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Replacement standards for HEPA filters Aug 14, 2018
  1. Check the air volume in the clean area regularly every year and other environmental parameters, the HEPA is tested at the same time.

  2. Air flow velocity detection, final resistance and leakage rate.

  3. When the HEPA filter is reduced to 75% of the rated air volume, the filter needs to be replaced.

  4. Replacement is required when the final resistance is twice the initial resistance.

  5. Replacement is required when the air flow velocity is below 0.35m/s


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Solutions:

1, There are too many factors influencing the service life if HEPA filter: Humidity and dust condition in workshop, operation mode of air etc., It is difficult to set the replacement cycle, GMP standards do not specific it, recommendations are based on validation results, HVAC is a key syttem of drug of production, so reverification should done once a year. According to the measured air speed efficiency filter leak detection and other conditions to detemine whether to replace.there must be no block, no leak, no moldy, sedimentation bacteria(planton) are up to the mustard. 

2, HEPA filtes should be replaced when down to 75% of rated air flow volume: There's no rule about it. Theoretically, should test the cleanliness level in clean room first, and then scan effectively only when the clealiness is not up to standard. The air flow velocity can also be measured with an anemoneter.As GMP stipulates that the high efficiency filter must be replaced when it's air flow velocity less than 0.35. The air supply of general clean room design is 60%~80% of rated air flow, in this way , the test resistance is more than 2 times of the initial resistance and should be replaced. The test resistance is more than twice the initial resistance and should be replaced.


3,CLean room design specification: The required conditions for replacement of HEPA filter.

1> The air velocity falls to the lowest limit.

2> The resistance is twice the initial resistance value

3> Unrecoverable leakabe occur.


The most practicla test method is:

1 Scan the wind speed to make sure there is no blockage; The wind speed was unifirm and reached the required value

2 Then leak test, make sure thereis no leakage and the test is basically qualified. DOP test the cost is much, it's improbable be measured every six months, there is also the risk of HEPA filer congestion by DOP test.There for , the method of measuring resistance are come to common use method. That is to install the differential pressure gauge at each HEPA teminal box, then use resistance changes to detemine whether need to replacement HEPA filter. And it can be auto-monitor, ther service life of HEPA filter can reach more than 3 years.