Reports of Dust Particle or Mold Levels in Buildings
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How to report levels of mold contamination in buildings:
This article discusses how to report levels of mold in buildings in order to promote consistent use of surface particle dust or mold test adhesive tape
sample descriptive language among microbiology lab and field investigation
Here we define levels of significance of mold findings in test results.
The definitions that follow are a work in progress and need
support by example lab photomicrographs and quantitative study. Our photographs here illustrate three very different densities of mold particles found in a series of indoor environmental samples.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Useful Definitions of Mold or Other Particle Densities in Indoor Environmental or Dust Samples
If collected by an expert during a careful visual inspection, and thus if
representative of conditions in a building, surface particle
samples collected in buildings provide an important building diagnostic
which can be expected to be more reliable than other popular mold
testing methods including some which, sadly, may be little more than junk science.
Take a look at our photograph of three adhesive tape sample collections (DUST / MOLD TEST KIT INSTRUCTIONS) on a moldy drywall surface in a laundry room. These samples are collected just one to 1.5" apart. Yet each of them will collect a completely different mold genera and species!
Watch out: in the case of drywall that has become wet from a flooded or wet floor, the moisture gradient in the drywall drops as we check levels higher above the wet floor or flood-water level.
A result of these moisture gradients is that completely different mold genera-species, each preferring different moisture levels, may grow at different heights on the drywall - sometimes just inches apart as in this photo.
In a compelling demonstration of the importance of mold sample location selection, for the three samples shown above, collected just an inch or so apart, in the lab we confirmed three different mold from the bottom up: Stachybotrys chartarum, Aspergillus sp., and Cladosporium sp.
Of these three molds, the Stachybotrys chartarum is most often the mold which consumers fear and which they ask their "mold expert" to find. But while Stachybotrys is indeed potentially harmful, Aspergillus sp. is far more likely to be airborne, to be breathed deeply into the lungs, and to be hazardous throughout a building where equally-sized reservoirs of the two molds are present. Therefore focusing on testing for "black mold" in buildings is a risky mistake.
Accuracy vs Precision: Nonsensical vs. Reasonable Reports of Mold Levels or Concentrations on Surfaces
Therefore quantitative reporting of mold concentrations found on surfaces (such as
spores/M3 or CFU/M2 on a surface) in buildings should not be attempted except for narrow purposes of scientific research under controlled conditions.
Shown at left, an example of test results for an airborne mold test. [Click to enlarge any image]
Why Some Mold Tests Are Not Helpful
OPINION: "air tests" for mold are unreliable: the actual mold spore count detected in an air sample can vary several orders of magnitude depending on just when, where, and how how a test is conducted, so a number of 270 could be 2.7 or 27,000 in actual truth.
Worse, when an air test finds high airborne problem mold spore counts that are high enough that it's very likely that there is an indoor mold problem needing to be addressed, such a report does not really tell us where the mold reservoir is, if there is one that needs action. So it is not telling us what needs to be done. Such a report is not prescriptive.
The building owner may have to pay a similar "mold inspection" fee all over again to actually find out what mold cleanup work is needed.
So the airborne mold count number is not so helpful unless accompanied by a competent, thorough onsite inspection to find the problem mold reservoir OR to tell you that enough looking in the most-suspect areas means that further action isn't justified.
Other types of "mold tests" have accuracy limitations too.
Once we are informed that only about 10% of the 1.5 million or so mold genera and species will grow on any culture whatsoever, even less credible than spores/M3 is CFU/M2 on a surface - as we elaborate at MOLD CULTURE TEST ERRORS.
indoor particle sample is representative of the area being inspected, then the
identity of significant or dominant particles present is important information
about conditions in the building.
If the indoor sample is not collected with intelligence, it is frankly, unreliable as a characterization of what contaminants are actually dominant or important in the building.
So can we make any use of a mold test report? Yes, maybe.
So do any mold numbers make sense? In our opinion, yes, as rough approximate counts, not as precise numbers.
In particular, very high counts of problem mold types indoors are almost certainly indicative of an indoor mold problem that needs to be addressed.
But low indoor mold counts might simply have missed a significant mold problem because of when, where, and how the test was conducted.
Experience tells us that there are general guidelines for airborne mold levels that suggest that a building is or is not harboring a significant, if hidden, problem mold reservoir.
Watch out: as we explain below at ENVIRONMENTAL TEST ERROR TYPES, while a high mold or other particle count number almost certainly has meaning, depending on test circumstances and how samples are collected, low numbers may be very unreliable.
Why then do we see these highly precise but inaccurate mold counts or dust counts? Some lab directors explain that such numbers are a response to marketing competition. "If we don't give numbers someone else will".
Reasonable & Useful Definitions of Indoor Mold or Dust Particle Levels: Not detected, Incidental, Present, Significant or Dominant
When we examine surface test samples collected in buildings, properly
obtained by following a visual inspection of the building and by using a clear,
consistent sampling procedure, then we can report the following
Non-Quantitative Particle or Mold Levels Based on Samples.
Our mold level terms "Significant/Dominant, Present, Incidental"
are defined below. Others may use similar terms such as "heavy, medium,
light", or "high, moderate, low. "
Particles not detected
in a dust or environmental air or surface sample means that the particle named was below the detection limit of
the inspection, sampling, and examination methods used in the field and
laboratory. It does not mean that none of these particles are present in
Watch out: "Particles not detected" does not mean that none of these particles are present in
the building. It means that the particles were not detected in the sample. The extent to which we are confident that the particle sample accurately represents building conditions is the extent to which we can generalize from "not detected" to "not present" in a building.
Particles Incidental in a
sample means that we found only occasional, or low-levels of fungal
spores in the sample provided-below the level we usually find in indoor air
samples in buildings where there has been a history of leaks, flooding, or
known mold contamination.
This is a positive description of the quality of
indoor air insofar as fungal spores are concerned, but one cannot
unequivocally conclude that there is no possible health hazard present
1. individual exposure, sensitivity, and health status vary
2. even a zero count does not guarantee that a particle is not
present in the building.
It means only that that particle was not in the
A careful, expert look at the building may disclose
particles that an occupant or inspector was unable to recognize and thus
did not send to the laboratory for determination.
Particles Present in a
sample means that these particles were frequently present in the
They are less likely to be of significance to occupants of the
building than "Significant/Dominant" particles except when
1. are particularly allergenic or toxic
2. suggest an
undiscovered building problem.
If the building has a history of leaks,
water entry, or other hidden moisture problems, the presence of even a few
toxic or allergenic spores which are not often found in outdoor air
samples may indicate a hidden problem.
If control samples from outdoors or
from non-complaint areas of a building do not show the presence of these
particles, further investigation is in order to determine if there is a
significant presence elsewhere in the building than from where this sample
Significant or Dominant in a sample means that within the sample these
particles were the most-frequent particle in the sample or that the
particle was present in most or all sample focal fields under the
microscope at 400x or higher magnification.
Problematic mold or allergenic
particles listed in this category are likely to be of significance to
occupants in the building.
Where the particle is a mold genera or species
capable of growing indoors a finding at this level makes it likely that
there is one (or more) mold reservoir or mold colony in the building. This
term refers to the sample content itself.
A visual inspection of the
property is needed to determine if the mold is present in extensive or
large areas in the building
. When the significant/dominant particle(s)
present is/are allergenic or toxic mold or an allergen, building
investigation to find and clean/remove the problem source is needed
This article explains how to report and understand the significance of the level of particles of mold or other particles found on indoor surfaces.
Readers should also see MOLD TESTING USING ADHESIVE TAPE where we provide a quick tutorial on "Mold Testing: Bulk or Tape Surface Samples and their interpretation"
If collected by an expert during a careful visual inspection, and thus if representative of conditions in a building, surface dust or settled dust and airborne debris particles (see DUST / MOLD TEST KIT INSTRUCTIONS) collected in buildings provide an important building diagnostic which can be expected to be more reliable than other popular mold
testing methods including some which, sadly, may be little more than junk science.
If an indoor particle sample is representative of the area being inspected, then the
identity of significant or dominant particles present is important information about conditions in the building.
Classes of Testing or Statistical Errors Applied to Mold or Other Environmental Tests, Inspections, Reports
At ENVIRONMENTAL TEST ERROR TYPES we explain in more detail the classes of testing or statistical errors and how in a practical sense they apply to mold or other environmental inspection, testing, lab and reporting procedures. Type 1 and Type 2 errors are defined along with practical examples taken from building inspection and testing for mold contamination.
Continue reading at MOLD TESTING & SAMPLING MISTAKES for more examples of how mold testing goes wrong, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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(June 3, 2014) Anonymous said:
we have some jute carpets which have been tested and the results are
Microfungi 2% malt --- 34 cfu/ 100cm2
microfungi DG 18 --- about 450 cfu/100 cm2
The mould is not visible to the eye.
Are these acceptable levels for Europe
Or are these dangerous levels
pl advise at my emai - firstname.lastname@example.org
Standards: Levels on Surfaces in Buildings provides information about allergenic, infectious, and levels of toxic
mold in residential buildings - at what point does the amount of mold in a building prove likely to be a problem for the occupants?
Mold Exposure Standards: Exposure Standards for Mold, Levels of Severity of Indoor Mold Contamination - Various Published Standards of Permissible Mold Exposure Limits: at what level is toxic or allergenic mold a problem? - What does your "spores per cubic meter of air" or "spore count" really mean - if anything?
MOLD EXPOSURE RISK LEVELS: How to Determine Mold Contamination Probability or Mold Exposure Risk Levels in Buildings Based on Visual Inspection
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home",
U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol
Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention in Home Vegetable Gardens,"
Department of Plant Microbiology and Pathology,
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Rot concerns in buildings-some building mold such as Meruliporia incrassata "Poria" risks serious rot and hidden structural damage
US EPA: Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol
OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold
Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold
cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.
Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings,
and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating
the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing
rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some
help from a licensed pest control expert.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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