HEPA Filter Patch Considerations 

Most companies which utilize HEPA filters, or are involved in the routine certification of HEPA filters in the pharmaceutical industry, are well aware of the Institute of Environmental Sciences recommended practices concerning the testing of HEPA filters.  The “recommended practice”, which outlines the acceptable testing and repairing of the HEPA filter is IEST-RP-CC034.2, HEPA and ULPA Filter Leak Test.  The recommended practice states the following:

Field repair should not block or restrict more than an additional 3% of the filter face area, and no single repair should have a lesser dimension exceeding 3.8 cm (1.5 in.).

When reading this statement it appears that it is in line with how a recommendation should be phrased.  Verbiage is very important in the pharmaceutical industry, as most know; “should” has a very different meaning than “shall”.  The recommended practice goes on to state:

…  Repairs to filter leaks may be made by procedures acceptable to the customer and the supplier…  Filter integrity requirements are a matter for agreement between the customer and the supplier.

For many past years this did indeed seem to be a recommendation.  Recently many pharmaceutical companies have been required to enforce the maximum recommendation patch size and filter coverage percentage as an absolute pass or fail criteria.  It is as if this recommended practice has now become a requirement concerning acceptable HEPA filter patches.

It appears that the location of the patch does not seem to be of any concern currently.  Take for example a HEPA filter located within an equipment pass through airlock or vestibule.  If this filter has a repair that exceeds the minimum dimension of 3.8 cm (1.5 in.) should the filter be replaced?  Again, apparently this is the case now within the pharmaceutical industry.  Location of the patch or proximity to any critical operation does not seem to be of any concern.  One would certainly agree that if a patched area of the HEPA filter was located directly above a critical filling operation it would be prudent to replace the HEPA.  What about a filter located twenty feet from any critical operation?  What about a filter which has a patch which measures two inches by two inches, and is located in the ceiling over the beginning of a fill line and is eight feet from the line?  Is the suggestion from the “required” replacement of the filter due to patch size because of the thought that the airflow will be impacted negatively?

As anyone who is somewhat knowledgeable within the HEPA filter testing industry can see, this example of a patched HEPA will not negatively impact the operation of the cleanroom, or quite frankly the airflow of the HEPA.  Why does the industry still recommend measuring the airflow “no more than 30 cm (12 in.) from the supply source.”¹?  If one is so concerned about the patch affecting airflow, shouldn’t the measurement of the airflow be at the precise critical operation level?

It appears that the industry as a whole has gotten away from the idea that we as an industry can make sensible proper decisions without being told exactly how to do it.  It is in the best interest of the pharmaceutical companies to maintain safety for their clients of the items they manufacture; otherwise they will loss in the end.

Where will this all end?  Maybe the next requirement will be that no patching of any HEPA filters is acceptable.  Believe it or not, there are already pharmaceutical companies implementing this in there own procedures.  Hooray for the HEPA manufacturers’, so sorry for the end users of the pharmaceutical items being produced, because as we all know, someone will be paying for it in the end.

Gertrude Stein once said:  “Everybody gets so much information all day long that they lose their common sense.”  Wouldn’t we all agree, in this industry there is much information, let’s not lose our common sense.

Michael D. Alleman

President

Air Safe, LLC. 

1.  IEST-RP-CC006.3; Testing Cleanrooms