Establishing Limits for Compressed Air Testing

Hello,

I am new here and I am also relatively new to the QA field (~1year). I work for a CBD/Hemp manufacturing company and I am looking for clarity regarding our compressed air results I have received (see below). The method our lab uses is the "impinger" method where they run the compressed air through water for 15 minutes. We implemented a new compressed air line in April and after the addition of the filters we see that it improved to below the lab's LOQ after our re test in April. In December we tested again and showed issues with the 0.5 micron filter. We decided to replace the filter with a 0.1 micron filter and somehow still received a count for yeast and mold. My question comes down to why did I get two counts of Y&M after the 0.1 micron filter installation when it showed below LOQ on the last test for the 0.5 micron filter. Additionally, due to having little data for this new line, i have no established limits and am wondering if a count of 2 for Y&M is acceptable or if I should be striving for non-detect. This compressed air blows directly on a food contact surface. Any help would be superb, thanks so much!

April 2023 (No Filter):                         APC = 2 CFU/10ft³

                                                           Y&M = 4 CFU/10ft³

April 2023 (0.5 micron filter):              APC = <2 CFU/10ft³

                                                           Y&M = <2 CFU/10ft³

December 2023 (0.5 micron filter):    APC = 36 CFU/10ft³

                                                                      Y&M = 2 CFU/10ft³

December 2023 (0.5 micron filter):    APC = 98 CFU/10ft³

                                                                      Y&M = <2 CFU/10ft³

December 2023 (0.5 micron filter):    APC = <2 CFU/10ft³

                                                                      Y&M = <2 CFU/10ft³

January 2024 (0.1 micron filter):        APC = <2 CFU/10ft³

                                                           Y&M = 2 CFU/10ft³

IMO its not your filter size.  There are almost no bacteria, yeast or molds smaller than 0.5 microns let alone 0.1 micron.  

1.  where is the filter in relation to the point of use?  IE is contamination occurring after the fact?

2.   I am not familiar with the method used.   Can you share this?  Any chance for poor aseptic sampling?  

3.  At first thought, I personally would not be alarmed by your recent findings.

4.  Perhaps test the surface where air contacts.  for some added assurance your not contaminating  your surfaces

5.  Does the compressor have dryer and moisture filters / traps.   what do they indicate?

Thank you! After further investigation we realized the filter line had been installed incorrectly leading to the increase in micro counts.