Why not take Outdoor Samples every time??
Basically it is because our “focus is on interior conditions of the space.” Many insurance companies and attorneys expect to see indoor-outdoor comparisons. So, reluctantly, NES takes them under those conditions. However, over the years NES has seen that indoor conditions, where there has been water intrusion of some kind, are vastly different in the mix of spores found, dominated by the “primary colonizers” or, as we call them, “moisture/leak indicators,” namely Asp/Pen-like spores or Cladosporium. Those values are the keys to interpreting the indoor conditions at the time of our sampling as to whether there has been amplification of molds indoors and whether Informal Guidelines are exceeded. Consider these issues:
The outdoor spores “today” are not reflective of interior conditions today! They will be mostly common “outdoor spores” as explained in our reports and have not had a chance to migrate through closed windows and doors, etc. much less amplify in response to interior conditions; they just do not do that. The spores that entered the house weeks and months ago are THE ones that are of concern since they, especially the “indoor” spores like Aspergillus/Penicillium, have been affected by subsequent moisture conditions in the house and could have amplified, as we often find.
In a research paper carrying out statistical analysis on 108 sets of data from across the country involving 235 outdoor and 422 indoor samples for total airborne fungal spores, “COMPARISON OF INDOOR AND OUTDOOR AIRBORNE FUNGAL SPORE CONCENTRATIONS IN RESIDENTIAL PROPERTIES,” by Joe C. Spurgeon, Daniel W. Bridge and Marshall E. Krotenberg (see www.bi-air.com) the authors conclude that “…under the conditions tested in this study, which were typical of residential mold investigations, the method of data interpretation based on comparing indoor to outdoor concentrations of airborne spores had limited utility” (emphasis added).
Also, NES’s focus is on the presence of settled spores (Condition 2 Contamination) since that category is important to confirm/refute our hypothesis (i.e. reason for sampling). The “Professional Mold Remediation Standard and Guideline” (IICRC S520-2008) referred to in our reports calls for cleaning Condition 2 as well as Condition 3 contamination (actual mold growth – active or inactive, visible or hidden) and does not worry about potential future entry of “outdoor” spores; hence our paired sampling technique (quiet/disturbed) and our focus on conditions impacting the occupants now.
Secondarily, there is some cost savings in not taking those outdoor samples that have “limited utility.”
Please contact NES to answer questions you may have about this topic.
© 2015 – Nauset Environmental Services, Inc.