"While there is no fixed (nor fix-able) standard of absolute allowable "spore counts" in air (we'd need a standard for every genera and species by toxicity, weight, mobility, etc.), investigators have now seen so many moldy and not-moldy buildings, and complaint and non-complaint areas that it's reasonable to have some general guidelines about what levels are probably a problem and what levels may not be a problem." Jan. 2010 http://www.inspectapedia.com/sickhouse/SampMeth.htm.
While mold air sampling, through the use of air o cell cassettes establishes elevated mold levels via a comparative exterior air sample test, it has been subject to criticism. Although some call for a conclusive set standard, it is naive to think that millions of molds (at varying levels) could be determined for each and every living person as harmful or not harmful, in an absolute and categorical way.
The current air o cell (air sampling) "standards" rely on cumulative scientific study (microbiology was established in the 19th century) to determine what molds are harmful to humans. Even after 200 years of microbiology research, science is unable to definitively pinpoint precisely what molds are harmful to humans at varying levels for each individual person. On the other hand, by using this cumulative research, mold laboratories are able to determine what molds are elevated in a building and also which ones can be potentially be harmful by analysis of air o cell (air sampling) tests and compared to cumulative microbiology research. Although this method is also somewhat generalized it uses the best research to this date.
Attempts have been made to "standardize" mold exposure thresholds, by the US government (via EPA, CDC, FEMA), in which vacuum bag samples were collected from approximately 1096 home owners in different regions of the US, and the results averaged to conclude what specifically defines a mold problem for all people. As a result, the ERMI and ARMI testing protocols were born. Although, more precise in identification of mold species, currently these tests have more drawbacks in their sampling methods than traditional air o cell (air sample testing) or swab sample testing.
"Quantitative Analysis producing low results is unreliable: Building conditions vary enormously, causing huge variations in what particles may be found in the air at any given time. Particle levels vary by a factor of at least several orders of magnitude due to common variations in building conditions such as fan on off, human activity, mechanical disturbance of moldy stuff, etc." Jan. 2010 http://www.inspectapedia.com/sickhouse/SampMeth.htm.
Buildings that have not been used for quite some time (bank-owned or for-sale properties) will have a lower level of human/mechanical activity. It is for this reason that a visual inspection for mold(s) and appropriate additional testing (if feasible) in addition to air o cell air sampling, are needed. Generally the total lack of human/mechanical activity will lower humidity levels and temperatures in the building, thus making molds more difficult to survive. Although, air o cell air sample testing is not as precise in the case of an unoccupied building, it is the best available general indicator at the time of this writing and under these circumstances. Combined with other tests (if feasible) and a certified mold inspection, this combination is the best available approach for evaluation mold issues in unoccupied & occupied buildings.
What happens if air sampling produces "higher" results due to human/mechanical activity?
The reason the air is being tested in the first place is because the home/building owner has suspected mold(s) usually due to ill health effects. Although some state that the varying conditions in the home are a drawback to accurate testing, we feel that the air sample testing should be conducted under normal operating conditions when the occupants are there. We encourage "human activity" when the owner walks on the carpeting "naturally" stirring up the mold spores that would be normally present upon occupation. We encourage natural human activity & mechanical disturbances in using the bathroom or cook top fans. After all if air levels were tested in a home that was not used for a few days or more, unnatural habitation levels will be detected thereby giving inaccurate results under normal operating conditions.
"Quantitative results which are superficially similar between indoors and outdoors may be misleading: An outdoor "Pen/Asp” count of 500 spores/M3 may have captured a genera or species which is completely different from a corresponding indoor "Pen/Asp" count which also found 400 spores/M3 ." http://www.inspectapedia.com/sickhouse/SampMeth.htm. Jan. 2010
First off air o cell mold air sampling bases it findings on genus (aka "genra") alone. What the statement should read is: "Quantitative results which are superficially similar between indoors and outdoors may be misleading: An outdoor "Pen/Aspergillus" count of 500 spores/M3 may have captured a species which is completely different from a corresponding indoor "Penicillium chrysogenum" count which also found 400 spores/M3 ."
If varying levels of "Pen/Asp" are found in the exterior and outdoor levels, that is completely normal. That is the whole basis of air o cell air sample testing and what is used to determine whether or not there is an elevated or non elevated mold condition in the exterior of the building. On the other hand, the statement is theoretically correct (after being re-worded) in that there are drawbacks in identifying different species of similar genus, "Pen/Aspergillus" versus "Penicillium chrysogenum" which would produce "misleading" results. Through our experience, it is rare to find a similar genus with varying species classifications in the same geographical area tested almost at the same exact time as the interior air sample is performed. This is why further testing may be needed (if possible) and a mold inspection performed.
"Quantitative results which seem "low" and qualify as a "clean building" may be misleading: a lab reporting an outdoor "Pen/Asp" count of 700 and an indoor "Pen/Asp" count of 450 may look like an acceptably "clean" building - the indoor count is "below the outdoor count." But suppose in fact the outdoor "Pen/Asp" is actually an unidentified amerospore, or a basidiomycete mis-classified, or is a common outdoor species of Penicillium, while the indoor "Pen./Asp" is actually representing Aspergillus Niger? This is an argument for doing some subsequent culture work or better lab microscopy (Aspergillus Niger can be identified by light microscope alone.) In this case the "low" level of 450 spores may in fact be a weak indicator of a large problem mold reservoir in the building." Jan. 2010 http://www.inspectapedia.com/sickhouse/SampMeth.htm.
This is, for the most part, the same statement/question as above but, stated in a more concise way. Although it is true that any microbiologist is subject to the human error in any mold analysis situation, it is rather alarmist to suggest this is a reason against mold testing. In the example of mistaken species (Pen/Asp versus Aspergillus Niger) if the exterior air sample showed a count of 700 for Pen/Asp and mistakenly classified the indoor sample to be elevated for Aspergillus Niger or vice versa, any mold testing "expert" would recommend mold remediation since Aspergillus Niger (or vice versa) was found in elevated levels in the building since both molds are harmful to humans. Say if the exterior sample was misread as Aspergillus Niger (the same as the interior), more than likely no elevated mold levels would theoretically exist since the exterior sample mistakenly matches the correctly analyzed indoor sample at similar levels. It would be highly unlikely that a microbiologist would look at 2 similar samples back to back and incorrectly differentiate mold samples that look remarkably the same under the microscope.
In Conclusion:
Critics & Mold Testers alike are aware of Air O Cell sampling limitations of these devices. Unfortunately, we can not rely on one single method to determine whether or not a building has elevated or unusual mold levels. Air O Cell sampling, even with its faults, is still the single, most cost effective way in determining air borne mold levels within a specific amount of space. Combined with a certified mold inspection and potentially, other methods of testing; there is no better way(s) at the time of this writing to as effectively determine elevated interior mold air levels.
But, the home/building owner are in ultimate control of what services are to be performed. Home/Building owners generally follow the least path of monetary resistance when choosing the type of inspection and/or testing performed. Recommendations can only be given by a professional mold services company in the hopes that the client understands the reasoning behind the recommendations.
Ohio Mold Inspections - Air Sampling Mold Testing Limitations