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5 Reasons a “Normal” Air Sample Result Might Not Mean Your Home is Safe

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.

  1. 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.
  2. 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.
  3. 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!
  4. 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.
  5. 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.