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High-efficiency filter leak test case and application
High-efficiency filter leak test case and applicationI. InstrumentAccurately detect the quality of high-efficiency filters to avoid leakage of high-efficiency filters and affect production. Method: Use a dust particle counter to detect whether the high-efficiency filter has leakage. Result: If the suspended particles at each point exceed the range required by the clean area, there is leakage, which needs to be plugged or replaced. Dust particle counter II. Experimental principle Applying the principle of light scattering, a photomultiplier tube is used to receive the light reflected by dust particles to measure their size and quantity during counting measurement and analyze the accumulation and digital display. Conclusion Through the above measurement, it can be seen that the high-efficiency filter No. 3 has leakage. It needs to be plugged or replaced. The filter must be retested after repair or replacement. Under normal conditions, the high-efficiency filter is generally tested for leakage at least once a year to see if there is any change. It is an important part of the cleanliness test. Appendix: Application of DOP leak detection method for high-efficiency filter High-efficiency filter (HEPA) generally refers to a filter with a capture efficiency of 99.97% or more 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 reach and maintain the designed clean level is related to the performance and installation of the high-efficiency filter to a certain extent. Therefore, leak testing the high-efficiency filter in the clean room to ensure that it meets the requirements is one of the important means to ensure the clean environment of the workshop. FDA also pointed out in the sterile drug production guide that a leak test should be carried out after the installation of the high-efficiency filter to check the sealing of the filter gasket, frame, and filter material. For the sterile preparation production workshop, the high-efficiency filter should be regularly tested for leaks. 1. Principle of DOP leak detection method The leak detection of high-efficiency filters usually uses a PAO generator to generate dust upstream of the filter and uses a photometer to detect the aerosol concentration upstream and downstream of the filter to determine whether the filter leaks. The purpose of dust generation is that the dust concentration upstream of the high-efficiency filter is low. It is difficult to detect leaks only by using a particle counter without dust generation. Supplementary dust generation is required to clearly and easily detect leaks. Artificial aerosol DOP has a history of nearly 40 years. For some time, it has been suspected of being carcinogenic to humans. It is now often replaced by DOS (Dioctylsebaeate) also known as DEHS [di(2-ethyl hexyl) sebacate] and PAO (polyaphaolefin), but the experimental method is still called the "DOP method". Atmospheric dust concentration varies with location and time, sometimes large and sometimes low, and is generally not used for leak detection. FDA pointed out that when leak detection is carried out, the selected aerosol should meet certain physical and chemical requirements, and aerosols that cause microbial contamination and microbial growth should not be used. PAO generators can be divided into two types: hot generation and cold generation. The hot generator uses the principle of evaporation and condensation. The aerosol particles are evaporated by a heater and condensed into tiny droplets under specific conditions. After removing the oversized and undersized droplets, the mist DOP of about 0.3um is left to enter the air duct, and the particle size distribution is 0.1~0.3um. Cold generator refers to the use of compressed air to bubble in the liquid, and then splash through the laskin nozzle to produce a physical multi-dispersed phase DOP aerosol, with a maximum distribution particle size of about 0.65um. Cold DOP is often used when scanning the filter for leak detection. There are two types of detection instruments, one is an aerosol photometer and the other is a particle counter. The commonly used detection instrument in high-efficiency filter leak detection is an aerosol photometer (hereinafter referred to as a photometer), which is a forward scattering linear photometer. It consists of a vacuum pump, a light scattering chamber, a photomultiplier tube, a signal processing converter, and a microprocessor. Its working principle is: that when the airflow is pumped to the light scattering chamber by a vacuum pump, the particulate matter in it scatters light to the photomultiplier tube. In the photomultiplier tube, light is converted into an electrical signal, which is amplified digitized, and analyzed by a microprocessor to determine the intensity of the scattered light. By comparing with the signal generated by the reference substance, the mass concentration of particulate matter in the gas can be directly measured, so it has a wide range of uses. The particle counter, on the other hand, reflects the concentration of the number of particles in the airflow! Particles" #$ It also specifies the particle size range. It has a high sensitivity and applies to all dust source aerosols. It has a wide range of choices, but it is rarely used in high-efficiency filter leak detection. The test results of the two instruments are difficult to quantitatively compare. 2. Purpose of high-efficiency filter leak detection The filtration efficiency of the high-efficiency filter itself is generally tested by the manufacturer, and a filter efficiency report and a certificate of conformity are attached when it leaves the factory. For pharmaceutical companies, high-efficiency filter leak detection refers to on-site leak detection of high-efficiency filters (www.klcfilter.com) and their systems after installation. It mainly checks for small pinholes and other damage in the filter material, such as frame seals, gasket seals, and leaks on the filter frame. The purpose of leak detection is to Check the sealing of the high-efficiency filter and its connection with the installation frame, defects in the high-efficiency filter itself and its installation can be found in time, and corresponding remedial measures can be taken to ensure the cleanliness of the area. 3. Detection method To determine whether there is obvious leakage in the high-efficiency filter itself and its installation, the following locations must be tested on site: the filter material of the filter; the connection between the filter material and the inside of its frame; between the sealing gasket of the filter frame and the filter group support frame; 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 aerosol photometer. The aerosol generator used by our company is ATI TDA-6C. Handheld Laskin nozzle aerosol generator uses air directly without compressed gas as power. Under 20Pa working pressure, when the airflow velocity is 50~2025f3/min, it can generate polydisperse submicron oil dust aerosol with a concentration of 10~100ug/mL. The aerosol photometer used is an ATI 2H photometer, with a dynamic measurement range of 0.00005~120ug/L and a sampling flow rate of 1F3/min (28.3L/min). 3.1 Introduce PAO aerosol on the upstream side of the HEPA to be tested For HEPA in the HVAC system, To make the concentration of aerosol uniform when it reaches HEPA, the aerosol can be introduced directly from the negative pressure side of the system fan. If it is to be introduced from the air duct, it should be introduced at least 10 times the diameter of the air duct away from the HEPA, and the bends should be minimized (American Society of Environmental Science and Technology). In general, it is sufficient to keep the upstream aerosol at the required concentration and the concentration fluctuation within a certain range. For HEPA on laminar flow hoods and clean benches, the aerosol is introduced directly from the negative pressure side of the system fan. 3.2 Initialization of aerosol photometer and setting of 100% and 0% reference standard values Initialize and set alarm values according to the operating requirements of the aerosol photometer. Connect the UPSTREAM sampling tube to the upstream sampling port to measure the concentration of upstream aerosol. Adjust the generated aerosol concentration according to the operating requirements of the aerosol generator so that the upstream aerosol concentration reaches 10~20ug/mL. 3.3 Scanning for leak detection Remove the HEPA diffuser and scan the entire filter surface, the seals between the filter and the frame, between the frames, and between the frame and the static pressure box. During 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. Scanning is performed back and forth in a straight line, and the lines should overlap. During the test, if there is an alarm (that is, the %LEAKAGE (leakage rate) exceeds 0.01%), it indicates a leak. The leak is plugged with silicone or tightened before scanning and inspection. It takes about 5 minutes to check a filter. During the test, the concentration of upstream aerosols should be frequently confirmed. Note that protective masks and protective goggles should be worn during the test. 4 High-efficiency filter leak detection cycle FDA recommends that sterile preparation production workshops be leak-checked every six months in the sterile drug production guide, and my country recommends that it is usually once a year in the GMP inspection guide. ISO14644 recommends a maximum time interval of 24 months for leak detection of installed HEPA. DOP leak detection should be performed after HEPA is installed or replaced. When environmental monitoring shows that air quality has deteriorated, or when the product sterility test fails, or the culture medium simulation filling test fails, leak detection can be performed as part of the deviation investigation. Filters that need to be leak tested also include HEPA used in drying tunnels and dry ovens. 5 Result judgment and processing The leakage rate of high-efficiency filters should be less than or equal to 0.01%. If the %LEAKAGE (leakage rate) of all points of the HEPA during the test does not exceed 0.01%, the HEPA is judged to be qualified. If one point exceeds 0.01%, it is judged to be unqualified and the point is marked and needs to be repaired or replaced. The leakage of 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. Problem discussion 6.1 High-efficiency filter efficiency and leak detection The filtration efficiency of high-efficiency filters refers to the efficiency of the filter itself, which varies with the implementation standards and test methods. The current test methods for the efficiency of high-efficiency filters are: DOP method, which uses a photometer for detection, is not as sensitive as the particle counting method. The relevant standards can be found in the US IEST-RP-CC001; the particle counting method, which uses a particle counter as a detection instrument and uses monodisperse or polydisperse aerosols, has high sensitivity and is mostly used for ultra-high-efficiency filters. The relevant standards can be found in IEST-RP-CC007; the most penetrating particle size method (MPPS), which uses a particle counter as a detection instrument and uses the same aerosol as before. This method is specified by the EU EN1822 standard. The difference from the particle counting method is that the particle size that is most easily penetrated by the filter is used as the test particle size; the sodium flame method uses a flame photometer to respond to the flame chromaticity of NaCL combustion. The relevant standards can be found in my country's "High-efficiency Air Filter GB13554-92", which has low sensitivity, and NaCl is harmful to the quality of microelectronic products and is no longer used abroad. For pharmaceutical companies, high-efficiency filter leak detection is mainly on-site leak detection, and the DOP method is used to find possible problems in the filter itself and during transportation and installation. Aerosol photometers and multi-dispersive aerosols are often used because they are more economical and convenient than monodisperse aerosols and can meet the requirements. 6.2 Aerosol photometers and particle counters The detection instrument can use an aerosol photometer or a particle counter. The particle counter detects the number distribution of particles, which is often expressed in "particles/L", while the photometer detects the mass concentration of particles, which is expressed in "mg/L". The particles with the largest number distribution and the particles with the largest concentration distribution are not at the same particle size, because the particle size and weight are in a cubic relationship, and large-size particles account for a larger proportion in the concentration distribution. Therefore, when testing the filter efficiency, the results obtained using a particle counter and a photometer will be different. Compared with a particle counter, the sensitivity and accuracy of the photometer are slightly worse, so it is not used to detect high-efficiency filters and ultra-high-efficiency filters above H13. For on-site leak detection of high-efficiency filters in pharmaceutical companies, photometers are widely used because they are easy to use, the test results are easy to judge, and they are sensitive to leak detection. 6.3 Leak detection standards Different standards also differ in the judgment of leak detection results. The US IEST-RP-CC034 stipulates that the on-site leak detection transmittance of C and D-grade high-efficiency filters is 0.3um, and the photometer scanning leak detection method) is 0.01. The EU EN1822 stipulates that the leak test is qualified as long as the local transmittance of the tested filter does not exceed the specified local value. The local transmittance corresponding to the H13 grade high-efficiency filter is 0.25%, but it should be noted that the transmittance here is obtained by the 0.3um monodisperse phase DOP test. In my country's "Cleanroom Design Specifications GB50073-2001 and High-efficiency Air Filters GB13554-92", regarding the leak test of installed filters, it is stipulated that atmospheric dust or other aerosols are used, and the leakage concentration is measured by a particle counter. For high-efficiency filters, the transmittance should not be greater than 2 times the factory-qualified transmittance of the filter. For the HEPA leak test of pharmaceutical companies, in actual testing, if there is a leak, the photometric count value will increase significantly, which is easy to judge. The high-efficiency filter leakage rate standard is set to less than or equal to 0.01% and does not affect the actual leakage detection. |
