I have questions for you regarding testing for clearance protocol and data interpretation for a two-story building: 1.  Is 150 liters of air evaluated for airborne fungal spore concentration a good measurement?  One sample collected in the downstairs living room and another sample collected in the upstairs central hallway, adjacent to the hall closet.  The particulate matter from the air samples shall be trapped in Air-O-Cell particle traps, designed for airborne fungal spore collection and evaluation.  The sample collection cassettes consigned to a microbiological laboratory for microscopic analyses for Total (Viable and non-Viable) fungal counts. 2.  Each surface sample collected on clear tape shall be submitted for microscopic analysis for total mold spore content.  Samples containing greater than 99% environmental dust and less than 1% of identifiable mold spores shall be considered acceptable latent mold concentrations within the unit.  Samples containing 1% or greater of identifiable mold spores shall have failed the test, and the living unit has unacceptable mold contamination. Is this a feasible clearance requirement?  I am just worried where the less than 1 percent is coming from?  What is going to be established? T.A. – South Carolina 

            This protocol has a number of limitations/deficiencies.  They are addressed in the context of your questions. 

            A volume of 150L is not commonly used in the airborne mold sampling either for culturable/viable or total mold spore sampling. More appropriately a sampling volume of 75L is recommended for total airborne mold sampling using Air-O-Cell cassettes. 

            The protocol should specify the count magnification (I recommend only 1000X) used by the analytical laboratory and the maximum acceptable level of airborne spores on clearance sampling (this can include specific mold types). 

            Sampling should be conducted in all areas subject to remediation as well as a reference area that has the potential for being contaminated as a result of remediation activities.  An outdoor sample should also be collected for comparison purposes to determine whether indoor and outdoor mold are from different sampling populations. 

Surface sampling by the use of sticky clear tape is a relatively new activity in post-remediation clearance.  As such, there is very little information available as to what analytical results mean.  The clearance criterion of 1% of identifiable mold spores has no relevance to normal levels in a building based on scientific studies.  On an intuitive basis a 1% mold concentration could be a relatively high level of mold in surface dust.  The actual concentration would depend on the amount of mold spores/particles present, the amount of dust, the ability of the tape to “lift” particles from the surface, the particle size distribution and the magnification used for analyses. 

            No matter what the clearance criteria is, results of surface sampling will be highly dependent on dust deposition patterns (which are not uniform) particularly in disturbance situations such as those that occur in remediation.  One would have to take multiple samples in each space to be assured that the results are valid. 

            As these comments indicate clearance criteria not sufficiently described and validated by scientific studies to provide building owners the confidence they want that a remediation has been completed in a manner that minimizes mold exposure risks.

 

July 9, 2004