etc. The purpose of leak detection is to detect the defects of the high-efficiency filter itself and its installation in time by checking the tightness of the high-efficiency filter and its connection with the installation frame, and take corresponding remedial measures to ensure the cleanliness of the area.

2. HEPA and HVAC Integrity PAO Test Principle

HEPA and HVAC integrity PAO test usually uses a PAO generator to generate dust upstream of the filter, using a digital aerosol photometer.

Detect the aerosol concentration upstream and downstream of the filter to determine whether the filter is leaking. The purpose of dust generation is that due to the low concentration of dust particles upstream of the high-efficiency filter, it is difficult to detect leaks with only particle counters without dust generation.

When the gas flow is pumped into the light scattering chamber, the particulate matter in it scatters the light to the photomultiplier tube. In a photomultiplier tube, the light is converted into an electrical signal, which is amplified and digitized and analyzed by a microprocessor to determine the intensity of the scattered light. It is very versatile because it can directly measure the mass concentration of particulate matter in the gas by comparing it with the signal produced by the reference substance.

3.Test Method

To determine whether the HEPA filter itself and its installation have obvious leakage, the following must be tested on site: the filter media of the filter; the connection of the filter media of the filter to the inside of the frame; the gasket of the filter frame and the filter between the support frame of the appliance group; between the support frame and the wall or ceiling.

The materials and instruments for DOP leak detection are: dust source (PAO solvent), aerosol generator, and digital aerosol photometer.

 It uses air directly without compressed gas for power. Under the working pressure of 20Pa, when the airflow rate is 50~2025f3/min, it can produce polydisperse submicron oil dust aerosol with a concentration of 10~100ug/ml. The digital aerosol photometer used was a GTI Model 3990 with a dynamic measurement range of 0.00005~120ug/L and a sampling flow of 1F3/min (28.3L/min).

Introduce PAO aerosol on the upstream side of the HEPA to be tested

For HEPA in the HVAC system, in order to make the concentration of the aerosol uniform when it reaches the HEPA, the aerosol can be introduced directly from the negative pressure side of the system fan. Introduced at the pipe diameter and minimized turns (American Institute of Environmental Science and Technology). In general, it is enough to keep the upstream aerosol to the required concentration and the concentration fluctuation within a certain range. For HEPA on laminar flow hood and ultra-clean bench, the aerosol is directly introduced from the negative pressure side of the system fan.

Digital Aerosol photometer initialization, set 100%, 0% reference standard value Initialize and set alarm value according to the aerosol photometer operation requirements. Connect the UPSTREAM sampling tube to the upstream sampling port to measure the upstream aerosol concentration. Adjust the generated aerosol concentration according to the operation requirements of the aerosol generator, so that the upstream aerosol concentration reaches 10~20ug/ml.

4. Scanning Leak Detection

 Remove the HEPA diffuser and scan the entire filter face, between the filter and the frame, between the frame and the frame, and between the frame and the plenum. When scanning, the sampling head is about 1 inch (about 2.54cm) away from the filter surface, and the scanning speed does not exceed 5cm/s. The scan goes back and forth in a straight line, and the lines should overlap. During the detection process, if there is an alarm sound (that is, the %LEAKAGE (leak rate) exceeds 0.01%), it indicates that there is a leak. After the leak is plugged or tightened with silica gel, the scanning inspection is carried out. It takes about 5 minutes to check a filter. During the test, the concentration of the upstream aerosol should be checked frequently. Note that protective masks and goggles should be worn during the test.

5. Result Judgment and Processing

The leakage rate of HAPA should be less than or equal to 0.01%. If the %LEAKAGE (leak rate %) of all points in the HEPA testing process does not exceed 0.01%, the HEPA is judged to be qualified; Repair or replacement is required. The leakage of the high-efficiency filter material is allowed to be repaired with special glue, but the area of a single leak cannot be greater than 1% of the total area, and the area of all leaks cannot be greater than 5% of the total area, otherwise it must be replaced.

6. HEPA Leak Detection Cycle

The FDA recommends that the production workshop of sterile preparations should be checked for leaks every six months in the sterile drug production guidelines. In my country, the GMP inspection guidelines recommend that it is usually once a year. ISO14644 For leak detection of installed HEPA, the recommended maximum interval is 24 months. DOP leak testing should be performed after HEPA installation or replacement. Leak detection can be performed as part of a deviation investigation when environmental monitoring shows deteriorating air quality, or when product sterility tests fail, or when a simulated media fill test fails. Filters subject to leak testing also include HEPA used in drying tunnels and drying ovens.