Redefining the expectations of a mold assessment - Part 2

In the first article of this series, our discussion highlighted the need to redefine the expectations of what a mold assessment should be and the need to consider the competence of the professionals performing the assessment. In this article, we will discuss the limitations associated with sampling and the overreliance of sampling in lieu of an informed physical inspection. Informed inspections are based on facts and data that are collected to determine the extent, origin, and cause of the mold growth and contamination.

Mold sampling options

While there are a variety of different sampling methods available to sample mold in the indoor environment, air samples, and in particular spore trap samples, are commonly used to determine the extent that visible mold growth is degrading the indoor air quality, the presence or location of hidden mold growth, or as part of a post-mold remediation verification assessment. Based upon an informed physical inspection, a site-specific sampling plan can be developed, and an informed interpretation of the laboratory analysis can then be made to determine whether the indoor environment is “normal,” or characteristic of a well-maintained and dry structure, or whether the interior air is similar to the outside air.

A spore trap is an air sampling method where a known volume of air is pulled through a plastic cassette that has an adhesive-coated slide in the center that particles are deposited onto as the air is drawn through the cassette (Figure 1). The samples are usually collected for a period of 5 or 10 minutes depending on the cleanliness of the area being sampled. Industry guidance and best practice recommend that samples are collected in affected area(s) for comparison to samples collected in unaffected area(s) and an outside control sample.

Control samples are collected outside as there are no numerical threshold levels or guidelines available for exposure to fungal spores; therefore, indoor spore counts should be similar to or lower than the outside sample. This comparison can help the practitioner determine if the indoor environment can be considered normal or atypical. There are many limitations associated with spore trap sampling to consider when interpreting the data such as:

• The limited length of time and volume of air that the samples are being collected at;
• The ability for many particles to bypass or bounce off the slide in the cassette;
• Variations in airborne concentrations at different times and locations within the structure;
• Differences in analytical methods used by various laboratories; and
• The sampling and analytical error for spore trap samples is believed to be between 30% and 200% per the AIHA.

Consider a five-minute sample of air collected at 15 liters (L) per minute equates to 75L of air passing through the cassette. There are approximately 22,600L of air in a 10-foot x 10-foot x 8-foot room. The air pulled through that sample is only a fraction of the air in the room. Can this sampling method be considered a definitive representation of everyday airborne conditions within the dwelling? No, that is why sampling is performed as part of an informed assessment and is only considered a screening tool. Air sampling cannot and should not be used to evaluate health risks because the margin of error is too great considering the previously mentioned limitations with the sampling method and the variances in airborne concentrations.

Descriptions of the purpose of the mold assessment in many reports are often described as being performed to “determine the quality of the indoor air,” to “see if fungal growth was present at the residence,” or to “provide indoor fungal information pertaining to the indoor air quality.” When reviewing reports, I frequently observe that data collection and written observations are limited, a cause is not provided and, on many occasions, one or two interior spore trap samples are collected for comparison to an outside control sample.

In some cases, an outside control sample is not collected at all as some laboratories provide representative control data of common fungi and their concentrations identified outdoors. There is no statistical significance for such a sampling plan; therefore, the data cannot be used to support any conclusion, and if a conclusion is based upon such a limited assessment, then the conclusion cannot and should not be considered definitive or defensible.

Another type of sampling method that is routinely misrepresented is the surface sample. Most surface samples are collected by applying a swab or piece of clear tape onto a surface. These samples aid in the determination that fungal growth or contamination is present on the specific surface sampled.

A common misrepresentation of this data is that the mold growth identified on the sample is contributing to poor indoor air quality. There are no currently accepted guidelines to substantiate a correlation between an inhalation exposure and the results of a surface sample. Another misrepresentation is that the results of the surface sample confirm the presence of an atypical and quantitatively elevated fungal ecology in the interior of a residence. Swab and tape samples generally represent an approximate area of 1 cm² or 1 inch,² which cannot be considered representative of a surface. Utilizing data from surface samples to substantiate the condition of the air quality or amount of contamination in a structure cannot and should not be considered definitive or defensible.

The flawed approach of treating sampling as a priority over an informed physical inspection is a systemic problem in the indoor environmental industry. Many of the assessments being performed are not based on good science, best practice, or industry guidelines. Furthermore, they provide no value for their client if the intent of the assessment is to determine if there is a mold concern within the structure. These limited types of assessments are often associated with an assignment of benefits or part of a water mitigation and mold remediation strategy where previously dried materials are removed because they were contaminated, which begs the question, “What was the purpose of the mold assessment that was performed?”

Jeremy D. Beagle, CIH, CMCC, CMC, is senior principal scientist with SDII Global and a Board Certified industrial hygienist. He has been performing origin and cause assessments and providing expert witness testimony pertaining to water damage, mold growth, and other indoor environmental concerns in the built environment for over 18 years. Contact him at jbeagle@sdii-global.com.

Related:

Redefining the expectations of a mold assessment – Part 1

How IoT is revolutionizing water-damage mitigation

Mold & marble: What’s it all about?