-
-
- MAN-MADE
VITREOUS FIBERS
(MMVF)
- by
Edouard
Bastarache
|
-
- Introduction
:
-
- Man-made vitreous fibers
(MMVF) or synthetic vitreous fibers (SVFs) are a class
of insulating materials used widely in residential and
industrial settings; they are made primarily from
glass, rock, slag or clay. The three general
categories are fiberglass, mineral wool , and
refractory ceramic fibers.
- In some situations, SVF
materials can release fine, airborne dust particles,
some of which are small enough to be respirable. Thus,
workers may be exposed to SVF fibers by dermal contact
and/or by inhalation.
- Fibrous particles having
long, thin geometry present a special problem to the
resiratory tract; because fibers are thin, they can
penetrate into the deep lung and, because they are
long, mobile lung cells may have difficulty in
removing them.
-
- The three general
categories may be divided in the following manner
:
-
- A-Fiber Glass
:
- 1-Glass Wool,
- 2-Continuous
Filament
-
- B-Mineral Wool
:
- 1-Rock Wool,
- 2-Slag Wool.
-
- C-Refactory Ceramic
Fibers :
- 1-Pure Oxides
- 2-Kaolin.
-
- SVFs can help to control
heat flow, absorb acoustic energy, filter impurities
from gases and liquids, and with a vapor barrier,
control condensation.
-
- An important attribute of
these fibers is that they do not split longitudinally
as do asbestos fibers. Because asbestos fibers tend to
split longitudinally, over time in the lung, the
number of lung, thin asbestos fibers can actually
increase, resulting in increasing lung irritation even
after exposure to asbestos has stopped.
- In contrast, SVFs tend to
break tranversely into shorter segments, which the
lung can clear more readily than it can long
fibers.
-
- Synthetic
Vitreous Fibers :
-
- A-Fiberglass
:
-
- Fiberglass is produced in
two basic forms, wool fibers and textile
fibers.
-
- 1-Glasswool fibers
:
- The current major uses of
glass wool are in commercial and residential thermal
insulation, noise-control (acoustic) products, linings
for air-handling ducts, pipe insulation, air filters,
roof insulation, and insulation for automobiles,
aircraft, mobile homes, refrigerators, domestic
cooking appliances, and a wide variety of other
appliances and equipment.
- Submicron glass wool fibers,
also known as glass microfibers , are generally used
in high-technology products, such as high-efficiency
particulate air filters, specialty filter papers,
battery components, and aerospace
insulation.
-
- 2-Glass textile fibers
:
- Also called continuous
filament, they are used in curtains and draperies,
screening, electrical yarns, roofing paper, shingles,
and industrial fabrics and as reinforcement for
plastics, papers, rubber, and other
materials.
-
- B-Mineral Wool
:
-
- Mineral wools include rock
or stone wool and slag wool. After formation, the
materials are sprayed with lubricating oils and
binders to reduce dustiness (mineral wools generally
contain a very high ratio of nonfibrous particles, or
shot) and fiber breakage.
- Mineral wool applications
are very similar to those of glass wool-thermal
insulation, including fire protection, and acoustic
insulation. Much of the mineral wool produced is used
for blown-in insulation in attics and side walls.
Another popular use of mineral wool is in the
manufacture of decorative and acoustic ceiling tiles
for commercial building.
-
- C-Refractory Ceramic
Fiber :
-
- Refractory ceramic fiber
(RCF) is formulated to help control heat flow in
high-temperature, industrial situations. All RCFs are
blends of alumina and silica and other refractory
oxides.
-
- The three general
categories of RCFs are :
-
- 1-Kaolin clay based
products, for which the clay is obtained by
mining.
- 2-Blends of alumina,
silica,and refractory oxides (e.g. chromous and
zirconia oxides)
- 3-High-purity products that
are a blend of purified alumina and silica and other
materials.
-
- Applications vary for RCFs,
but all are used in high-temperature, industrial
environments.
- RCF blankets are used as
furnace and kiln liners, as backup insulation to
refractory brick, as soaking pit covers, and in
annealing welds. Loose RCF is used as a filler in
packing voids and in expansion joints. Custom-molded
shapes of RCF are used widely in metal molding, in
catalytic converters, and as combustion chamber liners
in industrial furnaces.
-
- Health effects
:
-
- A-Skin Irritation
:
-
- SVFs may irritate the skin
of some workers who are engaged in manufacturing,
fabricating, or installing SVF products. This
irritation is a mechanical reaction to sharp, broken
ends of fibers that rub or become embedded in the
outer layer of the skin and does not appear to be an
allergic response. Typically, irritation does not
persist and can be relieved by washing exposed skin
gently with warm water and mild soap.
-
- B-Upper Respiratory Tract
Irritation :
-
- If large amounts of airborne
fine fiber are released during manufacturing or
handling of SVF products, and improper work practices
permit inhalation of the fibers, some workers may
experience temporary upper respiratory
irritation.
- The irritation consists of a
nonspecific, temporary respiratory condition, usually
manifested by coughing or wheezing. It is mechanically
induced by sharp fibers and does not appear to be an
allergic reaction. It subsides soon after the worker
is removed from exposure and should have no further
impact on his or her health and
well-being.
-
- C-Safety Precautions
:
-
- Occupational health
professionals recommend three levels of precautions
for protecting people when they are manufacturing or
handling SVF materials.
-
- 1-Whenever possible, SVF
products should be engineered and designed to limit
their release of airborne dust.
-
- 2-Manufacturing processes
and controls should be used to minimize airborne dust
in the work environment.
-
- 3-People should wear
approved respiratory protection and clothing that
covers the skin as much as possible when handling or
installing SVFs.
- These precautions
effectively reduce airborne SVF exposure and prevent
skin and upper respiratory irritation.
-
-
- Epidemiologic
studies :
-
- A-Fiberglass and Mineral
Wool Mortality Studies :
-
- Two major mortality studies
have been conducted on large groups of workers engaged
in the production of either glass or mineral wool, one
in Europe and one in the USA.
- A third one, more limited,
was conducted in Canada on fiberglass production
workers.
-
- 1-European study
:
-
- The researchers found an
overall mortality excess among the SVF workers, with
the excess particularly evident among workers with
less than 1 year of employment.
- Among the causes of death
that were more numerous were malignant neoplasms,
mental disorders, cardiovascular diseases, respiratory
diseases, digestive diseases, and external causes.
-
- a-Rock wool-slag wool
workers :
- Simonato et al. reported in
1987 an " excess of lung cancer among rock wool-slag
wool workers employed during an early technological
phase before the introduction of dust-suppressing
agents ", and concluded that " fiber exposure, either
alone or in
- combination with other
exposures, may have contributed to the elevated risk
".
- In their latest update, they
concluded that "the ensemble of these results is not
sufficient to conclude that the increased lung cancer
risk is related specifically to MMVF( SVF); however,
insofar as respirable fibres were a significant
component of the ambient pollution of the working
environment, they may have contributed to the
increased risk "
-
- b-Glass wool workers
:
- For these workers the report
stated that the findings " indicate some excess of
lung cancer , clearly reduced once local adjustment
factors are applied to national mortality rates, and
with no relation to duration of employment nor time
since first employment ".
- No anomalies were found for
the continuous glass filament workers.
-
- c-Mesothelioma :
- Five mesotheliomas have been
identified by death certificate, one in the glass wool
sub-cohort and four in the rock wool-slag wool
sub-cohort. No clear increased risk of mesothelioma
has been identified, altough the researchers have
concluded that
- " the possibility of such
increase is suggested by the results. "
-
-
- 2-American study
:
-
- As with the European study,
the U.S. study found a higher overall mortality rate
among SVF workers as compared to local and national
mortality.
- For deaths due to cancer or
nonmalignant respiratory disease, the study reported
that a positive evidence existed for fine glass and
mineral wool production workers.
- However, the researchers
point out, the data are not consistent with a causal
relationship because the excesses in mineral wool and
glass microfiber deaths were not directly related to
duration of exposure.
- The number of deaths from
mesothelioma in the study cohort is considered to be
within the expected range for the general
population.
- In the 1985 update, a small
but statistically significant excess in respiratory
cancer deaths was reported for workers employed in
glass wool and mineral wool plants but, the
researchers concluded that the evidence of an
association appeared " somewhat weaker " than in the
1982 update.
- In the 1989 update for the
rock wool and slag wool workers, the pattern of
findings was generally consistent with findings
obseved in previous updates; no consistent evidence
remains of an association between lung cancer or
non-malignant respiratory diseases and any of the
respirable fiber measures considered.
-
-
- 3- Canadian study
:
-
- It is a more limited
mortality study. The authors reported a statistically
significant excess in mortality due to lung cancer
among fiberglass production workers. They concluded
that the interpretation of this finding was difficult
because no relationship existed berween the excess of
lung cancer and the lenght of time since first
exposure to the fiberglass production
environment.
-
- It is concluded that the
relationship between work and health in the SVF
industry should continue to be explored.
-
- B-Fiberglass and Mineral
Wool Morbidity Studies :
-
- In the most widely cited SVF
morbidity study, Weil et al.(1983-1984) reported that
the study populations were generally healthy, with no
respiratory symptoms and no adverse lung functions
related to the fiber exposure.
- A low incidence of small
lung opacities was observed in the chest radiographs
(opaque areas sometimes observed in the lungs of
workers in potentially dusty trades).
- In summarizing their
findings they noted that, in general, " the minimal
evidence of respiratory effects detected in the
investigation , which cannot, at present, be
considered clinically significant, is encouraging
concerning the question of potential health effects of
exposure to MMFV ".
- This study was updated and
enlarged at the end of the 1980s and the authors
concluded that the " results indicate no adverse
clinical, functional, or radiographic signs of effects
of exposure to MMVFs in these workers ".
-
- C-Refractory Ceramic
Fiber Morbidity Studies :
-
- Only one known published
report is found in the medical literature on health
effects of occupational exposure to RCFs. The
researchers reported an association between exposures
to RCF and the occurrence of pleural plaques, which
are usually caused by exposure to asbestos fibers. It
was demonstrated that asbestos fibers exposure did not
account for the observed association.
- Also, among the RCF workers,
no significant increase was seen in parenchymal
changes consistent with interstitial
fibrosis.
-
- Animal
Toxicological Studies :
-
- A-Animal Implantation
Studies :
-
- Implantation studies
artificially inject fibers into the body cavities of
laboratory animals : into the pleural (chest) cavity
or peritoneal (abdominal) cavity or by instillation
into the trachea.
- Implantation experiments are
based on introducing large amounts of fiber into
animals by artificial means that bypass normal body
defenses. The circumstances of actual exposure are
totally different in humans. For these reasons, and
because the toxicology induced by implantation of
fibers into rodents does not parallel the findings
from inhalation studies, implantation studies are not
valid for risk assessment or for concluding anything
about the human health hazard associated with the
inhalation of airborne SVFs.
- On the other hand,
implantation studies have provided useful information
on the mechanisms of fiber toxicity. For example, long
fibers (longer than 10 to 20 µm) are most active
in implantation as well as in cell culture studies, so
scientists have hypothesized that biological activity
is directly associated with fiber length.
-
- B-Animal Inhalation
Studies :
-
- The animal inhalation model
is currently the only valid laboratory method for
assessing the hazard to humans of exposure to airborne
SVFs.
- In recent chronic studies,
test SVFs having similar dimensions but different
compositions have induced different biological
effects. Biological effects approximately parallel
fiber biological persistence in the lung. Fiber
compositions that are more lung-persistent would
accumulate during a chronic exposure and persist
longer after termination of exposure and would,
therefore, cause more lung irritation than
compositions that dissolve or fragment transversely
into shorter segments.
- Differences in biological
effects could also be related to fiber surface
reactivity.
-
- 1-Fiberglass
:
-
- In the 1970s and 1980s,
seven different rodent inhalational studies reported
no tumorigenesis for several forms of fiberglass. In a
recent study in rats fiberglass did not induce
fibrosis or tumors, whereas crocidolite asbestos
induced both types of lung disease.
-
- In an other study
(preliminary results) in hamsters conducted recently
comparing amosite fibers, 901 insulation wool and
durable 475 glass demonstrated, as in other studies,
that no permanent lung changes were caused by 901
wool. 475 fiberglass induced minimal lung fibrosis and
one tumor, a mesothelioma. Amosite asbestos also
induced fibrosis, but an earlier and more severe case
than that induced by 475 glass, and a low to moderate
incidence of mesothelioma. Differences between this
study and earlier ones, as far as glass wools are
concerned, seem to be related to differences in
experimental conditions.
- In this study, toxicity
somewhat parallels lung biological persistence of
fibers. After 12 months of exposure, the number per
lung of fibers longer than 20 µm was seven times
to eight times higher for high-dose amosite than for
475 glass, which was three to four times higher than
for 901 glass.
- In agreement with previous
findings, these data once again link fiber lenght and
biological persistence to toxicity.
-
- 2-Mineral Wool
:
-
- Before 1990 three inhalation
studies reported no fibrosis or tumors as a result of
chronic exposure to mineral wool. One more recent
study showed that rats exposed to rock wool developed
minimal fibrosis late in the inhalation
period.
-
- 3-Refractory Ceramic
Fibers :
-
- Two inhalation studies of
RCFs were published before 1990, with conflicting
results.
- The first study (Davis et
al.,1984) reported 5% pulmonary fibrosis and 17%
pulmonary tumors in rats after 8 months of RCF
inhalation.
- The second study (Smith et
al.,1987) reported RCF-associated fibrosis but no
tumors in rats; no fibrosis and only one mesothelioma
in hamsters .
- In more recent studies rats
exposed to RCF developed lung fibrosis, pulmonary
tumors (13% in the kaoalin-based RCF group) and
pleural mesothelioma. Hamsters exposed to RCF(exposed
only to kaolin-based RCF) developed lung fibrosis but
no lung cancers but, 42 of 112 animals developed
mesotheliomas.
- This study presents a
striking difference between rat and hamster responses
to the same test fiber that opens questions of
species-related differences and which species, if
either, is representative of humans.
-
- C-Cell Culture Studies
:
-
- A number of in vitro studies
have shown that fiber toxicity to cultured cells is
related directly to fiber lenght and perhaps
indirectly to fiber diameter. In vitro studies have
also contributed much to a better understanding of the
molecular mechanisms of fiber-induced
injury.
- Fibers induce an
inflammatory response on the part of the lung and the
activated inflammatory cells, in an attempt to destroy
foreign invaders, release biologically destructive
agents that also injure lung tissue. Repair and cell
proliferative responses to injury ensue. If the
initiating fibers are biologically persistent, the
cascade continues and expands and could result in
increasing lung injury, repair mechanisms, and
possibly, permanent lung damage such as fibrosis or
even tumorigenesis.
-
- Fiber
biological persistence & biotransformation
:
-
- A-In Vivo Studies
:
-
- Biological persistence of
fibers is the ability of fibers to persist in the lung
after they have been inhaled.
- Biotransformation is any
change in dimension, composition, or surface
morphology that occurs in a fiber during lung
residence.
- Researchers have only
recently begun to scrutinize the mechanisms of fiber
biological persistence and biotransformation and their
roles in lung injury. In the past, the simple model
offered was that fibers that enter the lung and
rapidly dissolve are innocuous, those that do not
rapidly dissolve are pathogenic.
- Now, the situation appears
more complex that this according to recent
experimental studies on E, 475, 901 glass fibers and
rock wool fibers.
-
- B-In Vitro Studies
:
-
- In vitro studies have
demonstrated widely varying dissolution rates for
different fiber compositions. These studies have
identified two different types of dissolution
:
- Fibers can dissolve
congruently (i.e., all components dissolve at the same
rate) or noncongruently (i.e., certain components
dissolve more rapidly than others, leaving a depleted
fiber residuum; also called leaching).
- Whereas congruent
dissolution can lead to the total dissolution and
disappearance of fine fibers, noncongruent leaching
can weaken the infrastructure of the fiber and thereby
trigger transverse fragmentation, resulting in short
fiber segments that are biologically less active and
more readily removed from the lungs by phagocytic
cells.
- Leaching-induced changes in
fiber chemistry could also have an impact on the
biological reactivity of the fiber
surface.
- So, fibers that undergo
rapid biotransformation may be less toxic and less
likely to cause lung tumours because their altered
dimensions or chemistry enhances their clearance and
may also decrease their biological
reactivity.
-
- Mechanisms of
fiber-induced pathogenicity :
-
- A-Lung Deposition
:
-
- Size and shape determine
whether a fiber is respirable. These two factors plus
specific gravity (density) determine where in the lung
the fiber will deposit. Aerodynamic diameter is a term
that combines all three of these
characteristics.
- Fibers longer than 5 µm
and less than 1.5 µm in diameter have the
greatest potential to reach the target areas of the
lung and pleura. Fibers longer than 20 µm may be
too long to be removed from the lung by alveolar
macrophages.
- Altough fiber aerodynamic
diameter controls the entry and final site of
deposition in the lung, fiber durability is the
critical basis for the accumulation of a lung burder
of fibers.
- Other factors that may
affect the intrapulmonary fate of fibers are their
rigidity, their surface properties, and the
architecture of their ends (smooth, spicule-shaped
edges, ect.)
-
- B-Inflammatory Response
:
-
- The initial response to
deposition of foreign agents, including fibers, into
the bronchio-alveolar region is inflammation
(alveolitis), which is initiated by lung macrophages
(one of the functions performed by this type of cell
is phagocytosis or " ingestion " of particulate matter
).
- Activated macrophages
migrate to the site of fiber deposition and
phagocytize (ingest) the fibers. Individual
macrophages appear to engulf short fibers completely,
but many macrophages may fuse as they engulf longer
fibers. The very long fibers may frustrate complete
ingestion, resulting in the release of a variety of
cell messengers, reactive oxygen species, and
proteases from the cell macrophages.
- The cell messengers signal
the influx and activation of more macrophages and
other inflammatory cells.
-
- C-Fibrosis
:
-
- Biologically destructive
agents that are released from lung cells during
inflammation attack the lung walls, resulting in
tissue necrosis. Tissue injury stimulates tissue
repair processes, including cell proliferation and
deposition of collagen by fibroblasts within the lung
wall. During prolonged tissue repair processes, normal
lung morphology is destroyed and replaced by scar
tissue that is characterized by an accumulation of
collagen in the lung interstitium. This lung scarring
is called " lung fibrosis ".
- Fibrotic scarring can also
occur in the mesothelial membranes (pleura) that
enclose the lungs and line the thoracic cavity.
- Fibrotic lesions in the lung
and surrounding membranes reduce the efficiency of gas
exchange, leaving the individual with an excess of
carbon dioxide and a deficit of oxygen.
-
- D-Neoplastic Tissue
Response :
-
- Very recently, rodent
inhalation studies demonstrated for the first time
that chronic inhalation of some durable SVF types
(RCF, E glass microfibers) at a dose 300-fold greater
than typical worker exposure could also be associated
with fibrosis and thoracic cancers.
- 475 durable glass as
microfibers may also induce mesothelioma in hamsters
at the same level of exposure.
-
- E-Lung Cancer
:
-
- Lung cancer could develop as
a by-product of the chronic fibrosis that results from
the chronic lung irritation and caused by durable lung
fibers. This mechanism would require that the fiber be
very biologically persistent in the lung. Tobacco
smoke is suggested to be a crucial factor in the
development of fiber-related cancers.
- A second possible mechanism
is that inorganic fibers may act by direct genotoxic
action to induce neoplams.
-
- F-Mesothelioma
:
-
- Malignant mesothelioma is
cancer of the mesothelial membranes, which cover the
internal organs and line the inner surfaces of the
abdominal and thoracic cavities.
- After chronic inhalation of
high concentrations of RCF, 42% of hamsters but only
1-3% of rats developed thoracic mesotheliomas. As with
lung cancer, the mechanisms of fiber induction of
mesothelioma are not well understood.
- After inhalation and
deposition of fibers, the next step in the development
of fiber-associated mesothelioma may be the
translocation of fibers through the lung wall into the
pleural membranes.
- Subsequent steps may involve
the development and advancement of pleural fibrosis in
the same way that lung fibrosis is theorized to be a
mechanism in the development of lung
cancer.
- As with lung cancer
mechanisms, a second potential mechanism of
mesothelioma development would be direct genotoxicity
of the fibers in the pleural space.
-
- G-Summary of Mechanisms
:
-
- Altough not completely
understood, the mechanisms of fiber-induced biological
effects are believed to include the following
:
- 1-Inhaled fibers enter the
deep lung.
- 2-Fibers resist lung
clearance and degradation mechanisms.
- 3-Fibers are translocated
into the lung interstitium and, possibly, also the
pleural membranes.
- 4-Fibers stimulate the
cellular release of inflammatory
mediators.
- 5-The mediators initiate
fibrosis and epithelial cell
proliferation.
-
- In addition, fibers may also
induce neoplastic changes directly in the genetic
material of the cell.
- Also affecting the potential
pathogenesis are other factors that compromise
pulmonary health, including previous or current
disease or exposure to toxic cofactors such as
cigarette smoke, other dusts, or industrial
fumes.
-
- It is important to note that
lung defense mechanisms can be overwhelmed by extreme
experimental exposure concentrations, resulting in
lung injury that is not specific to the particle
type.
- So, at overload
concentrations, lung injuries can be induced by
innocuous dusts that, at normal exposure levels, would
be cleared from the lung before they are able to
accumulate sufficiently to inflict injury.
- Many recent rodent studies
were conducted at exposure levels 300 times greater
than fiber aerosols typically experienced by SVF
workers (Research and Consulting
Co.Switzerland).
-
- Occupational
exposure to airborne fibers :
-
- A-Industrial Hygiene
Studies :
-
- Each year, industrial
hygienists analyze more than 1,000 occupational
exposure samples in at least 20 SVF manufacturing
plants in North America and Europe. Air samples are
also taken during insulation installation and in
buildings where SVF insulation and air filtration
products are in use.
- NIOSH method 7400 and the
WHO reference method established procedures for
microscopically determining the number of respirable
fibers per cubic centimeter of air.
-
- B-Synthetic Vitreous
Fiber Exposure Levels :
-
- In general, exposure to SVFs
during manufacture, installation and final use has
been very low or undetectable.
- In SVF manufacturing
workplaces, airborne fiber exposures have typically
been less than 0.2 fiber per cubic centimeter, with
total particulate matter less than 1.0
mg/m3.
-
- During installation of
fiberglass, fiber exposures averaged less than 0.5
fiber per cubic centimeter, with a range of 0 to 20
fibers per cubic centimeter, and total particulate
matter averaged less than 4.2 mg/m3, with a range of
0.04 to 114.00 mg/m3.
- Air samples were analyzed
from a number of public buildings in which fiberglass
air filters were in use or in which fiberglass
insulation had been installed; these analyses
demonstrated no significant fiberglass exposure to the
building occupants.
-
- Airborne concentrations of
dust and fibers in U.S. mineral wool plants are
generally higher than in U.S.glass wool facilities.
Exposures during application or installation are also
typical higher for mineral wool products than for
similar glass wool products.
-
- Industrial hygiene
monitoring data obtained on a regular basis at
locations where RCF products are manufactured show
that exposures are generally less than 1.0 fiber per
cubic centimeter and often lower than 0.2 fiber per
cubic centimeter. During installation of RCF products,
exposures can be 1 to 5 fibers per cubic centimeter or
higher if appropriate engineering controls and work
practices are not followed.
-
-
- C-Occupational Exposure
Limits :
-
- A fiber may be defined as a
lenghty particle whose lenght/diameter ratio is equal
or larger than 3. In order to reach the lung alveolar
region in man, a fiber must have an aerodynamic
diameter of less than 10 µm.
-
- When conducting occupational
exposure studies to man-made fibers, only fibers
considered hazardous to workers due to their
granulometric properties, are considered :
- 1-Lenght greater than 5
µm
- 2-Diameter less than 3
µm
- 3-Lenght/diameter ratio
>3
-
-
-
|
QUEBEC'S
EXPOSURE LIMITS
|
|
Substance
|
VEMP
|
Notes
|
|
1-Insulating
wool fiber, slag wool
|
1
fiber/cm³
|
C2,
EM
|
|
2-Insulating
wool fiber, rock wool
|
1
fiber/cm³
|
C2,
EM
|
|
3-Insulating
wool fiber, glass wool
|
2
fibers/cm³
|
C3
|
|
4-Fiberglass,
continuous filaments
|
10mg/m³
|
Total
dust
|
|
5-Refractory
fibers, (ceramic or others)
|
1
fiber/cm³
|
C3
|
|
6-Glass
microfibers
|
1
fiber/cm³
|
-
|
-
- C2 : suspected carcinogen to
humans
- C3 : confirmed carcinogen to
animals
- EM : substance that should
be kept at the lowest practicable level
-
-
- D-Occupational Exposure
to Other Compounds :
-
- To accurately assess the
toxicologic potential of a substance in the workplace,
all other substances present in the environment must
be considered.
- Many chemicals may be
present in man-made fibers, which is not the case for
asbestos fibers.
- During the fabrication
process many chemicals may be added and account for up
to 25 % of the weight of these fibers, which may also
be termed inorganic non-metallic artificial
fibers.
-
- The chemicals added may be:
- 1-Antistatic agents
- 2-Antifungic agents
- 3-Hydrophobic agents
- 4-Anti-dust agents( mineral
oils, polypropylene glycol)
- or
- 5-Binders(urea-formaldehyde
and epoxy resins, bitumen)
- The presence of these
additives may make research on the toxicology of these
fibers more complicated.
-
- The potential cumulative
effects of exposure to all these materials must be
considered in any operation to develop a sound plan
for employee and environmental health and
safety.
-
- Evaluation of
synthetic vitreous fibers :
-
- A-International Agency
for Research on Cancer Evaluation (IARC)
:
-
- In 1971, the International
Agency for Reserach on Cancer (IARC) iniated a program
by which to evaluate data regarding the carcinogenic
risk of chemicals to humans.
- In 1987, the IARC appointed
a working group of 20 scientists to evaluate the
carcinogenic risk of exposure to SVFs.
-
- IARC classification
:
-
- *Group 1 : sufficient
evidence of human carcinogenicity
- *Group 2A : probably
carcinogenic to humans
- *Group 2B : possibly
carcinogenic to humans
- *Group 3 : not classifiable
as to human carcinogenicity
- *Group 4 : probably not
carcinogenic to humans
-
- Glass wool was designated in
group 2B.
- Continuous filament (glass
textile) was designated as group 3.
- Rock wool was clasified as
group 2B.
- Slag wool was classified as
group 2B.
- RCF(refractory ceramic
fiber) was designated as a group 2B
substance.
-
- B-International Program
on Chemical Safety Evaluation (IPCS) :
-
- The IPCS is a joint venture
of the United Nations Environment Program, the
International Labor Organization and the
WHO.
-
- The1988 report, " Man-made
Mineral Fibres ", concluded the following
:
- 1-Possibility of transient
effects of skin and upper respiratory
irritation.
- 2-Considering all results of
animal studies, that an increased risk of lung cancer
in some sectors of the SVF industry is biologically
plausible.
- They also recommended
protective equipment to guard against a potential
elevation in lung cancer risk for workers engaged in
activities in which elevated airborne exposure levels
are possible.
-
- For SVF in general the IPCS
stated, " The overall picture indicates that the
possible risk of lung cancer among the general public
is very low, if there is any at all, and should not be
a cause for concern if the current low levels of
exposure continue ".
-
- Occupational
Health Considerations :
-
- A-Prevention and
Protection :
-
- Whenever there exists a
potential for employees to be exposed to substsnces
that either are known to be harmful or have not been
completely evaluated, the first step is to mini-mize
exposure to the lowest practicable level.
- In SVF occupational
settings, modifications to the product design can
sometimes reduce the amount of dust that it releases
during manufacture or installation.
- Exhaust ventilation can
remove dusts at their points of origin.
- Appropriate work practices
can also limit the amount of dust generated; for
exemple, vacuum cleaning is better than dry-sweeping
with a broom or with compressed air.
- SVF workers can further
protect themselves by wearing safety glasses or
goggles to prevent eye exposure, long-sleeved shirts
and long pants to minimize skin exposure, and
respiratory protection to minimize dust
inhalation.
- A careful evaluation of the
workplace should be conducted to determine the
appropriate devices to be used in an individual
situation.
-
- B-Monitoring Exposure and
Health :
-
- Whenever employees are
exposed to potentially harmful substances, a program
should be established to monitor their exposure levels
and health routinely.
- First, exposure ranges and
averages should be determined for each operation or
task.
- Next, the appropriate type
of personal protective equipment should be determined
for each task.
- A medical surveillance
program should be established, including a review of
general health, occupational history, physical
examination, clinical chemistries and blood count,
pulmonary function testing, a baseline chest
radiograph, and other testing as indicated by the
occupational history.
- For SVF workers, the focus
should be on respiratory and dermatologic
health.
- Exposure and health
monitoring should continue on a regular basis (e.g.,
yearly) or whenever processes or products change.
Findings should be reviewed regularly, both for
individuals and groups.
-
-
- Health effects
summary :
-
-
- The ban on the use of
asbestos resulted in a larger and larger use of
substitution materials in many industrial processes
and in particular the use of man-made vitreous fibers
(MMVF).
-
- In rodents, inhalational
studies show that glass insulation wools and slag wool
produced no permanent injury, even after 2 years of
exposure to high concentrations (at least 300-fold the
concentrations to which human SVF workers typically
are exposed). In recent rodent inhalational studies,
two durable SVFcompositions were associated with
permanent lung injury : rock wool (MMVF21) induced
fibrosis late in the study, and RCF induced fibrosis
and tumorigenesis. Other durable fibers are pathogenic
to animals : glass microfiber E may also induce
fibrosis and tumorigenesis in rats, fiber glass 475
induces fibrosis and mesothelioma in hamsters but not
in rats.
-
- In man, the main part of
known health effects comes from data collected among
workers of industries producing these fibers, where
the levels of exposure were low, much lower than those
encountered in many professional situations by the
finished product users.
- Even if the relationship to
the exposure to rockwool fibers/slag wool fibers is
not clearly established, the observation of an excess
of bronchopulmonary cancers among workmen producing
these fibres must prompt us to be vigilant and to
control levels of exposure to these fibers in the work
environment. The SMRs for bronchopulmonary cancer are
lower among workmen of glass wool production than
among workmen of rockwool/slag wool production.
- Taking into account data
observed in experiments (excess of tumours) and
preliminary information obtained from man (suspicion
of an excess of benign pleural pathologies, and of
respiratory functional impairment of the obstructive
type), an attitude even more careful is essential with
respect to refractory ceramic fibres.
- These fibres were classified
in category 2 (similar substances to cancerogenic
substances for man) by the European Communities.
- Nothing currently makes it
possible to affirm that a risk of nonmalignant
respiratory pathology exists for man with rock, glass,
and slag fibers. Nevertheless, experimental data
showed a real pathogenic effect for levels of exposure
close to those producing the same effects with
asbestos. Certain fibers, as some made from glass,
appear sufficiently soluble to have no irreversible
effects.Others like ceramic fibers are more
suspicious.
-
- The absence of sufficient
experience must prompt us to pursue epidemiologic and
experimental studies, and to introduce an effective
prevention policy.
-
-
-
-
-
|
|
- Edouard
Bastarache M.D.
- (Occupational
& Environmental
Medicine)
-
- Author
of " Substitutions for raw ceramic
materials "
- Tracy,
Québec, CANADA
- edouardb@colba.net
|
-
-
- References
:
-
- 1-Clinical Environmental
Health and Toxic Exposures, Sullivan J.B. &
Krieger G.R., 2001
- 2-Effets sur la
santé des fibres minérales
artificielles;Toxicologie, Pathologie Professionnelle,
De Vuyst P., Brochard P., Poiron
J.C.,Encyclopédie Médico-Chirurgicale,
Paris, 2000.
- 3-Les maladies
respiratoires d'origine professionnelle, Martinet,
Antoine et Petiet, Paris, 1999.
- 4-Règlement sur la
santé et la sécurité du travail,
décret 885-2001, Province de
Québec.
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