&EPA
United States
Environmental Protection
Agency
Industrial Environmental Research 1.
Laboratory
Cincinnati OH 45268 ~,w .\
Research and Development
EPA-600/S2-82-038 August 1982
Project Summary
Carbon Fiber Data Base:
Review and Assessment of
Carbon Fiber Release Into the
Environment
The investigation described in this
report was conducted as part of the
carbon fiber disposal research effort
undertaken by the Environmental
Protection Agency. The purposes of
this investigation were (1) to
determine, from a literature search,
the sources, extent, and frequency of
carbon fiber releases to the
environment, the risks related to these
releases, and means of coping with
the resulting problems, and (2) to
assess future requirements and
methodologies for minimum-risk
disposal of carbon fiber materials.
This Project Summary was
developed by EPA's Industrial
Environmental Research Laboratory,
Cincinnati. Ohio, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Carbon fibers are used in combination
with polymers to form lightweight, high-
strength composite materials that will
find increasing use in automobiles,
sports equipment, and aircraft parts.
During the manufacture of such
composites or during the production of
items made from them, some of their
carbon fiber content may be accidently
released to the environment. When
items containing the composites are
disposed of in municipal waste
treatment systems employing
conventional incinerators, significant
amounts of the carbon fibers may be
released to the environment with the
flue gases from the incinerator. The
freed carbon fibers, which are
electrically conductive, can cause
shorting out of electrical and electronic
equipment. The potential health effects
of short, small-diameter airborne fibers
are presently under investigation.
This Project Summary presents
results from an EPA-sponsored study on
problems related to the production and
use of carbon fiber materials. The final
report upon which this summary is
based identifies and evaluates potential
environmental and health impacts of
carbon fibers, and examines methods
for controlling their release to the
environment, in light of the increasing
prevalence of carbon fiber composites
in consumer goods and transportation
equipment.
The study evaluates overall systems
for disposal of carbon fiber materials.
The evaluation identifies major
potential sources of fibrous carbon
expected to enter municipal waste
streams, assesses the capabilities of
solid waste disposal techniques
applicable to carbon fiber materials,
estimates the quantities of carbon fibers
that will be released from municipal
incinerators under various degrees of
control, and estimates the number of
electrical equipment failures expected
to result from such releases.
The report reviews the carbon fiber
programs being conducted by various
Federal organizations. These programs
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focus on accidents that cause fires,
effects of airborne fibers, and
development of measurement
techniques for airborne fibers.
The report also presents the results of
a survey of current literature, which
reveals that the following types of
information are available: the effects of
combustion of carbon fiber composites;
the impacts of airborne carbon fibers,
including incidents involving electrical
failure; the present and projected future
applications of composites; trends in
current research into materials,
processes, use, and environmental
impacts; and the present manufacturers
and users of fiber and of carbon fiber
composites. Selected items from a
research bibliography of some 600
pertinent publications and data sources
are provided.
The study was performed by Bionetics
Corporation under EPAContract No. 68-
03-2848. The work was completed in
September, 1980.
Survey of Existing
Information
A major endeavor in the carbon fiber
project was to identify, acquire, and
summarize data relevant to carbon
fibers and composites in general and
specific information on evaluations of
projected risks of carbon fiber releases
into the environment. This program
involved an extensive survey of the
literature. Informational areas included
the determination of means of
producing carbon fiber materials and
their resultant properties, identification
of principal uses of carbon fiber
materials, identification of available
reports on composites evaluations,
investigations of fiber incineration
hazards, and results of current
assessments related to carbon fibers
and composites utilized in specified
applications.
Properties and Production of
Carbon Fiber Materials
The physical properties of carbon
fiber materials hinge on the type and
proportion of fiber, as well as the type of
resin matrix employed. The first
production stage forms long strands of
spun, multifilament fiber on spools. The
spooled material, called tow, is either
shipped to the ultimate parts fabricators
or utilized directly for weaving into cloth
or for chopping into matting/molding
elements. Particular applications (cloth
or tape formation) benefit from
prepregging — an impregnation of the
fiber tow with resin prior to layup. The
parts manufacturer then forms and
cures the layups or moldings in
fabrication of the carbon fiber
composite article. The degree of carbon
fiber graphitization (affected by curing
temperature, pressure, and time)
determines tensile strengths and
material stiffness characteristics. Step-
by-step flows of the materials and
processes in the production of carbon
fiber composites are presented in the
report. Important material properties
are numerically tabulated. Names and
locations of U.S. producers and users of
carbon fiber materials are listed in the
report. A listing of 138 users of such
materials, nationwide, is given.
Principal Applications of
Carbon Fiber Materials;
Anticipated Increases
Major uses foreseen for carbon fiber
composites include consumer pro-
ducts/sporting goods, surface transport
vehicles, industrial equipment/hard-
ware, medical equipment (orthopedic
implants, furniture), aircraft, and space-
craft.
The authors of the final report found
that the greatest potential growth area
for carbon fiber composites is in
highway vehicles.* In aircraft
applications, a nominal fleet of 3,000
commercial aircraft will probably
require about 3,000 metric tons of
carbon fiber composites, or about one
metric ton per aircraft. Some production
models of next-generation military
aircraft are expected to utilize
cumulatively in excess of 450 metric
tons of carbon fiber materials.
Reporting of Composites
Evaluations
Both U.S. and foreign publications
emphasized aerospace applications of
carbon fiber composites, principally
documenting the physical/mechanical
properties, analytical techniques,
design and fabrication methods, and
component testing. Somewhat less
research has been conducted in the
properties and production of fibers and
resins. About 400 U.S. documents and
more than 200 foreign documents were
reviewed in the literature search. A
selected research bibliography is
included in the report.
•Author's note. Since the final report was written, a
shift in potential carbon fiber use has occurred,
with automobile usage decreased and aerospace
industry usage increased
To facilitate interchange of
information, a "Directory and Locator
for the National Graphite Fiber
Program" is presented. Included in the
Interagency Data Exchange are Federal
offices, agencies, departments, and
support operations. Interagency
generators of data as well as potentially
interested recipients of data are
tabulated, and likely major subject
categories are cross-referenced.
Fiber Incineration Hazards
Categories of optically distinguishable
types of materials released from carbon
fiber composite fires are shown in Table
1. All categories except the single fibers
have settling rates generally sufficient
for their capture within the flow
passages of an incinerator. Low free fall
rates of single fibers contribute to their
remaining in the gas stream, thence
lofted from the stack to drift downwind
in the plume.
Test results of carbon fibers released
from burning of composites are
presented in Figure 1. Shown are the
typical distributions of free carbon
fibers, fire residue (multiple-fiber
constituents remaining after test
combustion) and completely oxidized
fiber (release of COz) to effect a mass
balance based on the initial preburned
weight of fiber in the composite. The
fraction of escaping single fibers
accompanying incineration tends to
increase with increased stirring or
agitation of the burning material.
Estimated releases of carbon fibers
from the fire zones of municipal
incinerators with low agitation are as
follows:
• Up to one percent by weight of the
input fibers -would appear in the
exhaust as single fibers greater than
1 mm long. These longer fibers vary in
length essentially within an
exponential distribution with a mean
of about 1.8 mm. Oxidation during
burning would reduce the diameters
of up to 80 percent of this population
of fibers from an as-produced
diameter of 8 micrometers to around
4 micrometers.
• Up to four percent of the incinerator
input fibers would appear in the
exhaust stream as discrete fibers less
than 1 mm long and with an average
length of about 0.25 mm. Oxidation
effects would again be expected to
reduce about 80 percent of the
population to diameters of the order of
4 micrometers.
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Table 1. Fire-Release Fiber Categories
Category Description
Free Fall Rate In Air
1. Single Fibers
2. Lint
3. Brush/Clump
4. Fragments
5. Strips
Single fibers up to Sum
in diameter, and up to
10mm in length
A group of fibers loosely
bound, randomly aligned
A group of fibers, bound
together with well defined
alignment
Pieces of burned compo-
site with dimensions
ranging from 2 mm to
25mm
Elements of composite
having lengths comparable
to the dimensions of the
item being burned
0.032 m/sec (max)
0.22 m/sec
0.88 m/sec
1.5 to 1.9 m/sec
2.0 to 10.0 m/sec
Source:
(1) Lieberman, P.. Chovit, A.R.. Sussholz. B.. andKorman, H.F.. "Data Reduction and
Analysis of Graphite Fiber Release Experiments." NASA CR-159032. 1979.
(2) Bell. V.L.. "Releases of Carbon Fibers from Burning Composites," NASA
Conference Publication 2119. December 4-5, 1979. pp. 29-57.
J*-3.5%
!
i
\
0.05% maximum
single fibers of
diameters less
than 4 micrometers
and less than
50 micrometers
long
Single fibers
longer than
1 millimeter
Single fibers
shorter than
1 millimeter
4%-*\
C
1 I Fire residue '
II *' Completely
J / x oxidized fiber
1 /
I''
>«
) 20 40 60 80 IOC
Percent of initial weight of fiber
Figure 1. Mass balance for carbon fibers from burned composites.
Source:
Bell, V.L, "Release of carbon fibers from burning composites," NASA Conference
Publication 2119. December 4-5. 1979, pp. 29-57.
• At the extreme short end of the short-
fiber population (the short dashed line
at the upper left edge of the curves in
Figure 1), about 0.05 percent of the
input fibers would appear as emitted
particles shorter than 50 micrometers,
with as-incinerated diameters
reduced below 4 micrometers.
In these three portions of the fiber
population emitted during burning at
low agitation, the longer fiber segment
is principally responsible for electrical
hazards and resultant system failures.
The shorter fibers fall into the category
which is currently under investigation
for health-related effects.
The tendency for airborne carbon
fibers to create electrical failures is
defined in terms of the exposure of
electrical equipment to time-integrated
fiber concentrations. Repeated tests of
specific items of electrical equipment at
established levels of airborne fiber
concentrations for extended times have
yielded an average value of exposure
that produces an electrical failure.
Based on actual operational exposures
compared with average test specimen
exposures to produce equipment
failure, probabilities of equipment
failure levels have been modeled.
Electrical equipment degradation that
causes electrical shock hazards to the
user appears to occur rarely. Downwind
dispersion of airborne carbon fibers is
generally adequate to dilute the plume
concentrations to the point where such
hazards appear to be random, i.e., not
readily distinguishable from insulation-
related failures from other causes.
As produced, carbon fibers have
diameters larger than the air passages
leading to the alveoli within the lungs.
Studies of animals exposed to chopped
fiber have produced no conclusive
results. Partial oxidation of fibers
reduces their diameters, making them
more respirable. At the present time,
the mechanism for human interaction
with respirable size fibers has not been
defined and studies in this area are
continuing.
Current Assessments
Assessments of incremental risks
from releases of carbon fibers conduct-
ed under governmental sponsorship as
well as by governmental laboratories
are reviewed and summarized. Losses
in terms of economic impact (malfunc-
tioning of electrical and electronic com-
ponents) have been investigated by
NASA, based on carbon fiber releases
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from accidents and fires involving com-
mercial aircraft; a counterpart study has
been conducted by the Department of
Transportation for fire-releases likely to
result from surface vehicle accidents.
The Department of Energy has evalu-
ated the economic losses of power sys-
tem outages due to carbon fiber short-
circuiting.
The Department of Health and Human
Services/NIOSH is conducting
experiments in which laboratory test
animals were exposed to fibers in the
respirable range (diameters less than
3.5 /urn and length-to-diameter ratios in
the range, 3:1 to 10:10). The Depart-
ment of Labor/OSHA is monitoring the
results toward establishing regulatory
needs, if they are deemed necessary.
The Department of Defense has
examined the effects of carbon fiber
fallout on the operation and availability
of electronics and electrical components,
vital for national defense.
Department of Commerce investiga-
tions (completed) have addressed
present and future production of carbon
fiber materials.
The President's Office of Science and
Technology Policy (OSTP) designated
other Federal organizations to perform
other research related to carbon fiber
utilization. In the EPA, the Environmental
Sciences Research Laboratory at
Research Triangle Park, North Carolina,
has the responsibility for conducting the
Carbon Fiber Monitoring Research
Program. The program focuses on the
development of instrumentation and
monitoring techniques for measuring
airborne emissions of carbon fibers.
Also, the Municipal Environmental
Research Laboratory in Cincinnati,
Ohio*, is overseeing studies in disposal
technology for carbon fiber materials.
The Federal Emergency Management
Agency is engaged in identifying,
analyzing, and reporting civil incidents
involving carbon fibers. The Federal
Aviation Administration is to
summarize identifying information on
aircraft incorporating the composites
and to report accidents related to
aircraft which contain carbon fiber
composites.
Assessment of Release
Mechanisms and Disposal
Techniques
Once a level of anticipated usage of
carbon fiber composites is determined,
"Disposal research responsibility has recently been
shifted within EPA to the Industrial Environmental
Research Laboratory, Cincinnati, OH
assessments of carbon fiber disposal
and damage hinge on factors such as
handling procedures thoroughout the
life cycle of the commercial products,
the characteristics of the disposal
techniques, and carbon fiber emission
mechanisms.
The likelihood of controlled or
uncontrolled releases of disposed
carbon fiber materials is expected to
depend on the type of application of the
material, whether in transport aircraft,
automobiles, sporting goods, or medical
devices..Any industries that dispose of
production scrap without control could
be expected to contribute to the overall
fiber release problem.
The potential releases of airborne
carbon fibers from waste composites in
disposal systems are evaluated. The two
major disposal methodsare/>t//fr(landfill-
ing and recycling) and combustion/'ox/da
tion. Adverse impacts associated with
carbon fiber material disposal aredeter-
ined by:
• the probability of fibers becoming
airborne, which in turn is a function of
fiber release from the matrix, fiber
destruction, and process retention of
the fibers (e.g., filtration and removal
in the exhaust)
• the released fiber characteristics
(e.g., dimensional, electrical)
• duration and magnitude of the
release.
The report evaluates three categories
of carbon fiber composite disposal
methods: (1) municipal disposal tech-
niques in current use; (2) potentially ap-
plicable techniques; and (3) special-pur-
pose disposal techniques that require
further development. Among the vari-
ous disposal techniques single-step,
mass burning and refuse-derived fuel
processes are considered "good" based
on potential for fiber oxidation, but are
expected to require particle control. The
mass-fired two-step burn process is
rated "good" and probably will not re-
quire downstream particle control.
Pyrolitic processing is similarly rated
"good" but may require a precipitatoror
scrubber to remove particles from the
exhaust stream. Molten salt and wet air
oxidation are two techniques which are
believed to possess an "excellent"
potential for fiber oxidation, and need no
downstream particle removal.
No obvious large-volume source of
carbon-fiber-type wastes currently
exists. Although automotive applications
and sporting goods scrap rates are
expected in the future to generate large
volumes of waste materials, projections
indicate that carbon fiber composites
will comprise only about 1.15 x 10~3
percent of the total mass of waste
handled in municipal waste streams,
with an assumed 5.2 percent of that
material being incinerated, or about 110
metric tons per year.
The report presents order of
magnitude calculations of the potential
effects of carbon fiber incineration in
the 1990's. By application of Bureau of
Census demographic projections and a
simplified plume dispersion model, the
resulting total release of incinerated
fibers, nationwide number of sources,
and prevalent depositions of fibers for
sizes of electrical and of respirable
concern are estimated. Only a small
number of household electrical
appliances are likely to fail annually as a
result of shorting by carbon fibers.
Correspondingly, individuals receiving
the maximum calculated exposure to
respirable carbon fibers downwind of
incinerators would require an estimated
7400 years of exposure to even
accumulate the equivalent of the
current NIOSH workplace limit on
asbestos fiber exposure.
Conclusions and
Recommendations
Projections of increasing usage of
carbon fiber composites indicate that
electrical electronic shorting problems
are a small but definable risk with
uncontrolled releases of unburned
fibers during incineration of expended
products or of scrap materials.
Manufacturing processes also may
release concentrations of fibrous air-
borne particles which require protective
measures for nearby production per-
sonnel; in production areas, exhaust
filtering/collection systems are con-
ventionally installed, and production
workers are customarily required to use
protective breathing apparatus. Also,
the diameters and lengths of the air-
borne raw fibers, prior to reduction by
combustion, generally exceed the
dimensions which can be carried into
the air cells of the lungs. Ongoing re-
search is focused on investigating the
potential for production of respirable
particulates during manufacturing.
While incinerators may produce
significant concentrations of released
carbon fibers, the emission of respirable
fibers has been observed to be low.
Health hazards of exposure to respir-
able carbon fibers are still under
investigation.
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The report authors anticipate that
properly designed and controlled
incinerators may be capable of
completely destroying most free carbon
fibers—to the point of even nullifying
any need for fiber entrapment.
Nevertheless, limited quantities of
uncontrolled carbon fiber composites
still would be expected to find their way
into the municipal waste streams that
feed conventional incinerators. Since
conventional incinerators may not be
designed exclusively for destruction of
carbon or graphite substances, the
flame temperatures and retention times
may be inadequate for complete
combustion of carbon fibers.
Carbon fiber composites will have
extensive use in aerospace structures
as well as in medical applications and
industrial hardware, but the major
sources of uncontrolled disposal are
likely to be consumer sporting goods
and automotive products (discarded
mainly by body shops or backyard
mechanics). Controlled disposal, as in
the case of wastes from manufacturers,
is expected to be directed to suitable
facilities such as dedicated incinerators
or secure landfills.
The following recommended re-
search activities should be accorded
prompt attention:
• Evaluation of particle control
technology, namely, the effectiveness
of electrostatic precipitators, wet
scrubbers, and baghouses in cleaning
up incinerator exhaust gases during
operations with carbon fibers of
various diameters and lengths and
mixed with other exhaust products.
• Estimation of possible levels of
airborne fibers produced from front-
end, pre-incineration operations
including refuse shredding,
screening, crushing, air classifying,
compacting.
• Determination of the efficiency of
mass-fired two-stage incinerators for
handling carbon fiber composites,
especially designs of units and
operational means to reduce
uncertainties in production of carbon
fiber emissions.
• In the longer term, it is recommended
that EPA evaluate the need for
dedicated facilities for disposal of
carbon fiber materials, especially
landfilling operations resulting in the
release of the loose carbon fibers.
The authors are staff of the Carbon Fiber Data Base Project Group. The
Bionetics Corporation, Hampton. VA 23666.
R. A. Carries is the EPA Project Officer (see below for contact).
The complete report, entitled "Carbon Fiber Data Base: Review and Assessment
of Carbon Fiber Release Into the Environment." (Order No. PB 82-236 027;
Cost: $19.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For information contact B. L. Blaney at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
OUSGPO: 1982 — 599-092/0475
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