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The penetration rate of hepa filters is also known as initial resistance.
The penetration rate of hepa filters is also known as initial resistance.The penetration rate is an important indicator for evaluating the purification effect of filters. It can be determined by experiments and test methods and is affected by the filter material and design. The specific formula is K=(1−α)×100%, where KKK represents the penetration rate of the high-efficiency filter, and α\alphaα represents the efficiency of the DOP high-efficiency filter. This calculation method is mainly used to evaluate the performance of the filter in the leakage test after installation, especially in laminar or turbulent environments that need to reach a cleanliness level of 10,000 or higher. It is particularly important to conduct leakage tests. According to experience, when the filter material performance is determined, the resistance of the high-efficiency filter is greatly related to the structure of the high-efficiency filter, and the resulting impact is about 50Pa. The high-efficiency filter accumulates dust and the resistance increases. When the resistance increases to a certain specified value, the filter is scrapped. The resistance of a new high-efficiency filter is called "initial resistance"; the resistance value corresponding to the scrapping of the high-efficiency filter is called "final resistance". When designing, a representative resistance value is often needed to calculate the design air volume of the system. This resistance value is called "design resistance. The usual method is to take the average of the initial resistance and the final resistance. It can also be tested at the rated air volume, or it can be tested at 0.45m/s. In addition, first, determine whether the filter frame is leaking or between the filter and the box. If the former leaks, it can only be repaired or replaced. For the latter, check whether the filter is not laid flat or the parallelism of the filter is problematic, and whether the sealing strip is intact. These may cause leakage. High-efficiency filter leak detection process and cycle High-efficiency filter leak detection process High-efficiency filter leak detection 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 is leaking. High-efficiency filter detection The leakage process mainly includes the following steps: (1) Prepare test equipment and materials: The tester needs to prepare PAO/DOP particle generator, aerosol photometer, protective equipment such as gloves and masks, and filter test stand or equipment. At the same time, it is necessary to check whether the equipment is in normal working condition. (2) Install the filter: Install the high-efficiency filter to be tested on the test stand and connect the aerosol photometer. During the installation process, it is necessary to check whether the filter is damaged or contaminated. (3) Spray PAO/DOP particles: Spray PAO/DOP particles evenly in the upstream area of the filter to simulate the particles in the indoor air. The time and method of spraying need to be carried out by relevant standards and operating procedures. (4) Detect PAO /DOP particle concentration: After spraying, use an aerosol photometer to measure the external PAO/DOP particle concentration. The tester needs to record the measurement results and conduct evaluation and analysis according to the standard requirements. (5) Analysis of test results: Based on the measurement results, the tester analyzes the leakage and location of the filter. If the photometer prompts an alarm, it means that the filter is leaking and the location of the leak needs to be further located. In addition, the performance of the filter can be evaluated and the test results and evaluation report can be recorded. (6) Scanning for leaks: Remove the HEPA diffuser and scan the entire filter surface, the seal between the filter and the frame, between the frames, and between the frame and the static pressure box. When scanning, the sampling head is about 1 inch (about 2.54cm) away from the filter surface. Scan The speed should not exceed 5cm/s. The scanning is performed back and forth in a straight line, and the lines should overlap. During the test, if there is an alarm (i.e. %LEAKAGE (leakage rate) exceeds 0.01%), it indicates a leak. The leaking part is sealed with silicone or tightened before scanning and inspection. It takes about 5 minutes to check a filter. During the test, the concentration of upstream aerosol should be confirmed frequently. Note that protective masks and goggles should be worn during the test. (7) 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 there is a point where the % exceeds 0.01%, it is judged to be unqualified and marked and needs to be repaired or replaced. The leakage of the high-efficiency filter material can be repaired with special glue, but the area of a single leakage point cannot be greater than 1% of the total area, and the area of all leakage points cannot be greater than 5% of the total area, otherwise, it must be replaced. High-efficiency filter leak detection cycle (1) The FDA recommends that leak detection be conducted every six months in the sterile drug production guide, and my country recommends that it be conducted once a year in the GMP inspection guide. (2) ISO14644 recommends a long interval of 24 months for leak detection of installed HEPA. DOP leak detection should be conducted after HEPA is installed or replaced. (3) 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. |
