Photograph of house dust by microscope HVAC Dust Study:
An Investigation of Indoor House Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust

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What is in house dust?

This article discusses analysis of building dust or house dust to trace its origins and to sort out whether or not dust problems are caused by the building HVAC system. A client called about an ongoing dispute with an HVAC contractor who had recently installed new heating and air conditioning equipment and duct work in her home. Mysterious thick "blue dust" was appearing throughout the home, reappearing soon even after vacuuming and cleaning.

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Killer house dust? a case history: Mystery dust identified as cotton, ending dispute with contractor

Fungal hypae in house dust sample © D Friedman at

Our photo illustrates a common finding in house dust, an occasional fungal hyphal fragment along with mostly non-fungal granular debris such as road dust particles.

Usual components of house dust include skin cells and fabric fibers. Individual occurrences or infrequent occurrences of individual spores in air or dust samples are usually, but not always, insignificant.

Significance may depend on the context of the investigation.

For example we may find low levels of a not-normally-airborne spore such as Stachybotrys chartarum in a building after demolition and remediation during a mold cleanup job - probably not a concern.

Finding the same particles in a home that has not been properly cleaned might indicate a need for a more careful investigation.

While there were no serious health complaints nor people at unusual medical risk, the occupants were concerned, and believed that something in the ducts or air handlers was causing a problem.

World trade center collapse dust photo © D Friedman at

In contrast, at left we include one of our photographs of analysis of dust from the World Trade Center collapse - not from the building discussed in this article. (See WORLD TRADE CENTER 9-11 DUST PHOTOS).

Now about our client's dust concern, while the dispute had been going on for months, at the time of this call no one had performed a forensic examination of the dust itself. The client mailed me a representative sample of surface dust from the home.

Here's one way surface dust can be easily collected and mailed: TAPE TEST FOR SETTLED DUST ANALYSIS

We'd be concerned about finding high levels of problematic mold spores, and I'd not like to find a lot of fiberglass in the sample either, both because it may be a health concern and because it'd argue for sloppy work by the contractor.

House dust from an occupied home contains lots of stuff, usually dominated by skin cells and fibers from clothing and upholstery or carpets. Animal dander, particularly from dogs, cats, or mice, may be present at high levels too. In inner-city apartments I find lots of insect fragments as well, possibly cockroach allergens.

And everybody's dust can be expected to have traces of dust mites, usually their fecal pellets. By examining the pellets I can often determine what the mites are eating, for example mold spores.

Forensic Microscopy Basics for Particle & Fiber Identification

The dust sample was examined for homogeneity and then prepared for a look at high magnification in my lab, using both ordinary and polarized light, along with special microscope light wavelength filters, and combination of an index of refractive index mounting liquids combined Becke line analysis to measure the refractive index of particles.

These methods can quickly separate out synthetic fibers such as Orlon or Nylon, as well as distinguishing typical road grit and fiberglass.

Remarkably the dust sample from this West coast home was unusually clean. The sample was 90% cotton fibers, mostly blue with a few red ones included. There were incidental (not statistically significant) wool fibers present too. Skin cells were another 8% of the sample, and typical drywall dust and road dust made up the rest.

The sample contained no mold spores, no fiberglass, no heating fuel combustion products, no ash, no paint droplets, in other words, it was cotton from a mostly blue fiber source.

This dust source was certainly not from the heating system components.

Without making a site inspection we can still offer some useful speculation:

Look for something new in the home, carpets, drapes, upholstery, bedding,

We would guess that mechanical disturbance like foot traffic, vacuuming, or other activity was combining with air movement from the HVAC system to spread dust around.

Naturally, an investigator is a lot smarter when on-site than when speculating by telephone or email. But in any case, this was the end of arguing with the HVAC contractor who was clearly not at fault.

See CARPETING & INDOOR AIR QUALITY for a broad discussion of indoor air quality concerns regarding carpeting, including chemicals, adhesives, odors, and VOCs associated with carpeting.


Continue reading at HOUSE DUST COMPONENTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AIR HANDLER DUST CONTAMINATION - drywall dust in furnace or air conditioner air handlers


Or see HOUSE DUST PARTICLE PHOTOS - a photo tour of what we found in dust from a London loft.

Or see HVAC DUST CONTAMINATION STUDY  - what do we find in dust in a heating or air conditioning system?

Or see DUST SAMPLING PROCEDURE where we also discuss finding mold in indoor dust samples


Or see these

Indoor Dust & IAQ Articles

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