Public Health Statement for Synthetic Vitreous Fibers
Spanish: Fibras Vítreas Sintéticas
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This Public Health Statement is the summary chapter from the Toxicological Profile for Synthetic Vitreous Fibers. It is one in a
series of Public Health Statements about hazardous substances and their health
effects. A shorter version, the ToxFAQsTM, is also
available. This information is important because this substance may harm you.
The effects of exposure to any hazardous substance depend on the dose, the
duration, how you are exposed, personal traits and habits, and whether other
chemicals are present. For more information, call the ATSDR Information Center
This public health statement tells you
about synthetic vitreous fibers (SVFs) and the effects of
exposure to them.
The Environmental Protection Agency (EPA)
identifies the most serious hazardous waste sites in the nation.
These sites are then placed on the National Priorities List
(NPL) and are targeted for long-term federal clean-up activities.
Synthetic vitreous fibers have not been detected in the 1,647
current or former NPL sites. Although the total number of
NPL sites evaluated for these substances is not known, the
possibility exists that synthetic vitreous fibers may be found
in the future as more sites are evaluated. This information
is important because these sites may be sources of exposure
and exposure to these substances may harm you.
When a substance is released from a large
area, such as an industrial plant, or from a container, such
as a drum or bottle, it enters the environment. This release
does not always lead to exposure. You are exposed to a substance
only when you come in contact with it. You may be exposed
by breathing, eating, or drinking the substance, or by skin
If you are exposed to synthetic vitreous
fibers, many factors determine whether you'll be harmed. These
factors include the dose (how much), the duration (how long),
and how you come in contact with them. You must also consider
the other chemicals you're exposed to and your age, sex, diet,
family traits, lifestyle, and state of health.
What are synthetic vitreous fibers?
Synthetic vitreous fibers are a group
of fibrous inorganic materials that contain aluminum or calcium
silicates and other trace oxides and metals, and are made
from rock, slag, clay, or glass. These fibers differ from
natural mineral fibers such as asbestos because they do not
have a crystalline molecular structure. The randomly oriented
molecular structure of synthetic vitreous fibers is called
an amorphous structure. There are two broad categories of
synthetic vitreous fibers: filaments and wools. The filaments
consist of continuous glass filaments, while the wools are
subdivided into glass wool, rock wool, slag wool, refractory
ceramic fibers, and other types of newer fibers. The primary
uses of synthetic vitreous fibers are for heat and sound insulating
purposes, to reinforce other materials, and as filtration
materials. Glass wools are some of the most widely used insulating
materials in homes and buildings. The production and use of
synthetic vitreous fibers has increased in recent years because
these products are often used as a replacement for asbestos.
A fiber is simply a long, slender particle.
Technically, to be counted as a fiber, the particle must be
at least 5 micrometers long (1 micrometer equals 1/1,000,000
of a meter and has the symbol μm), and have an aspect
ratio of at least 3 to 1 or sometimes 5 to 1 (the aspect ratio
is the ratio of a fiber's length to its diameter). The diameter
of a fiber is an important property because very thin fibers
are more easily suspended in air than thick fibers, and they
can be breathed in and deposited deep in the lungs. Only very
thin fibers with diameters less than 3 μm are able to
be breathed into the lower respiratory tract of humans. Thicker
fibers are deposited on the mucous-lined surface of the upper
respiratory tract, which includes the nose and mouth. The
World Health Organization (WHO) counts respirable fibers as
particles with lengths greater than 5 μm, diameters
less than 3 μm, and aspect ratios ≥3:1. Depending upon
the way that they are produced, fibers can have relatively
large or small diameters. Generally speaking, glass wool,
rock wool, slag wool, and refractory ceramic fibers have the
smallest diameters, while continuous filament glass fibers
have the largest diameters.
What happens to synthetic vitreous fibers when they enter the environment?
Synthetic vitreous fibers do not evaporate
into air or dissolve in water. They are generally not broken
down to other compounds in the environment and will remain
virtually unchanged over long periods. Eventually, synthetic
vitreous fibers will be broken down if the water or soil is
very acidic or very alkaline. Fibers can enter the air, water,
and soil from the manufacture, use, and disposal of synthetic
vitreous fiber-containing materials. Fibers with small diameters
become airborne more easily than thick fibers, and can be
transported by wind for longer distances. Synthetic vitreous
fibers are not likely to move through soil.
How might I be exposed to synthetic vitreous fibers?
If materials containing synthetic vitreous
fibers, such as insulation or ceiling boards in your home
or where you work, are disturbed, synthetic vitreous fibers
can become airborne. When these fibers become airborne, you
can be exposed to low levels of synthetic vitreous fibers
primarily by breathing air. Your skin and eyes can also be
exposed to synthetic vitreous fibers if you install your own
home insulation or come into contact with insulation in your
home without using protective equipment such as gloves, protective
glasses, or masks.
The vast majority of exposure to synthetic
vitreous fibers occurs to workers who produce or use synthetic
vitreous fiber-containing products. Employees at manufacturing
facilities where synthetic vitreous fibers products are produced,
as well as workers who regularly install or come into contact
with insulating material, are most frequently exposed to synthetic
vitreous fibers. Workers involved in demolition work, as well
as in building maintenance and repair, are potentially exposed
to higher levels of synthetic vitreous fibers once these materials
How can synthetic vitreous fibers enter and leave my body?
If you breathe synthetic vitreous fibers,
some will be deposited in the nasal and oral passages, and
on the surfaces that line your lungs. Most fibers deposited
in the nasal and upper lung airways are removed by being carried
away in a layer of mucous to the throat, where they are swallowed
into the stomach. This usually takes place within a few hours.
Fibers deposited in the deepest parts of the lungs where gas
exchange occurs are removed more slowly by special cells called
macrophages. Macrophages can engulf the fibers and move them
to the mucous layer and the larynx where they can be swallowed.
Swallowed fibers and macrophages are excreted in the feces
within a few days.
Synthetic vitreous fibers deposited in
the gas exchange area of the lungs also slowly dissolve in
lung fluid. Fibers that are partially dissolved in lung fluid
are more easily broken into shorter fibers. Shorter fibers
are more easily engulfed by macrophages and removed from the
lung than long fibers. Synthetic vitreous fibers dissolve
more readily in the lung than asbestos fibers. Refractory
ceramic fibers dissolve more slowly than most types of insulation
(e.g., glass wools, stone wools, and slag wools).
If you swallow synthetic vitreous fibers
(by eating, drinking, or by swallowing fibers that have moved
from nasal or lung airways to your larynx), nearly all of
the fibers pass through your intestines within a few days
and are excreted in the feces.
If you get synthetic vitreous fibers
on your skin or in your eyes, very few of these fibers, if
any, pass through into your body.
How can synthetic vitreous fibers affect my health?
To protect the public from the harmful
effects of toxic chemicals and to find ways to treat people
who have been harmed, scientists use many tests.
One way to see if a chemical will hurt
people is to learn how the chemical is absorbed, used, and
released by the body; for some chemicals, animal testing may
be necessary. Animal testing may also be used to identify
health effects such as cancer or birth defects. Without laboratory
animals, scientists would lose a basic method to get information
needed to make informed decisions to protect public health.
Scientists have the responsibility to treat research animals
with care and compassion. Laws today protect the welfare of
research animals, and scientists must comply with strict animal
Synthetic vitreous fibers can cause irritation
of the eyes and skin known as "fiberglass itch."
They can also irritate the upper respiratory tract (the nose,
throat) and parts of the lung, causing sore throat, nasal
congestion, and cough. These effects usually go away with
time. Because most people are not exposed to high levels of
synthetic vitreous fibers, serious health effects are not
expected to happen in most people.
Most of the information regarding the
possible effects of repeated exposure to synthetic vitreous
fibers in people comes from large studies of workers who make
synthetic vitreous fibers. Very few effects were detected.
A few workers who made refractory ceramic fibers had pleural
plaques on the lining of their chests. These plaques did not
seem to harm the workers. Other workers who smoked could not
breathe quite as well as smokers who did not work with refractory
ceramic fibers. Nonsmoking refractory ceramic fiber workers
could breathe as well as other nonsmokers. This suggests that
repeatedly breathing in refractory ceramic fibers from workplace
air worsens the effects of smoking. Pleural plaques and decreased
breathing ability have not been found in workers who made
glass wool and stone wool. Other studies have found that the
numbers of deaths from lung diseases, including lung cancer
or mesothelioma, in groups of workers involved in the manufacture
of glass wool, stone wool, or refractory ceramic fibers are
not consistently different from what is found in the general
U.S. population. Mesothelioma is a cancer of the membrane
lining the lung. Increased risk for mesothelioma has been
found in asbestos workers, but increased risks for this cancer
have not been found in workers involved in the manufacture
of synthetic vitreous fibers.
Results from animal experiments show
that when synthetic vitreous fibers or other inhaled dust
particles are deposited in the deepest part of the lung in
high numbers, the lung responds with a process called pulmonary
inflammation. In this process, macrophage numbers in the lung
increase so that they can engulf and move the fibers out of
the lung. When high numbers of fibers are deposited, the macrophages
can become clumped together. If pulmonary inflammation continues,
the cells lining the lung may thicken from a process called
bronchiolization. Bronchiolization may reduce the amount of
oxygen that the body gets from the air during breathing. If
exposure stops, deposited synthetic vitreous fibers slowly
dissolve in the lung fluid or are moved out of the lung by
the macrophages, and pulmonary inflammation disappears with
Results from animal studies also show
that repeatedly breathing high levels of some types of synthetic
vitreous fibers may cause a slow buildup of scar-like tissue
in the lungs and in the membrane surrounding the lungs. This
scar-like tissue does not expand and contract like normal
lung tissue, and breathing can become difficult. This condition
is called pulmonary fibrosis. The types of synthetic vitreous
fibers that cause this condition in animals stay in the lung
for longer periods of time than the types that do not. They
are called durable or biopersistent synthetic vitreous fibers.
Results from animal studies also show that repeatedly breathing
high levels of durable synthetic vitreous fibers may also
cause cancer of the lung and mesothelioma. The most common
types of glass wools, stone wools, or slag wools used for
insulation are less durable than refractory ceramic fibers.
In rat studies, they did not cause the severe lung effects
caused by the more durable refractory ceramic fibers.
Scientists studying pulmonary fibrosis,
lung cancer, and mesothelioma in animals from durable synthetic
vitreous fibers have shown that the development of these conditions
depends on four factors: dose, duration, dimension, and durability.
Dose is the amount of fibers deposited in the lung, and duration
is the time period when exposure occurs. High doses and long
durations of exposure are required for these conditions to
develop. Dimension refers to the length and diameter of the
fibers. Fibers with diameters greater than about 3 μm
are not inhaled into the deepest regions of the lungs. Fibers
with lengths greater than about 15-20 μm are not engulfed
by macrophages, and are more likely to lead to lung injury
than shorter fibers that are more readily removed by macrophages.
Durability refers to how readily a fiber dissolves in lung
fluid. Different types of synthetic vitreous fibers have different
durabilities due to differences in chemical makeup. Most synthetic
vitreous fibers used as insulation in homes and buildings,
such as fiberglass wools and stone wools, are more readily
dissolved in lung fluid than are refractory ceramic fibers,
which are used in insulation materials for furnaces. Long,
durable fibers deposited in the gas-exchange region of the
lung can lead to long-term inflammation, pulmonary fibrosis,
lung cancer, or mesothelioma.
Levels of synthetic vitreous fibers in
outdoor air, indoor air, and in most workplaces are usually
well below levels that caused reversible pulmonary inflammation
in animals or levels of durable synthetic vitreous fibers
that caused pulmonary fibrosis, lung cancer, or mesothelioma
in animals. For example, levels of a refractory ceramic fiber
that caused pulmonary fibrosis, lung cancer, and mesothelioma
in rats are about one million times higher than levels of
synthetic vitreous fibers detected in outdoor air close to
synthetic vitreous fiber manufacturing factories, or indoor
air from buildings with fiberglass or stone wool insulation.
The levels experienced by the diseased rats are about 50 times
higher than levels of synthetic vitreous fibers in the most
dusty workplaces where insulation containing synthetic vitreous
fibers was removed or installed.
In 2002, the International Agency for
Research on Cancer (IARC) considered all of the evidence regarding
the possible carcinogenicity of synthetic vitreous fibers.
Much of the evidence was collected in the 1990s and was not
available for earlier assessments made by the U.S. Department
of Health and Human Services (DHHS). IARC determined that
refractory ceramic fibers are possibly carcinogenic to humans
because of their high biopersistence. IARC also determined
that insulation glass wool, stone wool, and slag wool, and
continuous filament glass were not classifiable as to carcinogenicity
to humans because of inadequate evidence of carcinogenicity
in humans and the relatively low biopersistence of these materials.
EPA has not assessed the potential carcinogenicity of glass
wool, stone wool, slag wool, or continuous filament glass,
but has classified refractory ceramic fibers as a probable
How can synthetic vitreous fibers affect children?
This section discusses potential health
effects from exposures during the period from conception to
maturity at 18 years of age in humans.
Because synthetic vitreous fibers are
not absorbed into the body (when inhaled or ingested), it
is unlikely that they would cause birth defects or be transferred
in breast milk to nursing infants.
Like adults, children who are exposed
to synthetic vitreous fibers may experience irritation of
the eyes, skin, and upper respiratory tract. Children breathe
differently and have different lung structures than do adults.
It is not likely that these differences will cause a greater
amount of synthetic vitreous fibers to stay in the lungs of
children than in the lungs of adults.
It is possible that exposure of young
children to highly durable fibers could lead to pulmonary
effects after very long latency periods. However, there is
no evidence to support this possibility, and the durability
of many types of synthetic vitreous fibers in the lung is
low. This concern also has been raised for children exposed
to asbestos fibers, which are more durable than synthetic
vitreous fibers, but, as with synthetic vitreous fibers, there
is inadequate evidence to support the idea that exposed young
children may be at greater risk to develop pulmonary effects
from durable fibers than are adults.
How can families reduce the risk of exposure to synthetic vitreous fibers?
If your doctor finds that you have been
exposed to significant amounts of synthetic vitreous fibers,
ask whether your children might also be exposed. Your doctor
might need to ask your state health department to investigate.
Very low levels of synthetic vitreous
fibers can be found in virtually all homes, buildings, and
outside air, but there is little concern regarding these low
levels. The most important way that families can lower their
exposures to synthetic vitreous fibers is to be aware of the
sources of synthetic vitreous fibers in their homes and avoid
exposure to these sources. The most common source of synthetic
vitreous fibers in a home is from insulating material that
may be in your attic or walls. Damaged or deteriorating ceiling
boards are another potential source. As long as the materials
are not physically disturbed or breaking down, the levels
of synthetic vitreous fibers in the air should be very low.
Relatively high levels of airborne synthetic vitreous fibers
have been detected during the installation of insulating materials
in attics, but these levels decline rapidly in 1 or 2 days
as airborne dust settles. If you are installing your own insulation,
wear protective clothing and masks, and follow the recommendations
provided by the manufacturer for installing this material.
You can bring synthetic vitreous fibers
home in the dust on your hands or clothes if you work in facilities
that produce or use synthetic vitreous fibers, or install
or remove materials with synthetic vitreous fibers. Your occupational
health and safety (OHS) officer can and should tell you whether
chemicals you work with are dangerous and likely to be carried
home on your clothes, body, or tools. Your OHS officer can
also tell you whether you should be showering and changing
clothes before you leave work, storing your street clothes
in a separate area of the workplace, or laundering your work
clothes at home separately from other clothes. Your employer
should have Material Safety Data Sheets (MSDSs) for many of
the chemicals used at your place of work, as required by the
Occupational Safety and Health Administration (OSHA). Information
on these sheets should include chemical names and hazardous
ingredients, important properties (such as fire and explosion
data), potential health effects, how you get the chemical(s)
in your body, how to handle the materials properly, and what
to do in an emergency. Your employer is legally responsible
for providing a safe workplace and should freely answer your
questions about hazardous chemicals. Either OSHA or your OSHA-approved
state occupational safety and health program can answer any
further questions and help your employer identify and correct
problems with hazardous substances. OSHA or your OSHA-approved
state occupational safety and health program will listen to your formal complaints about workplace health hazards and
inspect your workplace when necessary. Employees have a right
to safety and health on the job without fear of punishment.
Is there a medical test to determine whether i have been exposed to synthetic vitreous fibers?
No tests are specific for determining
whether or not you have been exposed to synthetic vitreous
fibers. Because synthetic vitreous fibers leave the body quickly,
most nonspecific tests would not be very useful. A chest x
ray is a common method to determine if you have certain conditions,
such as pleural plaques, lung or pleural fibrosis, lung tumors,
or mesotheliomas, but x rays cannot show the presence of fibers
in the lung.
What recommendations has the federal government made to protect human health?
The federal government develops regulations
and recommendations to protect public health. Regulations
can be enforced by law. Federal agencies that develop regulations
for toxic substances include the Environmental Protection
Agency (EPA), the Occupational Safety and Health Administration
(OSHA), and the Food and Drug Administration (FDA). Recommendations
provide valuable guidelines to protect public health but cannot
be enforced by law. Federal organizations that develop recommendations
for toxic substances include the Agency for Toxic Substances
and Disease Registry (ATSDR) and the National Institute for
Occupational Safety and Health (NIOSH).
Regulations and recommendations can be
expressed in not-to-exceed levels in air, water, soil, or
food that are usually based on levels that affect animals;
they are then adjusted to help protect people. Sometimes these
not-to-exceed levels differ among federal organizations because
of different exposure times (an 8 hour workday or a 24 hour
day), the use of different animal studies, or other factors.
Recommendations and regulations are also periodically updated as more information becomes available. For the most current information, check with the federal agency or organization that provides it. Some regulations and recommendations for synthetic vitreous fibers include the following:
In 1999, a Health and Safety Partnership Program was established as a voluntary workplace safety program for workers involved in the manufacture, fabrication, installation, and removal of glass wool, rock wool, and slag wool products. The program was established as a result of negotiations between the OSHA, the North American Insulation Manufacturers Association, the National Insulation Association, and the Insulation Contractors Association of America. The program established a voluntary 8 hour time-weighted average (TWA) permissible exposure limit (PEL) of 1 respirable fiber per cc of air. Under this agreement, respirable fibers are counted as particles with length greater than 5 μm, diameter less than 3 μm, and aspect ratio greater than or equal to 3:1. The agreement specifies that when the PEL is exceeded in a workplace (such as when insulation is blown into attics or removed), workers will wear NIOSH certified dust respirators.
Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological profile for Synthetic Vitreous Fibers. Atlanta, GA: U.S.
Department of Health and Human Services, Public Health Service.
Where can I get more information?
If you have questions or concerns, please contact your community or state health or environmental quality department or:
For more information, contact:
Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
4770 Buford Highway
Chamblee, GA 30341-3717
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO
ATSDR can also tell you the location of occupational and environmental health clinics. These clinics specialize in recognizing, evaluating, and treating illnesses resulting from exposure to hazardous substances.