Air testing and mold inspections

Taking air samples during a mold inspection is important for several reasons. Mold spores are not visible to the naked eye and only laboratory analysis can identify the type of mold in question. Having samples analyzed is also useful for demonstrating the extent and severity of a mold problem, as well as for assessing human exposure to mold spores. After solving the problem, new samples are usually taken to ensure that all mold has been properly removed.

In addition, air samples can be used to collect data on mold spores inside a home. These samples are taken using a pump that forces air into a collection device to capture mold spores. The sample is then sent to a laboratory for analysis.

Air test: Air sampling devices

There are several types of devices used to collect air samples that can be analyzed for mold. Here are some examples:

  • impaction samplers that use a calibrated air pump to impact spores on a prepared microscope slide;

  • cassette samplers, either single-use or disposable, that use forced air to impact spores on a collection medium; and

  • collectors of airborne particles that trap spores directly on a culture dish. These can be used to identify found mold species.

When should I take a sample and do an air test?

It is generally best to take samples if a non-invasive visual examination reveals apparent mold growth or conditions that may be causing it, such as moisture intrusion or water damage. Musty odors can also be a sign that mold formation has spread. If no signs are apparent, one or two indoor air samples can still be taken each year to ensure good air quality at all times.

Outdoor air samples are generally used as a control for comparison with data from indoor air samples. Two samples, one on the downwind side and the other on the leeward side of the house, will help establish a more complete picture of what is in the air and can enter the house through windows and doors. To obtain an optimal comparison, it is strongly recommended to take the outdoor and indoor samples during the same day, or a few days apart at the latest.

What are the ideal conditions for sampling?

Air samples can be taken from all areas of a home where mold is suspected to check and gather more information. Moisture intrusion, water damage, musty odors, apparent mold growth or favorable conditions for such growth are all common reasons for collecting an air sample. They should be taken near the center of the room, with the collection device placed 3-6 feet from the ground.

Ten minutes is enough for the air pump to work during sample collection, but this time can be cut in half if you are concerned that the movement of air caused by intense indoor activity may alter the results. The sampling time can be even shorter if there is an active source of dust, for example from a construction in progress.

Sampling must take place in living spaces in the house, which will be closed so that no one enters, in order to contribute to air stabilization and reproducibility of sampling and measurements. During sample collection, windows and exterior doors should remain closed, except during normal entry and exit of the house. It is preferable that air exchangers (other than a furnace) or fans that exchange indoor-outdoor air are turned off during sampling.

Difficulties and practical aspects of the air test

It is important to note that air sampling is just one tool among many when inspecting a home for mold problems. Indeed, an air sample is not enough to confirm or refute the existence of a problem. Such tests should be accompanied by visual inspection and other data collection methods, such as a surface sample. Levels of spores suspended in indoor air can vary depending on several factors, which can skew the results if care is not taken to properly configure sampling. It is highly recommended to use an indoor air sampling professional to detect mold.

Air samples can be used to ensure that there is not a significant source of mold not yet found somewhere in the home. Indeed, they can detect long chains of spores still intact. Normally, these chains separate quickly as they move through the air. Thus, a sample revealing intact chains may indicate the presence of mold nearby, possibly not discovered during further tests and visual examinations.

In summary, when taken under controlled conditions and properly analyzed, air samples used to detect mold are useful for comparing relative particle levels between a problem and a control area. They can also be crucial for comparing particle levels and air quality in an area before and after mold removal.

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