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This article discusses Mold or Airborne Particle Levels versus Air Sampler Height when testing for airborne mold. This document is a brief tutorial which provides information about the accuracy of and sources of errors in 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 paper.

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 Sampling Methods in the Indoor Environment

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Variation in Airborne Particle Levels due to Placement Height of Air Sampling Device

How much difference does it make whether the air sampling machine is placed on top of or underneath a mold-contaminated table? The photographs above show microphotographs of representative sections of an airborne particle sample trace in the same room in a building, with a single variation: the left hand photograph of a mold spore sample shows just a few fungal spores was collected with our sample placed on top of a basement pool table.

The right hand photo of a mold spore trap sample shows a very high spore concentration in the same room, obtained when we placed our sampler on the floor below the (mold infected) pool table. In both samples we used passive methods.

Our photos above show a game table left in a basement where an airborne mold problem was suspected. The table looked "clean" but inspecting below (see our flashlight leaning on the left table leg?) shows thick yellow and green mold growth on the un-sealed chipboard structure.

Had we stirred room air (say by turning on a fan or waving a notebook, it is likely that these "under table" mold spores would have been distributed more uniformly in the building's indoor air and that they would have been present in an air sample at a much higher level than with passive spore trap air sampler use.

Many IAQ consultants place their air sampler at about chest or head height in a building, presuming that will best represent the particles that will be inhaled by building occupants. This sounds reasonable except that mechanical disturbance of local indoor dust will cause enormous variation in the actual particle level at any given time and will probably make the particle distribution more uniform in the space.

Our field and lab experiments show one to three orders of magnitude (or more) variation in airborne spore counts at the same location depending on the use of passive or aggressive sampling methods.

How many mold reports document the details of sampling such as where mold was visible, where the sampler was placed, and what possible variations in airborne particle level might obtain depending on details of how the sample was collected such as whether fans are turned on or off, the room was occupied or empty, windows open or shut, vacuum cleaners running, children playing nearby, etc. Virtually never is this information considered, gathered, or reported by the industrial hygienist or other mold investigator in residential indoor air quality investigations.

How to Interpret Airborne Mold Tests in View of Air Sampling Inaccuracy

We conclude that if an indoor air test for mold such as using a spore trap or air sampling device detects a high level of problem mold spores (or other airborne particles) we believe that those results have meaning and indicate a problem - although that type of test alone is faulty because it is not prescriptive: we still have not identified the source of the problem so we still do not know what action is needed.

But if an indoor air test for mold does not detect a high level of airborne mold or other problem particles, we cannot rely on this procedure alone to reach a confident conclusion about the air quality in the building.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

ACCURACY OF AIRBORNE MOLD SPORE COUNTS
  Causes of Variation in Airborne Particle Levels
  Indoor vs. Outdoor Spore Counts
  Extent of Variation of Airborne Particle Counts
  Particle Levels vs Sampler Height
  Particle Levels vs Windows/Doors
  Particle Levels in Ducts
  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.

More Information on Building Diagnostic Inspections and Repairs

• Mold Information Website Home Page
• Mold Classes: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
• Toxic Mold, Allergenic Mold: How Much is Bad?
• Validity of Bulk Surface or Tape Sampling
• Validity of mold cultures and "home test kits"
• Validity of culture methods for toxic mold inspections
• What to look for in a toxic survey report or toxic mold test lab report
• Plant Flower Tree Pollen - a Photo ID Library for asthma and allergy sufferers

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