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HEPA Filter Leak Detection System
HEPA Filter Leak Detection System
High-efficiency filter leak detection system for pharmaceutical factories and clean rooms
For enterprises, HEPA leak detection refers to the on-site leak detection of HEPA filters and their systems after installation, mainly to check for small pinholes and other damages in the filter media, such as frame seals, gasket seals, and filters. Slots in the frame, 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 sealing of the high-efficiency filter and its connection with the installation frame, and take corresponding remedial measures to ensure the cleanliness of the area.
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 enterprises, HEPA leak detection refers to the on-site leak detection of HEPA filters and their systems after installation, mainly to check for small pinholes and other damages in the filter media, such as frame seals, gasket seals, and filters. Slots in the frame, 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 sealing of the high-efficiency filter and its connection with the installation frame, and take corresponding remedial measures to ensure the cleanliness of the area.
Principle of DOP leak detection method
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 has leaks. 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.
Artificial aerosol DOP has a history of nearly 40 years. For a period of time, due to suspected carcinogenic effects on humans, it is now often referred to as DOS (Dioctylsebaeate dioctyl sebacate), also known as DEHS [di(2-ethylexyl)sebacate] and PAO (polyaphao lefin poly-alpha olefin) is used instead, but the experimental method is still called "DOP method". Because the concentration of atmospheric dust varies with location and time, sometimes it is higher and sometimes lower, and it is generally not used for leak detection. The FDA pointed out that when conducting leak detection, the selected aerosols should meet certain physical and chemical requirements, and aerosols that would cause microbial contamination and microbial growth should not be used.
PAO generators can be divided into two types: heat generation and cold generation. The heat generator uses the principle of evaporative condensation. The atomized aerosol particles are evaporated by a heater and condensed into tiny droplets under specific conditions to remove excessive and After the droplets are too small, a misty DOP of about 0.3 μm is left into the air duct, and the particle size distribution is 0.1~0.3 μm. The cold generator refers to the use of compressed air to bubble bubbles in the liquid, and splashing through the laskin nozzle to generate a polydisperse phase DOP aerosol in the physical state, and the maximum distribution particle size is about 0.65μm. Use cold DOP when scanning filters for leaks.
There are two kinds of detection instruments, one is an aerosol photometer, and the other is a particle counter. It consists of a vacuum pump, a light scattering chamber, a photomultiplier tube, a signal processing converter and a microprocessor. It works as follows: When the air flow is pumped into the light scattering chamber by a vacuum pump, 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. The particle counter, its test value reflects the concentration-particle size of the number of particles in the airflow, and specifies the particle size range, its sensitivity is high, it is suitable for all dust source aerosols, and the choice is large, but in the high-efficiency filter It is rarely used in leak detection, and it is difficult to quantitatively compare the test results of the two instruments. For the on-site leak detection of high-efficiency filters in pharmaceutical companies, the photometer is widely used because it is easy to use, easy to judge the detection results, and sensitive to leak detection.
Regulations on leak detection of high-efficiency filters
The tested aerosols were polydisperse PAO aerosols with a mass median diameter of 0.5-0.7 μm and a geometric standard deviation of 1.7.
There are two types of testing instruments: aerosol photometer and particle counter. Aerosol photometer measures mass concentration, in μg/L, and particle counter measures particle number concentration, in particle/L. Both methods are acceptable. Meet the requirements of leak detection. For the on-site leak detection of high-efficiency filters in pharmaceutical companies, photometers are widely used because of the convenience of use, the easy judgment of test results, and the sensitivity to leak detection. It is the development trend of efficient leak detection in the future.
When using a photometer for detection, the upstream concentration should reach 20~80μg/L, and it should not fluctuate too much, and it is allowed to fluctuate within 15% of the average value.
The downstream scanning leak detection should use an isokinetic sampling head to ensure the measurement accuracy. The scanning rate is related to the size of the sampling head. The judgment of the leakage position should be based on whether the leakage rate exceeds 0.01% when the sampling head is stationary.
Detection method
To determine whether the HEPA filter itself and its installation have obvious leakage, the following points must be tested on site: the filter media of the filter; the connection of the filter media of the filter to the inside of its frame; the gasket and filter of the filter frame between the support frame of the device group; between the support frame and the wall or ceiling. DOP leak detection materials and instruments are: dust source (PAO solvent), ZR-1300 series aerosol generator, ZR-6000 series aerosol photometer.
Introduce PAO aerosol on the upstream side of the HEPA to be tested
For the 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 bends (IEST 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.
Aerosol photometer initialization, setting reference standard value
Initialize and set the alarm value according to the operation requirements of the aerosol photometer. Connect the sampling tube to the upstream sampling port, and measure the concentration of the upstream aerosol. Adjust the generated aerosol concentration according to the operation requirements of the aerosol generator, so that the upstream aerosol concentration reaches 20-80 μg/L.
Scan 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 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 rate exceeds 0.01%), it indicates that there is leakage. After the leak is plugged or tightened with silica gel, the scanning inspection is carried out. It takes about 5~10 minutes to check a filter. During the test, the concentration of the upstream aerosol should always be confirmed. Note that protective masks and goggles should be worn during the test.
Result judgment and processing
The leakage rate of the high-efficiency filter should be less than or equal to 0.01%. If the leakage rate of HEPA at all points does not exceed 0.01% during the detection process, the HEPA is judged to be qualified, and if there is more than 0.01%, it is judged to be unqualified, and the point is marked and needs to be repaired or replaced. 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.
HEPA filter leak detection cycle
In the sterile drug production guidelines, the FDA recommends that the production workshop of sterile preparations should be inspected for leaks every six months. In my country, the GMP inspection guidelines suggest that it is usually once a year. ISO 14644-3:2005 for leak detection of installed HEPA with a recommended maximum interval of 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.
System and FAQ
The composition of the commonly used high-efficiency filter leak detection system is as follows:
Aerosol generator (PAO, DOP generator): ZR-1300 type, ZR-1301 type, ZR-1302 type;
Aerosol photometer (leak detector): ZR-6000 type, ZR-6010 type, packing box;
IQ, OQ, PQ certification documents.
According to the feedback of some users after actual use, the company has summarized some common problems.
1. How should the high efficiency filter be transformed?
Since the construction methods involved in the leak detection of high-efficiency filters are not clearly specified in the domestic standards, the leak detection structures of filters designed by many construction parties are not standardized, mainly because of the position of the end of the upstream aerosol injection pipe, and there is no distinction between the injection port and the The upstream detection port prevents the aerosol from being mixed evenly. Therefore, during construction, it should be strictly required that the end of the injection port pipeline should be kept away from the surface of the high-efficiency filter to provide enough space to mix the aerosol evenly. For the on-site leak detection of the clean room high-efficiency filter, the user should reserve two holes during construction, one for the upstream aerosol injection hole, and use a pipeline with a diameter of ¢5*8mm or more, and the pipeline should not be too thin, otherwise it will cause If the resistance is too large, the upstream aerosol concentration cannot reach the specified value. Connect the pipeline to the upstream air duct of the filter, and the distance from the surface of the high-efficiency filter should be at least 10 times the diameter of the air duct (IEST American Institute of Environmental Science and Technology). The purpose of the aerosol injection position being far away from the surface of the high-efficiency filter is to provide enough space to make the aerosol fully mixed evenly and ensure the accuracy of the test results. The other hole is the upstream aerosol detection hole, just connect the pipeline to the vicinity of the filter surface.
2. Efficiency and leak detection of high efficiency filters
The efficiency of the high-efficiency filter refers to the filtration performance of the filter itself, which varies with the implementation standards and testing methods. Detection methods include sodium flame method, oil mist method, counting method, etc. The detection of filtration efficiency is completed by the manufacturer.
For pharmaceutical companies, the leak detection of high-efficiency filters is mainly on-site leak detection, and the DOP method is used to find out the possible problems in the filter itself and in the process of transportation and installation. Aerosol photometers and polydisperse aerosols are often used for leak detection. The standard is based on the 2010 GMP guideline for pharmaceuticals (the test method adopts ISO14644-3).
3. Leak detection aerosol particle size
Many users have learned from the data that the high-efficiency filter has a filtration efficiency of 0.3 μm particles greater than 99.97%, so it is believed that the particle size of the leak detection aerosol should also be 0.3 μm. Depending on the method, the particle size of the aerosol used is also different. For the on-site leak detection of high-efficiency filters, the International Organization for Standardization stipulates that the polydisperse phase PAO (or DOS, DEHS, etc.) with a mass median diameter of 0.5~0.7 μm should be used. ) aerosol.
4. Which effect is better between aerosol photometer and particle counter for on-site leak detection?
Particle counters detect the number distribution of particles, often expressed in units of "particles/L", while photometers detect the mass concentration of particles, expressed in "μg/L". The particles with the largest number distribution and the particles with the largest concentration distribution are not in the same particle size, because the particle size and the weight have a cubic relationship, and the particles with the large particle size occupy a larger proportion in the concentration distribution. As a result, there is a difference between the results obtained using a particle counter and a photometer when examining filter efficiency. Compared with particle counters, photometers are slightly less sensitive and accurate, so they are not used to detect high efficiency filters and ultra-high efficiency filters above H13. For the on-site leak detection of high-efficiency filters in pharmaceutical companies, the photometer is widely used because it is easy to use, easy to judge the detection results, and sensitive to leak detection.
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