Room air sampling is the most common and perhaps most misunderstood form of mold testing.
Room air sampling works by using devices that collect air from a specific area. The air sampler draw air through an inlet and direct that air into a collector. A filter screen out larger particles and a media plate or filter media capture the mold spores.
Next, the captured spores can then be analyzed in a laboratory under a microscope to identify the type and concentration of mold spores, categorizing them by their appearance. This information may be valuable for assessing indoor air quality, particularly when compared with a baseline outdoors air sample.
If room air sampling detects toxic molds associated with water-damage, such as Stachybotrys, or excessively high levels of mold, the result indicates a probable indoor air quality issue.
If, however, there is no toxic mold or abnormally high mold level, the results are not necessarily conclusive. A “normal” air sample may or may not indicate an indoor air quality issue. A dangerous assumption is a “normal” air sample proves that a home has clean indoor air.
Here are 5 reasons a damp moldy building might be associated with normal room air sampling results.
- Overloading — In dusty environments, non-biological particles, such as soot, can obscure fungal spores. The background dustiness prevents visualization of the mold spores preventing them from being appropriately counted or categorized by type.
- Time constraints — Air samplers are typically run for minutes. But, in some cases, hours or even days of air collection may be needed to capture mold spores in certain environments.
- Inability to measure mold fragments — The focus of air sampling are whole intact mold spores. But mold fragments, which also constitute a health hazard, are not counted. And that’s a huge oversight because these fragments outnumber mold spores by between 300 to 1,000 times!
- Unidirectional collection — The air sampler inlet faces in one direction. Ideally, the inlet will face into the air flow, which allows a higher degree of sampling. By contrast, if the inlet is positioned facing awayfrom the air flow, spuriously low levels will be sampled.
- Collection efficiency — Mold spores with unusual sizes, shapes, and surfaces might not be efficiently collected. A water-loving mold such as Chaetomium has a lemon-shape that makes it elusive.
Case in Point
To conclude, I will describe a study of how room air sampling can have an over-80% error rate for detecting Stachybotrys (“toxic black mold”).
In 200 water-damaged houses in the Houston area, 58.5% of the houses contained Stachybotrys spores, proven by at least one of three sampling methods—room air sampling, wall cavity air sampling and surface swabbing. Yet only 9.6% of the room air samples contained Stachybotrys spores.
Put another way, room air sampling detects Stachybotrys less than 20% of the time in a room known to contain this toxic mold.
A normal room air sample therefore does not, by itself, establish safe building conditions.