Flashlight dust (C) D FriedmanDust Sample Types
Old Building Dust vs Recent Building Dust - locations & uses

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Dust samples may focus on "old dust" or "recent dust" found in buildings or on building surfaces.

This article defines old building dust, recent building dust, where each type of dust may be found, and why we may want to collect and examine old dust or recent dust in buildings.

The thick dust shown in our page top photo is probably an "old dust" accumulation.

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Recent vs Old Building Dust: Definitions, Locations, Uses in Indoor Environmental Testing

Dust sample using simple adhesvive tape and a clean plastic bag (C) D Friedman

At DUST SAMPLING PROCEDURE we discuss whether or not one should be testing for problem dust articles at all? So should we be collecting and testing building dust?

Probably not: If the building IAQ question is simply about mold identification, and you already see mold on indoor surfaces, NO mold testing is needed to just to confirm that mold is present in the building and that cleanup is needed

. Sure, it might be just cosmetic mold (seeCOSMETIC MOLD, RECOGNIZE ) but for small mold cleanup jobs testing is not normally appropriate.

Maybe yes: But if you need to identify the contents of dust, for example to help track down possible sources of building dust particles, or to screen for problem particles such as dust mite fecals, insect fragments, animal dander or hair, soot, fiberglass, etc., or if a large mold remediation project is planned, tests may be needed for project control.

Dust sampling theory: usefulness & definitions of "old dust" and "recent dust" in buildings & where these are found

fibers not fiberglass (C) Daniel Friedman

The following description of "old dust" and "recent dust" are my subjective opinion based on experience and are intended to supplement the building settled dust sampling method discussed at MOLD TEST KITS - how to collect settled dust from individual or multiple surfaces using clear adhesive tape as a means to characterize what particles have been in building air over time.

Also see VACUUM CASSETTE FILTER SAMPLE TESTS for DUST / MOLD - collecting settled building dust from one or multiple surfaces using vacuum cassettes.

Definition, Location, & Usefulness of Collecting "old" building dust

Old dust represents particles settling out of building air a time period of weeks, months, years, or dust conditions before, or at the end of a recent demolition, renovation, or cleanup project.

Even after recent cleaning, old building dust can often be found in locations rarely cleaned such as horizontal trim over a door, on window muntins or blinds, under radiators, etc.

An old dust sample is useful to get an idea of the historically dominant particles present in a building and to screen for unusual particles that should not be there. The common dominant particles in most residential buildings are fabric fibers, skin cells, often starch granules (photo above left) and at lower levels, typical airborne mold, dust mite fecals and similar material.

Definition, Location, & Usefulness of Collecting "recent" building dust

Flashlight dust (C) D Friedman

Recent dust represents particles settling out of building air only recently, such as dust falling onto a surface that we know was recently cleaned completely.

While statistically less robust since it represents only a shorter time interval (typically days or weeks), recent dust can serve as a screen to look for evidence that problem particles remain in a building at actionable levels - or not.

Just how much time needs to elapse between building cleaning and the collection of a meaningful sample of recent building dust varies from hours to a month, depending on building materials, contents, occupancy, HVAC systems, cleanliness of adjoining areas and similar factors.

Key is to collect recent dust from a surface that we know (and perhaps confirmed by earlier sampling) was previously cleaned and very low in settled dust particles at the start of the test period.

Using a reader's question (see FAQs in this article: VERMICULITE INSULATION) as an example, if loose-fill vermiculite insulation were accidentally spilled in a building and then cleaned properly, we should find only comparatively low levels of vermiculite particles (or very low levels of asbestos if the vermiculite insulation originally contained asbestos dust and fragments).

Vermiculite insulation contamination photos (C) David Grudzinski

In this case an old dust sample might find high levels, even dominant levels of vermiculite insulation in building areas near the spill or where HVAC systems transported building dust from the spill to other areas. A recent dust sample should find vermiculite fragments only low levels, perhaps just at incidental levels, and certainly not dominant level.

Interestingly, following a demolition and cleaning project, for example when mold contamination has been removed, it would be expected to find incidental levels of the original problem mold genera/species. Finding zero levels of such particles might raise question about the sampling approach.

Based on the theory above, which in turn is based on my field and lab experience in testing buildings for particulate contaminants, if you were worried that an original vermiculite spill had not been adequately cleaned, *or* if you wanted to know if the original vermiculite spill included asbestos, you might want to collect both a recent-dust sample and an old dust sample for comparison.

If, however, the cleanup was professionally conducted and post-cleanup testing was already performed properly, and if those steps indicated no problem remaining, in my *opinion* further testing would not be justified unless a new reason for further investigation is apparent. (Examples of such reasons are

and also at MOLD TEST REASONS.

If you have questions about the best particle sample collection procedure for your situation, Contact Us by email.


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