Variation in Air Sampling Tests for Mold
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How much variation occurs when using air sampling to test for mold?
What is the range of variation in air test samples for mold and what does that say about the accuracy of air tests used to state mold exposure?

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How much variation do we see when using Air Sampling to test for Mold Exposure or Contamination Levels in Buildings? Here we demonstrate that indoor airborne mold or other particle counts vary enormously from minute to minute, providing highly inaccurate (though precise) numbers of spores per cubic meter of air.

This document is a brief tutorial which provides information about the accuracy of tests for the level of allergenic and toxic mold in residential buildings: Are spore counts valid? Are cultures and swab tests valid? These critical questions are discussed in this series of articles. At Causes of Variation in Airborne Particle Levels we discuss the causes of this high level of airborne particle variability. Readers should also see MOLD LEVEL IN AIR, VALIDITY, and for a more in-depth critique of popular mold testing methods than this tutorial see MOLD TESTING METHOD VALIDITY

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Extent of Variation of Airborne Particle Counts

Photograph of parallel airborne particle traces on a microscope slide

There is normally very high variation in the level of airborne particles in indoor air from moment to moment in buildings.

Actual field data easily demonstrates that particle presence in indoor air varies by orders of magnitude from minute to minute.

Sampling identical quantities of air indoors just a few minutes apart regularly shows up in our data as enormous differences in particle density from interval to interval, as you can see in this photograph of parallel traces of airborne particles captured by an air sampler which collected these samples just minutes apart in the same location in a building.

We always see this phenomenon in buildings, since unless we are measuring airborne particles released at a fixed rate in a controlled test chamber there are quite a few site conditions that agitate airborne debris.

A simple visual examination of the five traces of airborne particles captured on this microscope slide make clear that the variation in particle level is significant.

Further examples of wide variation of airborne spore counts indoors are provided at Particle Levels vs Sampler Height where you can see microphotographs of traces such as the ones above.

What is the Difference Between Precision and Accuracy in Airborne Mold Spore Counts?

Some people are confused about the difference between precision and accuracy.

An airborne mold spore count obtained from a spore trap or similar air sampling device can be processed in an aerobiology lab or mold test lab by several methods of varying accuracy depending on not only the site variables (which dominate the airborne particle count, but also depending on the skill and experience of the lab technician, the quality of the microscope and slide preparation, and the percentage of the particle trace that is examined.

In the hands of a skilled microscopist who uses the best practices and who examines 100% of the particle trace, the resulting lab report can give mold spore count that is very precise - for example, citing 5,731 Aspergillus niger spores per M³ (cubic meter) of air.

But what the mold test field investigator and laboratory technician may not be able to report is that the variability from minute to minute in the airborne particle level was enormous, easily by a factor of 100.

If the mold test field investigator had collected her or his sample in the very next five minute interval using exactly the same equipment and methods and processing the sample in exactly the same lab with the same technician may produce a very precise count of 573,124 airborne mold spore count of Aspergillus niger spores per M³ of air.

The two counts are very precise (5,731 and 573,124), but the airborne mold spore count produced by this spore trap method is completely inaccurate: 573,124 mold spores per cubic meter of air is 100 times more mold spores per cubic meter of air than 5,731.

If your airborne mold spore count can easily vary by a factor of 100 from minute to minute it may be precise, but it is inaccurate, and therefore in many cases, especially in cases of low counts that appear to be below the threshold of concern in many mold standards, such counts are completely unreliable.

Just try waving a note book across a table before counting mold spores in air and check the difference in airborne spore levels.

Then review mold inspection and mold test reports to notice whether or not the field investigator has noticed and recorded building conditions that affect air current activity in a building: fans on or off, space occupied or unoccupied, heat on or off, air conditioning on or off, etc. Any one of these completely changes the airborne particle level indoors.

The realization that airborne mold spore counts or counts of any indoor airborne particle are inaccurate is a reason to perform a thoughtful visual inspection of and history taking of a building that is under investigation for air quality problems. But such investigations, properly performed, may be costly and often are unnecessary and should not be performed at all. See MOLD EXPERT, WHEN TO HIRE.

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ACCURACY OF AIRBORNE MOLD SPORE COUNTS
  Causes of Variation in Airborne Particle Levels
  Indoor vs. Outdoor Spore Counts
  Extent of Variation of Airborne Particle Count
  Particle Levels vs Sampler Height
  Particle Levels vs Windows/Doors
  PARTICLE & MOLD LEVELS in DUCTWORK
  Concentration Bursts of Mold Spores
  False Negative Results in Mold Tests
  Mold Culture Plate Test Errors
  Why Use Airborne Mold/Particle Sampling?
  Visual Inspection and History for Mold

Thanks to Susan Flappan, Flappan Consulting, moldetect.com, Overland Park KS, 913-402-1131, for contributing comments and some suggested text from ACGIH Bioaerosols: Assessment and Remediation 12/2006.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
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

Mold Contamination Testing, Cleanup, Prevention: references & products

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Aerobiology, Building Science, Microscopy, & Laboratory References, an extensive technical bibliography
Allergens: what they look like in buildings
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
Atlas of Mold Related Illness: Index of Symptoms and health, physical, neurological, psychological, and other complaint which people suspect may be mold or building-related.
Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
Black Mold that is Harmless Photos of recognizable, usually harmless black mold on wood, bluestain, ceratocystis, ophistoma
Building Floods: quick steps after a building flood or plumbing leak can prevent costly mold contamination
Classes of Mold: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
Clinical Mold References - Detailed bibliography of mold reference texts
"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 Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
"Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
"Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm
Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Fiberglass: Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
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.
Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English) (buy at Amazon)
Looking for Mold Procedure: what mold is often found where in buildings - simple technical presentation
Meruliporia: the house eating fungus or "poria"
Mold Action Guide: Step-by-Step Instructions, What to do about mold, mildew, and other indoor allergens
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE Photos of what mold looks like in buildings
MOLD APPEARANCE - STUFF THAT IS NOT MOLD Photos of NOT-mold material that is sometimes mistaken for mold
MOLD ATLAS & PARTICLES INDEX, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
MOLD BY MICROSCOPE Mold under the microscope - photo identification of the most common indoor molds found in buildings
Mold FAQs Answers to Most Questions about Indoor Mold, Mold Related Illness, Mold Cleanup, Mold Prevention
US EPA: Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab or to any mold lab you wish
Most Common Indoor Molds Found in Buildings, A Table of
Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)
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.

Fiberglass building insulation and HVAC duct work insulation hazards
Sewage and Septic backup contamination in buildings: inspection, testing, remediation, & references to expert sources
Other environmental risks: Asbestos, carbon monoxide, electromagnetic fields, environmental illness, fiberglass, MCS - multiple chemical sensitivity, toxic gases, etc
Indoor Gas Sampling Plan for Residential Buildings lists a number of toxic indoor gases which we test for, depending on the building complaint and building conditions
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Pet control - if you can't say goodbye to your bird, cat, dog, guinea pig, hamster, tropical fish, then limit the areas they occupy and limit the airflow from that area to sleeping or other areas of the building, use allergenic bedding, eliminate wall-to-wall carpeting, improve housecleaning including use of a HEPA-rated vacuum cleaner. For more details see our article Dog, Cat, and Other Animal Dander - Information for Asthmatics and Indoor Air Quality
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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Extent of Variation of Airborne Particle Counts

What is the Difference Between Precision and Accuracy in Airborne Mold Spore Counts?

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Mold Contamination Testing, Cleanup, Prevention: references & products

OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold