by Nick Gromicko, CMI® and Ethan Ward

During a mold inspection, taking air samples is crucial for several reasons. Mold spores aren’t visible to the naked eye, and laboratory analysis of air samples can identify the types of mold present. Analyzing these samples also helps determine the scope and severity of a mold problem and assess human exposure to mold spores. After remediation, inspectors usually take new samples to confirm that all mold has been removed.

Air samples provide data about mold spores inside a house. Inspectors use a pump to force air through a collection device that captures mold spores. They then send the sample to a laboratory for analysis. Many InterNACHI inspectors use air sampling during mold inspections, making it a standard practice.

Air-Sampling Devices

Several devices collect air samples for mold analysis, including:

• Impaction samplers that use a calibrated air pump to deposit spores onto a microscope slide.
• Cassette samplers, which may be disposable or single-use, and use forced air to deposit spores onto a collection medium.
• Airborne-particle collectors that capture spores directly on a culture dish, useful for identifying specific mold species.

When to Sample

Taking samples is most beneficial if visual inspection reveals apparent mold growth or conditions that could lead to mold, such as moisture intrusion or water damage. Musty odors can also indicate mold presence. Even if no visible signs are present, one or two indoor air samples may be taken at the inspector’s and client’s discretion, focusing on the most frequently used room and the HVAC unit.

Outdoor air samples are typically collected for comparison with indoor samples. Gathering two outdoor samples—one from the windward side and one from the leeward side of the house—provides a clearer picture of what might enter the home through open windows and doors. For the most accurate comparison, take outdoor samples as close in time as possible to the indoor samples.

Inspectors should avoid sampling if a resident is under medical care for mold exposure, if litigation regarding mold is ongoing, or if sampling could compromise the inspector’s health or safety. Residential inspectors should also refrain from sampling in commercial or public buildings.

Where to Sample and Ideal Conditions

In areas suspected or confirmed to have mold growth, take air samples to verify and gather more information. Common reasons for sampling include moisture intrusion, water damage, musty odors, visible mold growth, or conditions favorable to mold. Position the collection device 3 to 6 feet off the ground in the center of the room.

Allow the air pump to run for ten minutes for most samples. If significant indoor activity could affect results, reduce the sampling time to around five minutes. If there is an active dust source, such as ongoing construction, consider reducing the time further.

Conduct sampling in livable spaces under closed conditions to stabilize the air and ensure reproducibility. Keep windows and exterior doors shut during sampling, except for normal entry and exit. Switch off air exchangers (excluding the furnace) or fans that exchange indoor and outdoor air.

Weather conditions can impact data accuracy. Severe thunderstorms or strong winds can affect sampling results by altering air pressure differences between indoors and outdoors, which can skew airborne mold-spore concentrations. High winds or rapid barometric pressure changes can draw more spores inside, distorting sample results.

Difficulties and Practicality of Air Sampling

Consider air sampling as just one tool in the mold inspection process. It alone cannot confirm or refute the existence of a mold problem. Combine air sampling with visual inspections and other methods, such as surface samples, for a comprehensive assessment. Indoor spore levels can fluctuate, potentially skewing results if sampling is not conducted correctly. Additionally, since air samples capture only spores and may damage them during collection, identifying mold types can be more challenging compared to tape or cultured samples.

Air samples serve well as a background screen to detect large, undiscovered mold sources. They can reveal intact chains of spores, which usually break apart as they travel. A sample showing intact chains might indicate nearby, undiscovered mold.

In summary, when performed under controlled conditions and properly analyzed, air samples can help compare relative particle levels between problem areas and control areas. They are also crucial for assessing particle levels and air quality before and after mold remediation.