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ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY
MOLD: A COMPLETE GUIDE to TEST CLEAN PREVENT
ACTIVITY of MOLD in BUILDINGS
AGE of MOLD - Old is the Mold?
AIR CLEANER PURIFIER TYPES
AIR FILTERS for HVAC SYSTEMS
AIR TEST SAMPLING CASSETTE STUDY
AIRBORNE MOLD COUNT NUMBER GUIDE
AIRBORNE PARTICLE ANALYSIS METHODS
ALLERGEN TESTS for BUILDINGS
BROWN HAIRY BATHROOM MOLD
BIBLIOGAPHY for ENVIRONMENTAL HEALTH, MOLD, IAQ
BLACK MOLD, HARMLESS COSMETIC
BLACK MOLD, TOXIC & ALLERGENIC
BLEACHING MOLD, Advice about
BOOK MOLD, Moldy Book Cleaning
BOOKSTORE - ENVIRONMENTAL
CACTUS FUNGI / MOLD
CAR MOLD CONTAMINATION
CARPET DUST IDENTIFICATION
CARPET PADDING ASBESTOS, MOLD, ODORS
CARPET FUNGICIDAL SPRAY
CARPET STAIN DIAGNOSIS
CARPET & other STAIN TESTS
CARPET TEST PROCEDURE
CARPETING & INDOOR AIR QUALITY
CHAIN OF CUSTODY - TEST SAMPLE
CLEARANCE INSPECTIONS - MOLD CLEANUP
DIRECTORY of MOLD / ENVIRONMENTAL EXPERTS
DIRT FLOOR MOLD CONTAMINATION
Disinfecting Buildings with Bleach
DO-IT-YOURSELF MOLD CLEANUP WARNINGS
DUST ANALYSIS for FIBERGLASS
DUST, HVAC CONTAMINATION STUDY
EFFLORESCENCE, Salts & White / Brown Deposits
FEAR of MOLD - MYCOPHOBIA
Fiberboard Insulation Sheathing Mold
FIBERGLASS INSULATION MOLD
FIND MOLD, ESSENTIAL STEPS
MOLD in BUILDINGS
FIRE DAMAGE vs MOLD DAMAGE
FLOODS IN BUILDINGS-mold
FOXING STAINS on books & papers
FUNGICIDAL SPRAY & SEALANT USE GUIDE
GAS DETECTION INSTRUMENTS
GAS EXPOSURE EFFECTS, TOXIC
GAS EXPOSURE LIMITS & STANDARDS
GAS TEST PROCEDURES
HOUSE DUST ANALYSIS
HOUSE DUST COMPONENTS
HUMIDITY CONTROL & TARGETS INDOORS
LAB PROCEDURES MICROSCOPE TECHNIQUES
LIGHT, GUIDE to FORENSIC USE
MEDIA BLASTING for MOLD REMOVAL
METHANE GAS SOURCES
MICROSCOPE DIGITAL PHOTOGRAPHY
MEDIA BLASTING for MOLD REMOVAL
METHANE GAS SOURCES
MICROSCOPE DIGITAL PHOTOGRAPHY
MILDEW ERRORS, IT's MOLD
MILDEW REMOVAL & PREVENTION
MOISTURE CONTROL in BUILDINGS
MOLD: A COMPLETE GUIDE TO MOLD
MOLD EXPERT, WHEN TO HIRE
MVOCs & MOLDY MUSTY ODORS
MYCOPHOBIA, STAINS MISTAKEN for MOLD
MYCOTOXIN EFFECTS of MOLD EXPOSURE
ODORS GASES SMELLS, DIAGNOSIS & CURE
RENTERS GUIDE TO MOLD & IAQ
ROBIGUS & Wheat Rust Fungus
SMELL PATCH TEST to Track Down Odors
STAINS on & in BUILDINGS, CAUSES & CURES
THERMAL IMAGING MOLD SCANS
TRAPPED MOLD BETWEEN WOOD SURFACES
UV LIGHT BLACK LIGHT USES
VAPOR BARRIERS & CONDENSATION
VENTILATION in BUILDINGS
Volatile Organic Compounds VOCs
WATER ENTRY in buildings
Mold spore count validity: this document discusses a serious question about the currently-popular "spore counts" obtained by industrial hygienists, home inspectors, and "mold investigators" (and the mold testing laboratories they use). Airborne or other mold counts are used to estimate the toxic or allergenic mold exposure level of building occupants in buildings where mold may be present.
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First, should we be testing for mold at all? If you see mold on indoor surfaces, NO mold testing is needed just to confirm that mold is present in a this building and that cleanup is needed. The clean-up procedures for mold contamination do not depend on the mold genera/species, with the sole exception of cosmetic-molds on some framing lumber. (BLACK MOLD, HARMLESS )
Only an idiot, or perhaps someone out to prey on mold fear (MYCOPHOBIA, STAINS MISTAKEN for MOLD) would require a mold test to determine if the home at left needs professional mold remediation.
But there may be other reasons to test to identify the dominant mold genera/species in a building.
For example, if a large remediation project is planned, tests may be needed for project control - to be able to prove later that other building mold contamination or moldy dust did or did not come from an improperly-handled mold remediation job. We also may include tests for airborne mold as a part of a more thorough building investigation and screening for hidden mold contamination, but we would not rely on an air test alone in that case.
Finally, we may want to identify the dominant mold genera/species in a building as an aid to medical diagnosis and treatment. Details about reasons to test for mold and warnings about mistaking a "mold test" for a useful building inspection and diagnosis to find hidden mold or to determine how to prevent future mold contamination are found at
Mold Count Precision is Not Mold Exposure Accuracy
Counting indoor mold spore levels per cubic meter of air or "liter" produces numbers which may be very precise (many digits or decimal places) but which are generally highly inaccurate (wrong by one to three orders of magnitude).
Enormous variations in the level of airborne particles in buildings occur from even the simplest changes such as walking through a room or turning on a furnace blower.
While many laboratories, including our own, participate in programs to calibrate and standardize their in-laboratory particle counting, slide preparation, and microscopy procedures, no amount of precision in lab counting can overcome the several orders of magnitude in variation of indoor particle levels that actually occurs in a building over intervals as short as a few seconds and as long as days or months.
While there is a useful place for every environmental investigation tool, inadequacies in field procedure, field condition reporting, and visual inspection that would permit an interpretation of lab results limit the usefulness of "bare lab reports" which simply give a number. The number may be impressively precise, but highly inaccurate.
Thus airborne mold exposure levels based on single-time-interval use of these tools are unlikely to be accurate.
Details are at ACCURACY vs PRECISION of MEASUREMENTS
Warning: interpret all quantitative data, particularly counts of particles in indoor air, with great caution. Individual samples of particles in air show tremendous variation from minute to minute, making "ok" test results a thing to view with skepticism.
Examples of factors which can cause an exponential difference in particle levels in indoor residential air over short time intervals include: mechanical disturbance (walking across a carpet or moving a moldy cardboard box), operation of hot air heating system or central air conditioning system, operation of other building fans, particularly ceiling fans and vacuum cleaners, turning lights on and off, and opening or closing windows and doors. In situations of particular risk, additional or periodic testing should be considered.
Also see ACCURACY vs PRECISION of MEASUREMENTS where we argue that measurements should be reported to include their percentage of error or a +/- figure to give a realistic understanding of the actual reliability of the data.
The University of Minnesota fungal experts observe that an outdoor-baseline comparison to indoor air is not valid when the outdoor sample was taken during or immediately after precipitation (spore counts plummet outdoors in the rain and might soar right after it), and the comparison is probably not valid in winter when outdoor counts tend to be below indoors. We agree and add other constraints: snow cover practically eliminates spores from outdoor air.
Even in warm weather spore counts vary during the day as weather conditions (humidity, temperature, period after rainfall) affect sporulation and spore movement.
Similarly, tests which rely on culture to identify particles are at severe risk of giving a "false negative" result, missing a serious problem, or of giving a "misleading positive" result by asserting that a particular spore which grew on the culture is the problem in the building. Fungal spores grow at different rates on different culture media.
Spore "A" may "overgrow" spore "B" in a particular test, obscuring the presence of spore "B" which might be the real problem in the building. Some fungal spores won't grow at all in culture media (non-viable spores and many Ascospores) but may still be present at toxic levels in a building.
More about mold testing and the validity of air sampling and home test kits for mold:
As a collector of studies, papers, books on this topic, and as someone conducting our own studies, we have seen a very wide range of opinion among experts in the field. Spore allergenicity or toxicity varies widely among fungal genera/species. So does the sensitivity of humans and other animals to fungal spores.
Mold Spore Toxicity Variations by Species, Genera, particle size, even growth substrate
So no single number will be absolutely correct. Just as spore toxicity varies by species, so does the physical size of individual spores. The effect of breathing air contaminated by 5000 Penicillium sp. spores per cubic meter is unlikely to be identical to the effect of breathing 5000 Stachybotrys chartarum spores per cubic meter of air.
Not only does their chemistry and toxicity vary, but a typical Pen/Asp spore is about 2 microns in diameter (1/25th the width of a typical human hair) while a typical Stachybotrys chartarum spore might be 8 x 12 microns -- much larger and thus providing more potentially harmful material per individual spore.
Spore Toxicity Variation Precludes Credible Single Number Mold Exposure Standards
You can see that writing federal or state standards for permissible fungal spore exposure by "count" or "levels" is difficult. Not only are there many variables to consider, but using currently popular air sampling or culture methods, even a low or "OK" test result cannot guarantee that there is no problem in the building.
Fortunately one can become reasonably confident about the level of mold or allergen risk in a building through competent visual inspection, judicious use of various sampling tools and methods, and competent laboratory determination work. Because this expertise is costly and the work time consuming, it should not be ordered without reasonable justification.
Readers should see Shortcomings of air sampling and also see Extent of Variation of Airborne Particle Counts and Mold Testing: Air samples and their interpretation - a quick tutorial.
For a more in-depth critique of popular mold testing methods than this tutorial see Mold Sampling Methods in the Indoor Environment
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