1.0 PURPOSE:- To provide a guideline to ensure that HEPA filters are intact and suitable for operation.

 2.0 SCOPE:- Applicable to all HEPA filters installed in clean rooms.

 3.0 RESPONSBILITY:- Engineering Department.


 4.1 An aerosol photometer having threshold sensitivity below 10 microgram/litre for 0.3 micron particles of aerosolised Di Octyl Phthalate /Poly Alfa Olefin (DOP/PAO) and a sampling rate of 1 Cubic Feet Per Minute(CFM).

4.2 A DOP/PAO generator capable of producing a poly dispersed test aerosol having more than 92% of more than 1 micron.

4.3 Use vane type calibrated anemometer to measure the velocity of HEPA filter having accuracy of 1FPM.


 5.1 Start the AHU of which filter integrity checking is to be checked.

5.2 Ensure the power supply of photometer.

5.3 Start the compressed air/Nitrogen gas to generate the test aerosol at minimum pressure 20psi.

5.4 Direct the test aerosol at the return air point or fresh air intake of the AHU.

5.5 Put the photometer selector switch on upstream mode.

5.6 Connect the tube of photometer to the upstream port of HEPA housing.

5.7 Wait until the photometer displays 100% upstream concentration.

5.8 Remove the tube of photometer and close the upstream port of HEPA housing and ensure for Zero Leakage.

5.9 Put the photometer selector switch on downstream mode.

5.10 Wait until photometer displays ‘0’ (ZERO).

5.11 Measure the downstream concentration by holding the probe approximately 1 inch away from the face of filter.

5.12 Scan the entire filter face including perimeters with the probe of photometer in overlapping strokes, traversing at approximately 10 feet per minute (FPM).

5.13 Observe the percentage of leakage directly on the photometer.

5.14 If any leakages observed through the sealing of the filter inform engineering department and get things done, tighten the filter nuts and check again for any leakage.

5.15 Inform Quality Assurance and concerned department.

5.16 If the leakage is more than 0.01% of the upstream aerosol concentration then asks engg. department to repair it.