Overview – Non-culturable Sampling
Non-culturable spore trap samplers draw measured volumes of air through the sampling device for a specified length of time. The collection surface is a coated glass slide. Particles in the air (spores, dust, etc.) impact onto the sticky surface and are "trapped" for later analysis. Allergenco/Blewstone Press and Burkard Manufacturing both make spore trap sampling devices which accept standard glass slides which are greased by the user. Another company, Zefon International manufactures disposable spore trap Air-O-Cell cassettes. The primary advantage of Zefon's Air-O-Cell is their relatively low cost and small size (easy to transport, useful in small spaces). All of these devices have excellent aerodynamic characteristics and are very effective in monitoring airborne particles and organisms.
Our philosophy regarding the interpretation of biological air samples is formed primarily by two guiding principles. First, an effective interpretation is based on the comparison of indoor and outdoor samples. There are currently no guidelines or regulations to indicate "safe" or "normal" spore levels, however, we typically expect indoor counts to be 30 to 80 percent of outdoor spore counts, with the same general distribution of spore types present. And second, variation is an inherent part of biological air sampling. The presence or absence of a few genera in small numbers should not be considered abnormal.
Spore trap samplers are capable of capturing all spores and particulate matter in the air. Consequently, it is possible to accurately characterize problem environments where spores are present but either are no longer viable or are species that do not culture well (i.e. Stachybotrys). These are two situations where culturable sampling techniques, if used alone, may miss a potential indoor air quality problem.
While many mold spores have a unique morphology and are identifiable by direct microscopic examination, others do not and are more difficult to identify. These latter types must be counted in broader spore groups.
A few tips...
A five minute sampling time (at 15 lpm) for spore trap samples is a good starting point. Sampling times should be reduced if visible mold growth is present, if dust is excessive, or if semi-aggressive sampling techniques are utilized. Sampling locations should include problem areas, an indoor non-problem area if available, and an outdoor sample (or samples) for interpretation. Allergenco and Burkard samplers both require glass slides which are prepared with grease. We recommend that you use only a thin coating of clear grease. Lubriseal is a good choice. Please remember that air sampling data represents a specific moment in time, and that field observations are of equal importance. Sampling at multiple times may be helpful.
The recommended industry practice for the number of field blanks is to provide two field blanks for every 10 samples with a maximum of 10 field blanks for each sample set.
Reference: Jensen, Paul A., Ph.D., PE, CIH, and Schafer, Millie P., Ph.D., NIOSH/DPSE "Sampling and Characterization of Bioaerosols", NIOSH Manual of Analytical Methods, Chapter J, 1/15/98.