 |
|
The Facts About Biological Sampling |
| |
Biological air sampling is sometimes necessary to determine whether a particular environment is causing adverse affects in certain individuals. There are a number of testing methods available, but only certain ones provide sound scientific evidence in commercial or educational facilities.
Sampling with a gravity culture plate is likely to provide misleading information. In this process, the media plate is opened and is left uncovered on a horizontal surface. Air currents, air temperature, and the size and weight of the airborne spores can bias the kind of spores which settle onto the plate.
Swabbing surfaces for cultures, can also provide misleading information since spore types differ greatly in their ability to grow on laboratory media.
Scientific comparisons are possible when measured volumes of air are sampled and the results are expressed in terms of volumetric measurements, such as colony forming units (CFUs) per cubic meter of air sampled.
The most commonly used volumetric instrument is the Andersen Sampler. With this tool, measured volumes of air are drawn through the instrument which contains a petri dish (or dishes) with growth media. Airborne spores are drawn in, and they impact onto the surface of the media plate. The plate is then allowed to incubate and grow, after which colonies can be speciated and counted.
When the results of this type of study are compared to same-day sampling of the outdoor air, it can be determined if the indoor air represents an influx of outside contaminants or if there is a source for the contamination found indoors.
Other types of instruments used for this sampling (designed to draw airborne contaminants, but not to incubate) include the Burkhard, Allergenco, or Zefon spore traps.
Whatever method your IAQ investigator chooses to employ, make sure that the results can be justified in a scientific manner. Starting a survey with sound science means that any problems in your building can be addressed quicker and resolved easier. |
|
|
|