Photograph of a fiberglass HVAC air filter Fiberglass, Air Filters & IAQ

  • FIBERGLASS & AIR FILTERS - CONTENTS: Fiberglass, Air Filters & Indoor Air Quality. Do HVAC filters release fiberglass fibers or fragments to the building air or do they remove such particles. Do field investigators, hygienists, IAQ specialists or test labs see or even look for very small fiberglass insulation fragments? Characteristics of fiberglass fibers and the range of size of fiberglass insulation or other fiberglass product fragments found indoors. Variation in fiberglass test lab analysis and reporting may fail to identify very small fiberglass fragments
  • POST a QUESTION or READ FAQs about reader questions concerning fiberglass particle shedding by air filters, about labs and investigators who may fail to accurately test for small fiberglass fragments, and the variations in fiber size in different HVAC filters.
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Air filters & airborne fiberglass:

This article discusses HVAC system air filters as a potential source of airborne fiberglass versus the role of air filters as a means of removing fiberglass or other particles from indoor air: We describe a shortcoming of some field and lab investigations for airborne fiberglass: failure to sample or test for very small particles.

This website answers almost any question you might ask about air filters for heating or air conditioning systems.We explain how an air conditioning service technician will diagnose certain common air conditioning system failures or defects.

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Air Filters and Fiberglass Contamination in Indoor Air

Air filters and their contribution to fiberglass fragments found in building air and dust

Fiberglass fragment (C) D FriedmanIn our experience, concern for filter shedding, say of fiberglass fragments, is usually not a significant issue.

The contribution of an air conditioning or heating furnace air filter fiberglass to the overall level of airborne or dust-borne fiberglass particles in a building is likely to be insignificant, probably below the limits of detection by other than the most rigorous means, and certainly in most buildings will be insignificant compared with the contribution of other fiberglass sources such as building insulation in unprotected ceilings or walls.

In fact most fiberglass that we find in building air and dust seems to originate in building insulation, especially where there is traffic or air movement in and out of areas where fiberglass insulation is exposed, and more so if that insulation is mechanically damaged such as by being walked-on.

A second source of fiberglass particles in buildings is from damaged fiberglass-lined HVAC ductwork, such as ducts that use an internal fiberglass liner that was damaged by an inept attempt at mechanical cleaning.

If necessary we can usually identify the source of the dominant fiberglass fragments in building air and dust. Samples of settled dust and building air are compared with samples of fiberglass from common building sources such as fiberglass building insulation and fiberglass HVAC duct insulation.

Our next photo illustrates the variation in fiberglass fiber diameter as well as resin color and deposition patterns. We describe this variation further below.

Fiberglass fiber diameter variation (C) Daniel Friedman

Fiberglass fiber metric consistency and the color of fiberglass binders are often sufficiently distinct to permit positive identification of the source of fiberglass fragments in the building environment.

Also see our article on laboratory identification of fiberglass found at LAB IDENTIFICATION OF FIBERGLASS

HVAC Air Filters Are More Likely to Reduce than Increase the Indoor Airborne Fiberglass Particle Level

In sum, it is very doubtful that a fiberglass-based HVAC air filter is a meaningful contributor to the total load of airborne fiberglass particles in a building. There are simply too many enormously larger fiberglass particle sources that overwhelm the measurement.

Any air filter, properly selected and installed and maintained, will be expected to reduce the overall level of airborne particles, including fiberglass fragments which are contributed to the building air and dust from other building sources.

Do field investigators, hygienists, IAQ specialists or test labs see or even look for very small fiberglass insulation fragments?

Photograph of chopped fiberglass insulation

What about fiberglass particles? As we discuss in more detail in our fiberglass and asbestos IAQ articles some of the research on the possible hazards of airborne fiberglass is confusing because it asserts that the probable hazard of "large" fiberglass particles is low.

What's tricky is that hygienists or others who check indoor air or dust for the level of fiberglass contamination, and even the labs which process these samples may examine and report particles only in the larger size range.

That makes sense insofar as it's apparent that large particles dominate fiberglass dust.

But let's consider just a tiny bit further.

Fiberglass, particularly mechanically-damaged fiberglass insulation, say in a fiberglass-lined air duct which was mechanically cleaned, can break to release very small glass fragments, even in the 1u range and below.

These ultra-small fiberglass fiber fragments or particles (such as shown in our photo at left, magnified approximately 2000x) are very hard to detect in the laboratory unless the lab is specifically looking for them.

Small fragments of fiberglass fibers (C) D Friedman

In fact, unless the laboratory uses a slide preparation media with a refractive index nowhere close to that of glass, they won't see the particles at all in the microscope, no matter how many of them are present!

In our experience, few environmental testing labs except those specializing in forensic microscopy bother to vary the refractive index of their mounting liquids to search for specific types of particles when analyzing an indoor dust or air particle sample..

In other words, you won't find what you're not looking for.

A reasonable conclusion from these observations about the presence and difficulty in seeing small airborne particles below 10u and especially below 3u is that the better we filter the air the less we need to worry about them.

Variations in fiber size in air conditioning and heating air filters

Fiberglass fiber size variations (C) D FriedmanOur forensic lab photo (left) illustrates that fiberglass fibers of quite different diameters can be observed even in the same particle or material sample.

Those dark blobs on the small-diameter vertical fiberglass fiber at the right of our photo are resin. The larger diameter fiberglass fibers in the left of the photo do not happen to carry resin.

One of our clients wrote that her fiberglass-based air conditioning and heating air filters were described by their manufacturer as using fibers of 20-27u (in fiber diameter).

The maker promises the filters do not shed fiberglass fragments and that the fibers are too big in micron size to become repairable even if they do shed.

Laboratory examination of a filter sample sent by the client to an independent microscopy laboratory found that the filter fibers were 31 microns in diameter, and had a blue coating on them [probably the binder, and not the fragments shown in our photos here.].

The binder coating increases the effective fiber diameter.

These measurements of fiberglass fiber diameters were within a normal range of variation in product manufacture that we've seen in own forensic laboratory.

Furthermore, the diameter of a fiberglass air filter fiber is as an indicator of the health hazard should the filter shed fibers is unlikely to be as useful measure as the number of particles released and their overall size.

For example, a fiberglass fiber can break so as to release several sub-micron glass fragments - as we illustrated in our fiberglass fragment photo earlier on this page and in the additional fiberglass fragment photograph below.

Fiberglass insulation fragment, small (C) Daniel Friedman

This ultra-small (1-5 micron range) fiberglass fragment photo is a digital enlargement of a photograph we took at 1,900x, close to the practical limits of transmitted or reflected light microscopy.

The actual filtering efficiency of an air filter should not be estimated simply on fiber diameter since more than diameter goes into the filter design, including fiber placement, randomness, average remaining opening diameter, total filter thickness, electrostatic properties of the filter, and other variables such as whether or not the filter has a gasket or is bypassing lots of air around the filter itself.


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