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How to set wind speed, leak detection process, and cycle when testing high-efficiency filters
How to set wind speed, leak detection process, and cycle when testing high-efficiency filtersHow to set wind speed, leak detection process, and cycle when testing high-efficiency filtersIn the purification project, some customers reported that more than 100 particles were leaked in the gap between the high-efficiency filter and the high-efficiency air supply box, but they could not find the reason. What is the appropriate value of the surface wind speed of the high-efficiency filter when leaking? After the high-efficiency filter is installed, before the workshop cleanliness test, when picking up the leak of the high-efficiency filter, what range should the wind speed of the high-efficiency filter be controlled within? The installed high-efficiency filter leaks a lot of particles. What causes it? The air volume used by the high-efficiency filter: Experienced designs generally take 80% of the rated air volume, which is more reasonable. For example, 484*484*220, the rated air volume given by the manufacturer is 1000, and the actual air volume used is less than 800, which is more economical and reasonable. When the filter is leaking, the effect may be better when the wind speed is lower. (Especially when using DOP leak detection) During the leak detection process, if the filter is determined to be intact and the side seam detection fails, there are two main reasons. One is the quality of the box, which makes it difficult to seal during installation. The other reason is the impact of the environment, which can be identified by doing enclosure detection on the air outlet. High-efficiency filter leak detection process and cycle 1. High-efficiency filter leak detection process 1.1 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 the 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 turning 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. 1.2 Initialize the aerosol photometer and set the reference standard values of 100% and 0%. Initialize and set the alarm value according to the operating requirements of the aerosol photometer. Connect the UPSTREAM sampling tube to the upstream sampling port to measure the concentration of the 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. 1.3 Scanning for leak detection Remove the HEPA diffuser and scan the entire filter surface, the seal between the filter and the frame, between the frame and the frame, and between the frame and the static pressure box. During the scan, 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 is carried out back and forth in a straight line, and the lines should overlap. During the test, if there is an alarm sound (that is, %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 aerosol should be frequently confirmed. Note that protective masks and goggles should be worn during the test. 2. Result determination and processing The leakage rate of the high-efficiency filter 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 for repair or replacement. The leakage of the high-efficiency filter material is allowed to 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. 3. Leak detection cycle of high-efficiency filters FDA recommends that the production workshop of sterile preparations should be leak-checked every six months in the sterile drug production guide, and my country recommends that it should be done 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 testing should be performed after HEPA is installed or replaced. Leak testing can be performed as part of a deviation investigation when environmental monitoring shows deterioration in air quality, when product sterility tests fail, or when simulated culture medium filling tests fail. Filters that need to be leak tested also include HEPA filters used in drying tunnels and dry ovens. |
