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T his month newsletter provides additional guidelines for interpreting numerical data of 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. 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.
- 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., Ic ≤ Oc 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., Ic ≤ Oc 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., Ic > Oc x 2, then indoor source is likely and immediate further investigations are required.
- 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., Ic - Oc ≤ 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., Ic - Oc > 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., Ic - Oc > 800, then indoor source is likely and further investigations are required immediately.
- Consider the concentration of Chaetomium spp.
- If the concentration in indoor air is lower or equal to the concentration in outside air, i.e., Ic ≤ Oc, 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., Ic - Oc ≤ 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., Ic - Oc > 5, then indoor source is likely and further investigations are required immediately.
- Consider the concentration of Stachybotrys spp.
- If the concentration in indoor air is lower or equal to the concentration in outside air, i.e., Ic ≤ Oc, 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., Ic - Oc ≤ 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., Ic - Oc > 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., Ic - Oc ≤ 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., Ic - Oc > 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., Ic - Oc > 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., Ic - Oc ≤ 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., Ic - Oc > 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., Ic - Oc > 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 newsletter. Visit our website for more mould and bacteria information at www.moldbacteria.com
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.
ABOUT THE AUTHOR:
Dr. Jackson Kung’u is a Microbiologist who has specialised in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America and also a technical member of ASTM International, Subcommittee D22.08, currently working on standards for air sampling and analytical methods for mould. Jackson has analysed thousands of mould samples from across Canada. He helped one of the labs in Ontario to obtain AIHA accreditation. Jackson provides how-to advice on indoor mould and bacteria issues. Get more information about indoor mould and bacteria at http://www.moldbacteria.com.
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