Winter brings a unique situation for environmental consultants, and mold testing in winter presents a unique advantage. With the colder weather and snow cover on the ground that comes with winter in Chicago, there are usually very low outdoor mold levels. Occasionally we can even see outdoor air samples that have no spores present. If you recall from my last blog post on interpreting mold results, environmental professionals use outdoor air samples as a primary guide for determining if there is evidence of indoor mold growth. In areas where there are consistent sub-freezing outdoor temperatures or where snow cover persists for the entirety of winter, some inspectors will choose not to collect an outdoor sample. Here in Chicago, our winters can be dynamic. We can go from 40 degrees and no snow cover to sub-zero and 5” of snow on the ground in the blink of the eye. Even periods of a brief thaw can cause outdoor fungal levels to spike, and therefore affect the natural levels of mold in the indoor air. Because of this, we always collect an outdoor reference sample. So, how do they know if something is elevated when the outdoor control sample is very, very low?
Without the scope of an outdoor air sample, we have to be extra careful with interpreting the indoor results. We use indoor control samples in unaffected areas as one guide. This helps establish what “normal” levels would be expected in the building. Moderate levels of common outdoor types such as Aspergillus/Penicillium and Cladosporium indoors, which in the warmer months may be similar to the outdoor levels, in winter can be signs of possible indoor mold growth when an outdoor source can be ruled out. Also, any amount of water damage indicating mold found indoors, such as Chaetomium, Stachybotrys, or Fusarium to name a few, found in the indoor samples raise concern.
Interpreting air samples can be one of the largest challenges for an environmental professional. There are no concrete guidelines available and the results are unique to each job. Having someone who is well trained and experienced reviewing your results is one of the most important factors in identifying mold concerns indoors.