Asbestos is a naturally occurring strong mineral
fiber that is resistant to heat and has many desirable properties. The most
common asbestos types are the amphiboles amosite and crocidolite (which are
brown and blue) and chrysotile (white). In the U.S., about 95% of asbestos used
is chrysotile.
Because
asbestos fibers are resistant to heat and most chemicals, they have been used as
insulation materials in many residential and commercial buildings throughout the
country. Examples of materials that may contain asbestos include: vinyl floor
tiles, pipe insulation, thermal system insulation on mechanical equipment,
acoustical plaster ceilings, structural steel fireproofing, ceiling tiles,
roofing materials, transite panels in laboratory hoods, and lab bench tops.
These materials do not pose a health risk to building occupants when they are
intact and well maintained. 1
Contrary
to popular belief, not all asbestos is truly hazardous. When asbestos-containing
materials (materials containing 1% or more asbestos) are structurally intact,
they are generally not hazardous as their fibers aren't available for
inhalation. However, when the fibers are damaged, they are rendered friable. The
official working definition for friable materials is those which are able to be
crushed or destroyed by human hand pressure. If any asbestos-containing material
is in this condition it is potentially hazardous and necessitating abatement.
2
Asbestos fibers can cause health problems if inhaled. When asbestos fibers
become airborne, they can be inhaled deep into the lung. Many fibers deposited
in the lung are retained there for long periods of time, others may be
translocated to other parts of the body (e.g., the lining of the lung and
abdomen), and others are completely cleared, albeit slowly. The fibers can cause
chronic local inflammation and disrupt orderly cell division, both of which can
facilitate the development of asbestosis and cancer. Thus, inhalation of
asbestos fibers can initiate a chain of events resulting in cancer or other
asbestos-related illness, which may not become apparent for years, even long
after the exposure has ended.
Chrysotile (Mg6Si4O10(OH)8) is a white or
greenish color and is considered to be the softest of the asbestos minerals. It
is used in insulation and fireproofing products, as well as spun and woven into
asbestos clothes and tapes. Chrysoltile is primarily mined in Canada, Africa and
the former USSR. Scientists believe this to be the least toxic of all
asbestiform minerals. This fiber is the most common (>95%) type of asbestos
found.
Amosite (Fe7Si8O22(OH)2), a
brownish-yellow to white asbestos mineral, has excellent properties for use in
heat insulation. It has a needle-like morphology and is found in mines in South
Africa.
Crocidolite
(Na2Fe2+3Fe3+2Si8O22(OH)2) is a blue sodium iron silicate fiber which may be
woven or spun into cloth or tape. Mined in South Africa and Australia, it is
believed to be the most toxic of asbestiform minerals. The use of crocidolite is
very limited in the United States.
Anthophyllite, a white magnesium
silicate, contains various forms of iron. This fiber has a harsh texture, but
has excellent resistance to chemicals and heat. Although limited in the United
States, it has been found in decorative and acoustical material.
Tremolite has a white to yellowish color
and is a calcium magnesium silicate. It has been a major ingredient in
industrial and commercial talc.
Actinolite, a calcium iron magnesium
silicate, has a greenish to white color. It has poor resistance to chemicals
with a harsh texture. These properties limit its commercial use.
Common Items Containing Asbestos
Most products
made today do not contain asbestos. However, until the 1970s, many types of
building products and insulation materials used in homes contained asbestos.
Common products that might have contained asbestos in the past, and conditions
which may release fibers, include:
STEAM PIPES, BOILERS, and FURNACE
DUCTS insulated with an asbestos blanket or asbestos paper tape. These
materials may release asbestos fibers if damaged, repaired, or removed
improperly.
RESILIENT FLOOR TILES (vinyl
asbestos, asphalt, and rubber) and the backing on VINYL SHEET FLOORING,
and ADHESIVES used for installing floor tile. Sanding tiles can release
fibers. So may scraping or sanding the backing of sheet flooring during removal.
CEMENT SHEET,
MILLBOARD, and PAPER used as insulation around furnaces and wood burning stoves.
Repairing or removing appliances may release asbestos fibers. So may cutting,
tearing, sanding, drilling, or sawing insulation.
DOOR GASKETS in
furnaces, wood stoves, and coal stoves. Worn seals can release asbestos fibers
during use.
SOUNDPROOFING
or DECORATIVE MATERIAL sprayed on walls and ceilings. Loose, crumbly, or
water-damaged material may release fibers. So will sanding, drilling, or
scraping the material.
PATCHING
and JOINT COMPOUNDS for walls and ceilings, and TEXTURED PAINTS.
Sanding, scraping, or drilling these surfaces may release asbestos.
ASBESTOS CEMENT ROOFING,
SHINGLES, and SIDING. These products are not likely to release asbestos
fibers unless sawed, drilled, or cut.
ARTIFICIAL ASHES AND EMBERS
sold for use in gas-fired fireplaces. Also, other older household products such
as FIREPROOF GLOVES, STOVE-TOP PADS, IRONING BOARD COVERS, and certain
HAIRDRYERS.
