Glass fiber, as used here, is any isotropic fiber with a cross-section consistent with formation by surface
tension, sharp or abrupt terminations, and with visible inclusions limited to elongated bubbles.
Acoustic ceiling tile that contains glass fiber can be divided into two basic groups by their gross
appearance. The body of the tile is either compact and gray or loose and yellow. The gray tile
exhibits the greatest variability in composition, from nearly 90% glass fiber to about 10% glass fiber.
The other materials in the body of the tile may include perolite, paper fiber, clay, calcite, glass
shot, glass blebs, and asbestos. Glass fiber from acoustic ceiling tile is identified by the other
materials still attached to it. Clear epoxy binder, sodium silicate, or similar clear binder containing
small particles of calcite filler and binding the glass fiber to any of the other possible materials
used to make these tiles identifies the glass as coming from acoustic ceiling tile.
The yellow bodied acoustic ceiling tile that contains glass fiber is composed of glass fiber and
yellow phenolic resin. The amount of resin and the amount of mineral filler used in the resin varies
from one grade to another and from one manufacturer to another. Glass fiber from yellow bodied
acoustic ceiling tile can often be distinguished from other yellow phenolic bound glass fiber.
Yellow phenolic bound glass fiber from sound board in the HVAC system is generally covered with
small impacted particles of natural minerals, soot, pollens and other airborne particles. Yellow
phenolic bound glass fibers from blanket insulation typically contain much less mineral filler in
the resin. Yellow phenolic bound glass fiber from cubicle divider panels tends to contain much
more yellow resin than the yellow bodied acoustic ceiling tile. See the "Glass Fiber" section of
the gallery for examples of all these materials.
A common structure for a cubicle divider consists of a metal frame supporting a resin stiffened glass
fiber pannel. The glass fiber pannel is then covered with a thin loose glass fiber blanket and an outer
layer of cloth. Glass fiber from the cubicle divider is heavily coated with heavily filled yellow or orange
phenolic resin. The deterioration of the glass fiber pannel is typically due to the pannels use as a
pincushion or to other forms of mechanical damage.
The HVAC system is a common source of glass fiber in indoor office and school environments. These
glass fibers are generally coated with particles impacted onto their surfaces that mark them as having
been exposed to a moving air stream. These impacted particles typically have diameters smaller than
that of the fiber on which they rest. The color of the resin associated with glass fiber from the
HVAC system varies. It may be yellow, orange, red, green, gray, or black. The same "soundboard" may
have more than one color of resin on it. One common combination is a yellow resin used for the bulk
of the glass fiber mat with a coating of black, mineral-filled resin on the outer surface of the panel.
The resin used for the soundboard panels is generally heavily filled with clay or silica.
Thermal blanket insulation is made from glass wool with a small amount of resin to bind the fibers
together in order to maintain loft. The resin is typically yellow, pink, or colorless (white). The fibers
tend to be clean other than the presence of the resin when found in environmental samples though
is some instances, where they have been exposed to air flow, they can become coated with particles and
look similar to ventilation system glass fibers.
Identifying Glass Fiber
Glass fiber can only be acurately identified using a polarized light microscope and by being aware of the possible
interferences. The images below provide examples demonstrating the importance of polarized light and natural substances
that can be confused with man-made mineral fiber.
The first set of four photographs show particles that without polarized light may have been identified as glass fiber.
The next set shows particles that are natural materials that may look like glass fibers and that contain elements
consistent with glass fibers. These may cause the same symptoms as glass fibers but they are not man-made and controlling
these fibers will generally involve the control of contaminants coming in from outdoors.
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