Hidden mold in a basement wall cavity - (C)Copyright 2008-1995 Daniel Friedman Indoor Air Quality &Toxic Mold & Toxic Gas Testing Methods Compared

  • INDOOR AIR QUALITY METHODS COMPARED - CONTENTS: What to do about toxic or allergenic mold in buildings. Mold Testing Methods & Validity Comparisons. Air tests for mold., Surface, tape, & bulk tests for mold -which tests are really useful? Why mold Culture tests are not reliable to screen buildings for mold. Why mold sniffing dogs, infra red, thermography, MVOC detection, & moisture detection are useful tools but unreliable as mold detection methods. Mold lab procedure articles. Indoor air and toxic mold investigation report guidelines
  • POST a QUESTION or READ FAQs about IAQ, Toxic Gas, & Indoor Mold contamination testing methods & procedures

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Indoor air quality methods and methodology: T

his article lists and compares classes of mold, air, gas, test methods used in indoor air quality investigation methodology in searching for possible causes of respiratory illness, asthma, immune system disorders, rashes, skin disease, psychological and neurological disorders, eye infections, or other symptoms which may have a physiological and environmental component.

Methods of inspection and testing building air quality for toxic mold, allergen or other sick house investigations, mold lab testing services, information on mold, mildew, moisture, pollen, dust mite, & environmental testing for home buyers, home owners, consultants, as well as a service to provide on-site field investigations and expert mold laboratory testing, and mold identification services are offered.

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Air Sampling Equipment & Mold Testing Protocols

Photograph of a mold culture plate home test kit for mold.Links here organize the indoor air quality methods portion of our environmental website and take the reader either directly to an in-depth article or to the collection of such articles addressing a particular environmental or IAQ topic.

Air sampling equipment used for particle or mold sampling in buildings includes some useful, expensive tools, but if used alone, air sampling is not reliable for characterization of building conditions.

In short, a "negative" (no mold problem detected) result is not reliable because the level of airborne particles in indoor air varies by several orders of magnitude from minute to minute in a building. Waving a notebook, turning on or off a fan, opening a door, even walking across carpeting can completely change the level of airborne particles.

A mold inspector who relies only on tests and who omits thorough visual inspection, history taking, occupant interviews,etc. is not making a reliable mold-assessment of a building.

Bulk & Surface Tape Sampling Mold Testing Protocols

Photograph of devices compared in studying mold on a couch. This photo shows some sampling devices we used in comparing the effectiveness of vacuuming a couch to test thick upholstered furnishings for mold contamination.

We collected comparison samples using different collecting devices as well as by using adhesive tape, for laboratory analysis.

Vacuuming furniture to test for mold contamination may be useful for general qualitative assessment when an expert has examined the building and its content.

Vacuuming building insulation may be the most reliable non-quantitative approach to detecting mold-contaminated fiberglass insulation.

Quantitative analysis of such samples is questionable.

Tape to collect mold or other surface sampling methods provide useful, inexpensive tools which, combined with careful visual inspection, are reliable and inexpensive for characterization of building conditions. Particles collected are very useful for genera and often mold species identification.

  • Bulk & Tape Samples: Tape lift from mold-covered surfaces; scrapes onto microscope slide and other methods also used by do-it-yourselfers and by experts
  • How to prepare and send a mold sample to our laboratory
  • Wall Check type vacuum pump and canister permits "sampling" of mold and allergens in wall, ceiling, and floor cavities but our direct field testing indicates that this method is highly unreliable. Working with Louis Relle, a Louisiana mold remediation expert on a New Orleans building which was to be demolished we collected wall-check samples from every suspect building cavity. When the building interior surfaces were demolished we then performed a visual inspection and collected bulk surface samples using tape.

    The wall check samples were completely unable to detect large and significant mold contamination in the cavities of this building. We postulate that even with mechanical agitation (banging on the wall during wall check sampling) the flow rate of the sampling method does not move enough air to reliably pick up surface contamination unless the mold genera/species happens to be at a particularly high state of active sporulation. The tool remains in the professional's arsenal, to be used with discretion.
  • Vacuum samples of carpeting, drapes, furniture, clothing permits testing for mold contamination. We use this method for screening of areas where mold is not visible, and in clearance testing.

Cultures, Swabs, "Home Test Kits" Mold Testing Protocols

Photograph of a mold culture plate home test kit for mold.

MOLD CULTURE TEST KIT VALIDITY describes the testing limitations or INVALIDITY of these methods for determining what contaminants are in a building - see Validity of Cultures (settlement plates or swabs) to find toxic mold in buildings .

Only about 10% of all molds will grow on any culture medium whatsoever, and there are literally hundreds of culture media mycologists have developed to try to coax mold to grow in the laboratory.

90% wrong to start: So the moment you open your "mold culture test kit" you're roughly 90% wrong in whatever conclusion you and your kit are going to reach. (We're exaggerating slightly because not all of the 1.5 million mold species will grow indoors in buildings anyway).

The mold that likes the culture media and grows on it may not be the mold that is a problem in the building anyway - it may just be a nice marriage between what fell onto the plate and the chemistry of the mold growth media.

The rate that particles fall out of the air has no reliable correlation to how many of them are in a building or where they're coming from.

So where's the mold? The most troubling thing about this and some other mold test kits, when used by someone who's not an expert, is that even if the mold test kit indicates the presence of a problem mold, and even if the kit "got it right" in a particular case (that is, the mold it detected is actually the main problem in the building), we don't know where the problem is nor how big it is nor what to do about it.

Mold Sniffing Dogs as a Building Screen for Mold

Mold sniffing dogs are unreliable, though fun. For details, see   INEFFECTIVE MOLD PRODUCTS for an explanation of why mold sniffing dogs make poor mold detectives and why it's not good for them anyway.

There's no doubt that a dog can be trained to smell mold. What is the dog smelling? MVOCs.

Not all molds generate MVOCs, and even molds that do generate MVOC's don't do so all the time. If the humidity, temperature, light, and other factors don't cause a particular MVOC-generating mold to release this gas, you're not going to detect it on the day of the inspection and test. Just later. Even if we detect MVOCs, is that the problem mold in the building?

Beagles are short as dogs go - and are not good at sniffing out MVOC's that telltale a mold problem high in a building wall or in a ceiling.

Beagles are cute, though.

Infrared, Thermography, & MVOC Testing as a Building Screen for Mold

These good tools form a part of the arsenal of building investigation tools for many uses and problems, but they are unreliable as a building screen for mold.

IR and Thermography detect temperature differences, not mold. In short, IR, or thermography, which are wonderful and fun tools to use, only detect temperature differences. If your building has a mold problem in a wall or ceiling due to a leak that occurred a long time ago, the cavity may now be quite dry. The mold is happily growing along on ambient moisture, but the IR won't detect a thing.

IR and thermography are good at seeing leaky windows and doors, though. At one of our investigations a "mold killing" company had charged our client a few thousand dollars to "spray biocide into the moldy walls". Our acquaintance who owns the company was excited with his new IR camera and used it as a "mold detector" - now this is a smart thing to do if you're looking for what building cavities have just gotten wet due to a leak.

But in this case what he detected was cool spaces around windows and doors - which is where he sprayed his biocide and "mold killer". When we cut open those walls we found absolutely no indication that there had ever been mold present, nor leaks, nor anything but lower temperatures. The mold problem (there was one) was in a completely different area of the home.

IR and thermography are great tools in the hands of an expert. They're not a mold detector.

For details see   INEFFECTIVE MOLD PRODUCTS for an explanation of why this is so.

Sampling for Mold Volatile Organic Compounds - MVOCs and other Mold-Related Gases in buildings

Not all molds generate MVOCs, and even molds that do generate MVOC's don't do so all the time. If the humidity, temperature, light, and other factors don't cause a particular MVOC-generating mold to release this gas, you're not going to detect it on the day of the inspection and test. Just later. Where's the mold smell or musty odor problem source? Even if we detect MVOCs, is that the problem mold in the building? If we don't detect MVOC's does that promise there is no problem mold? No.

Please see MVOCs & MOLDY MUSTY ODORS for details about this topic.

Readers should also see MOLD ODORS, MUSTY SMELLS


Production of toxins and microbial volatile organic compounds (MVOCs) by fungi in an environmental sample is dependent upon many factors, such as the substrate on which mold is growing, relative humidity and temperature in the moldy environment; the relative importance of each of these factors in toxin production is poorly understood.

Our Indoor Gas Sampling Plan for Residential buildings describes gas testing procedures, instruments, detection limits, and it lists some of the toxic (or other) indoor gases for which we can test, depending on the building complaint and building conditions.

Good Mold Testing Laboratory and Microscope Procedures

TECHNICAL PROCEDURES describes proper mold testing laboratory procedures, and sample processing not by a "supervised" technician but by a qualified expert are critical in making sense of field samples.

Competent, trained, experienced aerobiologists, mycologists, and microbiologists can identify sample contents with good accuracy.

Depending on the experience of the laboratory, it is also possible to interpret the meaning of the sample for the building and its occupants.

Laboratory professionals who have also performed the field inspection can often offer useful interpretations of even low levels of certain particles or classes of particles found in indoor air or surface dust. For example, if a field test for mold detects certain fungi not usually found on indoor surfaces, those molds may not themselves be a likely health hazard to building occupants, but they may be common water-indicators that suggest that further investigation of the building is in order to look for the presence other, more problematic molds that the initial investigation failed to detect.

Indoor Air / Toxic Mold Investigation Reports

MOLD INVESTIGATION REPORTS provides a document outlining what to look for in a toxic mold field investigation report or mold test laboratory report. we have been troubled that some very costly "mold investigators" simply collect a few air, culture, or swab samples, toss them over to a mold testing lab, and give their clients the lab report.

A valid and useful mold investigation needs to include a detailed visual inspection to identify problem sources, the presence and extent of a mold or other problem reservoir, and then it needs to provide the supporting lab work to justify what may be a costly cleanup (i.e. let's not spend a lot cleaning up "cosmetic" mold). The end product of the investigation needs to include the following

  • Where are the problem mold or other reservoirs in the building?
  • What is the extent of cleanup needed? Exactly where are the problems actually located?
  • What do lab results indicate about toxicity, allergenicity, medical implications of potential exposure, and the need for expert cleaning services?
  • What needs to be changed or fixed on the building to prevent a recurrence of the original problem?

What to do About Mold - Here are the Key References

Photograph of mold in a basement following building flooding.



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