Good points raised here.
Compressed Air Testing can assist the manufacturer in several ways.
- Proving or disproving that your filters are working properly
- Showing if you have an issue with your system and the air being used for your product, pre or post filter
- Assisting with narrowing the location of the actual problem
Contamination can happen anywhere in the system as pointed out previously. Filters are great but they can fail and/or something can go wrong after the filter. Testing at the point of use is the best way to see what is actually happening where the air is finally used. Also, each point of use can have a different result. Just because one point of use performs as intended does not mean they all do. This is why testing all points of use should be implemented even if it is on a rotation basis.
ISO 8573 is a great spec to refer to and possibly the most comprehensive on the subject. I would be interested in any other comprehensive specifications on the subject if anyone knows of any.
As far as the original poster's questions:
- should there be any colonies? No, if there are you should identify them to assist in determining your problem
- should yeast and mold tests also be conducted? Yes
- where is the literature on industry standard? http://www.webstore.ansi.org/ You can type in ISO 8573 and find it.
It does seem odd that you are getting any count after using a 0.01 micron filter when you relate the size of bacteria to this. I have to say that monthly testing is more frequent than most companies that I have come across.
Points to consider:
Is the filter at point of use or at the compressor itself.
Where is the filter(s) in relation to the sample points.
You can get microbial growth within the compressed air pipework, particularly if it is designed on a ring main basis.
Check for dead legs in the pipework.
Mould spores do germinate in compressed air pipework, but if the filter is at point of use this should not be a problem.
Clarify how the engineers/contractors monitor the air filters. In my experience, engineers look at a dial/gauge and change the filter when it goes into the 'red' or blocked zone. From a food safety perspective rather than an engineering view, the danger is the reverse ie when the filter has broken down and the pore size is no longer as small as it was when installed. When the filter breaks down, the guage will not show as blocked and they may not change it. Before and after differential pressure gauges will show if the filter has broken down.
There are a couple of relevant(ish) ISO Standards - ISO8573 for compressed air and ISO 12500 for air filters. I don't have copies unfortunately.
There is another grade of filter commonly called "medical grade" which may be appropriate depending upon your application
