Yes, this confusion among professionals is why companies have been advised to stay away from the expensive testing and filter replacements until you get dinged for it.
Lots of strong language in The Guidance, but lots of leeway to risk assess away for your product.
22.214.171.124 Testing can be conducted to validate the compressed air-filtration control system’s effectiveness based on the risk to the product; however, testing must be conducted at a minimum of once a year. Testing can be done in-house or by a contracted party. Test requirements and number of samples will be based on the risk to the product and process. Microbiological testing can include testing for aerobic plate count and/or indicator organisms as appropriate to the operation. Testing for moisture is to be considered if moisture is a potential risk to the product (e.g., dry operations).
Aseptic sample collection needs to be used. There are a wide variety of measures available, including the use of air sampling equipment, use of sterile sponges, membrane filtration and others.
The site may consider the following controls for particulates
i. Intake filters to remove atmospheric dirt and solid particulates.
ii. Microorganisms – A point-of-use filter, minimum 0.01 micron, prevent pathogenic microorganisms from contaminating food. An effective PM program should be in place to maintain the integrity of the filter. Validation from the filter manufacturer is often considered adequate validation.
iii. Water, including vapor, liquid, condensed. A dryer in the compressed air system provides effective control. An effective PM program should be in place.
iv. Oil, including vapor, liquid and aerosols. The presence of coalescing filters in the compressed air system effectively removes contamination. An effective PM program should be in place to maintain the integrity of the filter.
We installed a 0.01 micron filter, and the filter manufacturer says as long as the "Purity" Read Out on the machine does not go up, then the filter is still effective. I log this number twice every day.
The" ideal" practical solution from the lengthy verbiage in links in Post 24 and posts in this thread is surely to install a so-called "sterile" filter (SF) (which typically includes 0.01 micron level "control" ).
A commercial filter supplier analysis of SQF's requirements and a suitable filter response is detailed in sheets 3, 5 of the excel in Post 8 of the 2nd link in Post 24 above.
Note that the above sheets imply that for the filter set shown, microbial "content" is monitored but specific microbiological testing such as APC etc should be avoidable.
I assume the in-built Purity meters of Post 13 "somehow" integrate the, typically, 3 types of class measurement used in iso8573 (see sheet 4 in above referenced excel). IMO the acceptability of this option will depend on the availability of appropriate Validation (see red ^^^^)(eg Post 18).
NONETHELESS I speculate that it is possible (and presumably cheaper) that some people may be renting to use or have someone apply portable "air quality tester" kits. This option may have technical limitations from a strict ISO compliance POV but may perhaps "indicate" that the compressed air is of an acceptable "purity" Class (eg sheet 4 in above referenced excel). Such methods and their caveats are illustrated/discussed in attachment/link below.
Compressed Air Purity Testing,2019 - Validation to iso8573.pdf 2.09MB 6 downloads