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HEPA filter leak detection purpose
HEPA filter leak detection purposeThe filtration efficiency of the HEPA filter itself is generally tested by the manufacturer and is accompanied by a filter filtration efficiency report card and a certificate of conformity when it leaves the factory.For pharmaceutical enterprises, high-efficiency filter leak detection refers to the on-site leak detection of high-efficiency filters and their systems after installation, mainly to check small pinholes and other damages in the filter material, such as frame seals, gasket seals, and leaky seams on the filter frame. The purpose of leak detection is to check the tightness of the HEPA filter and its connection with the installation frame, to detect any defects in the HEPA filter itself and in the installation, and to take appropriate remedial measures to ensure the cleanliness of the area. The DOP generator can be divided into two kinds of hot generation and cold generation, the hot generator use of the principle of evaporation and condensation, the atomized aerosol particles evaporate with a heater and condense into tiny droplets under specific conditions, remove too large and too small droplets leaving about 0.3um of foggy DOP into the duct, particle size distribution in 0.1 to 0.3um. the cold generator is the use of compressed air in the liquid drum bubble, splashing through the Laskin nozzle to produce a polydisperse phase DOP aerosol in the material state, with a large distribution particle size of around 0.65um. Cold DOP is often used when scanning filters for leak detection. There are two kinds of testing instruments, one is an aerosol finisher and the other is a particle counter. The common testing instrument used in leak detection of high-efficiency filters is the aerosol finisher (hereinafter referred to as finisher), which is a pre-scattering linear finisher, consisting of a vacuum pump, finisher scattering chamber, finisher multiplier tube, signal processing converter, and microprocessor. The principle of operation is that when the airflow is pumped to the completion chamber by the vacuum pump, the particulate matter in it scatters the completion line to the completion multiplier tube. This signal is then amplified and digitized and analyzed by the microprocessor to determine the intensity of the scattered finish. The comparison with the signal generated by the reference substance enables the mass concentration of particulate matter in the gas to be measured directly, making it very versatile. Particle counters, on the other hand, reflect the concentration of the number of particles in the gas stream and provide for a range of particle sizes, are more sensitive and applicable to all dust source aerosols and have a wider choice, but are less frequently used in leak detection of high-efficiency filters and it is difficult to compare quantitatively the results of both instruments. The DOP leak detection method is usually used to detect leaks in high-efficiency filters by using a DOP generator to generate dust upstream of the filter and a photometer to detect the aerosol concentration upstream and downstream of the filter to determine whether the filter is leaking. The purpose of dust generation is to detect leaks without dust generation because the concentration of dust particles upstream of the HEPA filter is low and it is difficult to detect leaks with a particle counter. The artificial aerosol DOP has a history of nearly 40 years, but for some time now it has been replaced by DOS (Dioctylsebaeate sebacate), also known as DEHS [di(2-ethyl hexyl)sebacate] and PAO (polyaphaolefin), due to suspected carcinogenic effects on humans, but the experimental method is still called the "DOP method". The FDA states that when conducting leak detection, the aerosol chosen should meet the physical and chemical requirements and should not use aerosols that can cause microbial contamination and breeding. High-efficiency filters (HEPA) are generally filters with a particle size greater than or equal to 0.3um with a capture efficiency of 99.97% or more and are usually used as end filtration devices in the cleanroom of pharmaceutical companies to provide clean air. Whether the clean room can achieve and maintain the designed clean level is related to the performance of the high-efficiency filter and its installation. The FDA guidelines for sterile pharmaceutical production also state that leak testing should be carried out after installation of the HEPA filter to check the tightness of the filter gasket, frame and filter material, etc. Leak testing of HEPA filters should be carried out regularly in sterile manufacturing plants. High-efficiency filter DOP leak detection method To determine whether there are visible leaks in the HEPA filter itself and its installation, the following areas must be tested on site: the filter media; the connection between the filter media and the inside of its frame; between the gasket of the filter frame and the support frame of the filter set; between the support frame and the wall or ceiling. The aerosol generator used is the ATI TDA-6C. Hand-held Laskin nozzle-type aerosol generator, which uses air directly without compressed gas as power. It can produce polydisperse submicron oil and dust aerosols at a concentration of 10-100ug/mL at an air velocity of 50-2025f3/min at an operating pressure of 20Pa. The aerosol finisher used was an ATI 2H finisher with a dynamic measurement range of 0.00005 to 120ug/L and a sampling flow rate of 1F3/min (28.3L/min). Introduce PAO aerosol on the upstream side of the HEPA to be measured. For HEPA in HVAC systems, to achieve a uniform concentration of aerosol when it reaches the HEPA, the aerosol can be introduced directly from the negative pressure side of the system fan or, if introduced through the duct, at least 10 times the diameter of the duct from the HEPA, with a minimum of bends (American Society for Environmental Science and Technology). In general, it is sufficient to keep the upstream aerosol at the required concentration and to keep the concentration within the range. For HEPA on laminar flow hoods and ultraclean tables, aerosols are introduced directly from the negative pressure side of the system fan. Aerosol integrity meter initialization, setting, 0% reference standard value Initialise and set the alarm values according to the operating requirements of the aerosol integrity meter. Connect the UPSTREAM sampling tube to the upstream sampling port and measure the upstream aerosol concentration. Adjust the aerosol concentration occurring by the aerosol generator operating requirements to achieve an upstream aerosol concentration of 10-20ug/mL. |
