1. No damage to the material of the high-efficiency air filter;
2. Proper installation.
The filtration efficiency of the high-efficiency filter itself is generally tested by the manufacturer, and the filter filtration efficiency report card and certificate of conformity are attached to the filter when it leaves the factory. For pharmaceutical companies, high efficiency filter leakage detection refers to the high efficiency filter and its system after the installation of the site leakage detection, mainly to check the filter filter material in the small pinhole and other damage, such as frame sealing, gasket sealing, and filter frame leakage joints. The purpose of the leakage check is to discover the defects in the high-efficiency filter itself and in the installation in time by checking the sealing of the high-efficiency filter and its connecting parts with the installation frame, etc., and to take corresponding remedial measures to ensure the cleanliness of the area.
High-efficiency filter leakage detection methods
The leakage test of high-efficiency air filters is basically to apply challenging particles upstream of the high-efficiency air filters, and then search for leakage on the surface of the high-efficiency air filters and the borders with a particle detection instrument. There are several different types of leakage tests that are used in different situations.
The test methods are:
1. Aerosol photometer test method
2. Particle counter test method
3. Full efficiency test method
4. Outside air test method
Descriptions are as follows.
PAO leakage detection belongs to the aerosol photometer test method
Aerosol photometer:
The aerosol photometer test method is the earliest test method, but because of the very good results, it is still used today.
The Aerosol Photometer (Aerosol Photometer) is a type of particle counter that also uses laser technology, but it scans air samples for particles and gives the overall intensity of the particles, not the number of particles. DOP is an oily chemical that, when pressurized or heated and atomized, produces sub-micron particles, which can be used to mimic cleanroom particles. particles and is therefore treated as a validation particle. Leakage is defined as leakage out of the upstream concentration of one part in 10,000. Scanning for HEPA filters is very convenient because the aerogel photometer directly displays the ratio of the upstream and downstream particle concentrations. Because of its accuracy and reliability, the U.S. Food and Drug Administration (FDA) requires that all leakage tests of HEPA filters within its jurisdiction (food processing sites and medical and pharmaceutical sites) must be performed using DOP and aerosol photometers.
For a period of time, because it is suspected of having a carcinogenic effect on people, is now often DOS (Dioctylsebaeate decanedioic acid dioctyl ester), also known as DEHS [di (2-ethylexyl) sebacate] and PAO (polyaphaolefin poly a olefin) and so on instead of the experimental method is still called. The experimental method is still called "DOP method".
Atmospheric dust, because its concentration varies with location and time, sometimes larger, sometimes lower, generally not used as a leak detection. FDA pointed out that in leak detection, the choice of aerosol should meet certain physical and chemical requirements, and should not be used to cause microbial contamination, resulting in microbial growth of the aerosol.
DOP generator can be divided into hot and cold generation of two kinds, hot generator is the use of the principle of evaporation and condensation, the atomized aerosol particles with a heater to evaporate and condense into tiny droplets under specific conditions, remove the oversized and small droplets to leave a mist of 0.3um or so of the DOP into the air ducts, the size distribution of the particles in the range of 0.1 ~ 0.3um. Cold generator refers to the use of compressed air bubbles in the liquid, through the laskin nozzle splash to produce the material state of the polydisperse phase DOP aerosol, the maximum distribution of particle size of about 0.65um. There are many hot DOPs in common use, so the efficiency of the filter should be guaranteed.
Testing Instruments:
The instruments used are an Aerosol Photometer and an Aerosol Generator. The Aerosol Photometer has both analog and digital displays and must be calibrated once a year. There are two types of Aerosol Generators, one is the normal Aerosol Generator, which requires only high pressure air, and the other is the Heated Aerosol Generator, which requires high pressure air and a power supply, and the Aerosol Generator does not need to be calibrated.
Tools/Materials
Aerosol Photometer
Aerosol Generator
High Efficiency Air Filter
Dust Free Suit
Methods/Steps
1
. Record the number of HEPA filters on the chart and number them.
2
Make sure that the air conditioning system is functioning properly and is ready for testing, and that the air speed and air volume must be adjusted and balanced.
3
Using an aerosol generator to apply challenge particles upstream, PAO is pumped upstream of the HEPA filters at a concentration of about 10 to 20 micrograms of PAO per liter of air. the more particles the easier it is to find leaks, but there is not much difference after 50 micrograms, and it is difficult to use them with fewer than 10 micrograms. The concentration of particles can be roughly calculated by airflow and confirmed by an aerosol photometer.
4
After the upstream particle concentration is confirmed, the surface of the HEPA filter can be scanned for leaks, and if necessary, the HEPA filter can be surrounded by a plastic curtain to ensure the accuracy of the test.
5
Scanning the surface of the HEPA filter, the scanning path can be from the outside to the inside or along the long/short edges of the meandering test, in the following ways:
a. Each HEPA filter and its frame should be tested.
b. For the surface of the HEPA filter, set up the leak detector as shown in Fig. (b), and move forward with the short side to cover the whole HEPA filter.
c. When scanning the edges of the HEPA filter, especially between the HEPA filter and the Ceiling Grid, the Leak Detector can be positioned as shown above to cover all the seams.
d. Use the square cone-shaped (10mm*60mm) sampler of the particle counter to place about 25mm under the HEPA filter, and then move it at a speed of 50mm/sec.
e. Aerosol photometer readings are upstream and downstream percentage values, so if the value is greater than 0.01, you can suspect leakage, can be returned to about 100mm repeatedly retest, if there is no sustained high readings, you can continue to test, and vice versa that is, there is a leak, need to be documented and repaired or replaced in the future.
6
High-efficiency air filters should be repaired or renewed if they are damaged, and then retested.
7
If there is any leakage in the frame, it should be re-installed and adjusted until there is no leakage.
8
Documentation must register the scanning results, leakage status and treatment.
Note: For HEPA in HVAC systems, to achieve uniform concentration of aerosol when it reaches the HEPA, introduce the aerosol directly from the negative pressure side of the system blower, or if it is to be introduced from the duct, introduce it at least 10 times the diameter of the duct from the HEPA, and minimize the bends (American Academy of Environmental Science and Technology). In general, it is sufficient to keep the upstream aerosol at the required concentration and the concentration fluctuating within a certain range. For HEPA on laminar flow hoods and ultra-clean benches, aerosols are introduced directly from the negative pressure side of the system fan.
Acceptance criteria
1. Any continuity reading of more than 0.01% is considered to be leakage, and there shall be no leakage in each HEPA filter after testing and replacement, and there shall be no leakage in the border.
2. The repair area of each HEPA filter shall not be greater than 3% of the area of the HEPA filter.
3. The length of any repair shall not be larger than 38㎜.