HEPA Filter Replacement

Dear Sir,

In validation of HEPA filter , while performing leak test by PAO/DOP if it passes the test than what should be the frequency fo replacement of HEPA filter and what are the criteria for the same. Please guide on the same

Hi there,

During commissioning (before validation) the room flows are set up to the drawing requirements. With the correct flows established, the filter ‘clean’ pressure drop can be observed or measured. The filter flow and filter pressure drop can now be used to calculate (using the filter makers flow graph) the filter dirty pressure drop - the pressure drop at which the filter is considered ‘blinded’ and requires changing.

This calculation must be documented (SOP or Method Statement) and is often the subject of regulatory reviews. It is obvious that this must be establish with a new filter that is certified to be clean.

The answer to your question therefore is; the filter must be changed when the dirty filter change pressure drop is arrived at. That might be years or months depending how hard the filter has to work.

Alex Kennedy

I agree with Alex for his scientific answer but to have an arrangement & measure pressure drop of each and every filter is not practicable. Rather I would prefer to have following logical criteria for replacement of HEPA filter.
1- Filter does not deliver required air flow/velocity: This shall take care of air balancing, ACPH or velocity whatever is expected. (Being periodic activity, it can be detected)
2- If it meets above on border but clean room shows poor behavior with regard to particulate count and the reason of which is attributable to HEPA.(This too is routine activity)
3- If HEPA fails in Integrity test.

Dear All,

As our validation frequency ( PAO/ DOP test ) is 1 year. But if in meantime there will be leakage in filter how can we come to know ? Or if only one filter is observed the ruptured. will we have to validate it ? Or If the third party is too long from the site how to comply?

Dear Sir,

Can any body reply this query ?

Vinod Kumbhar

Your validation frequency is based on ISO-14644-2 GUIDELINE.
Normally there will not be any problems.
When you have a HEPA filter integrity problems, you will have high bacterial counts , high particulate counts in your facility.
Bacterial counts are monitored frequently and such increase should be attented immediately.
Particulate counts are checked in some facilities every 3 months or 2 months once to see that there is no problem with HEPA.

If you fail to detect the reason why your microbial counts are increasing go and test for air praticle count. Any slight breach would tell you where the problem is.Call the third party and test the filter integrity.

I personally do not know if you are an engineer or a Microbiologist. This particular problm should be attended by Engineering section based on the micribial count data given by your Microbiology departments.

Sudden breach of HEPA will be only caused if it acidentally punctured by another hard material during cleaning or other procedures.Some times the silicon sealent will peel off if you use some cheap materials.
First identify the cause why it breached suddenly.
You have to do a root cause analysis study.
Before and after intallation of a new HEPA you have to decontaminate all your clean rooms and revalidate the whole area and show both Microbial and particulate counts are with in regulatory limits along with the air flow pattern tests.
Any replacement of a part in a validated system will become useless.You have to revalidate whole system.
Its a big work for both Engineering and Microbiology staff.

Dears sirs,

all the above mention information are very helpful regarding the HEPA filters replacement.

What i want to ask is if there is any article or guideline indicating the required frequency for the HEPA filters?

Thank you in advance

Hello liliadis,

I am not aware of guideline about HEPA replacement frequency.
There are many installations and machines with HEPAs, running under different operational (one or more shifts, continuous operation) and environmental conditions, which affect filter lifetime.
You should consider the results of HEPA regular tests, supplier recommendations and also own experience. Or experience of the other users with the same/similar HEPA installation and conditions.

HEPA filters should be replaced always when:

  1. the recommended air velocity under filter cannot be readjusted any more. This can indicate that HEPA is clogged.
  2. the filter resistance reaches HEPA supplier’s max. admissible pressure. This indicates that HEPA is clogged. But in practice HEPAs used to be replaced sooner due to energy savings.
  3. the pressure drop reaches approx.-10% of the initial pressure. This indicates leak.
  4. the leak test not passed
  5. replacement is necessary according to the replacement intervals (recommended by supplier or based on own experience) .

FAQ from the one HEPA supplier is attached.


FAQ HEPAs and ULPAs Technical Bulletin.pdf (643.7 KB)

Dear Adrian,

thank you vary much for your reply.

the PDF file you send me is very usefull.

Best regards!

Lazaros Iliadis