Guidelines for Interpreting Numerical Data of Non-viable (Spore Traps) and Viable Airborne Mould Samples

In this article we discuss additional guidelines for interpreting numerical data for viable and non-viable airborne mould samples.

The guidelines may be used to decide whether further investigations are required after initial investigations. However, numerical laboratory results cannot be used as the primary determinant of whether there is a mould problem but should always be used together with visual inspection data and other available information such as the building history. See our course How To Interpret Mold Results.

Generally, indoor airborne mould concentrations are compared with those of outdoor. The presence of one or more species of mould indoors, but not outdoors, suggests presence of a growth source in the building. This comparison may not be possible during winter since outside concentrations may be below the detection limits as mould growth is slowed by the cold weather. The same principles for comparing outside with indoor can be used to compare the test rooms with the control rooms.

These guidelines are mainly summarized from those developed by the German Federal Environmental Agency (Umweltbundesamt, 2002) and the Health Canada (Indoor Air Quality in Office Buildings: A Technical Guide, 1993).

Guidelines for Interpretation of Numerical Data of Non-viable Mould Air Samples

For a comprehensive assessment of the sample results, all the six steps require to be followed where applicable.

1. Consider the concentrations of spore types which may reach high concentrations in the outside environment (for example Ascospores, Alternaria/Ulocladium, Basidiospores, Cladosporium).
   • If the total concentration of these spore types in the indoor air is lower than or equal to 1 to 1.4 times the outside concentration, i.e., I_c ≤ O_c x 1 (+0.4), then indoor source is unlikely (background level).
   • If the total concentration of these spore types in the indoor air is lower than or equal to 1.6 (± 0.4) times the outside concentration, i.e., I_c ≤ O_c x 1.6 (± 0.4), then indoor source is possible and further investigations are required.
   • If the total concentration of these spore types in the indoor air is more than twice the concentration in outside air, i.e., I_c > O_c x 2, then indoor source is likely and immediate further investigations are required.

1. Consider the concentration of Penicillium/Aspergillus spore types.
   • If the difference in concentration between indoor air and outside air is lower than or equal to 300 spores/m3, i.e., I_c – O_c ≤ 300, then indoor source is unlikely (background level).
   • If the difference in concentration between indoor air and outside air is greater than 300 spores/m3 but lower than or equal to 800 spores/m3 i.e., I_c – O_c > 300 ≤ 800, then indoor source is possible and further investigations are required.
   • If the difference in concentration between indoor air and outside air is more than 800 spores/m3, i.e., I_c – O_c> 800, then indoor source is likely and further investigations are required immediately.

     

2. Consider the concentration of Chaetomium spp.

•  If the concentration in indoor air is lower or equal to the concentration in outside air, i.e., I_c ≤ O_c, then indoor source is unlikely (background level).

• If the difference in concentration between indoor air and outside air is lower than or equal to 5 spores, i.e., I_c – O_c ≤ 5, then indoor source is possible and further investigations are required.
• If the difference in concentration between indoor air and outside air exceeds 5 spores, i.e., I_c – O_c > 5, then indoor source is likely and further investigations are required immediately.
• Consider the concentration of Stachybotrysspp.
  • If the concentration in indoor air is lower or equal to the concentration in outside air, i.e., I_c ≤ O_c, then indoor source is unlikely (background level).
  • If the difference in concentration between indoor air and outside air is not more than 2 spores, i.e., I_c – O_c ≤ 2, then indoor source is possible and further investigations are required.
  • If the difference in concentration between indoor air and outside air exceeds 2 spores, i.e., I_c – O_c > 2, then indoor source is likely and further investigations are required immediately.
• Consider the concentration of various other unidentified fungal spores that do not belong to the basidiospore or ascospore types.
  • If the difference in concentration between indoor air and outside air is not more than 400 spores/m³, i.e., I_c – O_c ≤ 400, then indoor source is unlikely (background level).
  • If the difference in concentration between indoor air and outside air is greater than 400 spores/m³ but not more than 800 spores/m³, i.e., I_c – O_c > 400 ≤ 800, then indoor source is possible and further investigations are required.
  • If the difference in concentration between indoor air and outside air is exceeds 800 spores/m³, i.e., I_c – O_c > 800, then indoor source is likely and further investigations are required immediately.
• Consider the concentration of hyphal fragments.
  • If the difference in concentration between indoor air and outside air does not exceed 150 fragments/m³, i.e., I_c – O_c ≤ 150, then indoor source is unlikely (background level).
  • If the difference in concentration between indoor air and outside air is greater than 150 fragments/m³ but not more than 300 fragments/m³, i.e., I_c – O_c > 150 ≤ 300, then indoor source is possible and further investigations are required.
  • If the difference in concentration between indoor air and outside air exceeds 300 fragments/m³, i.e., I_c – O_c > 300, then indoor source is probable and further investigations are required immediately.

Guidelines for Interpretation of Numerical Data of Viable Airborne Mould Samples

These will be covered in Part II of this article. Or feel free to visit our homepage to view more mould and bacteria testing information, resources and services.

References

Health Canada (1993). Indoor air quality in office buildings: a technical guide. A report of the Federal Provincial Advisory Committee on Environmental and Occupational Health. 55 pp.

Umweltbundesamt (2002). Leitfaden zur Vorbeugung, Untersuchung, Bewertung und Sanierung von Schimmelpilzwachstum in Innenräumen. Erstellt durch die Innenraumlufthygienekommission des Umweltbundesamtes.

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Dr Jackson Kung'u

Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at www.drjacksonkungu.com.

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