CMI Mold Identification & Sampling Techniques 3

Question 1

Which sampling method is considered the 'gold standard' for determining whether a mold colony is viable (alive)?

Accepted Answer

Culture-based sampling on agar media

Answer

Culture-based sampling on agar media is the gold standard for viability because only living (viable) spores can germinate and form colonies, confirming active biological growth. Tape lift with direct microscopy and spore trap air sampling can detect spores but cannot differentiate live from dead. PCR analysis on bulk samples detects DNA from both living and dead organisms, making it unable to confirm viability.

Question 2

An outdoor air sample collected at the same time as indoor samples serves which primary purpose in a mold investigation?

Accepted Answer

To provide a baseline for comparing indoor spore types and counts

Answer

An outdoor (background) air sample establishes a baseline of naturally occurring fungal spore types and concentrations in the ambient environment, allowing the inspector to determine whether indoor levels are elevated above normal. This comparison is essential for interpreting results — indoor counts must exceed outdoor counts of the same species to indicate an indoor source. Outdoor samples do not measure CO2, HVAC performance, or building material species.

Question 3

Aspergillus and Penicillium spores are often reported together in laboratory results because:

Accepted Answer

Their spores are morphologically indistinguishable under light microscopy

Answer

Aspergillus and Penicillium produce small, round, smooth conidia that are morphologically identical under light microscopy, making species-level or even genus-level separation impossible without culture or molecular methods. They do not always grow on the same substrate, and many other molds (like Stachybotrys and Fusarium) also produce mycotoxins. Reporting them together as 'Asp/Pen' is a laboratory convention based on this morphological limitation, not biological similarity.

Question 4

A moisture meter reading above what percentage in wood framing is generally considered a threshold indicating conditions favorable for mold growth?

Accepted Answer

19%

Answer

A moisture content above 19% in wood framing is the generally accepted threshold at which conditions become favorable for mold growth, as established by building science standards and referenced in IICRC S520 guidelines. Readings below 10% are considered dry and safe. At 30%, significant mold growth and wood rot would likely already be occurring. The 19% threshold is a key number CMI candidates must memorize for field assessments.

Question 5

When an inspector observes a white fuzzy growth that turns black near the base on drywall, the most likely identification is:

Accepted Answer

Chaetomium indicating deep water damage and cellulose degradation

Answer

Chaetomium species characteristically begin as white to gray cottony mycelium and develop darkening flask-shaped perithecia at the base as the colony matures, producing the two-toned white-over-black appearance on wet drywall. This indicates deep, sustained cellulose degradation from prolonged water damage. Penicillium/Aspergillus would appear uniformly powdery blue-green. Efflorescence is a mineral deposit with no fuzzy texture, and Fusarium requires different moisture conditions.

(CMI) Certified Mold Inspector Practice Test

(CMI) Certified Mold Inspector Practice Test

CMI Mold Identification & Sampling Techniques 3