HEPA filter leak testing procedure

- May 25, 2018-

Purpose of leak detection
  1. The material of high efficiency air filter is not damaged;

  2. Proper installation

    The filter efficiency of the efficient filter itself is usually detected by the manufacturer. The factory has the filter efficiency report and the certificate of qualification. For pharmaceutical companies. Efficiency report and the certificate of qualification. For hphmaceutical companies.HEPA filter leak detection means: High efficiency  filter and its system after installationon site.It is mainly to check the small pinhole and other damage in filter  material. Such as the frame seal, gasket seal and filter frame on the leankage seam. The purpose of the leak detection is by checking the sealing of the high efficiency filter and its connection to the installation frame, etc. Timely detection of defects in the filters them selves and the defects in the installation.

  3. Take appropriate remedial measures to ensure the cleanliness of the area. 

Test methods

1, Aerosol photometric method.

2, Particle counter test.

3,Full efficiency testing.

4,External gas test

Descriptions as follows

PAO detection is and aerosol photometer test.

Aerosol photometry is the earlist test method. But because it worked so well, it's still in use taday.

Aerosol photometer, one kind of particle counter, It's also using laser technology. But when after scanning the particles in the air sample what is the overall tensity of the particle. Not the nunber of particles in the air sample. DOP it's an oily chemical after pressure or heat atomization.It can produce sub-micron particles, Can be used to imitate the particles in the clean room. The definition of a leak is one in ten thousand leaked out of the upstream concentration. Because the aerosol photometer can directly show the ratio of upstream and downsteam particle concentrations so it's very convenient to scan high efficiency air filters. And because of it's accuracy and reliability, the U.S food and drug aadministration(FDA)rules: Within its jurisdiction(food processing place and medical and pharmaceutical place) All high-efficency air filter leakage tests must use DOP and aerogel photometer.

For some time, It is suspected to be carcinogenic to humans, Now often in DOS(Diotylsebaeate)to also be called DEHS[di(2-ethylexy1) sebacate]and PAO(polyaphaolefin to substitute) But the experimental method is still called DOP method. As the concentration of atmospheric dust varies with location and time sometimes larger some times lower. Usaually not used as a leak detector.

The FDA point out that when it comes to leak detection, Selected aerosol it shold meet certain physical and chemical requirements. Do not use aerosols that cause microbial contanination and cause microbial growth.

DOP generator it can be divided into heat generation and cold generation. The heat generator uses the principle of evaporation and condensation aerosol particles atomized, and it condenses into tiny droplets under certain conditions. Remove large and small drops the foggy DOP left about 0.3um into the duct the particle size distribution is from 0.1 to 0.3um. Cold generator refers to through the laskin nozzle  use compressed air to bubble up in liquid, the splash produces a polydisperse phase of the physical state aerosol.The maximun grain size of distribution is about 0.65um. At present, there are more commonly used thermal DOP.

Aerosol photometer Aerosol generator.

Aerogel Photemeter display screen have two kinds anolog and digital display , It must be rectify once a year. Aerosol generator have two kinds:one is and ordinary particle generator, only require high pressure air, the other is a heated particle generaor. High pressure air and electric power are required. Aerosol generator do not require correction.

Testing instrument

●Aerosol Photometer

●Aerosol Generator

●HEPA filter

●Dust-free services


Record the nunmber and number of HEPA filter on the graph

DOP test filter method.jpg

Make sure the air-conditioning system is working properly and ready for testing, wind speed and volume must be adjusted and balanced.

Apply challange particles upstream using aerosol generators, put the PAO upstream of the high efficiency air filter, Particle concentrations is about 10 to 20 micrograms of PAO per liter of air. The more particles there are, the easier it is to find the leak, but over 50 micrograms, the difference was small. Less than 10 is hard to use.the particle concentraiton can be calculated roughly by air volume then reconfirm with aerogel photometer.

When the upstream particle concentration is confirmed, you can scan the surface of the high efficiency air filter, check for the leaks, when necessary, the HEPA filter can be covered with plastic curtain to ensure the accuracy of testing. Scan the surface of the high efficiency air filter the scan path can be from outside to inside or circuitous detection along the edge. 

Here's how it works

A: Each HEPA filer and its border shall be tested 

B: When the detector is on the surface of HEPA filter , the detector is arranged as shown in the figure.

Goin with the short side edge, cover all air filters

C: When scanning the high efficiency air filter border, Especially between efficiency air filters and the ceiling grid, The leak detector can be arranged as shown above. or (B) Cover all seams. 

D.Using conical sampling apparatus of particle counter, put under high efficienccy air filter about 25mm. Move with a 50mm/sec speedometer,Therefore, if the value is greater than 0.01, the leak can be suspected. It can be returned to about 100mm for repeated measurement/If the reading is not consistently high , The test can ve continued. If there is a leak, it should be recorded and repaired or replaced. HEPA filters should be repaired or renewed if it damaged. If the border is leaking, reinstall and adjust until no leakage occurs. Scan results, leak status and solve method must be recorded.


For HEPA in HVAC system, In order to make the aerosol reach the HEPA in a uniform concentration. The Aerosol can be introduced directly from the negative pressure side of the system fan, To be introduced from the HEPA, and minimize turning,(American institute of environmental science and technology). Normally keep the upstream aerosol at the required concentration, And the concentration fluctuation can be within a certain range.For the laminar flow cabinet ultra- clean platform HEPA, The aerosol is introduced directly from the negative pressure side of the system fan.


Acceptance of the benchmark,

1, Any continuous read value greater than 0.01%is considered a leak 

2, No leakage is allowed after each piece of high efficiency air filter is tested and repaired. And the border should not leak. The repair area of each high efficiency air filter shall not be greater than 3% of the high efficiency air filter area

3, Any repair shall not be greater than 38mm length.