Filter Integrity Test

Filter Integrity Test

Filter Integrity

PAO Method

(For testing HEPA) In the PAO test, a gas type of smoke will be generated by the PAO generator. After using the photometer to test the concentration on the upstream of the HEPA, a particle counter will be put at the air exhaust area to test the PAO concentration that passes through HEPA. The distance between the particle counter and HEPA will be around 25mm with testing speed at 50mm/sec. The test range includes HEPA filter and its connecting area. However, there are no related guidelines on the measurement method. Just make sure the whole HEPA covered area are tested for leakage. If there are particles over 0.03 are tested, hold the particle counter for 10 sec and then test back and forth at the range of 100mm. Once the particles are less than 0.03, proceed the test.

PAO efficiency (%) = ( 1-particle concentration at the HEPA air exhaust area / particle concentration at the HEPA upstream area ) × 100%.


(For testing Medium Filter or Bag Filter) This is to test the integrity of the Medium Filter mainly for particle size ≧1μm. There will be the same filter indicator paper at the up/downstream of the filter. After sampling, we calculate the filter integrity based on its transparency variation. Normally the NBS method and ASHRAE method ( 52.1 —92 Standard ) are applied. In 1968年, after modification and consolidation, it is called ASHRAE Efficiency or NBS. Both represent Colorimetry.

Q1:The sampling air volume through the upstream indicator paper.

Q2:The sampling air volume through the downstream indicator paper.

O1:The opacity of the upstream indicator paper with particles on it.

O2:The opacity of the downstream indicator paper with particles on it.

Colorimetry efficiency (%)=( 1- Q1/Q2×Q2/Q1)×100%


(For testing pre-filter) This is to test the efficiency of the pre-filter on larger particles which sizes are ≧5μm.

Normally AFI method (in 1960) and ASHRAE method (52.1—92 Standard) are applied.

It is called ASHRAE Arrestance or AFI. Both represent Arrestance.

Wf:The particle quantity supplied at the upstream of the filter(g)

Wp:The weight of the particles attached on the filter(g)

Arrestance efficiency (%)=( 1- Wp/Wf)×100%

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