CONTROL TECHNIQUES
FOR ASBESTOS
AIR POLLUTANTS
U. S. ENVIRONMENTAL PROTECTION AGENCY
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CONTROL TECHNIQUES
FOR ASBESTOS AIR POLLUTANTS
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
February 1973
For sole by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. MMf
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The AP series of reports is published by the Technical Publications Branch of the Information
Services Division of the Office of Administration for the Office of Air and Water Programs,
Environmental Protection Agency, to report the results of scientific and engineering studies, and
information of general interest in the field of air pollution. Information reported in this series
includes coverage of intramural activities and of cooperative studies conducted in conjunction
with state and local agencies, research institutes, and industrial organizations. Copies of AP
reports are available free of charge to Federal employees, current contractors and grantees, and
nonprofit organizations - as supplies permit from the Air Pollution Technical Information
Center, Environmental Protection Agency, Research Triangle Park, North Carolina 27711,or
from the Superintendent of Documents.
Publication No. AP-117
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EPA
^ PREFACE
X
^L This document contains information about the nature and control of a hazardous air pollutant
^ - asbestos. The primary purpose of this document is to provide information useful to those
g_i involved in the control of emissions of asbestos from industrial sources. The language and
x\ approach are largely technical, but the first two sections should be of interest and value to the
\T* general reader.
^- The requirement to publish this document was established when the Administrator of the
^3 Environmental Protection Agency listed asbestos as a hazardous air pollutant by notice in the
A Federal Register (Vol. 36, p. 5931) on March 21, 1971. The Administrator acted under the
~ authority granted him by Section 112 of the Clean Air Act, which defines a hazardous air
^ pollutant as ". . . an air pollutant to which no ambient air quality standard is applicable and
^ which in the judgment of the Administrator may cause, or contribute to, an increase in mortality
J^ or an increase in serious irreversible, or incapacitating reversible, illness."
^ Mr. J.U. Crowder and Mr. G.H. Wood of the Office of Air and Water Programs, Environ-
*£ mental Protection Agency, were primarily responsible for compiling the information contained in
vS this document. This information represents the efforts of the Environmental Protection Agency,
as well as the advice of the members of the advisory committee listed on the following pages and
the contributions of many individuals associated with other Federal agencies, State and local
^j governments, and private industry.
75202
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NATIONAL AIR POLLUTION CONTROL TECHNIQUES
ADVISORY COMMITTEE
Chairman
Mr. Donald F. Walters
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Environmental Protection Agency
Research Triangle Park, N.C. 2771 1
Mr. Raynal W. Andrews
150 Guyasuta Road
Pittsburgh, Pennsylvania 15215
Mr. Robert L. Chass
Air Pollution Control Officer
Los Angeles County Air
Pollution Control District
434 South San Pedro Street
Los Angeles, California 90013
Mr. Charles M. Copley, Jr.
Commissioner, Division of Air
Pollution Control
City of St. Louis
Room 419 City Hall
St. Louis, Missouri 63103
Mr. C. G. Cortelyou
Coordinator of Air and Water
Conservation
Mobil Oil Corporation
150 E. 42nd Street - Room 1650
New York, N.Y. 10017
Mr. Arthur R. Dammkochler
Air Pollution Control Officer
Puget Sound Air Pollution
Control Agency
410 W. Harrison Street
Seattle, Washington 98119
Dr. Aaron J. Teller
Teller Environmental Systems, Inc.
295 Fifth Avenue
New York. N.Y. 10016
Mr. William W. Moore
President, Belco Pollution Control Corp.
100 Pennsylvania Avenue
Paterson, New Jersey 07509
Mr. William Munroe
Chief, Bureau of Air Pollution Control
State of New Jersey
Dept. of Environmental Protection
P.O. Box 1390
Trenton, New Jersey 08625
Mr. Vincent D. Patton
Executive Director
State of Florida Air and Water
Pollution Control
315 S. Calhoun Street
Tallahassee, Florida 32301
Dr. Robert W. Scott
Coordinator for Conservation Technology
Esso Research and Engineering Co.
P.O. Box 215
Linden, New Jersey 07036
Dr. R. S. Sholtes
University of Florida
Environmental Engineering Department
College of Engineering
Gainesville, Florida 32001
Mr. W. M. Smith
Director, Environmental Control
National Steel Corporation
Box 431, Room 159, General Office
Weirton, West Virginia 26062
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Mr. George P. Ferreri
Chief, Division of Compliance
Bureau of Air Quality Control
Maryland State Department of
Health and Mental Hygiene
610 N. Howard Street
Baltimore, Maryland 21201
Mr. Benjamin F. Wake
Director, Division of Air Pollution
Control and Industrial Hygiene
Montana State Department of Health
Helena, Montana 59601
Mr. Charles M. Heinen
Executive Engineer
Materials Engineering
Chrysler Corporation
Box 1118,Dept. 5000
Highland Park, Michigan 48231
Mr. A. J. von Frank
Director, Air and Water
Pollution Control
Allied Chemical Corporation
P.O. Box 70
Morristown, New Jersey 07960
VI
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FEDERAL AGENCY LIAISON COMMITTEE
Chairman
Mr. Donald F. Walters
Office of Air and Water Programs
Office of Air Quality Planning and Standards
Environmental Protection Agency
Research Triangle Park, N.C. 2771 1
FEDERAL POWER COMMISSION
Mr. T. A. Philips
Chief, Bureau of Power
Federal Power Commission. Room 3011
411 G Street, N.W.
Washington, D.C. 20426
GENERAL SERVICES ADMINISTRATION
Mr. Haiold J. Pavel
Director, Repair and Improvement Division
Public Building Service
General Services Administration
9th and D Streets, S.W.
Washington, D.C.
NATIONAL AERONAUTICS AND
SPACE ADMINISTRATION
Mr. Ralph E. Cushman
Special Assistant
Office of Administration
National Aeronautics and Space Administration
Washington, D.C. 20546
NATIONAL SCIENCE FOUNDATION
Dr. O. W. Adams
Program Director for Structural Chemistry
Division of Mathematical and Physical Sciences
National Science Foundation
1800 G Street, N.W.
Washington, D.C. 20550
POSTAL SERVICE
Mr. Robert Powell
Assistant Program Manager
U.S. Postal Service
Room 4419
1100 L Street
Washington, D.C. 20260
DEPARTMENT OF TRANSPORTATION
Dr. Richard L. Strombotne
Office of the Assistant Secretary
for Systems Development and Technology
Department of Transportation
400 7th Street, S.W.
Washington, D.C. 20591
DEPARTMENT OF DEFENSE
Harvey A. Falk, Jr., Commander, USN
Office of the Assistant Secretary
of Defense
Washington, D.C. 20301
DEPARTMENT OF HOUSING AND
URBAN DEVELOPMENT
Mr. Samuel C. Jackson
Assistant Secretary for Metropolitan Development
Department of Housing and Urban Development
Room 7100
7th and D Streets, S.W.
Washington, D.C. 20410
vu
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DEPARTMENT OF AGRICULTURE
TENNESSEE VALLEY AUTHORITY
Dr. Theodore C. Byerly
Assistant Director of Science and Education
Office of the 'Secretary
U.S. Department of Agriculture
Washington, D.C. 20250
DEPARTMENT OF COMMERCE
Dr. James R. McNesby
Room A361, Materials Building
National Bureau of Standards
Washington, D.C. 20234
DEPARTMENT OF THE TREASURY
Mr. Gerard M. Brannon
Director, Office of Tax Analysis
Room 4217 MT
Department of the Treasury
15th and Pennsylvania Avenue, N.W.
Washington, D.C. 20220
DEPARTMENT OF THE INTERIOR
Dr. LeRoy R. Furlong
Research Advisor to the Assistant Secretary
Office of Assistant Secretary Mineral
Resources
Bureau of Mines
Interior Building
Washington, D.C. 20240
DEPARTMENT OF HEALTH, EDUCATION,
AND WELFARE
Dr. Douglas L. Smith
Department of Health, Education, and Welfare
National Institute of Occupational Health
Rockville, Maryland
Dr. F. E. Gartrell
Director of Environmental Research and Development
Tennessee Valley Authority
715 Edney Building
Chattanooga, Tennessee 37401
ATOMIC ENERGY COMMISSION
Dr. Martin B. Biles
Director, Division of Operational Safety
U.S. Atomic Energy Commission
Washington, D.C. 20545
VETERANS ADMINISTRATION
Mr. Gerald M. Hollander, P.E.
Director of Architecture and Engineering
Office of Construction
Veterans Administration
Room 619 Lafayette Building
811 Vermont Avenue, N.W.
Washington, D.C. 20420
DEPARTMENT OF JUSTICE
Mr. Walter Kiechel, Jr.
Land and Natural Resources Division
Department of Justice
Room 2139
10th and Constitution Avenue, N.W.
Washington, D.C. 20530
DEPARTMENT OF LABOR
Mr. Robert D. Gidel
Deputy Director, Bureau of Labor Standards
Department of Labor
Room 401, Railway Labor Building
400 1st Street, N.W.
Washington, D.C. 20210
via
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TABLE OF CONTENTS
Page
LIST OF FIGURES xi
LIST OF TABLES xiii
ABSTRACT xv
SUMMARY xvii
1. INTRODUCTION 1-1
2. BACKGROUND INFORMATION 2-1
2.1 DEFINITIONS 2-1
2.2 PHYSICAL, CHEMICAL, AND MINERALOGICAL
PROPERTIES OF ASBESTOS 2-1
2.3 ORIGINS AND USES OF ASBESTOS 24
2.4 CHARACTERIZATION OF EMISSION FORMS 24
2.5 MAJOR SOURCES OF ASBESTOS EMISSIONS 2-8
2.6 REFERENCES FOR SECTION 2 2-10
3. ASBESTOS EMISSION SOURCES, CONTROL TECHNIQUES,
AND CONTROL COSTS 3-1
3.1 MINING OF ASBESTOS ORES 3-1
3.1.1 Emissions 3-1
3.1.2 Control Techniques 3-2
3.2 MILLING OF ASBESTOS ORES 3-5
3.2.1 Emissions 3-8
3.2.2 Control Techniques 3-9
3.2.3 Control Costs 3-15
3.3 MANUFACTURE OF PRODUCTS CONTAINING ASBESTOS 3-15
3.3.1 Common Emission Sources in Manufacturing
Processes 3-15
ix
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Page
33.2 Control Techniques for Manufacturing Processes 3-18
3.3.3 Asbestos-Cement Products 3-22
3.3.4 Vinyl-Asbestos Tile 3-26
3.3.5 Asbestos Paper 3-28
3.3.6 Friction Materials Containing Asbestos 3-29
3.3.7 Asbestos Textile Products 3-36
3.3.8 Asbestos-Asphalt Paving Compounds 3-40
3.4 END USES OF PRODUCTS CONTAINING ASBESTOS 3-42
3.4.1 Sprayed Asbestos-Containing Insulation Materials 3-42
3.4.2 Field Fabrication of Products Containing Asbestos 3-46
3.4.3 Friction Products 3-48
3.5 DISPOSAL OF ASBESTOS WASTE MATERIALS 3-49
3.5.1 Emissions 3-50
3.5.2 Control Techniques 3-51
3.6 REFERENCES FOR SECTION 3 3-53
4. COSTS OF CONTROL BY GAS CLEANING DEVICES 4-1
4.1 CAPITAL INVESTMENT 4-1
4.2 MAINTENANCE AND OPERATION 4-3
4.3 CAPITAL CHARGES 4-6
4.4 ANNUALIZATION OF COSTS 4-6
4.5 EXAMPLES 4-7
4.6 REFERENCES FOR SECTION 4 4-8
5. EVALUATION OF ASBESTOS EMISSIONS 5-1
5.1 REFERENCES FOR SECTION 5 5-1
6. DEVELOPMENT OF NEW TECHNOLOGY 6-1
APPENDIX A. GAS CLEANING DEVICES A I
A.I FABRIC FILTERS A-l
A.2 DRY CENTRIFUGAL COLLECTORS A4
A.3 WET COLLECTORS A-4
A.4 REFERENCES FOR SECTION A A-5
SUBJECT INDEX
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LIST OF FIGURES
Figure
2-1 Domestic Supply of Asbestos 2-5
3-1 Fabric Filter Mounted to Drilling Machine 3-3
3-2 Crushing of Massive Asbestos Ore 3-5
3-3 Flow Sheet of an Asbestos Milling Process 3-7
3-4 Control of Emissions from Transport of Ore 3-10
3-5 Dust Capture Hood Fitted to Ore Crusher 3-11
3-6 Configuration of Fabric Dust Collector for Ore Dryer 3-12
3-7 Dust Emissions from Ore Dryers 3~'3
3-8 Vibrating Screens with Hooding for Dust Control 3-14
3-9 Air Ventilation System with Local Dust Capture Hood 3-18
3-10 Dust Capture Hood Fitted to Radial-Arm Saw 3-19
3-11 Dust Capture Hood Fitted to Lathe 3-20
3-12 Bag Opening and Conveying Station with Dust
Collecting Hood 3-21
3-13 Examples of Good and Bad Hood Configurations for
Controlling Asbestos-Laden Dust Emissions from
Receiving Hoppers 3-21
3-14 System for Controlling Emissions at Conveyor Transfer
Points 3-22
3-15 System for Removing Dust from Return Side of Belt
Conveyor 3-23
3-16 Flow Chart for Manufacture of Asbestos-Cement Pipe 3-24
3-17 Row Chart for the Manufacture of Vinyl-Asbestos
Floor Tile 3-27
3-18 Fourdrinier Paper Machine 3-28
3-19 Manufacture of Dry-Mixed Molded Brake Linings 3-31
3-20 Two-Roll Fonning of Brake Linings and Clutch Facings 3-32
3-21 Manufacture of Woven Brake Linings 3-34
3-22 Manufacture of Endless-Wound Clutch Facings 3-35
3-23 Process of Bonding and Debonding Brake Shoes 3-36
3-24 Manufacture of Asbestos Textile Products 3-38
3-25 Dust Capture Hood for Dry Weaving Loom 3-41
3-26 Mixing Section of Manufacturing Plant for Asphalt Paving 3-42
3-27 Spray Processes for Asbestos-Containing Insulation Materials 3-43
3-28 Dust Capture Device Fitted to Portable Hand Saw 3-47
3-29 Dust Capture Device Fitted to Portable Drill 3-48
4-1 Purchase Cost of Fabric Filters 4-2
4-2 Purchase Cost of Dry Centrifugal Collectors 4-3
4-3 Purchase Cost of Wet Collectors 4-4
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Figure Page
A-l Sectional View of Baghouse A-2
A-2 Reverse-Flow Cyclone with Tangential Inlet A-4
A-3 Reverse-Flow Cyclone with Axial Inlet A-5
A-4 Venturi Wet Collector A-5
A-5 Centrifugal Fan Wet Scrubber A-6
Xll
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LIST OF TABLES
Table Page
2-1 Physical, Chemical, and Mineralogical Properties
of Varieties of Asbestos 2-2
2-2 World Production of Asbestos by Countries 2-6
2-3 Estimated United States Asbestos Consumption by Use
Category and Product Asbestos Content, 1968 2-7
2-4 Fiber Size Distributions by Manufacturing Operation 2-7
2-5 Ratio between Fiber Size Distribution at 970X and 430X
by Manufacturing Operation 2-7
2-6 Fiber Size Distributions by Manufacturing Operation 2-8
3-1 Air Flow Rates of Typical Drilling Machines 3-4
3-2 Conveyor Emission Control Design Data 3-23
3-3 Uses of Asbestos Paper 3-28
4-1 Air Pollution Control Equipment Collection Efficiencies 4-4
4-2 Cost-Capacity Factors for Gas Cleaning Devices 4-4
4-3 Installed Cost Expressed as a Percentage of
Purchase Cost for Types of Control Devices 4-5
4-4 Conditions Affecting Purchase and Installation Costs 4-5
4-5 Equations for Calculating Annual Operation and
Maintenance Costs 4-6
4-6 Annual Maintenance Cost Factors for Types of Control
Devices 4-6
4-7 Cost and Engineering Factors for Determining Operating
Costs for Emission Control Equipment 4-7
A-l Applications of Fabric Filters A-3
Xlll
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ABSTRACT
Asbestos is the generic name for a group of hydrated mineral silicates that occur naturally in a
fibrous form. The technological utility of asbestos derives from its physical strength, resistance to
thermal degradation, resistance to chemical attack, and ability to be subdivided into fine fibers.
The subdivision of asbestos into fine fibers produces particulate matter that is readily
dispersed into the atmosphere. Adverse effects of airborne asbestos on human health have been
associated primarily with direct and indirect occupational exposures, but a level of asbestos
exposure below which there is no detectable risk of adverse health effects to the general
population has not yet been identified. Because of the lack of a practical technique of adequate
sensitivity for measuring small concentrations of airborne asbestos, neither accurate emission
factors nor emission-effect relationships are available.
Engineering appraisals, based on limited data, indicate that the milling and basic processing of
asbestos ore (crushing and screening the ore and aspirating the fiber to cyclones for grading) and
the manufacture of asbestos-containing friction materials, asbestos-cement products, vinyl-
asbestos tile, asbestos textiles, and asbestos paper account for over 85 percent of total asbestos
emissions. Other sources include: (1) the manufacture of other products containing asbestos,
such as paints, coatings, adhesives, plastics, rubber materials, and molded insulating materials; (2)
the use of spray-on asbestos products, such as those used for fireproofing or insulating; (3) the
demolition of buildings or structures containing asbestos fireproofing or insulating materials; and
(4) the sawing, grinding, or machining of materials that contain asbestos, such as brake linings
and molded pipe insulation. In most of the manufacturing operations, the major emissions of
asbestos occur when the dry asbestos is being handled, mixed with other dry materials, or
dumped into the wet product mix, but the weaving of asbestos fibers into textiles and the
machining or sanding of hard asbestos products also produce major emissions.
Emissions are controlled in several ways: (1) by careful handling of dry materials to avoid
generating dust; (2) by enclosing dusty operations; (3) by substituting wet processes for dry
processes; (4) by wetting dry materials before handling, sawing, or grinding; (5) by cleaning the
dust-laden air by drawing it into ducts that lead to fabric filters; and (6) by reducing the amount
of asbestos added to products the use of which leads to the generation of emissions. The last
technique is particularly applicable to situations where the control of emissions by other methods
is very difficult, as with spray application of insulation or demolition of structures. The costs of
needed emission control techniques can be estimated from those associated with existing prac-
tices.
Key words: asbestos emissions, control techniques, costs.
xv
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SUMMARY
BACKGROUND INFORMATION
Asbestos is the generic name for a group
of naturally occurring, hydrated, mineral
silicates. Asbestos can be separated into fine
fibers and further subdivided into even finer
fibrils, as small as approximately 0.03
micrometer (jurn) in diameter, which
contribute to particulate air pollution. To
date, the evidence of an association between
exposure to airborne asbestos and adverse
effects on human health has been restricted
primarily to direct and indirect occupational
exposures. A level of asbestos exposure below
which there is no detectable risk of adverse
health effects to the general population has
not yet been identified.
Most measurements of asbestos fiber
concentrations in industrial environments are
economically practical only for those fibers
visible by light microscopy, and an analytical
technique that employs 430X magnification
and phase contrast illumination has been
standardized. Fiber counts obtained more
recently by the application of electron
microscopy have revealed that only a small
percentage of the total population of fibers
present in a sample is included in the data
obtained by light microscopy. Numerous
technical problems remain to be resolved,
however, before a standardized method can
be adopted that enumerates total numbers of
fibers and fibrils in a sample by use of the
electron microscope.
Asbestos is domestically mined in only
four states, and approximately five-sixths of
the asbestos consumed in the United States is
imported. Asbestos is used in a vast array of
products ranging from those that take
advantage of its resistance to thermal attack
to the numerous products in which it serves as
a filler material.
Estimates of emissions indicate that the
extraction of asbestos from ore constitutes
the largest single domestic source of
atmospheric asbestos. A number of industrial
processes associated with the manufacture of
asbestos-containing products are also
significant sources of emissions. Several end
uses of asbestos contribute emissions in the
process of installation or application of the
material and/or during an extended period of
product usage.
ASBESTOS EMISSION SOURCES AND
CONTROL TECHNIQUES
Mining
The mining of asbestos ores is
accompanied by emissions from drilling for
explosive charges; surface scraping, screening,
and ore loading at mines; transportation to
mills; unloading at mills; and exposure of
mine waste and ore piles to the atmosphere.
Adequate control by gas cleaning has been
achieved only for drilling operations. Quite
limited progress has been made toward
preventing asbestos-bearing material in
exposed deposits, such as ore deposits and
tailings dumps, from becoming entrained in
the atmosphere; such limited control has been
achieved by providing vegetation cover for the
deposits or, for temporary deposits, by
employing surface wetting. Emissions
generated during transportation can be
diminished by surface wetting, use of vehicle
covers, or use of enclosed vehicle bodies.
Blasting and the various handling operations
are, at present, essentially uncontrolled.
xvn
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Basic Processing
In the milling or basic processing of
asbestos ores, direct emission sources are
exposed ore and tailings piles, effluents of ore
crushers, exhausts of ore dryers, and
atmospheric exhausts of mill ventilation
and/or process air. Emissions to a mill work
space originate from numerous screening
operations, transport of dry
asbestos-containing materials by conveyor
systems, and packaging of asbestos. Emissions
from some ore dryers operated by the
Canadian asbestos industry are now
controlled by thermally insulated, fabric
filter collectors; this control method is
undergoing further development. Emissions of
asbestos in ventilation and process air streams
from mill buildings are frequently controlled
by the use of fabric filters; a prime
requirement for the attainment of design
collection efficiency is a strict maintenance
program for the collector. Emissions from ore
crushers and vibrating screens have been
controlled to some extent by fitting
ventilated enclosures or dust-capture hoods to
the equipment and by cleaning the ventilation
streams by means of fabric filters. Some
conveyors have been completely enclosed as
an emission control measure.
M a nu fac lu ri ng
Emission sources within plants that
manufacture asbestos-containing products are
important because a portion of the plant
ventilation air always reaches the exterior
environment. Because atmospheric emissions
can be controlled through the application of
fabric filters, the task of overall emission
control is largely one of capturing airborne
local emissions from various manufacturing
processes and conveying the fibers to the
filter. These processes include handling and
dumping of asbestos contained in bags, dry
mixing of asbestos-containing materials,
dry-processing operations, finish machining of
products, and packaging. Dust capture hoods,
some of which are generally applicable for
ventilating dust-producing operations such as
bag opening and others of which are tailored
to remove dust from specific pieces of
equipment such as textile carding machines,
are widely employed at present. The adoption
of good housekeeping practices that are
accompanied, for example, by central
vacuuming systems is another effective
control method. In some instances, emissions
can be controlled by substituting a wet
process for a dry one.
End Uses
An emission control technique
applicable to some end uses of
asbestos-containing products is the
elimination of asbestos in favor of substitute
materials. Sprayed insulation materials that
contain no asbestos are now in use, and it is
anticipated that asbestos-free molded pipe
insulation will be marketed in the near future.
Shielding of work spaces from the exterior
environment and use of good housekeeping
practices are the primary control measures,
aside from the use of asbestos-free materials,
that have been used to control emissions from
spraying of fireproofing and the field
installation of products containing asbestos.
Also, dust capture hoods for the local
collection of machining wastes are available
for both stationary and portable power tools.
Control techniques for the handling and
final disposal of waste products containing
asbestos are currently available in the form of
recommended handling and disposal practices.
These have not been widely adopted.
Asbestos emissions, in some instances,
can be controlled by techniques other than the
utilization of gas cleaning devices. External
conveyors can be enclosed, storage and tail-
ings piles can be coated with dust suppres-
sants, and spray fireproofing and insulating
products containing little or no asbestos can
be developed at costs that are not unreason-
able relative to total plant investment and/or
product value.
XVlll
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COSTS OF CONTROL BY GAS CLEANING
DEVICES
Air pollution control costs for gas
cleaning by dry centrifugal collectors, wet
collectors, and fabric filters can be estimated
by evaluating average costs for capital
investment, maintenance, and operation.
Installed equipment costs can be expressed as
percentages of equipment purchase costs fora
wide range of special conditions that
influence applications to differing processes.
Ranges of annual maintenance costs, per unit
of gas handling capacity, facilitate estimates
among differing practices of control
equipment operators as well as among the
three types of control devices. By combining
the estimates of the various facets, the total
cost of control can be appraised.
EVALUATION OF ASBESTOS EMISSIONS
Emission factors are useful in estimating
rates and quantities of atmospheric emissions
from sources in the absence of measurements
of emissions from stacks and other points of
introduction into the atmosphere; however.
accurate asbestos emission factors are not
currently available. Extensive emissions
testing data must be compiled if reliable
estimates of mass rate emission factors and
their relation to fiber concentrations are to be
determined.
GAS CLEANING DEVICES
Brief descriptions of geometrical
configurations, principles of operation, and
performance characteristics of fabric filters,
dry centrifugal collectors, and wet collectors
are presented in an appendix in which specific
design parameters and operational features of
fabric filters in use in asbestos mills and plants
that manufacture asbestos-containing
products are also discussed.
xix
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CONTROL TECHNIQUES
FOR ASBESTOS AIR POLLUTANTS
1. INTRODUCTION
Control Techniques for A sbcstos A ir Pol-
lutants is issued in accordance with Section
1 12 (b) (2) of the Clean Air Act as amended
by the Clean Air Amendments of 1970.
The existence of an association between
human disease and inhaled asbestos has been
known for a half-century. In the main, these
relationships have been established within
groups that have experienced indirect or
direct occupational exposures; the range of
activities extends from mining and milling of
asbestos to the manufacture of asbestos
textiles to the application and eventual
removal of asbestos-containing insulation
materials. The conjecture that large segments
of the general population of the United States
might be exposed to asbestos to the extent
that adverse health effects would result is of
more recent origin. Accordingly, the need for
more stringent control of asbestos emissions
into the atmosphere has been recogni/.ed.
Asbestos is emitted from both stationary
and mobile sources. Emissions of asbestos
resulting from the wearing of large numbers
of motor vehicle brake linings are the subject
of current investigation; the extent to which
asbestos in the waste particulates has been
thermally degraded prior to emission is in
question.
Technology in the form of specific gas
cleaning devices can control asbestos
emissions from many source categories with
high efficiency; corresponding air pollution
control costs are moderate. For example,
installations that routinely recycle large
volumes of cleaned process and ventilation air
back to work spaces for general ventilation
are in operation. These control methods.
however, are practiced in the absence of a
thorough knowledge of either the equipment
collection efficiencies for submicron
particulates or the potential adverse health
effects of these smallest fibers.
The nature of some operations that ac-
company mining and milling of asbestos ores
precludes, in a practical sense, emission con-
trol by gas cleaning methods. Control tech-
niques applicable to blasting, storage of large
quantities of raw ore, transportation on road-
ways surfaced with asbestos-containing
wastes, and disposal of mine wastes and mill
tailings are available to reduce emissions,
ever, through the application of wetting
agents and surface coatings. Other operations
ranging from rock drilling at mines to ore
crushing, drying, and screening in mills are
amenable to emission control by gas cleaning
devices.
Asbestos emissions result from numerous
processes in the manufacture of a vast array
of products that contain asbestos as either a
primary or subsidiary component. Available
control techniques are based upon the con-
tainment of potential emissions at the source
or upon the entrainment, at the source, of
potential emissions and waste into an air
stream that is subsequently cleaned. Other
emission control methods substitute a wet
process for a conventional, dry technique.
End-uses of asbestos-containing
products, particularly those that are friable.
can be accompanied by emissions during
installation, during an extended period of
usage, and ultimately during final demolition
or disposal. In recognition of the extreme
1-1
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difficulty of controlling emissions from a
relatively small number of these products,
substitute materials for asbestos have been
adopted, and development of appropriate
substitutes for inclusion in additional
products is in progress. The adoption of the
following measures constitutes a generalized
control technique for emissions from the
usage, conversion to waste, and disposal of
asbestos-containing products:
1. Identification of significant sources
of direct exposure of the general
population to asbestos emissions.
2. Development of an appreciation for
the adverse effects of asbestos on
human health on I lie part of all
workers who handle
asbestos-containing materials.
3. Application of existing control
technologies for dust containment,
capture, and collection.
4. Enforcement of appropriate
methods for the disposal of
asbestos-containing wastes.
Some estimates of quantities of asbestos
emitted to the atmosphere are presented
herein. Discussion of the specific effects of
asbestos on human health is, however, outside
the scope of this report.
1-2
-------
2. BACKGROUND INFORMATION
2.1 DEFINITIONS
The term "asbestos" refers to any of six
naturally occurring crystalline mineral
silicates: actinolite, amosite, anthophyllite,
chrysotile, crocidolite, and tremolitc.1 Each
of these materials is a hydratcd silicate; the
degree of hydration varies from
approximately 1.5 percent in some deposits
of crocidolite to approximately 14.5 percent
in the majority of the deposits of chrysotile.1
These minerals display a wide range of
chemical compositions, as is indicated in
Table 2-1.
The several types of asbestos were formed
by the metamorphosis of serpentine and
amphibole minerals, both classes of which
contain silica. Chrysotile, which is a hydrated
silicate of magnesia, is the principal crystalline
form of serpentine. The remaining five types
of asbestos are crystalline forms of amphibole
minerals. Crocidolite, frequently called blue
asbestos, is associated with riebeckite. Amosite
is the only asbestos of grunerite that is of
commercial value. Anthophyllite is thought to
be evolved from the metamorphosis of
olivine. Tremolite occurs in crystalline, dolo-
initic limestone and is called actinolite when
iron is present in amounts greater than 2 per-
cent.'
The technological utility of asbestos
derives from its occurrence in a fibrous state
and from its properties of exceptional
physical strength, resistance to thermal
degradation, and resistance to attack by acids
or alkalis in one or more of the materials. For
example, slender chrysotile "fibers" with
lengths exceeding 3/4-inch are commercially
available; subsequent to blending with small
quantities of synthetic or organic fibers, these
asbestos "fibers" can be spun into yarn and
then converted into a variety of textile
products. Each asbestos "fiber" can usually
be subdivided into a large number of "fibers"
of the original length. This feature permits
significant alterations in the transverse
stiffness, or flexibility, of "fibers" of given
length to be made by controlling the degree
of subdivision or opening of the "fibers" in an
asbestos milling process.
Electron microscopy reveals that the
smallest fibrous subdivision of a chrysotile
fiber, called a fibril, has an average outside
diameter of 0.034 micrometer Gum). Further,
it has been shown that the chrysotile fibril is a
hollow tube, rather than a solid cylinder, with
an average inside diameter of 0.018 ym.2 A
suggested model views the chrysotile fiber as a
tightly packed collection of fibrils, the
interiors and interstices of which are filled
with crystal fragments or amorphous material
of the same chemical composition; the
interfibril binding forces are relatively weak.5
The elementary crystal structure, or fibril, of
the amphibole asbestoses forms a solid
cylinder considerably larger in outside
diameter than the chrysotile fibril; the average
outside diameter ranges from 0.1 to 0.2 /urn.2
Although the majority of dry-milled asbestos
fibers each contain many fibrils, smaller
numbers of fibers composed of only one or
two fibrils are always present; a considerable
number of these fibers of smaller diameter are
found in asbestos dust.5
2.2 PHYSICAL, CHEMICAL, AND
MINERALOGICAL PROPERTIES OF
ASBESTOS
Table 2-1 ranks the six varieties of
asbestos according to such physical
characteristics as spinability and flexibility of
2-1
-------
Table 2-1. PHYSICAL, CHEMICAL, AND MINERALOGICAL PROPERTIES OF VARIETIES OF ASBESTOS2-3
Property
Chemical
formula
Essential
composition
Percentage
chemical
composition
ao,
MgO
FeO
Fe,03
Al,03
H;0
CaO
Na2O
CaO and
NajO
pH
Resistance to
acids
Veining
Color
Texture
Luster
Hardness3
Flexibility
Spinn ability
Tensile
strength,
Ib/m2
Fusion
point, °F
Specific heat,
Btu/lb-°F
Ctiryiotllt
Mg,Si,O, (OH),
Hydrous silicate
of magnesia
37. to 44.
39. to 44.
0.0 to 6.0
0 1 to 5.0
0.2 to 1.5
12.0 to 15.0
trace to 5.0
9.2 to 9.8
Poor
Cross and
slip fibers
Green, gray,
amber to
white
Soft to harsh,
also silky
Silky
2.5 to 4.0
High
Very good
824,000 max.
2,770
0.266
Croddollt.
Na,Fe,SI.O,i(OH|,
Silicate of sodium
and iron with
some water
49. to 53.
0. to 3
13. to 20.
17. to 20.
2.5to 4.5
4.0 to 8.5
Good
Cross fiber
Blue
Soft to harsh
Silky to dull
4
Good
Fair
876,000 max
2,180
0201
Amoilte
FeMgl.Si.OjilOHl,
Silicate of iron
and magnesium.
higher iron than
nthophyllite
49. to 53.
1. to 7.
34. to 44.
2. to 9.
2. to 5.
0.5 to 2.5
__
Cross fiber
Gray, yellow
to dark
brown
Coarse but
somewhat
pliable
Vitreous,
somewhat
pearly
5 5 to 6.0
Good
Fair
16,000to
90,000
2,550
0193
' Jnthopnylllte '
-------
Table 2-1. (continued) PHYSICAL, CHEMICAL, AND MINERALOGICAL PROPERTIES OF
VARIETIES OF ASBESTOS
Property
Electric
charge
Filtration
properties
Specific
gravity
Cleavage
Optical
properties
Refractive
index
Resistance to
destruction
by heat
Temperature
at ignition
loss, °F
Magnetite
content, %
Crystal
structure
Crystal
system
Mmeralogical
structure
Mineral
association
Chrysotile
Positive
Siow
2 4 to 2.6
010 perfect
Biaxial positive,
extinction
parallel
1.50 to 1.55
Good, brittle
at high
temperatures
1,800
00 to 5.0
Fibrous and
asbestiform
Monoclmic and
orthorhombic
In veins of
serpentine, etc
In altered
peridot ite
adjacent to
serpentine
and limestone
near contact
with basic
igneous rocks
Croadolite
Negative
Fast
3.2 to 3.3
1 1 0 perfect
Biaxtal ±.
extinction
inclined
1.7
pleochroic
Poor, fuses
1,200
3.0 to 5.9
Fibrous
Monoclmic
Fibrous in
iron stones
Iron rich
SlIlCIOUS
argilhte
in quartzose
schists
Amosite
Negative
Fast
3.1 to 325
1 1 0 perfect
Biaxial positive,
extinction
parallel
1.64+
Good, brittle
at high
temperatures
1,600 to 1,800
0
Prismatic,
lamellar to
fibrous
Monoclmic
Lamellar,
coarse to
fine fibrous
and asbestiform
In crystalline
schists, etc.
AnthophyHite
Negative
Medium
2 85 to 31
110 perfect
Biaxial positive,
extinction
parallel
1.61 +
Very good
1,SOO
0
Prismatic,
lamellar to
fibrous
Orthorhombic
Lamellar,
fibrous
asbestiform
In crystalline
schists and
gneisses
Tremolite
Negative
Medium
2 9 to 3.2
1 1 0 perfect
Biaxial negative,
extinction
inclined
1.61 +
Fair to good
1,800
0
Long and thin
columnar to
fibrous
Monoctmic
Long, prismatic
and fibrous
aggregates
In Mg limestones
as alteration
product of
magnesian
rocks, metamorphtc
and igneous
rocks
ActtnoJite
Negative
Medium
3.0 to 32
1 1 0 perfect
Biaxial negative,
extinction
inclined
1 63±
weakly pleochroic
~
Long and thin
columnar to
fibrous
Monoclmic
Reticulated
long prismatic
crystals and
fibers
In limestones and
m crystalline
schists
forking Scale of Hardness 1, very easily scratched by fingernail, and has greasy feel to the hand, 2, easily scratched by fingernail; 3, scratch by brass pin or
copper coin; 4, easily scratched by knife, 5, scratch with difficulty wtth knife, 6, easily scratched by file; 7, little touched by file, but will scratch window glass.
All harder than 7 will scratch window glass.4
2-3
-------
fibers, resistance to destruction by heat, and
resistance to the action of acids. Physical
characteristics together with pertinent
physical properties, such as tensile strength,
govern the application of asbestos to
numerous end-uses. Mineralogical properties,
such as the veining of fibers, mineralogical
structure, and mineral association, are
relevant to the mining of asbestos-containing
ores. Chemical compositions are also listed in
Table 2-1.
2.3 ORIGINS AND USES OF ASBESTOS
Production of asbestos in the United
States in 1970 totaled 125,314 short tons and
was valued at an estimated S10,696,000.6
Approximately 60 percent of the total was
chrysotile mined in California by four
producers located in Calaveras, Fresno, and
San Benito counties. In decreasing rank, the
remainder was mined in the states of Vermont
(one producer, Orleans County, chrysotile),
Arizona (three producers, Gila County,
chrysotile), and North Carolina (one
producer, Yancey and Jackson counties,
anthophyllite). The apparent consumption of
asbestos by the United States in 1970
amounted to 728,131 short tons.6 Figure 2-1
illustrates the relationship between net
imports and domestic production for the
United States during the period 1960 to
1970.
As listed in Table 2-2, the world
production of asbestos for 1969 was
3,640,017 short tons. The preliminary
estimates of 1970 production for the three
largest suppliers are 1,663,355 short tons for
Canada; 1,150,000 short tons for the
U.S.S.R.; and 316,822 short tons for the
Republic of South Africa. Chrysotile from
Canada and crocidolite from Africa constitute
the majority of asbestos imported into the
United States. The six mining areas of
Asbestos, Black Lake, Coleraine, East
Broughton, Robertson, and Thetford Mines in
the southern portion of the Canadian
province of Quebec are of particular interest
as potential emission sources because of their
proximity to the United States. The Canadian
asbestos deposits are located between Danville
and East Broughton in an area approximately
70 miles in length by 5 to 6 miles in width.
The major categories of asbestos usage
are listed in Table 2-3 together with the
corresponding 1968 United States apparent
consumption and the range of asbestos
content for the individual classifications.
2.4 CHARACTERIZATION OF EMISSION
FORMS
The biological effects of asbestos are
assumed to be related to concentrations of
those fibers that are respirable. In numerous
instances, individual fibers embedded in lung
tissue of persons occupationally exposed to
asbestos have been observed; the fibers have
been identified as asbestos in some cases.9
Accordingly, the quantitative specification of
amounts of airborne asbestos should
emphasize the number of fibers, or particles,
per unit volume of gas rather than the mass
concentration of entrained asbestos fibers.
Even the geometrical characterization of
asbestos emissions presents a number of
technical difficulties. These difficulties are
largely related to the relative ease with which
the extremely small-diameter fibrils of
asbestos, both chrysotile and amphibole, can
be separated from larger fiber bundles.6
Crude milling of asbestos can yield fibers
exceeding 2 inches in length with diameters
up to 1/32 inch. Fundamental fibrils,
however, some with lengths only slightly
greater than the diameters, are present in large
numbers in asbestos dust.5 Fibers sometimes
preferentially subdivide at the extremities and
exhibit longer residence times in air as a result
of the increased drag force.6 Further, there is
a tendency of very small asbestos particles to
agglomerate and form much larger masses of
fluff.6
The hydraulic benellciation of asbestos
ore, carried out in the United States by a
single facility, produces asbestos that is
2-4
-------
i,uuu
800
600
I/)
§
O
CO
CO
° 400
oo
O
C*D
UJ
CO
GO
-------
Table 2-2. WORLD PRODUCTION OF
ASBESTOS BY COUNTRIES3-6
(Short tons)
Country
North America
Canada (sales)
United States (sold or used by producers)
Latin America
Argentina
Bolivia
Brazil
Europe
Bulgaria
Finland6
France
Italy
Portugal
USSRC
Yugoslavia
Africa
Mozambique
Rhodesia Southern0
South Africa Republic of . . . .
Swaziland
United Arab Republic
Asia
China mainland0
Cyprus
India
Japan
Korea Republic of (South)
Philippines
Taiwan
Turkey
Oceania: Australia
Total
1968
1 ,509 699
120,690
381
1
4,806
2,300d
14484
551
114,020
94d
900 000
11,456
132
95,000
260 531
42946
2,868
170,000
21,293
9992
24251
3650
35
1,323
3,905d
895
3315,303
1969
1 576876
125,936
359
9,981
3,100
15487
550°
124,039
224
1 100000
12,634
868
88,000
284 588
43,086
180,000
23,927
10734
23,148
6,515
49
3,396
5,698
822
3,640,017
1970b
1 663 355
125,314
350°
14,330
3,900C
15019
550°
130,747
200
1 150000
13,342
NAf
88,000
316822
43,100°
190,000
28,253
1 0,840
23,576
1,513
1,337
3,133
1,857
700°
3,826,238
aln addition to the countries listed, Czechoslovakia, North Korea, and Romania also produce
asbestos, but information is insufficient to make reliable estimates of output levels.
Preliminary.
GEstimate.
dRevised.
Includes asbestos flour.
Not available.
magnification is available to render visible all
fibers of interest; Table 2-6 lists median fiber
lengths and percentages of all visible fibers
that exceed 5 ,um; in length for some of the
manufacturing operations of Table 2-5. Only
small percentages of the total numbers of
fibers emitted from the various operations are
longer than 5 nm; therefore, the standardi/.cd
analytical techniques that employ 430X
magnification count only small fractions of
2-6
-------
Apparent asbestos
consumption.
Use
Asbestos-cement products
Asbestos-containing floor tile
Asbestos paper
Asbestos-containing friction
materials
Asbestos-containing paints,
roof coatings, and caulks
Asbestos textiles
Asbestos-containing plastics
Miscellaneous asbestos-
containing products
10-* short tons
566
82
57
25
16
16
8
47
Percent asbestos
15
10
80
30
80
0.
to 30
to 30
to 90
to 80
-
to 100
5 to 60^8
-
aEstimated from data for individual Standard Industrial Classification (SIC) Codes.
Includes products in which asbestos is used as a thixotrope.
Table 2-4. FIBER SIZE DISTRIBUTIONS
BY MANUFACTURING OPERATION3-11
Operation
Asbestos textiles
Fiber preparation
and carding
Spinning, twisting,
and weaving
Asbestos friction products
Mixing
Grinding, cutting,
and drilling
Asbestos-cement pipe
Mixing
Finishing
Asbestos insulation
Mixing
Finishing
>5j/m
50
61
68
63
57
58
55
50
>10Mm
25
38
30
31
28
27
27
29
Percent total fibers
aFiber counts made at 430X magnification with
phasecontrast illumination.
Table 2-5. RATIO BETWEEN FIBER
SIZE DISTRIBUTION AT970X AND
430X BY MANUFACTURING OPERATION3-11
Operation
Asbestos textiles
Fiber preparation and carding
Spinning, twisting, and weaving
Asbestos friction products
Mixing
Grinding, cutting, and drilling
Asbestos-cement pipe
Mixing
Finishing
Asbestos insulation
Mixing
Finishing
Total
fibers
2.0
1.8
1.1
1.0
1.2
1.6
1.0
1.8
Fibers
>5jum
2.1
1.9
1.1
1.1
1.2
1.8
1.1
2.0
aFiber counts made at 970x and 430x magnification
with phase-contrast illumination.
2-7
-------
Table 2-6. FIBER SIZE DISTRIBUTIONS
BY MANUFACTURING OPERATION3-11
Operation
Asbestos textiles
Fiber preparation and carding
Spinning, twisting, and weaving
Asbestos friction products
Mixing
Grinding, cutting, and drilling
Asbestos-cement pipe
Mixing
Finishing
Fiber
median
length.
pm
1.4
1.0
0.9
0.8
0.9
0.7
Percentage
>5/Lim
4
2
2
2
2
1
aFiber counts made with a 5000X electron
microscope.
the total numbers of fibers present. The areal
density of fibers collected on a membrane
filter for electron microscope analysis is
preferably much larger than that appropriate
for light microscopy; otherwise, the counting
of a large number of fields selected by an
appropriately random method is required. Of
particular significance is the properly
weighted inclusion of large groups of fibers
approximately 0.1 jum in diameter by 1.0/^m
in length, which are occasionally observed;
these fibers may be present in emissions as
coherent collections of fibers rather than
having resulted from the deposition of many
single fibers onto a sampling filter.11
Good agreement has been observed
between fiber counts obtained by light mi-
croscopy and those determined by electron
microscopy for relatively long fibers. The pri-
mary discrepancy between the methods ap-
pears in the counting of fibers shorter than
ljum.11 Electron microscopic fiber- or
particle-counting techniques are yet to be
standardized, but some procedures that over-
come many of the problems, such as identifi-
cation of asbestos fibers from among a collec-
tion of other inorganic and organic
particulates collected simultaneously with the
asbestos, have been developed.
Characteristics of asbestos emissions that
might prove to be relevant in the study of
adverse health effects are:
1. Type of asbestos.
2. Distribution of length-to-diameter
ratio for fibers of various lengths.
3. Contamination of fibers with
inorganic and organic materials
from ores or from mining, milling,
processing, shipping, and usage.
4. Contamination of fibers with
inorganic and organic substances
present in the atmosphere or in the
respiratory tract.
In view of the present uncertainty as to
which parameters of asbestos emissions are
most significant, biologically, it appears
advisable to provide characterizations as
complete as present technology permits; and
the development of new technology that
would extend the range of description is
warranted. Future developments may permit
the limitation of these tasks. For example, it
has been suggested that the total fiber counts
obtained by electron microscopy are not
necessarily more appropriate indicators of
asbestos exposure than are total counts
determined by 430X magnification.11 As a
second example, it may be possible to develop
rather detailed, standardized specifications of
emissions from classes of emission sources and
to subsequently monitor only the most
significant parameters of these descriptions to
determine emission levels.
2.5 MAJOR SOURCES OF ASBESTOS
EMISSIONS
Asbestos as it exists in a natural state,
for example as veins of chrysotile embedded
2-8
-------
frequently mechanically bound in such a
manner that the thin fibers that contribute to
air pollution are not readily emitted.
Exceptions to this natural constraint are
found in the chrysotile ores of Fresno and
San Benito counties in California where
high-concentration ores of loosely bound,
short-fiber asbestos are exposed to the
atmosphere and also in the soil of farm lands
in Bulgaria that contain anthophyllite.11
Airborne asbestos emissions result from the
mining of asbestos ores, the milling of asbes-
tos ores to exploit the property by which
asbestos can readily be separated into an ex-
tremely fine fibrous material, and the manu-
facture and use of numerous asbestos-
containing materials.
No data base of asbestos ambient air
concentrations for the United States exists;
however, preliminary d?ta, which are accurate
to within a factor of 2 or 3, indicate asbestos
concentrations ranging from 1 1 x 10"9 to 60
x 10~9 grams per cubic meter (g/m3) in New
York City.13
The role of asbestos in air pollution
differs significantly from that of many other
pollutants, such as nitrogen oxides and some
elemental metallic participates, in that it does
not enter into a natural cycle of organic
growth. Rather, asbestos precipitated from
the atmosphere is extremely stable with
respect to chemical decomposition and is
subject to reen train me nt into the atmosphere.
Engineering appraisals based primarily on
visual inspection of a limited number of facili-
ties, estimates of typical participate collection
efficiencies for currently installed control
equipment, and typical percentages of asbes-
tos in the material from which the participate
originated have been used to estimate the rela-
tive percentages (on a mass basis) of asbestos
emissions from stationary sources in the
United States.14 More data are necessary in
order to determine absolute total mass emis-
relaled, fiber count emission rates.
Asbestos mines and mills are estimated
to contribute 85 percent of the total
emissions of asbestos from stationary
sources.14 Of these emissions, over 90
percent are from asbestos mill operations,
which include the crushing, drying, and
concentrating of asbestos ore and the disposal
of tailings.14 Typically, emissions from
crushing operations are uncontrolled, and
emissions from drying operations are
controlled only by centrifugal collectors.
Most mills attain some degree of emission
control by using either centrifugal collectors
or centrifugal collectors in combination with
fabric-filter collectors to clean process air
streams. The potential for emissions from
wet-process milling is much less than the
emission potential of typical dry milling
operations.
Air ventilation systems that exhaust to
air cleaning devices are frequently used to
control emissions from processes incorporated
in the manufacture of asbestos-containing
products. These partially controlled emissions
are estimated to account for 10 percent of the
total of all asbestos emissions.14 The
manufacture of friction materials,
asbestos-cement products, vinyl-asbestos tile,
asbestos textiles, and asbestos paper
represents the source of over 90 percent of
the emissions from manufacturing
processes.14 The sum of the emissions from
numerous miscellaneous manufacturing
processes, such as the production of calcium
silicate-asbestos fiber pipe insulation,
asbestos-asphalt coatings, asbestos-containing
paints and coatings, and various
asbestos-reinforced plastic products is also
significant and is estimated to be of the same
magnitude as the sum of emissions from the
manufacture of both asbestos textiles and
asbestos paper.14 In each case, the emissions
are principally from the mixing and handling
of the dry fiber; thus, emissions can be
significantly reduced by the addition of more
2-9
-------
efficient control of handling and mixing
operations.
The major sources of asbestos emissions
from the end-uses of asbestos-containing ma-
terials include the grinding and fitting of re-
placement brake linings; the spray application
of asbestos-containing fire proofing; the ero-
sion of the interior insulating linings of boiler
breechings, ducts, and economizers; the instal-
lation of asbestos-containing pipe insulation;
and the cutting of asbestos-containing siding,
wallboard, shingles, and other construction
materials. The end-uses of asbestos-containing
products are estimated to account for 5 per-
cent of total asbestos emissions.14 In many
cases, such as the grinding and fitting of re-
placement brake linings, emissions are con-
trolled by fabric filters that collect more than
96 percent of the particulate emissions; such
partially controlled emissions represent
approximately 50 percent of the emissions
attributed to end-uses.14 Emissions to the
atmosphere from the abrasion of vehicle
brake linings during usage and from demoli-
tion operations are not included. Although
emissions from the spray application of
asbestos-containing fireproofing are estimated
to be only slightly more than 1 percent of
total asbestos emissions, these emissions are
very significant because they occur in densely
populated areas.1 4
Emissions from the use of an asbestos
precoat as a filter aid for certain fabric dust
filters applied to streams with low particulate
loadings are considered negligible because of
the small number of such applications and the
extremely long periods (often 2 or 3 years)
between applying the precoat and cleaning
the filter.
2.6 REFERENCES FOR SECTION 2
1. Carroll-Porczynski, C. Z. Asbestos, from
Rock to Fabric. Manchester, The Textile
Institute, 1956, p. 7, 12-18.
2. Berger, H. Asbestos Fundamentals. New
York, Chemical Publishing Company,
Inc. 1963. p. 51,58, 90.
3. Handbook of Asbestos Textiles, 3rd Ed.
Pompton Lakes, Asbestos Textile Insti-
tute. 1967. p. 3-1 1.
4. Lange's Handbook of Chemistry. Lange,
N. A. (ed.). Sandusky, Handbook
Publishers, Inc. 1956. p. 150.
5. Gaze, R. The Physical and Molecular
Structure of Asbestos. Annals of New
York Academy of Sciences, 732:23-30,
December 1965.
6. Clifton, R. A. Asbestos. Preprint from
Minerals Yearbook 1970. U.S.
Department of the Interior, Bureau of
Mines, Washington, p. 1,3, 7.
7. May, T. C. and R. W. Lewis. Asbestos.
In: Mineral Facts and Problems, 1970
Ed. U.S. Department of the Interior,
Bureau of Mines, Washington. Bulletin
Number 650, 1970. p. 855.
8. Rosato, D. V. Asbestos: Its Industrial
Applications. New York, Reinhold
Publishing Corporation, 1959. p.
142-177.
9. Sullivan, R. J. and Y. C. Athanassiadis.
Preliminary Air Pollution Survey of
Asbestos, A Literature Review. U.S.
Department of Health, Education, and
Welfare, National Air Pollution Control
Administration. Raleigh, N. C.
Publication Number APTD 69-27.
October 1969. p. 3, 15, 18,38.
10. Myers, J. L. New Additives Induce
Thixotropy, Provide Sag and Viscosity
Control. (Presented to Western Coatings
Technology Society, Denver, Los
Angeles, San Francisco, Portland,
Seattle, and Vancouver, B.C., May
1969.) P. 3,4.
2-10
-------
11. Lynch, J. R., H. E. Aver, and D. L.
Johnson. The Interrelationships of
Selected Asbestos Exposure Indices.
Amer. Indust. Hygiene Assoc. J.
31(5): 5 98-604, 1970.
12. Zolov, C. T., T. Bourilikov, and L.
Baladjoa. Pleural Asbestos in
Agricultural Workers. Environ. Res.,
1(3): 287-292, 1967.
13. Nicholson, W. J., A. N. Rohl, and F. F.
Ferrand. Asbestos Air Pollution in New
York City. (Presented at 2nd
International Air Pollution Conference,
Washington, December 1970.) p. 12.
14. National Inventory of Sources and
Emissions, Asbestos, Section III.
Leawood, W. E. Davis and Associates.
National Air Pollution Control
Administration Contract Number CPA
22-69-131. February 1970. p. 12.
2-11
-------
3. ASBESTOS EMISSION SOURCES, CONTROL TECHNIQUES, AND
CONTROL COSTS
3.1 MINING OF ASBESTOS ORES
Chrysotile, which is the fibrous form of
serpentine, and crocidolite, amosite,
anthophyllite, tremolite, and actinolite, which
are fibruous forms of the amphibole minerals,
usually occur in veins embedded in massive
rock deposits. The three fiber types are cross,
slip, or bulk. None of the asbestoses is
characterized by a single type of fiber;
however, chrysotile and crocidolite occur
predominantly in the cross fiber.1
Anthophyllite occurs in all three forms.1 The
concentration of asbestos in commercial ores
is as large as 60 percent in California's
short-fiber Coalinga ores, but the largest
deposits of longer fiber chrysotile contain
from 4 to 10 percent asbestos. After
extraction from the ore, typically only 3 to
25 percent of the asbestos is of sufficient
length for use in spinning applications.1 None
of the California chrysotile fiber mined in
Fresno and San Benito counties, however, is
suitable for spinning.
When deposits of asbestos occur near the
surface of the earth and are not bound within
massive rock deposits, surface mining
methods are employed; the shallow
overburden and the ore are removed by power
shovel and bulldozer or by other scraper-type
vehicles. Those California deposits noted
above are mined by this technique. The North
Carolina deposits are also worked, on a small
scale, by surface mining. The open-pit mining
of some ore deposits, such as those in
Vermont that extend both laterally and to a
considerable depth below ground level,
requires extensive blasting to loosen the
overburden and ore for removal. The mining
proceeds along either parallel or spiral
amphitheater-like terraces, which extend to
the floor of the pit. Where narrow bands of
asbestos veins extend far below the surface, as
in Arizona, it is necessary to resort to
underground mining in which shafts that
follow the deposits are opened. In addition,
open-pit and underground mining are
sometimes applied concurrently, as in the
Quebec mines. In these cases, galleries or
shafts are initiated from the base of the pit,
the pit wall, or a mountain slope.
The transformation of asbestos deposits
into ores suitable for processing by an
asbestos mill involves any or all of the
following operations: (1) drilling to place
explosive charges, (2) primary and secondary
blasting, (3) surface scraping, (4) sorting, (5)
screening, (6) conveying, (7) shoveling, (8)
transporting by truck, and (9) dumping.
3.1.1 Emissions
Each of the processes associated with
asbestos mining that are listed above is a
potential source of asbestos emissions. Local
meteorological conditions can significantly
influence the degree of emission. For
example, rain, sleet, and snow are favorable
influences because they result in wetting or
covering exposed ore deposits in addition to
scavenging the atmosphere. Conversely, strong
winds that are capable of widely distributing
existing emissions, in addition to entraining
loosely bound asbestos fibers from material
exposed to the atmosphere by mining
operations, are an adverse influence.
Furthermore, the natural phenomena of earth
movement, temperature cycling, wind
erosion, and water erosion present
3-1
-------
opportunities for the emission of asbestos
from virgin surface-ore deposits.
In those surface mining operations that
require blasting, the use of rotary or
percussion drilling machines that incorporate
air-flushing is a potential source of
appreciable amounts of dust emissions.2
Air-flushing refers to the use of an air stream,
operated by pressure, vacuum, or
pressure and vacuum in combination, to cool
the drill bit and lift cuttings out of the hole
formed for placement of explosive charges.
Air travels down the hollow center of the drill
bit as the drill cuttings move upward along
the outside of the bit. Smaller dry suction
drills employ an injector to exhaust air from a
hood or cowl that encloses the drill bit at the
hole collar. Even in a wet-drilling process, in
which compressed air and water are injected
in the downward-flow mode, a portion of the
dust generated by drilling escapes without
being converted into sludge. Further, a
respirable aerosol of water droplets having
entrained drilling dust can be emitted.2
Detonation of explosive charges in the
open-pit mining of various minerals breaks up
massive deposits of asbestos-bearing rock, and
the blast can produce a cloud of dust that
may contain asbestos fibers. Similar emissions
can occur when secondary blasting is used to
reduce boulders to a size acceptable by the
mill or to dislodge large rock deposits in
open-cast mining.
In surface mining, the operations of
removing overburden, scraping and shoveling
of ore, preliminary screening of ore,
conveying of ore, loading of ore into trucks,
and the unloading of ore from trucks into
hoppers at the mill can generate emissions of
asbestos dust. Some ores have a high moisture
content (as much as 20 percent in Fresno and
San Benito counties), and, therefore,
emissions from processing these ores are less
than those encountered with dry ores. The
emission sources associated with underground
mining installations include sorting,
conveying, loading, and unloading operations,
which are performed outside the mines. The
exhaust of ventilation air from underground
mines to the atmosphere can also produce
emissions.3
The transit of ore-loaded trucks over
distances of perhaps hundreds of miles
between a mine and the processing mill
represents another potential emission source.
If the moisture content of ore hauled in
open-truck bodies or of the unsealed surface
of roads constructed of asbestos-containing
overburden or mill tailings is low, asbestos
dust can be entrained by the atmosphere as
the ore load is jostled and the road surface is
abraded.
3.1.2 Control Techniques
Overall emissions from asbestos mining
facilities are not stringently controlled at
present. The absence of a higher degree of
control is traceable to the fact that most
operations are completely exposed to the
atmosphere, with the result that emissions are
diluted with ambient air over relatively large
surface areas such as mining pits and roads.
Both dry centrifugal dust collectors and
fabric filters have been applied to allay the
dust generated during air-flushed drilling of
holes for explosive charges.2-4-5 It is well
known that the collection efficiency of fabric
filters, expressed on a total mass basis,
exceeds that of conventional cyclone
collectors.6 In Figure 3-1, the application of a
fabric filter of envelope type to a primary
percussion drilling machine employed in
asbestos mining is illustrated.4 Several treated
synthetic filter materials, such as Rayon*
acetate and Nylon* acetate treated with
silicate, have been shown to release dust
loadings readily during the cleaning cycle and
to dry quickly if accidentally wetted in use.
Air flow rates of several typical drilling
machines are shown in Table 3-1.4
The use of wet drilling methods to
control emissions has been excluded from
*Mention of a specific product or company name does
not constitute endorsement by the Environmental
Protection Agency.
3-2
-------
MATERIAL HANDLING FAN
< DRILL
"XCOMPRESSED AIR MOTOR ROD
C] \_^ 2.6 HP
'"" -CLEAN AIR
DUST
FILTER
CAPACITY:
l,500cfm
RIITTFRFI Y
VALVE 6 in. FLEXAUST
DUST HOOD-
L--RUBBERSEAL
iXIPENING FOR
DRILL ROD
ASPIRATION DUST HOOD
OPENING TO ALLOW
SMALL ROCKS
TO ESCAPE
Figure 3-1. Fabric filter mounted to drilling
machine.4
regulations. Other types of surface mining
operations have overcome prohibitively cold
weather by heating water on the drilling
machine and insulating the water storage tank
and all exposed piping.2 Even heated water,
however, can freeze after discharge from the
drill hole. Since primary drill holes are often
located within 10 feet of the edge of a bench,
which may range from 30 to 75 feet in height
in asbestos quarries, the presence of ice can
pose a serious occupational hazard. In warmer
climates, the tendency of the drill cuttings to
cement together as water seeps into asbestos
seams in the fractured rock is an operational
problem that limits the effectiveness of wet
drilling. In the case of wet drills smaller than
those used for primary drilling, the inclusion
of special design features, such as front-head
release ports for the venting of compressed air
or an external water feed mechanism, can
control the emission of unwetted dust or
respirable water-dust aerosols.
The atmospheric emissions that result
from primary and secondary blasting in
asbestos surface mining are essentially
uncontrolled at present.7 An optimum
combination of amount, depth, and location
of explosive charge should be sought that will
produce complete combustion of the
explosive compounds, along with the required
loosening and breaking of a deposit, without
unnecessary expulsion of material into the air.
Multi-delay devices for the initiation of
detonation have been used successfully at
limestone quarries,5 but incomplete
combustion of multi-delay charges, resulting
from the highly fractured nature of the ore,
has been observed at one domestic asbestos
mine. Detailed technical assistance in
implementing good blasting practice is
available from explosives manufacturers.6
some asbestos mining operations because of
extremely cold climates or restrictions
imposed by water pollution control
The spraying of water or chemical
wetting agents onto a surface prior to blasting
could reduce emissions. The application of a
3-3
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Table 3-1. AIR FLOW RATES OF
TYPICAL DRILLING MACHINES4
Type of machine
Percussion drill, air
Rotary drill, diesel
Rotary drill, electric
Secondary drill, diesel
Hole diameter,
in.
4
6%
63/4
Tk
Filter capacity,
ftS/min
1500
2000
3000
500
Fan drive
Air (90psi)
Hydraulic
Electric
Air (90psi)
pressurized water spray to asbestos mining
would not be novel; the cleaning of deposits
subsequent to the removal of overburden has
been accomplished by high-pressure water
sprays.8 The surface area of the blasted
fragments, however, is so large in comparison
with the surface area prior to blasting that the
effect of surface wetting alone is likely to be
minimal.
The use of liquid or paste stemming
materials in blasting holes is a promising dust
control method.2 In European coal mines,
reductions of 20 to 80 percent in dust
concentrations have resulted from placing
plastic cartridges filled with water, or water in
combination with a wetting agent, into holes
betore blasting. This technique has also been
tested in copper mining operations.2 As an
alternative to the use of liquid-containing
cartridges, pastes with a cellulose or bentonite
base can be employed.2 Container materials
and wetting agents that would not interfere
with the required purity of the milled
asbestos should be developed.
Effective primary blasting minimizes the
need for secondary blasting and is, therefore,
an indirect method of controlling emissions
from secondary blasting. The use of drop-ball
cranes and pneumatic or hydraulic rock
splitters as substitutes for secondary blasting
has proved to be effective in controlling
emissions from limestone quarrying ,5
however, the extent to which the elasticity of
asbestos-bearing rock might limit the
effectiveness of drop-ball cranes for secondary
fragmentation has not been fully evaluated.
The removal of overburden from ore
deposits, shoveling of loosened ore, surface
scraping of ore, preliminary screening and
conveying of ore at the mine, and loading of
ore into trucks produce asbestos emissions
that are substantially uncontrolled at present.
These operations, as well as primary and
secondary blasting, should be scheduled to
coincide to the maximum extent practicable
with meteorological conditions favorable to
the suppression of atmospheric emissions. In
particular, cognizance should be taken of
seasonal variations in weather conditions. The
limiting of operations to periods of favorable
weather conditions may occasionally be
impractical because of the large amount of
equipment involved and because of safety
precautions requiring that blasting be carried
out on the same day that the charge is loaded.
The application of water or chemical sprays
can alleviate emissions from ore loading in
some cases. Limiting factors are the possible
freezing of the water or the introduction of
chemicals that would interfere with the end
use of the asbestos.
The atmospheric entrainment of asbestos
dust emitted from loads of ore in transit from
mine to processing mill can be controlled by
transporting the ore in a closed-body vehicle
or by fitting a flexible, impervious cover over
the exposed ore load. Where roadways
connecting mine and mill have been surfaced
with asbestos mill tailings, emissions can be
reduced by periodic spraying of the roadways
by water trucks.4 Care must be taken,
however, to ensure that hazardous driving
3-4
-------
conditions are not created. Tests have shown
that tiie application of lignin sulfonate to
roadways at mining facilities reduces
markedly the emission of dust caused by
vehicular traffic;9 a solution of 10 to 25
percent solid lignin in water has given the best
results. More recently, the application of
emulsified asphalt to roads servicing open-pit
mines has provided even greater emission
reduction than the use of lignin sulfonate.10
In the planning of mining and milling
operations, the possibility should be
examined of reducing roadway emissions
through minimizing the number of
vehicle-miles by using trucks of maximum
practicable capacity and by reducing the
distances between mines and mills. The
operating speed of vehicles is an important
parameter that can affect emissions from
un paved roadways.
Asbestos emissions that result from the
dumping of ore from trucks at the mill site
can be abated by the use of water sprays or
by the application of capture hoods or
enclosures combined with gas-cleaning
devices. Some domestic mills currently use
partial enclosure and water spraying
techniques.
Attempts have been made to stabilize
mine overburden dumps where the waste
rock, sand, and clays of hard-rock asbestos
deposits are chemically neutral.4 These
efforts have been successful to the extent that
grasses and trees have been established over
the surface of some waste dumps. Most areas
exposed by open-pit mining, other than steep
slopes, can probably be revegetatcd.
3.2 MILLING OF ASBESTOS ORES
Separation of asbestos fibers from
accompanying masses of rock typically is
initiated by conveying mine ore, via a large
hopper and pan feeder, to a primary crusher.8
In some instances, larger bodies of crude
asbestos fibers, freed from massive rock
deposits, are removed by hand sorting at the
mine. In typical commercial practice, a
primary, jaw-type crusher then accepts
boulders of up to 48 inches in "diameter" and
reduces these to fragments with "diameters"
not larger than 6 inches. Subsequently, this
crushed rock is transported by belt conveyor
to trommel screens, which are rotating
cylinders with openings of various sizes, or to
a stationary-bar grizzly, a type of screen, for
the sizing operation. Ore fragments of greater
than 1-1/4-inch "diameter" are routed to a
secondary cone-type crusher for further
reduction in size, and the outputs of primary
and secondary crushers are conveyed to a
wet-ore storage pile exterior to the mill. This
stockpile usually contains a sufficient
quantity of ore to sustain mill operation for
an extended period of time. The above
sequence of operations is illustrated in Figure
3-2.
WET ROCK
(MAXIMUM 48 in. DIAMETER)
PRIMARY CRUSHING STAGE
(JAW CRUSHER TO MAXIMUM 6 in. DIAMETER)
SCREENING
(PASSAGE OF MAXIMUM 1-1/4 in. DIAMETER)
(OVERSIZE)
(UNDERSIZE)
SECONDARY CRUSHER STAGE
(CONE CRUSHER TO
MAXIMUM 1-5/16 in. DIAMETER
WET-ORE STOCKPILE
Figure 3-2. Crushing of massive asbestos
ore.
3-5
-------
The C'oalinga deposit of asbestos ore in
California presents an exception to the above
practices in that no primary crushing is
carried out prior to drying of the ore.
Typically, trucks dump mine ore adjacent to a
mill to form a wet-ore stockpile, which is
exposed to the atmosphere.
In larger milling operations, wet ore is
extracted from the bottom of the wet-ore
stockpile by a vibrating-chute feeder located
in an underground tunnel. As indicated in
Figure 3-3, which illustrates a specific facility
in operation, the larger fragments of the ore
being conveyed upward to a stationary-rod
screen can be routed to bypass the dryers if
the moisture content of the fragments is
sufficiently low. The wet ore enters
cylindrical dryers that slowly rotate 10 permit
baffles internal to the dryers to pick up and
release the wet ore continually and thereby
thoroughly expose it to a drying current of
hot air. This air, heated in a firebox at one
end of the dryers, is forced co-currently
through the dryers in the axial direction. Ore
is heated typically to 110°F, and a downward
inclination of about 4 degrees fixes the
residence time of the ore in the dryers at
approximately 15 minutes.8
As illustrated in Figure 3-3, the dried ore
is conveyed by belt to a vibrating screen that
sizes the ore for fine crushing. Ore of more
than 1-3/8 inches in "diameter" is sent to a
cone crusher connected in a closed circuit
with the screen, whereas the ore of particles
larger than 5/8 inch and smaller than 1-3/8
inch is diverted to cone crushers that produce
material of approximately 1/4-inch
"diameter." The undersized screenings and
the output of the latter crushers form a
dry-rock stockpile, which is housed so that it
is protected from the exterior environment.8
The finely crushed, dried asbestos ore
next traverses a rock circuit. The principal
purpose of this set of operations is to separate
asbestos fibers from the coexisting rock, but
the circuit secondarily functions to grade
fibers according to length. The oversized
material from the first vibrating screen shown
in Figure 3-3 passes to fiberizers that further
disintegrate the rock and release additional
fibers. Undersized material from this same
screen is routed to shaker screens of finer
mesh; these screens are equipped with air
suction (aspiration) hoods that facilitate the
entrapment of asbestos fibers in an air stream
and' thereby separate them from the
surrounding rock. This air flow conveys the
asbestos to fiber-cleaning circuits. The
continuation of the process is accompanied
by additional screenings, air aspiration to
remove freed asbestos fibers, and further rock
disintegration in an impact mill.8
In the rock circuit, cleaned rock is
finally expelled to an exterior tailings dump.
As the air streams that convey aspirated
asbestos fibers are passed through cyclone
collectors, the fibers are removed for cleaning
and for additional grading. Exhausts from
these collectors are ventilated to gas cleaning
devices. At this step of the process, the
asbestos fibers have been graded according to
long, medium, and short lengths.8
It is intended that the fiber-cleaning
circuits perform additional fiber opening,
classify and separate opened fibers from rock
and unopened material, and carry out further
fiber-length grading. Initially the fibers pass
through graders constructed of perforated
plates in which rotating beater arms further
open the material. Undersized fractions are
added to short fibers from the rock circuit,
and the oversized material undergoes
aspiration on shaker screens to transfer the
fiber to the grading circuit. Various other
stages of screening, aspirating, and opening
are involved in this circuit; in addition, some
material is rejected as waste. The aspirated
asbestos fibers are deposited into cyclone
collectors and subsequently delivered to the
grading circuit as long, medium, short, and
extra short fibers. As in the case of the rock
circuit, the exhausts of the cyclones are
directed to a gas-cleaning device.8
The separation of asbestos fibers into
numerous standard grades, in addition to
further fiber cleaning, is accomplished in the
3-6
-------
DRIED-ROCK
STORAGE
^ LEGEND
DRY £-§ <8) FIBERIZER | \ SCREENS
jOVERSIZE o.| OCONECRUSHER HHGRADER
§TUJ!J ©IMPACT MILL * ASPIRATOR
0=1-1 "" c^-\CYCLONE AIR-CONVEYED
X COLLECTOR FIBER
^p O BAGGING MACHINE
ONE OF DUPLICATE , ,
CIRCUITS^HONE OF DUPLICATE4- FIBER CLEANING AND BAGGING-
FIBER-CLEANING CIRCUITS
PAN-EXHAUST SETTLING CHAMBER
BAG-TYPE DUST FILTER
TO
WAREHOUSE
Figure 3-3. Flow sheet of an asbestos milling process.8
3-7
-------
grading circuit shown in Figure 3-3. Standard
grading machines effect additional opening of
fibers and facilitate the removal of shorter
fibers. The process of air aspiration from
vibrating screens separates out additional fine
dust, fine rock fragments, and unopened
fibers. To control asbestos-containing dusts,
the cyclone collectors are exhausted through
fabric filters.
Asbestos fibers are machine packaged
either by compressing the material into a
dense bundle or by blowing the material into
a container. The longest fiber grades are
loosely packed to minimize damage to the
fibers and to eliminate the subsequent
necessity for excessive willowing of
compressed material. Valved, multi-ply paper
bags are commonly used to package the
shortest fibers.8
One domestic asbestos mill, which
processes short-fiber Coalinga ore, employs a
wet process.11 An ore-water mixture is
carried through a proprietary grinding and
separating process to mill the asbestos almost
entirely into fibrils; a subsequent dewatering
operation produces pellets of asbestos fibers.
The cylindrical pellets measure approximately
3/8 inch in diameter by as much as 3/4 inch
in length and are formed and subsequently
dried without a binder. Some of the asbestos
is marketed in pellet form to end users. If a
completely opened form of asbestos is needed
for a manufacturing process, the dry pellets
can be ground either at the mill or by the end
user.
3.2.1 Emissions
The milling of asbestos ore by a dry
process requires an extensive amount of
handling and subdividing of the material in
both a damp and a dry state. Consequently,
there are numerous potential sources of
asbestos emissions at a milling facility.
The dumping of mine ore from trucks
onto a wet-ore stockpile or into receiving
hoppers is a potential emission source at the
mill site (previously noted in Section 3.1.2).
Further, asbestos-containing dust at the
surface of an ore pile is susceptible to varying
degrees of atmospheric entrainment,
depending upon the moisture content of the
ore and the strength of local winds.
The separating, cleaning, and grading of
asbestos fibers requires large volumes of air,
which are ventilated through fabric filters
before being exhausted to the atmosphere or
re circulated to mill buildings. Because
makeup air is drawn in to replace the
exhausted air, process areas of a mill are
frequently under negative pressure. When the
volume of air exhausted to the atmosphere is
sufficient for the entire mill to be under
negative pressure, emissions to the
atmosphere are reduced.
As asbestos ore, asbestos fibers, and
asbestos-containing tailings are transported
among the numerous processing devices of the
mill by belt conveyors, the jostling motion,
combined with the large surface area of
material exposed to the environment, can
produce significant asbestos emissions either
directly into the exterior atmosphere or into
the surrounding work space. Examples of
such emission sources are transportation of
material from a wet-ore stockpile to a dryer,
from a dryer to a grading screen, from one
vibrating air aspiration screen to another, and
from the undersized side of a vibrating air
aspiration screen to a tailings conveyor. The
potential for particularly severe emissions
exists whenever asbestos-containing materials
are handled at the transfer points of conveyor
systems.
The severe fracturing of rock by primary
and secondary crushers frees additional
asbestos fibers from the ores; the
accompanying mixing action of the crushers
facilitates the emission of asbestos-containing
dusts to the interior spaces of the equipment.
Because feed and discharge ports must be
provided for crushers, an opportunity exists
for the emission of asbestos to the exterior
environment.
A primary source of emissions from
asbestos mills is the effluent from ore
3-8
-------
dryers.4-12 The mechanical agitating action
of the dryer and the necessity for contacting
the ore with large volumes of air contribute to
the entrainment of asbestos-containing dust in
the heated gas stream. In addition to
contaminants from the ore, the dryer exhaust
contains a significant amount of moisture and
the products of combustion from the
air-heating device. The effluent temperature
varies widely and can range from 140°F to
500°F.<
The vibratory or oscillating motion of
grading screens and the resulting sifting action
of the screens as the asbestos-containing
material is separated into a range of sizes
expose large surface areas of material to the
surrounding air; the surface of a typical screen
measures 5 feet by 11 feet.8 Accordingly, this
process results in appreciable quantities of
airborne dust. If there are no provisions for
capturing and containing the dust, it is
emitted directly into the mill work space.
Even though the packaging of asbestos
fibers by machine minimizes handling and
exposure of the material to the atmosphere,
emissions can occur at the interface between
the material and the package during the filling
and sealing of containers. The packaging of
fibers into coarsely woven bags8 or otherwise
non-dust-tight containers can yield emissions
during further handling operations. The
potential emissions associated with those
operations, which range from packaging to
shipping of asbestos, are discussed in Section
3.3.1.
Large quantities of dry, finely divided
rock that contain asbestos dust must be
removed from most asbestos mills as waste
material. The transfer of this rock by a
moving-belt device or by vehicle to an
exposed tailings dump can generate emissions
to the atmosphere. Emissions can also result
from the placement of tailings'onto an exist-
ing dumps, from the leveling of the dump to
permit further deposition of wastes, and from
direct entrainment of surface dust by ambient
air currents.
3.2.2 Control Techniques
To control asbestos emissions from the
surface dusting of ore stockpiles, water can be
sprayed onto the material from adjacent
towers. This technique has also been
successfully applied in the control of
particulate emissions from exposed limestone
stockpiles.5-13 In a typical limestone
application, water is sprayed at a rate of 500
gallons per minute from towers 40 feet high;
the spray covers a circle 200 feet in radius.13
For asbestos applications, it may be necessary
to use the lowest feasible flow rates in order
to avoid the discharge of asbestos-containing
water from the facility and to comply with
applicable water pollution control regulations.
It is technically feasible to house
exterior belt and bucket conveyor systems in
completely enclosed galleries to prevent
asbestos emissions from material in transit
and from the emptied return side of the
systems. Furthermore, the attainment of safe
occupational asbestos exposure levels may
require the enclosure of in-plant conveyor
systems. The asbestos milling industry is
currently applying these control techniques to
a limited extent.4 Points at which asbestos
ore, asbestos fiber, and asbestos-containing
waste materials are transferred between
process equipment and conveyor systems, as
well as conveyor system transfer points, can
be hooded and ventilated to gas-cleaning
devices to control emissions.4 A schematic-
diagram of this technique, as applied to the
transport of asbestos ore from a crusher to a
storage bin, is shown in Figure 3-4.
The feed and discharge ports of ore
crushers can be fitted with dust capture hoods
to control asbestos emissions; the hoods
should be ventilated to a gas cleaning device
such as a fabric filter. Figure 3-5 illustrates a
device of this type, having an air flow
capacity of 3000 cubic feet per minute,
attached to the inlet of a 48-inch by 60-inch
jaw crusher.4 A hinged suspension permits
convenient displacement of the hood to
provide access in cleaning ore blockages from
the crusher.
3-9
-------
Figure 3-4. Control of emissions from transport
Reference 4)
Historically, cyclone collectors have
been applied more widely than any other type
of gas-cleaning device to control asbestos
emissions from ore dryers, largely because of
the relatively low initial cost, simplicity of
construction, and low maintenance cost of
these devices. Also, the dust collection
efficiency of cyclones is relatively insensitive
to variations in process gas temperature and
to the condensation of moisture within the
collector; however, the fact that the
efficiency of these dry centrifugal collectors is
considerably less than that attainable with
some other widely employed gas-cleaning
devices has prompted attempts to gain
incieased collection efficiency. For example,
one milling facility has employed 200
small-diameter cyclones, each with a capacity
of 100 cubic feet per minute, as a substitute
for a single cyclone of 20,000 cubic feet per
minute air-handling capacity.4 Partial
plugging of the small collector elements
occurred, possibly as a result of internal water
condensation, with the result that collection
efficiency was greatly decreased, rather than
increased. As a compromise between the
of ore. 4 (Conveyors not shown enclosed in
commonly applied 10-foot-diameter cyclones
and the potentially more efficient
small-diameter devices, twin cyclones 4 feet in
diameter were chosen, In recognition of the
relatively low efficiency of cyclones for the
collection of finer participates, the Canadian
asbestos industry is seeking control
techniques that exceed the performance of
dry centrifugal collectors.4
Wet collectors are presently employed
by the Canadian asbestos industry on at least
two ore-drying installations: the process gas
flow rates are 100,000 and 65,000 cubic feet
per minute.4 In these two collectors, the
particulate-laden gas stream passes through a
water spray and then enters into a centrifugal
fan that dynamically separates dust and
particulate water from the stream as air is
drawn through the blades; the
asbestos-containing particulates are removed
as a slurry. Corrosion resulting from sulfur
oxides present in the dryer effluent,4 and the
limited collection efficiencies of 85 to 95
percent are significant disadvantages of these
wet collection devices.
3-10
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PILLOW BLOCK
ROTATING BEARING-
-H-BEAIVI
FEEDER
SWIVEL BEARINGS
AND SHAFT
-TO BAG
'FILTER
AIR FOR
DUST CONTROL
(3000 ft3/min)
Figure 3-5. Dust capture hood fitted to ore crusher.4
In spite of low pressure loss and the
theoretically high collection efficiencies,
electrostatic precipitators are not widely
applied to the control of asbestos emissions
from ore dryers. This is a consequence of the
necessity for maintaining close control of gas
velocity, gas temperature, and particulate
moisture content in order to realize design
collection efficiency. An electrostatic
precipitator of 170,000 cubic-feet-per-minute
capacity is now in operation at a Canadian
asbestos mill.4
Fabric filters have been successfully
applied to the control of emissions from
asbestos ore dryers,4J2 and it is reported
that asbestos emission levels of approximately
2 x 106 particles per cubic foot (ppcf) have
been realized.4 Two new units were scheduled
to be placed into operation in Canada in
1971; Figure 3-6 shows an asbestos ore dryer
of the fluidized-bed type and accompanying
bag filter installation that are to be installed
at a Canadian mill in 1972.4 The filtering
chambers of these baghouses are thermally
insulated to prevent excessive cooling of the
effluent gas streams and the possible
condensation of water; the occurrence of
condensation could irreversibly cement
adhering dust cakes. Orion, Dacron, Nomex,
Teflon, Terylene, or Fiberglas, which can
withstand the high temperatures of the gas
streams, are required as filter materials.
Additional protection against excessively high
temperatures or condensation of moisture
during short time periods can be provided by
the use of by-pass arrangements. For effective
3-11
-------
STACK TO
ATMOSPHERE
TO ATMOSPHERE
ET
:NUM
_N
>" BAG FILTER
li
STORAGE
BIN
|/V\AA/WWV|
V
T-HHn
U L,r,J
INLET FAN
FIREBOX
JLJLJ
WET-ORE
FEED
DRY-ORE
DISCHARGE
NOTE:
BAG COLLECTOR
14 COMPARTMENTS, 50,000 cftn EACH
OPERATING TEMPERATURE RANGE 170°F TO 250°F
BAGS OF SPUN ACRYLIC CLOTH
t f
TO ATMOSPHER
i . i i
4
1
^ \
B
(
E
j1
i
AG FILT
3N BYP/
*
I
CQSjMSQ
«
BA
K
i/
L I
G FILTE
INO
]
*
\
R COMPJ
PERATI
:
*
ER
\SS
fBC^K
Y-
i\RTME
3N
\
a>4-
r-
*JT
DRYERS
3/4 in. MATERIAL DRIED FROM 10% TO 2% MOISTURE.
150 TONS/HOUR.
Figure 3-6. Configuration of fabric dust collector for ore dryer.4
3-1:
-------
control of asbestos emissions, engineering
design and operational procedures should
minimize the duration and number of periods
in which bypass devices are utilized.
Figure 3-7 provides relative comparisons
of asbestos-containing dust emissions from
ore dryers subsequent to cleaning of the
effluent stream by one of five control
devices.4 These calculated estimates of
emissions are based upon operating
experience of the Quebec asbestos milling
industry. The emission rates are based upon
an assumed value of 1 pound per hour for
fabric filter collectors.
Asbestos emissions from the bed of a
vibrating grading screen can be controlled by
covering the screen, with a dust capture hood,
as completely as practicable without
interfering with the required screen motion.
Figure 3-8 shows a group of enclosed screens;
the hood exhaust streams are passed through
a fabric filter to remove the entrained dust
after asbestos fiber has been deposited in
cyclone-type collectors. Quantitative tests of
a rotary, air-swept screen have shown that
refinements in dust shielding and ventilation
of the screen can reduce material emissions
from 36.9 pounds per day to less than 0.5
pounds per day; local dust counts were
diminished from 12 x 106 ppcf to less than 2
x 106 ppcf.4
Asbestos emissions that accompany the
bagging of fibers can be controlled by
installing high-volume, low-velocity
ventilation hoods (Section 3.3.2) over packing
operations. Further, low-volume,
high-velocity systems (Section 3.3.2) can,
during packaging, collect dust m the
immediate vicinity of bag-filling valves and on
bag support platforms. Control techniques
applicable to the handling of packaged
asbestos between the operations of bagging
and shipping from the mil! are discussed in
Section 3.3.2.
As one method of controlling emissions
when dry, asbestos-containing mill tailings are
placed on a relatively flat disposal pile, a
mobile dumper is used at the end of a belt
CYCLONE COLLECTOR
LEi
3.
MULTIPLE CYCLONES
WET COLLECTOR
4.
BAG FILTER
5.
7
COLLECTOR
ELECTROSTATIC
PRECIPITATOR
EMISSIONS,
Ib/hr
300
100
7
1
6
Figure 3-7. Dust emissions from ore dry-
ers. 4 (Emission based on an assumed
rate of 1 Ib/hr for bag filters.)
3-13
-------
Figure 3-8. Vibrating screens with
conveyor that transports the wastes. As
disposal proceeds, the location of the dumper
is periodically changed in order to maintain
the tailings pile as nearly level as possible and
thereby minimize emissions caused by shifting
the tailings with earth-moving equipment. An
inverted funnel mounted to the dumper
discharges the wastes in close proximity to
the surface of the dump in order to assist in
reducing emissions at the point of deposition;
however, the elimination of visible emissions
at the point of deposition may also require
that a water or chemical spray be used. In
other milling complexes, mixtures of water
and wetting agents have been applied to
tailings during their discharge onto waste
piles, and this has proved to be moderately
successful.4 Visible emissions generated by
hooding for dust control.14
the dumping of tailings have been totally
eliminated at one domestic asbestos mill by
the mixing of tailings with v/ater prior to
deposition. This control technique is
promising for mills that have access to
sufficient water and that can overcome the
problem of freezing conditions.
In some cases, asbestos mill tailings form
large mounds across which long belt conveyor
systems with several transfer points are
deployed. The transfer points can be enclosed
and ventilated to gas-cleaning devices to
provide emission control. Potential emissions
from segments of the conveyor system
between transfer points can be controlled by
enclosing the equipment.
Emissions from the surfaces of tailings
dumps can be controlled by providing a
3-14
-------
protective covering or seal. Because of the
large surface areas involved, most o! the
control methods are expensive. Wherever the
eventual surface of the dump is reasonably
level, soil can be spread as a sealing medium
The establishment of vegetation on dumps is
hindered by the liigh alkalinity (pH - 9) of
the tailings. In preliminary tests, grass h,>
been grown on tailings by first mixing then;
with the acidic tailings of a copper mine
across a soil depth of about 2 inches.4
Chemical agents that can be sprayed onto
waste dumps to form a protective surface
crust that is permeable to water are
commercially available. The penetration of
moisture through the crust controls nic
potential erosion and disintegration of the
cover by heavy rainfall. In some instances.
tailings piles from the milling of long-fiber
asbestos ores are somewhat self-stabiii/inp
because of tiie relatively low percentage '>f
very fine dust, the tendency of meteorologies
conditions to form a layer of larger particles
that protect the interior of the pile, and the
consolidation ot the pile by freezing during
long periods of the year,
3.2.3 Control Costs
Standardized conveyor housings that
cover the carrying runs of conveyor belts and
thereby shield exterior belts and the material
being transported from atmospheric
precipitation are commercially available. A
measure of emission control is also provided
by protecting the material from tiie winds.
These housings are typically in the form of
curved sections of corrugated sheet metal, one
side of which is hinged 10 the corn e\ or
system. This type of construction permits
each section of the belt housing to be lifted so
that access is provided to potential blockages
of the conveyor system. The additional
equipment cost of such housings, above that
for completely exposed conveyors, is
approximately $10 to $15 per lineal foot of
conveyor system, depending upon the width
of the conveyor belt.
dimcsp'-enc c.ir.s-,k.;;s than is possible \vith
conveyor h" at, in, ,;-.-; This can be arco-.iphshed
by >vro\idiiig iooi ,.iid sidewaii coven r.gs for
sia'T.Lirdized co.nnv-rci-'t . omevor \\siv -i> ...!
«aikr\ cv:ii^lriK''o;",. In tins type o! -.,--','",, ,
trusi , t ' ' e -Vii1. . "> o>
aVs'um ;r .1 i-.'ijue.hL !i\j,siien uu : >v .!s,vi .!_..-,
aCIOs-> ',O' ,'. . f.^li1-:, ' h'J aduiJO!"!, I v } ' i! j ' .' .'!' '
COM" ot lui e^c'Osecl galkry section i;
approximate.')' '<"> lr^ pel hncu; :'or,i o!
con\',"yo" i!i i»cc:-;s oi tl" . cost <! a
cunespordmg fui'y exposed sy>,cni. A
s: 'in. lard open ->.:!l a^ueyor, 7 'in v, ,,:ku ay
a- nig one MUC , ,-, ,;r.ed a: ..-proxi' :>.*..}
S?00 ner lii'.oo! i'o-'i.
CheiiiiC.i! coatir.gs iOi'iauu.K i> -.\ ;ni a ;:o.!-
!o\ic oipanit' hasi. J'~d ,'; npu.iVial!\
jvaiiabie, .:i::. br ^ iraycri t>;> .V',-..'!
material L-t.ij^;.],^ vi ,vjvic p:n. siiJi; a-.
asbestos nii:> toi-sng-, v'.umps, 10 :XT '.; : l!1.-.
entrainrntnt o, 'nau-i'-.i cy ar.ihicni -..ruN.
Temporal y ^.MuJ.gs ;:;.:1 P'tuvit'e pr^tei-i.oii
for 1 m.inrn rcvpiir :", on 17 to ! 7>! galluns
per JCR. ,) -,.!' luce area ai a materiai i.^,: o;"
4-', >,iilo'iN ,/er H.TO .r j :naur;:il t.v-,:
of i-480 to .\; ; ;(, p-,; iciv ;. a;C' d' ;v ..s.iiu
upo',1 the c,Lu.aiH' v>f i-vieiiU! ./.!>. ni:-; ,i . id
the pu, rtiL aljf ., o.ii'i"v fot iiiul ilio-ii tiiat ^
compan!;ie -A;!!: '\^ ,,,atmjjti ,>e encii.',t"ii.
The cost Oi ...jpii^a'c,,1., e-,tiiiiaiea if; lie V'/O
per acre ;~o - aj'i"il!v'tii:''iri. is j i MI.;K'; ian*
factor to !'.: v\.iiM.,'.;i\u n; ;iic u, uT:iiUUtii ir,
ot wnich ;v,x 01 c :aiij.'j to LU.I./ '.
3.3 MANUF\CTLR1 OF PRODUCTS
CONTAINING 4SBESTOS
3.3.1 Emission Sources in Manufacturing
Processes
Many potential asbestos emission sources
that are encountered during the manufacture
of numerous products have been identified.
3-15
-------
Specific examples of such potential sources
are:
1. Unloading of asbestos packaged in
containers.
2. Warehousing of asbestos packaged
in containers.
3. Transporting of asbestos to
bag-opening areas.
4. Opening and emptying of
containers of asbestos.
5. Unloading and in-plant transporting
of asbestos by pneumatic conveyor
systems.
6. Willowing (fluffing) of asbestos
fibers.
7. Blending and mixing of asbestos
fibers.
8. Conveying of dry asbestos-contain-
ing materials.
9. Handling of products that bear
surface deposits of asbestos dust.
10. Dispersing asbestos dust from
workers' clothing.
Packaged asbestos is commonly
unloaded from railway boxcars and trucks.
Bags, either loosely filled or pressure packed,
are attached to pallets by means of tensioned
steel bands when large shipments are involved;
tork-lift trucks elevate and transport the
loaded pallets. In smaller lots, bags are
manually handled on an individual basis.
When exposed to the atmosphere, fugitive
asbestos dust in railway cars and truck bodies
and on the exterior of containers can be
entrained. The leakage of asbestos-containing
material from new or existing punctures in
containing bags, in addition to that from bags
that are not impervious to asbestos fibers or
that are originally sealed in a non-dust-tight
manner, can also result in atmospheric
entrainment of asbestos. The extent to which
the unloading operation is systemized helps
determine how often spillage of asbestos
fibers occurs.
The storage of containers of asbestos in
close proximity to work areas or
transportation aisles increases the possibility
of packages being ruptured. Even with
cautious, systematic procedures, bags of
asbestos can be weakened and occasionally
broken open during handling. If spilled
asbestos is not promptly removed from the
floors of storage areas, the fibers can be
spread and emitted from the wheels of
vehicles and from workers' clothing.
Potential emission sources that
accompany the transport of bags of asbestos
from storage areas to sites for bag opening are
similar to those discussed above for the
unloading of packaged asbestos. Emissions to
the work space resulting from the accidental
puncturing of containers and the airborne
entrainment of asbestos dust deposited on
packages, pallets, and transporting vehicles
can be appreciable.
Asbestos bags are usually opened
manually, either with a knife or by impacting
them against a stationary blade. Such opening
operations and the subsequent dumping of
the contents onto a conveyor system or into a
loading hopper can emit excessive amounts of
asbestos dust if the operator fails to observe
appropriate emptying procedures and if the
working area is not properly ventilated
through a collection hood. The surfaces of
emptied containers carry loosely bound
asbestos that can become entrained.
Certain short-fiber types of asbestos can
be pelletized, transported in bulk quantities,
and subsequently unloaded, warehoused, and
transferred in-plant at manufacturing facilities
by the use of pneumatic conveying
systems.16 Pneumatic railway hopper cars or
pneumatic motor vehicle bulk trailers can be
loaded at an asbestos mill site and sealed for
transport to manufacturing plants that accept
this pelletized form of asbestos. For example,
railway containers of 60-ton capacity and
motor vehicle containers of 20-ton capacity
are available. For transfer of the asbestos
from a shipping car to a user's intermediate or
primary storage bin, a sealed pneumatic
conveyor system produces a suction on the
loaded car to assist in removing the material.
3-16
-------
Gravity hoppers permit unloading to be
accomplished without the use of
pressure-differential cars or fluidized-hopper
cars. The entrained asbestos pellets are
subsequently separated from the conveying
air stream by a cyclone-type product
collector. Unloading rates of up to 10 tons
per hour have been demonstrated for a
conveyor conduit 4 inches in diameter. From
the product collector, the asbestos can be
pneumatically conveyed in a compressed air
stream to an intermediate or primary storage
bin. The use of either a live bottom or a
fluidized hopper on the primary storage bin
facilitates the eventual continuous, metered
transfer of the asbestos to process operations.
The handling of pelletized asbestos
results in the freeing of some asbestos fibers
and fibrils from the pellets. Consequently,
exhausts of conveying air streams from the
cyclone product collectors and storage bins
cited above are potential sources of
atmospheric asbestos emissions. If the air
stream exhausted from a product cyclone
collector contains an excessive quantity of
dust, the protection of the blower that
produces suction on the collector requires,
independent of air pollution control, that the
air be filtered prior to introduction into the
blower.
Attempts to reduce emissions from the
handling of bags of asbestos have resulted in
the increased use of pressure packing. In
pressure packing, the asbestos is pressed into a
hard, consolidated mass. As a result, the fiber
is less likely to leak from the bag, and that
which does leak is less likely to become
airborne. Several mills pressure pack all fibers
except when the order calls for loose-packed
fibers.
The longer grades of fully opened
asbestos fibers that have been pressure packed
are given a willowing or fluffing treatment to
reopen the material before further processing
is initiated. The severe agitation used to open
the fibers produces a strong concentration of
dust within the processing equipment;
potential emissions are subject to control.
Examples of opening machines are willows,
vertical openers, carding willows, beating
openers, and beating mills.1 The practice of
manually charging and unloading some of this
equipment can yield appreciable asbestos
emissions to the work space.
Blending and mixing processes that
employ dry asbestos involve the mechanical
agitation of the fibers in the presence of air.
Consequently, these processes are potential
sources of asbestos emissions. Specific
examples of this type of operation are the
blending of synthetic fibers with long asbestos
fibers for textile applications, the mixing of
silica and asbestos in the manufacture of
asbestos-cement pipe, and the mixing of
asbestos and bonding resins into formulations
for brake and clutch linings. The mixing of
the respective ingredients is carried out in a
wide variety of equipment, ranging from
rotating blending drums to mixing or carding
willows.
When materials that contain asbestos in a
dry, loosely bound state are transported on
open conveyor belts, asbestos fibers can be
released into the adjacent work space. The
jostling motion induced by the conveyor
system and the exposure of a large surface
area of material to the surrounding
atmosphere are conducive to emissions.
Examples of this type of emission source are
the transport of asbestos fibers between pairs
of textile carding machines and the
conveyance of automatically weighed
mixtures of synthetic and asbestos textile
fibers to a blending machine. More severe
mixing occurs at belt conveyor transfer points
and can produce appreciable emissions.
If asbestos-containing dust deposits
borne on the surfaces of manufactured
articles are not promptly removed, emissions
during subsequent liandling and processing
steps can result. Ultimately, these potential
asbestos emissions can even carry over to end
uses of the products. Dusts formed by the
machining of the ends of asbestos-cement
pipe to size and by the grinding of asbestos
3-17
-------
friction products arc potential emissions of
this type.
Asbestos collected on workers' clothing
from exposure to manufacturing processes
can be carried outside the plant and emitted
into the atmosphere. If emissions from the
various processing activities within the
manufacturing facility are well controlled, the
deposition of asbestos on clothing is
minimized.
3.3.2 Control Techniques for Manufacturing
Processes
As previously indicated, the handling of
uncontained masses of asbestos fiber and the
sawing, drilling, cutting, and trimming of
materials that contain asbestos can produce
significant quantities of airborne asbestos
dust. When the general ventilation air of a
plant has been contaminated by the emission
of asbestos into the work space, potential
atmospheric emissions from the discharge of
this air to the exterior of the plant can be
controlled by maintaining the work space at a
slight negative pressure and by treating the
exhaust air in a gas-cleaning device. As a
preferable alternative to this approach,
industry commonly employs an
arrest-at-the-source method for collecting this
particulate material. An air ventilation system
comprised of local dust capture hoods,
interconnecting ductwork, fans for air
movement (usually on the clean-air side of the
collector), and a gas-cleaning device for
separating asbestos fibers and dust from the
air stream, is used (see Figure 3-9). Some of
the benefits of this system are:
1. Reduced atmospheric emissions
when a plant at atmospheric
pressure is exposed to ambient
conditions, as when doors and
windows are open.
DUCTWORK
COLLECTOR!
COLLECTED DUST
DISCHARGE
FAN
/LA
Figure 3-9. Air ventilation system with local dust capture hood.1
3-18
-------
2. Reduced atmospheric emissions
resulting from fibers transported
outside of a plant on workers'
clothing and on manufactured
products.
3. Reduction in amount of plant
housekeeping, such as vacuuming of
deposited asbestos-laden dust,
required for the control of
atmospheric emissions.
Two types of ventilation systems are in
use, the low-volume, high-velocity design and
the high-volume, low-velocity design. In the
former case, the velocity of the dust-capturing
air stream is relatively large; velocities of
10,000 to 12,000 feet per minute and flow
rates of 10 to 250 cubic feet per minute are
common.17 If the hood or nozzle is placed
close to the point at which particulate
emissions are generated, most of the material
is captured, the air (low rate required for a
specified degree of capture is reduced, and
heavier particles or fibers can be entrained
than would otherwise be possible at the same
air flow rate. This technique has been
successfully applied to the control of
emissions from portable power tools and
machine tools; Figure 3-10 shows a
low-volume, high-velocity system fitted to a
radial-arm bench saw. The dust and chips
produced during sawing are directed by the
saw toward the middle nozzle of the
ventilation system; the top nozzle assists in
removing material from the blade; and the
remaining nozzle removes material from the
bench. Figure 3-11 illustrates a second
application of the system, a partially enclosed
lathe for macluning asbestos-cement products.
The hood is opened for mounting work in the
lathe and closed during the turning operation.
A high-velocity air stream captures the
products of machining. By contrast,
high-volume, low-velocity air ventilation
Figure 3-10. Dust capture hoods fitted to radial-arm saw.
3-19
-------
Figure 3-11. Dust capture hood fitted to lathe.
systems are applied to operations in which
closely localized capture of particulates
containing asbestos is not feasible. These
require that an air flow of a velocity of at
least 150 feet per minute be induced toward
the collection hood.17 Representative
examples include ventilation systems for
asbestos bag-opening stations, fiber mixing
areas, and asbestos textile cards and looms.
Figure 3-12 indicates the configuration of a
bag opening and conveying station that is
fitted with a dust collecting hood.
A considerable amount of ductwork is
required to interconnect the numerous dust
capture hoods of a large plant to a central
gas-cleaning device such as a baghouse.
Circular ducts with a minimum of sharp bends
are recommended. To provide for inspection
and for the removal of possible accumulated
dust from the ducts, access doors should be
installed near bends and at appropriate
intervals along straight sections of ducting.17
The preferred location of the air
handling fan for the ventilating system is at
the exhaust, rather than at the intake, side of
the gas-cleaning device. This places the entire
ducting and gas-cleaning system under
negative pressure and thereby draws ambient
air inward through structural leaks instead of
forcing dust-laden air outward.
Methods for controlling dust emissions
from belt conveyor systems are illustrated in
Figures 3-13 through 3-15.18 Figure 3-13
shows a hooding arrangement for the transfer
of material from a belt conveyor to a hopper.
Geometrical configurations and design
parameters for the enclosure and ventilation
of three types of conveyor transfer points are
included in Figure 3-14 and Table 3-2. A
method for removing dry dust from the
return side of a belt conveyor is shown in
Figure 3-15.
Bags for asbestos fiber should be
fabricated of dust-tight materials, be sealed
3-20
-------
-EXHAUST TO BAG FILTER
HOOD OVER BAG-OPENING
STATION
MRAY FOR FIBERS
ENCLOSED AND VENTILATED
CONVEYOR TO WILLOW
Figure 3-12. Bag opening and convey-
ing stationwith dust collecting hood.
Figure 3-13. Examples of good and bad
hood configurations for controlling asbes-
tos-laden dust emissions from receiving
hoppers. A completely enclosed source
requires less air for control.18
dust-tight (e.g., end folded before sewn or
stapled), and meet certain strength
requirements in order to control emissions.
Where possible, bags should be placed on
pallets for handling by fork-lift vehicles
during shipping and storage operations to
minimize the handling of individual bags.
Spilled asbestos fiber that is being
handled, stored, or transported in
manufacturing plants should be promptly
removed by vacuuming or by wet sweeping.
Emissions from punctured or ruptured bags
can be controlled by repairing bags with
masking tape or by placing slipover covers on
badly damaged bags, [emissions that result
from the manual opening and dumping of
bags of asbestos can be collected at the source
by a dust capture hood.
The bulk handling of short-fiber asbestos
in pellet form is in some instances a means of
controlling those emissions that might be
generated during the transporting, unloading,
warehousing, in-plant transferring, and
emptying of asbestos contained in bags. The
number of potential emission sources
associated with vhe handling of bags can be
reduced; the primary potential source of
emissions in bulk handling is the
asbestos-containing exhaust streams from
pneumatic conveying systems that transport
the pelletized asbestos. Pneumatic
transporting of pelletized asbestos in bulk
quantities is not limited to those processes
that can accept pellets directly; where
necessary, devices such as impact mills can be
incorporated into the handling operation to
grind the pellets into an opened configuration
prior to introduction into the manufacturing
process. Economic and technological
considerations, however, limit the use of bulk
handling as a control technique to those
manufacturing facilities that consume large
quantities of asbestos. Pelletizing is presently
limited to short-fiber asbestos because of
difficulties in briquettmg the long-fiber
asbestos and in sufficiently opening the long
fibers after they are pelletized.
Exhaust streams from pneumatic
conveying systems that carry pelletized
asbestos can be cleaned by means of
conventional fabric filters. Pneumatic
conveying systems with integrated fabric
air-cleaning devices are commercially
available.
3-21
-------
24 in. min
CLOSE FACE TO
BOTTOM OF BELT
1. CONVEYOR TRANSFER
LESS THAN 3 ft. FALL
2 X BELT WIDTH-*-
Js
* .-»- *
Q
1/3 BELT
WIDTH
c
45°
y-
» i
24 in. min 1
* ;
C )
J j XV
MINIMIZE
TOTE BOX
[ 1
\
\
-^ ^
ELEVATOR
EXHAUST
2. CONVEYOR TO ELEVATOR TRANSFER
MU
in. mm
RUBBER SKIRT
3 CHUTE TO BELT TRANSFER AND CONVEYOR TRANSFER, GREAT-
ER THAN 3 ft FALL
NOTE: FOR DUSTY MATERIALS USE ADDITIONAL EXHAUST AT A
AS FOLLOWS: BELT WIDTH 12 in,, to 36 in.;Q = 700 cfm
>36 in.; Q = 1000 cfm
P'coooQcf 2 in. CLEARANCE FOR
LOAD ON BELT
4. DETAIL OF BELT OPENING
Figure 3-14. System for controlling emissions at conveyor transfer points.18
3.3.3 Asbestos-Cement Products
The largest single domestic use of
asbestos fibers occurs in the manufacture of
asbestos-cement products. These products
contain 15 to 30 percent by weigiit of
asbestos, usually of the chrysotile variety.
Crocidolite is used to a limited extent.
whereas use of amosite is limited because of
its low tensile strength. The largest sector of
the asbestos-cement industry is that which
produces asbestos-cement pipe. Typical
applications of the pipe, in sizes ranging from
3 to 48 inches in diameter, involve
conveyance of the following materials'
1. Potable, drainage, and irrigation
water.
2. Sewage.
3. Industrial products.
4. Air and other gaseous substances
for heating, cooling, and gas
venting.
Other asbestos-cement products, such as
siding shingles and flat or corrugated sheets,
are used in a variety of applications.
The interwoven structure formed by the
asbestos fibers in asbestos-cement products
functions as a reinforcing medium by
imparting increased tensile strength to the
product. As a result, there is a 70 to 80
percent decrease in ttie weight of the product
required to attain a given structural
strength.19 It is important that the asbestos
be embedded in the product in a completely
3-22
-------
SLOT AGAINST BELT
UNDERSIDE OF BELT
BELT TRAVEL
1 NOTE:
Q = 200 cfm ft OF BELT WIDTH
SLOT VELOCITY = 2000 fpm
DUCT VELOCITY = 4000 fpm MINIMUM
Figure 3-15. System for removing dust from
return side of dry belt conveyor.18
fiberized (willowcd) form. The necessary fiber
conditioning is frequently executed prior to
dry or wet mixing of the fiber with Portland
cement and finely ground silica; however, in
some cases, this fiber opening is accomplished
as the wet mixture is agitated by a pulp
beater, or Hollander.
Asbestos-cement products are
manufactured by the molding process, dry
process, wet process, or wet mechanical
process; extrusion processes are not widely
employed.19 Articles of irregular shape are
formed by the molding process, which
accounts for a quite limited production
volume. In the dry process, which is not
utilized extensively but is suited to the
manufacture of siding shingles and other sheet
products, a uniform thickness of the mixture
of dry materials is distributed onto a
conveyor belt, sprayed with water, and then
compressed against rolls to the desired
thickness and density. Rotary cutters divide
the moving sheet into shingles or sheets,
which are subsequently removed from the
conveyor for curing. The wet process
produces dense, flat or corrugated, sheets of
asbestos-cement material by introducing a
slurry into a mold chamber and then
compressing the mixture to force out the
excess water. Then, a setting and hardening
period of 24 to 48 hours precedes the curing
operation. The wet mechanical process, as it is
applied to the manufacture of
asbestos-cement pipe, is illustrated in Figure
3-16; the equipment is similar in principle to
some paper manufacturing machines. In
Figure 3-16, the asbestos fiber that has been
fluffed and separated by a willow is
transferred to a production line bin, weighed
and mixed with silica and cement, conveyed
by a water stream to a wet mix vat, formed
Table 3-2. CONVEYOR EMISSION CONTROL DESIGN DATA3'18
Item
Indraft at all openings
Air capacity transfer points
For belt speed less than 200 fpm
For belt speed greater than 200 fpm
For magnetic separators
Belt length between transfer points
(30 foot intervals)
Duct velocity
Entry loss
Minimum value
150 to 200 fpm
350 cfm/ft belt width
500 cfm/ft belt width
500 cfm/ft belt width
"35CTcfm/ft belt width
3,500 fpm
0.25 velocity pressure
Good design requires enclosure or covering where practicable.
3-23
-------
0'
c
I
c
LLJ tt!
1 §i
S "Si
I- cc i
o? o ffi
I O CJ 5 00 L_ __
^z5§^! p._Js>:i
o * ! LU to
00
s
EC
O
O O
O
X oo ^
O O S-
O3 D- .
a
o
O = > = 2 L_ . .
LU>-ZI Q-OIZ
-JCCOLUo^tLUcE
LUQO*«^>LL.S
c^J oo ^ uo co r^- oo o^
o
U
c
0
-C
o
o
U
0)
a.
c
0)
01
o
Q)
_a
w
CO
"o
CD
o
CO
CO
E
1
LL
CD
I
CO
3-24
-------
into a homogeneous slurry, and delivered to
cylinder vats for deposition onto one or more
horizontal screen cylinder molds.
Gravity-dried of excess water tlirough the fine
wire mesh screen that forms the
circumferential surface of each mold, the
asbestos forms a layer of asbestos-cement
material, 0.02 to 0.10 inch thick.19 The layer
from each mold is transferred to an endless
felt conveyor in order to build up a single
sheet for further processing. The sheet is
further dried in a vacuum box and transferred
to a mandrel, or accumulator roll, which
winds the sheet into pipestock of the desired
thickness. The pipe section wrapped around
the mandrel is removed from the machine and
then freed from the mandrel by an
electrolytic loosener. Precure time is provided
by a slow-down conveyor before the mandrel
is removed and the pipe is stenciled for
identification. The pipe is transported to a
temperature- and humidity-controlled air-cure
room before entering the autoclaves where
high-pressure steam curing imparts maximum
strength and chemical stability. The pipe
sections are machined to size on lathes,
tested, and transferred to the shipping area.
In the manufacture of products other
than asbestos-cement pipe by the wet
mechanical process, the layer of
asbestos-cement material on the accumulator
roll is periodically cut across the roll and
peeled away to form a sheet. The sheet is
passed through a pair of press rolls to shape
the surface and cut the sheet into shingles, is
formed into corrugated sheet, or is placed on
a flat surface for curing as a Hat sheet.
Asbestos-cement products are
strengthened by one of three curing
procedures: wet curing, atmospheric steam
curing, and autoclave curing. The oldest
procedure, wet curing, is carried out in a
warm, humid atmosphere for 21 to 28 days.
Subsequent storage under water for 7 days,
frequently performed in the wet curing of
asbestos-cement pipe, produces additional
strength. Atmospheric steam curing is a form
of wet curing in which steam at atmospheric
pressure is used to accelerate the wet curing
process. In autoclave curing, pressurized
steam (100 to 250 pounds per square inch) is
used to accelerate the process and initiate the
chemical reactions that harden the product.19
3.3.3.1 Emissions
Significant amounts of asbestos can be
emitted throughout manufacturing processes
in which asbestos is not thoroughly wetted to
form a slurry. The major sources of potential
asbestos emissions during the manufacture of
asbestos-cement products by the wet
mechanical process are associated with
operations that precede the inclusion of
asbestos in a wet processing mixture and with
those carried out to size the cured products.
Wastes dispersed in a wet condition to the
vicinity of processing machinery can become
secondary emission sources if not removed
prior to drying. The possible generation of
asbestos-containing emissions when bags of
asbestos are opened and when the fiber is
dumped into a blender, blended, willowed,
transferred to raw material storage bins, and
dry mixed is discussed in Section 3.3.1.
Large quantities of dry,
asbestos-containing dust are produced when
the ends of cured pipe sections are machined
to ensure proper mating with connectors.
Some characteristics of emissions from
finishing operations, as well as from mixing
operations, of asbestos-cement pipe
manufacture are included in Section 2.4. The
manufacture of those asbestos-cement
products, such as sheets and siding shingles,
that do not require precise sizing by dry
machining does not present such severe
emission problems.
3.3.3.2 Control Techniques
Potential emissions from those processes
beginning with the opening of bags of
asbestos and terminating with the inclusion of
the fibers in a wet slurry can be controlled by
the application of local dust capture hoods as
3-25
-------
described in Section 3.3.2. The collection of
the entrained asbestos-containing dust by a
fabric filtering device can control emissions to
the atmosphere. Also, asbestos fibers have
been conveyed pneumatically from a willow
to production line feed bins; this method, in
conjunction with a gas-cleaning device for the
conveying air stream, can control emissions
that would otherwise accompany the
transport of dry, loosely bound material on
an open conveyor system.20
Dust capture hoods, vented to fabric
illters, can be used also to control emissions
from the machining of pipe ends at the
finishing end of the process.
3.3.4 Vinyl-Asbestos Tile
Vinyl-asbestos floor tile, which contains
between 18 and 25 percent asbestos by
weight, is widely used in residences, schools,
public buildings, theaters, and exhibition
halls. Attractive features of this product are
non-combustibility, resistance to water and
dampness, and high strength. Polymers of
vinyl compounds are commonly employed as
the primary resins.
Various mixers, for example, those of
the Banbury type, are employed to knead the
plasticized resin binder, asbestos fibers,
ground limestone, and pigments into a heated
batch of base material. After the base material
has been decorated by adding granules of the
proper shapes and colors to the material as it
passes through a two-roll differential speed
mill, the relatively thick sheet is cut and
joined to a similar piece that has been
previously formed and is in the process of
being calendered (smoothed and reduced in
thickness between two revolving cylinders).
The sheet then traverses a two-roll calender
that reduces the sheet to a thickness slightly
greater than that of the finished tile; the
manufacturing process at this stage is
continuous, as opposed to batch. The passage
of the tile sheet through a second, and
sometimes a third, two-roll calender produces
tile of the desired thickness and surface finish.
Subsequently, a blanking press die cuts tiles
to final size before cooling and hardening of
the compound. Waste material is recycled to
the mixing operation for immediate
reworking.19
The flow sheet of a typical vinyl-asbestos
floor tile manufacturing operation is
illustrated in Figure 3-17.
3.3.4.1 Emissions
Because vinyl-asbestos floor tile is
processed as a mass of semisolid material,
emissions are limited primarily to those
generated by the operations of introducing
dry asbestos fibers into the formulation and
of mixing the asbestos with other dry granular
components of the mix. Semisolid wastes,
however, can also generate smaller quantities
of emissions if they are not removed from
work areas for disposal or recycling. Specific
potential emission sources include the
handling of packaged asbestos from receiving
location to bag-opening site, opening and
emptying of bags into raw material bins for
the process, dry mixing of the tile compound,
and discharge of the dry mixture into a
kneading apparatus for the base tile material
(see Figure 3-17). Emission sources of this
type are discussed in Section 3.3.1. The
crushing of waste materials prior to recycling
to the process can also generate asbestos
emissions.
3.3.4.2 Control Techniques
Dust capture hoods of the high-volume,
low-velocity type discussed in Section 3.3.2
can be employed to ventilate bag opening and
dumping areas, dry mixers, and equipment for
crushing scrap material in the manufacture of
vinyl-asbestos tile. The gas streams can be
subsequently cleaned by passing them
through fabric filtering devices before
exhausting the dust control air streams to the
atmosphere.
3-26
-------
HOOD
BROKEN
FRAME
STRAP
HOOD/
CHIP MOTHER
/ MHOOD
COOLING CHAMBER
oo
CALENDER ROLLS
TILES
\
\
PACKAGING
COOLING CHAMBER
Figure 3-17. Flow chart for the manufacture of vinyl-asbestos floor tile.
3-27
-------
3.3-5 Asbestos Paper
Asbestos paper, containing chrysotile as
the principal type of asbestos, has a wide
variety of uses; Table 3-3 indicates the extent
of these applications.21 Frequently, product
requirements dictate that other materials be
combined with the asbestos paper. For
example, asbestos paper is impregnated with
asphalt to form asbestos felt roofing and pipe
wrapping; in addition, the paper is sometimes
laminated into plastic molded articles to
provide reinforcement and thermal stability.
A primary user of asbestos paper is the
electrical equipment industry in which the
paper serves as a low-cost, thin spacing
material that possesses desirable electrical
insulating and heat resisting properties. This
industry requires paper produced from
specially processed asbestos fibers from which
the iron oxides have been removed.
Asbestos paper is manufactured on
machines of the Fourdrinier and cylinder
types that are similar to those that produce
cellulose paper. The cylinder machine is much
more widely employed.
The operation of a Fourdrinier paper
machine is shown in Figure 3-18.19 The
mixing operation combines short-fiber
asbestos with binders selected for the desired
Table 3-3. USES OF ASBESTOS PAPER
Air cell and other pipe coverings
Boiler jackets
Asbestos roofing felt
Asbestos-protected metal roofing
Gaskets (plain and metal reinforced)
Wicks in oil burning apparatus
Tubes for electrical insulation
Electrical insulation of wire and cable
Insulation for hot air pipes
Linings for stoves and heaters
Linings for filing cabinets, cartridges, carpets, auto
mufflers, drum controllers, cookers, electrical
appliances, armored car roofs, motors, etc.
Drip catchers in enameling ovens
Insulation for ovens and dry kilns
Table pads and mats
Insulation in heat- and chemical-resistant reinforced
plastic pipe and other laminated products
Diaphragms in electrolytic cells
Tank covers
Filters
Protection from heat in welding and other processes
Crumbled paper in annealing
Insulation in chemical and physics laboratories
Insulation for automobile exhausts
Clutch facings in automatic transmissions
Baking sheets
Hot-air ducts or linings of paper ducts for hot-air
service
Base for floor covering
Saturated paper for cooling tower fills
properties and application of the paper.
Typical binders are starch, glue, water glass,
CALENDER
ROLLS
REWIND REEL
DRYERS
(HEATED ROLLS)
Figure 3-18. Fourdrinier paper machine.19
TAKE-UP
REEL
3-28
-------
resins, latex, cement, and gypsum.1 A pulp
beater, or Hollander, mixes the asbestos,
binder, and water into a stock that typically
contains between 6 and 12 percent fiber.
After it exits from the stock chest, the stock
is diluted to as little as 1.5 percent fiber in the
discharge chest. From the discharge chest, a
thin, uniform layer of the stock is deposited
by gravity onto an endless, moving wire
screen through which a major portion of the
water is removed by suction boxes or rolls
adjacent to the sheet of paper. The sheet is
then transferred onto an endless, moving felt
and pressed between pairs of rolls to bring the
paper to approximately 60 percent dryness.19
Subsequently, the continuous sheet of paper
passes over heated rolls, while supported on a
second felt, to effect further drying. This is
followed by calendering of the paper to
produce a smooth surface and cutting the
paper to size as it is wound onto a spindle.
The operation of a cylinder paper
machine includes a mixing operation for
stock, as indicated for the Fourdrinier paper
machine. The stock is then delivered,
however, to a cylinder vat for deposition onto
a horizontal screen cylinder mold. The fine
wire screen that forms the circumferential
surface of each mold permits water to be
removed from the underside as a layer of
slurry is picked up by the mold. As the layer
of paper is transferred to an endless belt
conveyor, the paper is sandwiched between
two layers of felt and is then passed over
vacuum boxes in order to remove some of the
water. The subsequent press rolls, drying rolls,
and calender rolls are similar to those
described for the Fourdrinier machine.
Both types of paper manufacturing
incorporate the recycling of the
asbestos-containing water, or "white water,"
which is removed from the stock prior to
passage across the heated drying rolls. Little
asbestos is lost to waste.19
3.3.5.1 Emissions
In addition to the emissions that occur
during handling operations as asbestos is
brought to the preparation end of a paper
machine, there are potential emissions from
the mixing of ingredients in a pulping mill.
Since this mixture is next converted into a
thin slurry for further processing, the
potential for the subsequent emission of
asbestos into the work space is diminished
until the paper has been dried. Wet wastes
can, however, eventually generate emissions if
not removed for disposal. The slitting of
finished stock, 3 to 12 feet wide, by knives
while it is winding onto spindles can produce
asbestos dust.
3.3.5.2 Control Techniques
The control of asbestos emissions from
dumping of bags and from dry mixing is
accomplished by the use of high-volume,
low-velocity dust-capture hoods as described
in Section 3.3.2; passage to a fabric filtering
device provides control of potential
atmospheric emissions. Additional control can
be provided by the use of pulpable bags that
can be added to the mix (which obviates the
need to open the bags). Emissions from the
slitting process are subject to control at the
source by low-volume, high-velocity
dust-capturing devices as discussed in Section
3.3.2.
3.3.6 Friction Materials Containing Asbestos
Asbestos-containing friction materials
are used extensively in the fields of
transportation, mining, and heavy
construction. Specific applications are of
drum, disk, outer jaw, and band brakes and in
dry and oil-immersed clutches.
The various types of friction materials
can be classified according to structure and
method of fabrication. Molded brake linings
or clutch facings encompass all products that
are preformed under pressure in molds or
between rolls; materials included are friction
compounds, asbestos fibers, sulfur, zinc
oxide, litharge, rubber, and resins. Paper and
3-29
-------
millboard friction materials include plied
asbestos papers that are impregnated prior to
or subsequent to plying and asbestos papers
that are formed from pulp to which friction
compounds have been added.19 Woven linings
are constructed of resin-impregnated woven
asbestos fabrics that are hot pressed or
calendered and baked to form linings.19 The
classes of bonding materials are drying oils,
plastics, bitumens, and natural and synthetic
rubbers;1 they are used either separately or in
combination and either in the presence or in
the absence of solvents. Rubberized linings
are widely used except when high
temperatures are involved.19 The variety of
asbestos predominantly used in the
applications mentioned is chrysotile.19
Desirable characteristics of friction
materials are (1) the maintenance of a
constant coefficient of friction under varying
contact stress, moisture, and temperature in
combination with (2) minimum wear of the
friction material and corresponding bearing
surface. Although all common friction
materials become inoperative when immersed
in water, the materials are designed to shed
the water quickly and recover fully. Quality
control must be sufficient to ensure the
attainment of uniform properties so that
hazardous, unbalanced braking will not occur.
In addition, the structural integrity of the
friction material must be maintained at the
high temperatures inherent in braking and
transmitting energy.
In the manufacture of friction products,
many materials are used in varying
proportions in order to design the product for
a particular application. Since the exact roles
of many of these constituents are not known,
the products are designed on the basis of
results of operational tests. For example, the
addition of 1 percent of 600-mesh aluminum
oxide increases the frictional resistance by
approximately 15 percent.22 Most brake
linings are self-scavenging (i.e., self-cleaning of
congealed binder), but some require a
scavenger, such as 40-mesh brass chips.22
Ribbon blenders are frequently utilized
to mix the bonding agents, metallic
constituents, and asbestos fibers in the
production of molded linings by dry
processes. The major binder for dry processes
is a "b" stage resin that is thermoset when
fully cured, but is also intermediately set in
the partially cured condition.22 A uniform
layer of the material is heated sufficiently,
under pressure, to cause the resin to flow and
set but not be fully cured. The resulting flat
sheet is removed, cut into product-sized
segments, reheated to soften the resin, and
formed to the proper arc by cold molding,
which resets the resin. A final baking of the
segments in compression molds at 1000 to
4000 pounds per square inch to retain the
shape converts the resin to a thermoset or
permanent condition.19 Figure 3-19
illustrates the manufacture of brake linings by
a dry-mixed molding process in which curing
is performed in multiple stages.
Wet-mixed molding materials are
commonly combined in a sigma blade blender
for incorporation into a wide variety of
manufacturing processes. In the wet board
process, the mixture is fed to a paper machine
where the material is placed in a preform,
which carries a perforated metal screen on
one side; when suction is applied to the
outside of the screen, solvent is removed and
a deposit of the molding mixture remains on
the screen.22 The deposit is transferred to a
revolving cylinder, where it builds up to the
product thickness. The deposit is removed
from the cylinder, dried, cut into
product-sized segments, saturated in a liquid
binder, and either air-dried or oven-dried to
remove the solvents. The binder at this stage
is still sufficiently flexible to allow forming in
a curved mold for final curing. In an alternate
process (see Figure 3-20) for less dilute
mixtures, a free-flowing but slightly tacky
mixture is forced from a hopper into the nip
of two form rollers which compress the
mixture into a continuous strip of friction
material.22 Sometimes the mixture consists
of damp aggregates, which must be ground in
3-30
-------
ASBESTOS AND
t FRICTION COMPOUND
MOLD
J-
, v STEAM
UUPREHEAT
pa^-^W^;fe:(]
PREFORMING
PRESS
IL f I
STRIPS CUT
TO LENGTH
MOLD
REMOVED
ROUGH
GRINDING
[I CURING
PRESS
I
suFFTniT INTO
STRIPS
STEAM-HEATED
BENDING
CLAMPING IN
LUNETTES
RADIUS
GRINDING
DRILLING,
COUNTERBORING
PACKAGING
Figure 3-19. Manufacture of dry-mixed molded brake linings.
3-31
-------
START: ROLL FORMED CLUTCH FACINGS
PACKAGING
DRYING
OVEN
FINISHING
OPERATIONS
I SEE FIG"3'22
BAKING
OVEN
START: ROLL FORMED BRAKE LININGS
ASBESTOS,
SOLVENT,
AND
FRICTION
COMPOUND
BAKING
OVEN
FORCED-
AIR DRYING l
CHAMBER
!HIGH-SHEAR
MIXER
RACKING
o
>-
o
LU
CC.
-Ttl_.
HAMMER
MILL
CHOPPER
TWO-ROLL"
1 ' MILL
Figure 3-20. Two-roll forming of brake linings and clutch facings.
ARC FORMER
3-32
-------
order to ensure homogeneity. The continuous
strip is either cut to length to form brake
linings or punch pressed to produce clutch
facings prior to curing in pressure-clamped
forms. A variation of the process is the
introduction of a thin wire mesh on the
bottom to form a product with improved heat
conduction properties.22 In a manner similar
to the roll extrusion (two-roll forming) of a
damp mixture, the sheeter process feeds a
mixture of solvated rubber and asbestos fiber
into the nip of a large, heated roll and a small,
cold roll, which rotates in the opposite
direction.22 As the plastic mixture builds up
slowly on the heated roll, the gap between the
rolls is automatically enlarged. The sheet is
slit from the roll in product-sized widths and
formed and cured in the same manner as
those in other wet processes. Standard plastics
extrusion machines with orifices of
appropriate profile are also employed to
shape wet-mixed molding materials into a
continuous tape.19 After extrusion, the tape
is dried in rolls, cut to size, and finish-cured
to shape in compression molds.
Woven brake linings and clutch faces
frequently are manufactured of high-strength
asbestos fabric reinforced with wire; brass
wires of 5-mil diameter or larger are com-
monly used. The fabric is predried in a batch
oven, continuous process oven, or autoclave.
The fabric is impregnated with resin by
several techniques: (1) immersion, (2) intro-
ducing the binder into an autoclave under
pressure, (3) introducing dry impregnating
material into carded fiber prior to the pro-
duction of yam, or (4) forcing the binder into
the fabric from the surface of a roll. After the
solvents have dried from the binders, the
fabric is densified by calendering or hot
pressing, cut to length, cured, and machined
to produce brake linings (see Figure 3-21).
Endless woven clutch facings are produced by
a similar process in which the facings are
blank-pressed from saturated cloth. Figure
3-22 illustrates the manufacture of endless
wound clutch facings by the process of
slitting impregnated cloth into narrow (less
than 1/2 inch) strips or using impregnated
yarn, spiral winding the strips around a
mandrel, densifying and curing the preform,
and machining to finished specifications.
Ranges of compositions for these products are
40 to 60 percent asbestos, 10 to 20 percent
cotton, 20 to 40 percent wire, and 5 to 20
percent binder.
Friction materials are either riveted or
cemented to the carrier structure. Thin (1/32
inch) friction materials, such as are used in
automatic transmission plates, can not be
riveted practically. Bonding by the use of
heat-setting cements, such as phenol formal-
dehyde, allows longer wear since the lining
can be worn more closely to the carrier
member.2 2 For large bonding production, the
cement is applied in a solvent by spraying or
roll-coating one of the two members being
bonded. The coated member is passed
through a low-temperature oven to drive off
the solvent, and then the friction material and
carriers are assembled in fixtures and baked
by passing the clamped assembly through a
conveyor oven or high-frequency unit to flow
and set the cement.2 2
In order to supply brakes for an annual
brake lining replacement market in excess of
25 million vehicles, more than 500 brake
relining companies debond worn, cemented,
brake linings in order to reuse the metal brake
shoes.23 Debonders vary from small-scale,
batch process companies that debond and
reline less than 50,000 shoes per year to brake
lining manufacturers that utilize mechanized,
continuous process equipment for debonding
and relining. The debonding relies upon the
incineration of the adhesive portion of the
lining at temperatures that will not warp the
shoes. A typical small-scale debonder (see
Figure 3-23) utilizes a 55-gallon drum as the
primary combustion chamber for a batch
charge of 200 brake shoes. The primary gas
burners are designed to heat the charge to
850° F to initiate combustion of the adhesive.
After ignition of the adhesive, the gas flow to
3-33
-------
J\
WIRE-REINFORCED
WOVEN TAPE
ROLL
CLAMPING IN
LUNETTES
DRYING
OVEN
r
ROUGH
GRINDING
IMPREGNATING
BATH
ROTARY
CUTTER
n
t
BAKING OVEN
FINISHING OPERATIONS
SEE FIG. 3-22
DRYING
OVEN
PRESS
DENSIFIER
PACKAGING
Figure 3-21. Manufacture of woven brake linings.
the primary burners is stopped and combust-
ion is maintained below 1000°F until all the
organic constituents are consumed. As the
adhesive chars, the linings usually fall off the
shoes; however, occasionally the shoes must
be tapped lightly to accomplish separation.
After cooling, the metal shoes are blast-
cleaned, soaked in solvents and surface pre-
parations, pressure-assembled with new
linings, and heated to 650° F to thermoset the
bond. Following a grinding operation to
ensure a true braking surface, the assemblies
are packaged for sale as sets of four shoes for
two wheels.
3.3.6.1 Emissions
Aside from emissions related to the
handling of asbestos in bags, operations that
involve asbestos in certain dry-mixed molding
compounds (such as weighing of raw mater-
ials, charging of mixers, blending of compon-
ent ingredients, and discharging of mixers) are
major potential emission sources in the pro-
duction of friction products. Finishing oper-
ations, however, can generate much greater
quantities of asbestos-containing dust from
the use of band saws, abrasive wheels, drills,
cylindrical grinders, disk grinders, and circular
saws. For example, the drilling and grinding
of brake linings during manufacture release as
much as 30 percent of the lining material as
waste.23 Brake debonders are not considered
to be major sources of asbestos emissions
since the adhesives are burned without any
physical disruption of the surface integrity of
the brake linings. Data that quantify the
percentage of asbestos in the parti culate
matter and the extent of thermal degradation
of the asbestos are not currently available.
3-34
-------
WIRE-REINFORCED
CLOTH ROLL
o
STEAM-HEATED
ROLL
t
SLITTING TO
TAPES
WATER-COOLED
ROLL
PREFORM
WINDING
FRICTION COMPOUND
BATH
METAL
PLATES
g !
L_L
STACKING
BAKING
OVEN
PRECURING
PRESS
u
HOT
PRESSING
DRILLING,
COUNTER BORING
PACKAGING
Figure 3-22. Manufacture of endless wound clutch facings.
3.3.6.2 Control Techniques
As in the manufacture of numerous other
asbestos-containing products, emissions from
the production of asbestos friction products
are controlled by applying dust capture
hoods. Hoods of both the low-volume, high-
velocity and high-volume, low-velocity types
described in Section 3.3.2 are applicable. Dust
entrained in the air streams is frequently
cleaned with fabric filtering devices. In order
to avoid fire hazards inherent in the dry
collection of some solvent fumes, high-energy
wet collectors have been utilized. Almost all
brake debonders employ gas afterburners
capable of raising the temperature of the
3-35
-------
USED BRAKE
SHOES
LININGS
DISCARDED
RACKING
DEBONDING
OVEN
FORCED-AIR
COOLING
DEBONDING_
~BONDiN(f~
SOLVENT AND RUST
INHIBITOR BATH
SHOT-BLAST
CLEANING
D_EBONDING_
BONDING
NEW
LININGS
RADIUS
GRINDING
INSPECTION PAINTING BRANDING PACKAGING
Figure 3-23. Process of debonding and bonding brake shoes.
effluent to between 1400° and 1800°F.Proper
operation of such an afterburner can eliminate
visible emissions and reduce particulate emis-
sions to below 0.05 grain per standard cubic
foot at 12 percent CO2.2 4 Conclusive data on
the thermal degradation of asbestos is not
available; the asbestos content of the effluent
is considered to be unchanged by the after-
burner.
3.3.7 Asbestos Textile Products
Of prime importance relative to the in-
clusion of asbestos in textile products are the
properties of exceptionally strong resistance
to the action of heat, fire, acids, and mechan-
ical abrasion. The textile grades of asbestos
require fibers that are preferably long, fine,
and flexible, and possess superior tensile
3-36
-------
strength. Of the five varieties of asbestos
utilized industrially, only chrysotile, crocido-
lite, and amosite have these properties to a
degree that justifies their use in textiles;
chrysotile is the dominant variety. Textile
goods of interest include roving, carded lap,
yarn, cord, rope, square-plaited goods,
braided tubing, tape, webbing, and cloth.
Figure 3-24 illustrates the operations required
for the production of various asbestos textile
products.
The majority of the fibers received by the
textile plant are of the milled variety. Crude
or unniilled fibers in the form of small
unopened fiber bundles are sometimes used,
however, and must be processed through an
edge mill or other milling device to effect
preliminary opening and removal of waste
products. The output from the milling oper-
ation is delivered to vibrating screens, where
the fibers are removed by an air aspiration
system and graded. Pre-milled (opened) fibers
have frequently been compressed during pack-
aging for shipment and must be separated and
loosened again. This action is accomplished
by passing the fiber through a fluffer.
Hither in a preliminary mixing process or
during carding, the separated asbestos fibers
are blended with small amounts of organic
fibers, such as cotton or rayon, which func-
tion as carriers and supporting agents for the
shorter asbestos fibers, thereby improving the
spinning characteristics of the asbestos. The
usual organic fiber content is between 20 and
25 percent. The blended fibers undergo a final
opening and cleaning process by the carding
machine, which combs the fibers into a
parallel arrangement to form a coherent mat
of material. Next, strips, or slivers, are separ-
ated from the mat and mechanically com-
pressed between oscillating surfaces into un-
twisted strands. These strands are wound onto
spindles to form the roving, from which
asbestos textile yarn is produced.
By the twisting and pulling operations
performed by a spinning machine, the re-
latively weak roving is converted into a
stronger structure, yarn. Spinning machines
used are the single-wire or double-wire
machines of the fly-frame type and the ring
type, which are similar to those that work
cotton and worsted yarns.1 In comparison
with normal organic yarns, asbestos-con-
taining yarns can be drawn only slightly,
however.
Asbestos twine or cord is produced from
yarn by twisting together two or more yarns
on a fly- or ring-type spinning frame in a
manner similar to that used in the production
of cotton cord. Braided asbestos textile pro-
ducts are manufactured on various types of
packing braid machines. More than one type
of machine is needed because of the desire to
impart various shapes to the products by the
plaiting operation rather than by mechanical
deformation. Asbestos yarns are woven into
fabric on looms that operate similarly to
those that produce conventional cloth goods.
3.3.7.1 Emissions
In the manufacture of asbestos textile
products, emissions can result from un-
loading, warehousing, transporting to bag
opening areas, bag opening, and dumping of
asbestos, as discussed in Section 3.3.1. The
fluffing operation, which is also noted in that
section, and the grading operation involve
beating and combing processes that generate
heavy dust concentrations. These concentra-
tions can escape to the surrounding environ-
ment if equipment enclosures do not have
suitable local exhaust ventilation and fabric
filters. A considerably larger amount of dust
results from fly willowing to recover fibers
from wastes collected by cyclones.25 Both
the blending of various grades of asbestos
fibers and the blending of asbestos with
non-mineral fibers involve dumping of dry
materials into hoppers and, frequently, auto-
matic weighing of them prior to depositing
onto conveyor belts, which discharge into a
blending machine. Potential emissions assoc-
iated with blending or mixing operations are
identified in Section 3.1.1.
3-37
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BAGGED ASBESTOS FIBER
AS RECEIVED FROM MILL
CARDED
FIBER
LAP
TWISTED
ROPE
COTTON OR OTHER
CELLULOSE FIBER
LIGHT
GAUGE
WIRE
THREAD
TREATED
YARNS
TWISTED
CORD
TAPE CLOTH WOVEN BRAIDED BRAIDED BRAIDED
TUBING TUBING CORD ROPE
Figure 3-24. Manufacture of asbestos textile products.14
3-38
-------
Fiber blends are often loaded by hand
into mobile hoppers, transported in these
open bins to carding machines, and then
manually loaded into the cards. These oper-
ations result in significant emissions of as-
bestos to the surrounding work space. Asbes-
tos-containing dust is generated from the
swift roller of carding machines as the worker
and stripper rollers assist in converting the
masses of blended fibers into coherent
blankets of material. The periodic cleaning of
cards, perhaps on an interval of 7 to 10 days,
can release large amounts of dust and fleece
to the surroundings.2 6
The major source of asbestos emissions
from twisting machines is the release of
material from the yarn undergoing twisting as
it is rapidly whipped through the air.2 5 An
end of roving is supplied from a jack spool,
passed over rollers and guides, and then
rapidly wound onto a spindle as twisted yarn.
Emissions also result from the breakage of
yarn and the subsequent rotation of the loose
end by the spindle.
Weaving potentially generates more dust
than any other textile operation; however,
present control technology can reduce emis-
sions to the extent that this process can be
one of the cleanest of all textile operations.26
It has been suggested that the principal
emission source is the abrasion of yarn against
eyelets of heddle frames as the frames move
upward and downward in the weaving pro-
cess.25 Emissions also accompany the rapid
traversing of the shuttle and fill yarn across
the width of the fabric.
3.3.7.2 Control Techniques
Direct emissions from asbestos textile
plants to the atmosphere are frequently con-
trolled by the use of fabric filtering devices.
In some cases in the United States, it has
proved to be economical to control the
temperature and humidity of ventilating air of
large work spaces such as carding, twisting,
and weaving rooms. Flow capacities capable
of changing the entire volume of air in these
work spaces.as frequently as once every 6
minutes are used. To minimize heating and
cooling requirements, air removed from work
spaces is sometimes recycled (rather than
being exhausted to the atmosphere) after it
has been sufficiently cleaned by fabric filters
to meet occupational hygiene standards. In
contrast to the practice of maintaining work
spaces at slight negative pressures in order to
alleviate emissions through windows, doors,
and structural leaks, the production areas of
these mills are maintained at a slight positive
pressure relative to the outside environment.
Plant operators consider this necessary to
provide a temperature and humidity seal for
the work areas. Accordingly, it is important
to control strictly the emission of asbestos at
the source in order to prevent atmospheric
discharge through structural openings at these
facilities. Control methods for asbestos emis-
sions that accompany unloading, transporting,
warehousing, transporting to bag-opening
areas, and the opening and dumping of
asbestos contained in bags are discussed in
Section 3.3.2.
Air-ventilated partial enclosures and dust
capture hoods of the high-volume, low-
velocity type are effective in controlling
emissions from openers or willows. Also,
emissions can be reduced by opening and
dumping bags in a centralized, isolated area
and then conveying the fibers for automatic
charging into feed bins of the opener.2 s
In blending operations, the use of auto-
matically preweighed quantities of the various
fibers that are ejected onto conveyor belts
and transported to blenders provides emission
control by comparison with the previous
practice of manual layering and piling in open
spaces.25 An oil emulsion is commonly
applied to fibers prior to blending;2 5> 26 it has
been reported that the sole purpose of appli-
cation of the emulsion is to facilitate dust
suppression.26 Drum mixers have been totally
enclosed for dust control.2 6
It is possible to pneumatically convey
fibers directly from blending processes to feed
hoppers of carding machines and reduce
3-39
-------
asbestos emissions from the eorresponding
manual operations.25 The operator must
"overblend" in order to compensate for the
tendency of the fibers to separate while being
conveyed. Most carding macliines are equip-
ped with air-exhausted partial enclosures, or
dust-capture hoods.25 The designs are com-
promises between thorough dust removal and
minimum extraction of longer-fiber stock
from the material undergoing carding.
Hooding of both the high-volume, low-
velocity and the low-volume, high-velocity
types is in use. The latter design is a refine-
ment of the former and is reported to collect
approximately 0.0025 pound of dust per 100
cubic feet of air handled.2 6 <2 7 Further, the
feasibility of completely enclosing cards to
control asbestos emissions has been investi-
gated.26 Carding machines can be cleaned
with a revolving brush, fitted with air suction,
which is passed across the card cylinder.26 As
far as emissions to the mill work space are
concerned, this technique is markedly
superior to stripping with a jet of compressed
air.
The application of dust-capture hoods to
control emissions from beaming machines is
being investigated.26
Spinning frames are not frequently fitted
with dust control devices. Machines are now
available, however, that stop the rotation of a
spindle when an end of yarn breaks; emissions
from the whipping of the loose end are
therefore eliminated. In a British installation,
a spinning frame has been outfitted for
emission control by shielding long sections of
the frame from the floor upward and venti-
lating the enclosure. One section behind the
winding spools remains unshielded to provide
for air entrance across the spools and oscil-
lating yarn. A long baffle plate shields the
spool area from the working aisle and serves
as a type of high-volume, low-velocity hood
to collect and prevent dispersal of dust as air
is drawn across, above, and below the plate.2 5
In some asbestos textile mills, emissions
from weaving looms have been controlled to
the extent that weaving is the cleanest of all
textile operations.26 Control methods include
dust-capture hooding and the substitution of
wet weaving for the original dry processes.26
Wet weaving is carried out by passing the
warp through a trough of water on the loom,
by spraying water on the frame, by spraying
water on the yarn, or by a combination
process.2 7 A primary requirement of dust
capturing hoods and enclosures is that they
incorporate convenient accessibility to repair
frequent thread breaks.2 s
Figure 3-25 illustrates a dust-capture
hood of high-volume, low-velocity type that is
applicable to the control of asbestos emissions
from a loom; dust is collected from the top of
the heddle frame and shuttle areas. Hinged
windows of transparent plastic at the front
permit visual observation and ready acces-
sibility to the shuttle-heddle frame area. A
dust settling pan and ventilated hopper are
located at the lower rear portion of the
loom.25 This particular configuration does
not catch dust that settles downward from
the center portion of the loom, but this
emission is subject to control. The degree of
emission control attainable by the hooding of
a loom can be evaluated from published
results of a decrease from 14 to 0.5 pound per
week of dust and fiber collected from under a
loom with, respectively, no emission control
and extensive hooding.26 Braiding operations
can either be hooded or carried out with wet
yarn to provide emission control.
3.3.8 Asbestos-Asphalt Paving Compounds
When asbestos is added to asphalt paving
compounds in the amount of 2 to 3 percent
by weight, the quantity of asphalt in the mix
can be increased by between 30 and 100
percent to yield a material containing from 7
to 11 percent by weight of asphalt.2 8 The
result is an improved pavement overlay with
increased cohesion and abrasion resistance
and decreased water permeability and mater-
ial embrittlement.2 8 This type of paving has
been applied extensively in California, where
it is estimated that more than 20 percent of
3-40
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9 in, DIAMETER
DAMPERED EXHAUST
FROM PAN AT
LOWER REAR OF LOOM
»-1500 dm
SHEET METAL
PLYWOOD
PLEXIGLASS
HINGED
PANELS
2 ft. 6 in.
FRONT OF LOOM
PLYWOOD \
"END PANEL' '.
1 MAX. FORWARD THROW
3 in.
OF SHUTTLE BEAM
Figure 3-25. Dust capture hood for dry weaving loom.25
the population resides in proximity to asbes-
tos-asphalt paving; other applications include
the New Jersey Turnpike and the Trans-
Canadian Highway.2 8
Figure 3-26 illustrates the mixing section
of a manufacturing plant for asphalt paving
compounds. The typical practice for the
introduction of asbestos into a mixture in-
cludes the manual opening of bags of asbes-
tos, discharging of asbestos into the receiving
hopper for limestone and tlyash, conveying to
a storage bin, and discharging into the pug
mill for blending with other components of
the formulation. The laying of asbestos-
asphalt paving compounds is by standard
paving equipment.
3.3.8.1 Emissions
In the manufacture of asbestos-asphalt
paving compounds, the handling of bags of
asbestos, emptying of asbestos into receiving
hoppers, and the discharge of dry fibers into
storage hoppers, weighing devices, and mixers
are potential sources of asbestos emissions.
No conclusive data have been presented to
ascertain the extent to which asbestos emis-
sions accompany the gradual and continual
wearing away of asbestos-asphalt road sur-
faces.
3.3.8.2 Control Techniques
The enclosure of bag opening and empty-
ing areas, storage bins, conveyor systems, and
mixers can provide control of atmospheric
emissions of asbestos from manufacturing
facilities for asbestos-asphalt paving materials.
Also the use of pulpable bags could reduce
emissions. In cases where it may be desirable
to maintain relatively low asbestos concentra-
tions within an enclosure by providing dilu-
tion ventilation (such as in a bag-opening
area) or in cases where air displaced by the
addition of solid material must be vented to
the atmosphere, emissions can be controlled
by treating exhaust streams by fabric filters.
3-41
-------
HOT AGGREGATE
ELEVATOR
DRIED
AGGREGATE
400°F
FILLER
ELEVATOR
LIMESTONE
OR FLYASH
Figure 3-26. Mixing section of manufacturing plant for asphalt paving.29
3.4 END USES OF PRODUCTS
CONTAINING ASBESTOS
3.4.1 Sprayed Asbestos-Containing Insulation
Materials
Spray application of asbestos-containing
insulation materials is used extensively for
fireproofing of steel-reinforced structures. De-
pending upon the particular formulation of
sprayed material, acoustical insulation can be
simultaneously provided. Thermal insulation
for high-temperature equipment such as
chemical process vessels, steam turbine shells,
furnace walls, and boiler walls is also installed
by spraying. Requirements for the two appli-
cations differ in that the layer of insulation
must withstand thermal cycling in insulating
high-temperature equipment as opposed to
the design for a single thermal shock in the
fireproofing of steel structures. Other asbes-
tos-containing materials applied by spraying
are specifically formulated to provide either
ambient temperature thermal insulation or
acoustical insulation.
The spraying technique has been deve-
loped to accommodate those situations in
which the presence of irregular shapes and
large areas would lead to difficulty and
excessive cost in insulating by conventional
block, mat, and hand-troweling techniques.
Some types of sprayed insulation materials
can be tamped prior to drying to produce a
decorative finish. A coat of sealer or paint can
be applied either for decorative purposes or
for improving resistance of the surface to the
loss of material by abrasive action.
These spray-applied insulation materials
contain asbestos fibers, a water-setting binder
such as cement, and in some cases other fibers
such as glass wool or mineral wool. Amosite,
crocidolite, and chrysotile in amounts from 5
to 80 percent by weight are used; the major-
ity of formulations contain either chrysotile
or amosite. The materials are usually dry-
mixed at an off-site manufacturing facility
and are delivered to a spraying location in
kraft bags of approximately 50-pound capac-
ity.
Two types of spraying processes in com-
mercial use are shown in Figure 3-27. For
cementitious spraying, the bags of premixed
insulating material are emptied into the
hopper of a spray machine; the material is
mixed with water to form a slurry; and the
slurry is pumped to the point of application,
which can be hundreds of feet removed from
the mixing operation. A jet of compressed air
3-42
-------
FIBER SPRAYING
FIBER & WATER AT 25 Ib/ft3 (TYPICAL)
^
LOOSENS AND
FLUFFS MATERIAL
SPRAY NOZZLE (2 in. TO 3 in. OPENING)
PRESSURIZED WATER LINE
BLOWER HOSE
CEMENTITIOUS SPRAYING
PLASTER GUN WITH 3/8 in. TO 1/2 in. ORIFICE
PLASTER TYPE AT
60 Ib/ft3 (TYPICAL)
COMPRESSED AIR
AT NOZZLE
PLASTER MIXER
PLASTER PUMP
Figure 3-27. Spray processes for asbestos-containing insulation materials.
is emitted at the spraying nozzle together
with the slurry to assist in dispersing the
insulating material into a spray and propelling
it onto the surface to be insulated. In fiber
spraying, the second type of application, the
bags of fibrous insulating material are likewise
manually emptied into the hopper of a spray
machine, but the insulation is pneumatically
conveyed in a dry condition to the spraying
nozzle. The insulation passes from the spray
machine hopper to carding brushes, which
perform a combing operation, and then to a
blower, the impeller of which forces the
material through a feed hose that supplies the
spray nozzle. A compressed-air jet atomizes
water supplied to the nozzle and facilitates
wetting of the insulating material either with-
in or immediately outside the outlet of the
nozzle, depending upon the particular design.
The spray nozzle is typically held 12 to
24 inches away from the surface to be
insulated. Insulation is often applied in more
than one layer and to a thickness of more
than 2 inches.
3.4.1.1 Emissions
Asbestos-containing insulation is fre-
quently sprayed in spaces directly open to the
atmosphere. Asbestos spray fireproofing ap-
3-43
-------
plied to buildings during construction, partic-
ularly high-rise structures in large metropol-
itan areas, is the most extensive single use of
this type. Also, sprayed high-temperature
thermal insulation is frequently applied to
such equipment as steam turbines and chem-
ical process vessels that are not housed within
structures.
Visible atmospheric emissions of asbes-
tos-containing particulates resulting from the
spray application of asbestos insulation are
not uncommon. For example, emissions ac-
companying the spray fireproofmg of struc-
tures in New York and other metropolitan
areas have been described as "extensive snow-
falls of asbestos-containing material."30 In
some cases, these emissions are traceable to
the incomplete wetting of dry insulating
material either interior to, or slightly
downstream from, the outlet of a fiber
spraying nozzle. Further, both the
ceinentitious and fiber spraying techniques
produce large quantities of wet insulation that
does not adhere to the target surfaces. A
portion of this wet material can be emitted
directly to the atmosphere external to the
work space, and large quantities settle onto
surfaces of the work space beneath the
sprayed area. The latter deposits can become
secondary sources of asbestos emissions via
dispersal by vehicular and human traffic in
the work area, particularly if the wet
insulation dries before it is removed for waste
disposal.
When asbestos-containing insulation is
applied by spraying techniques within
structures that are essentially shielded from
the external atmosphere, forced gas streams
exhausted from the structures and incidental
discharges of work-space ventilation air
through windows and doors are potential
sources of atmospheric asbestos emissions. In
the course of transporting bags of dry
spraying mixture to a job site and during the
handling, stacking, and storing of these in a
work area, asbestos can be emitted to the
work space from punctures through bags and
from bag closures that are not dust tight. A
non-dust-tight type of bag seal is formed, for
example, by stitching together the end of a
bag without initially folding over the end and
sewing through four layers of composite
packaging material. The manual opening of
bags of spraying mixture and the subsequent
dumping of the contents into the hopper of a
spray machine are potential emission sources
that are similar to those encountered in the
preliminary steps of manufacturing processes
(see Section 3.3.1). Emissions produced by
the spraying process and potential secondary
emissions from wet oversprayed material have
been cited above. Potential emissions that can
be generated by the disposal of overspray
material and of empty insulation-mixture
shipping bags are discussed in Section 3.5.1.
3.4.1.2 Control Techniques
Initial attempts to control excessive
atmospheric asbestos emissions from the
spray fireproofing of buildings under
construction were directed toward the
adoption of good housekeeping procedures at
spraying sites and the containment of
potential emissions within the structures. This
method of emission control was generally
recommended by the spray insulation
industry.3'
The open perimeters of entire floors of
new buildings have been shielded with
tarpaulins and plastic sheets for the purpose
of containing emissions from spray
fireproofing. Further, recommended work
practices include an initial cleaning of floor
areas and the removal of portable objects (or
the covering of such articles with
dust-impervious tarpaulins or plastic sheets)
to facilitate cleanup of spraying areas and
thereby reduce potential emissions from this
phase of waste disposal
The development of spray fireproofing
and high-temperature thermal insulating ma-
terials that contain little or no asbestos has
been undertaken in direct response to the
3-44
-------
need for control of asbestos emissions. One
cementitious type of spray fireprooI'm g com-
pound containing no asbestos is how in use
This substitute compound in applied in the
same manner as the previous asbestos-
containing material, and equivalent fire resist-
ance ratings approved by Underwriters1
Laboratories, Inc., for a large number of con-
struction systems are attained with compa-
rable thicknesses of the two materials. Several
asbestos-free spray fireproof ing materials of
fiber type are also available, and other manu-
facturers of asbestos fiber spray fireproof ing
have asbestos-free substitute materials in a
state of active development. In addition,
several asbestos-free, fiber-type products are
marketed for application as high-temperature
sprayed thermal insulation.
If sprayed asbestos insulation is employed
within enclosed structures, potential asbestos
emissions to the atmosphere can be controlled
by sealing all openings through which
contaminated air could be discharged to the
exterior of the structure. In situations
requiring ventilated spraying areas, fabric
filters can clean the exhaust air prior to
discharge to the atmosphere. Appropriate
control measures can limit emissions to the
work space, but the practical implementation
of these may result in excessive labor costs in
comparison with the use of an asbestos-free
material that might not require such stringent
control practices. Suggested techniques for
controlling potential work space emissions are
discussed in the following paragraphs.
To control asbestos emissions from
packaged spray insulation materials, the bags
should be factory sealed with a dust-tight
closure and should possess sufficient strength
to withstand normal handling without damage
that would expose the asbestos. Minor bag
punctures can be promptly sealed with
masking tape; whereas, more extensively
damaged bags can be protected by a plastic
slipover bag that can be sealed dust tight.
The airborne disperson of emissions that
accompany the manual opening of bags and
the charging of dr\ insulation material into
the hopper of a spraying machine can be
lessened by enclosing and ventilating the
immediate work space. Because it is not
necessary to relocate the hopper as insulation
is applied at various locations within a
building, the opportunity exists for
conveniently employing a portable
high-volume, low-velocity capture hood in
conjunction with a gas-cleaning device to
control emissions. A hood configuration of
this type, applied to a bag opening and
conveying station, is shown in Figure 3-12.
Proper technique by the operator in opening
and emptying bags can minimize the amount
of emissions that must be controlled. Fmpty
bags should be immediately placed into
dust-tight containers and then disposed of, as
indicated in Section 3.5.2.
As an alternative to fiber spraying
processes that incompletely moisten the
insulating material, the use of cementitious
spraying can be considered as a control
technique for the reduction of asbestos
emissions during spraying. If fiber spraying is
employed, the atomized water spray should
be in operation prior to passing insulating
material into the nozzle and should be
removed from operation only after the fiber
supply is cut off. Otherwise, the ejection of
dry insulating material from the nozzle yields
asbestos emissions. For either type of
spraying, an initial cleaning of floor areas and
covering of exposed articles in the spraying
area facilitates cleanup and reduces potential
asbestos emissions. The enclosure of a
spraying area with tarpaulins or plastic slieets
can,, when properly applied, significantly
reduce the spread of airborne asbestos to
other areas of the work space during both
spraying and cleanup. Proper implementation
is seldom practicable in terms of labor cost,
however.
In collecting asbestos-containing wastes
for subsequent disposal, wet overspray should
be removed from floors and other surfaces,
and dry wastes should be vacuumed from
tarpaulins as soon as no further material is
3-45
-------
being deposited. The waste materials should
he wetted before sweeping.
Particular attention should be given to
the removal of asbestos-containing wastes
subject to entrainment by ventilating air, such
as material in the plenum space of a building
or in ventilation ducts. Coating the sprayed
insulation with a surface sealant provides
additional protection against the possibility of
emissions through abrasion of the material.
3.4.1.3 Con fro I Costs
The cementitious and fiber spray
processes for fireproofing structures with
asbestos-containing materials are
commercially competitive. The installed cost
for 500,000 board feet of fireproofing is
approximately $0.13 per board foot of applied
material when the density of the cured
coating is 12 pounds per cubic feet.
A non-asbestos-containing substitute for a
cementitious spray fireproofing is currently
marketed at a material cost, per unit weight,
equal to that of the original asbestos spraying'
mix. The yield of the substitute material, as
well as the fire rating (where approved) of a
given thickness of coating, matches that of
the asbestos-containing material. The method
of application is unchanged by the
elimination of asbestos. Consequently, the
installed cost of the substitute fireproofing is
the same as that of the original material.
The material cost of one asbestos-free
fiber spray fireproofing compound is
approximately equal to that of the
asbestos-containing material that it replaces.
The exclusion of asbestos from several other
fiber spray fireproofing formulations, which
are undergoing development, is estimated to
result in an increase of 10 to 15 percent in
material costs. The method of application and
the fire rating attainable with a given
thickness of applied coating of these
substitute products are not significantly
different from those of the original
asbestos-containing systems of protective
coating.
3.4.2 Field Fabrication of Products
Containing Asbestos
Insulating materials that contain asbestos
as either a primary or secondary ingredient
are frequently applied on-site by techniques
other than spraying. Typical examples are the
insulation of pipes, boilers, breechings,
turbines, and industrial furnaces. The
chrysotile variety of asbestos is usually
employed; sheets and boards composed of
crocidolite are not well suited for thermal
insulation.19
Preformed sections or blacks are available
as molded asbestos, molded calcium
silicate-asbestos, molded 85 percent magnesia,
and molded high-temperature insulating
block. These materials can also maintain cold
temperatures, but a surface sealant such as
asphalt, silicate or cement must be used to
keep the insulation dry.19 The widely used,
calcium silicate insulation contains
approximately 10 percent asbestos fiber,
which serves as a binding and reinforcing
agent; the final product contains
approximately 10 percent solid material by
volume.1 9
To fill crevices between preformed
sections and to insulate extremely irregular
shapes, powdered material of similar
composition is mixed on-site into a slurry and
applied by hand trowel. Typical materials are
calcium silicate asbestos cement, hard-setting
asbestos cement, and asbestos skinning
plaster.
Asbestos-cement products, such as siding
shingles, building boards, and drain pipes,
often require cutting and trimming operations
during field fabrication. The surfaces of these
products are less susceptible to dusting and
surface abrasion than are most insulating
materials.
Millboard,19 which is a heavy form of
asbestos paper, and flexible asbestos paper are
examples of insulating materials that
incorporate asbestos as a major component.
Asbestos air cell insulation is a sandwich
structure of corrugated asbestos paper and
3-46
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asbestos-cement sheets. Other asbestos
products that are frequently installed in the
field are asbestos blanket, rope, tape, yarn,
and sealing compounds.
3.4.2.1 Emissions
The storage, handling, and transportation
to fabrication sites of both
asbestos-containing thermal insulation
products and products that contain unbound
asbestos present opportunities for asbestos
emissions.2' '3 2 Cartons and bags are subject
to being unsealed and broken open. Also, the
abrasion and breakage that sometimes
accompanies the handling of individual
unpackaged units of material can produce
emissions.
Significant amounts of asbestos-laden
dust are produced during (1) the sawing, cut-
ting, and sanding of pipe and block insulation
to fit the contours of specific equipment; (2)
the wiring and banding of insulation and the
application of jackets and facings to insula-
tion;31 and (3) the transfer of loose mixtures
of materials from bags into hoppers and the
subsequent mixing into a slurry application by
troweling (see Section 3.4.1.1).
The exposure of material fragments, such
as trimming scrap, broken wastes, and spillage
from containers, to traffic aisles of the job
area and to the attendant further
disintegration by human and vehicular
movements is a significant source of dust
emissions.32 The consolidation and packaging
of these wastes for disposal can also produce
asbestos emissions.
3.4.2.2 Control Techniques
Asbestos emissions resulting from the
transportation of materials to fabrication sites
can be minimized by protecting cartons and
packing bags from rupture. When the stacking
of molded products onto vehicles is likely to
abrade or fracture away small pieces of
material, the use of either fully enclosed
vehicle bodies or scalable containers can limit
emissions.
The following recommended techniques
have been applied to the control of asbestos
emissions from the on-site fabrication of
a s b e s t o s - c c in e n t products and
asbestos-containing insulation materials:
1. Isolation of work area from exterior
environment by installation of
dust-impervious tarpaulins or plastic
sheeting.
2. Collection of refuse from sawing,
drilling, and sanding operations at the
source of emissions.
3. Implementation of efficient
housekeeping practices.
The effectiveness of the first measure is
diminished by the need for supplying some
degree of ventilation for workers' comfort
and by the inherent difficulty of sealing
around irregular shapes, the exterior walls of
buildings under construction, and exterior
operations. Low-volume, high-velocity hoods
that capture the wastes produced by
stationary power tools are described in
Section 3.3.2. This method of effectively
collecting asbestos-laden dust at the source of
emission has also been incorporated into
portable cutting tools. Figures 3-28 and 3-29
illustrate this type of device fitted,
respectively, to a portable hand saw and to a
portable electric drill, the required suction is
Figure 3-28. Dust capture device fitted to
portable hand saw.33 /Coupes/ of Johns-
Manvi//e J
3-47
-------
Figure 3-29. Dust capture device fitted to
portable drill.33 (Courtesy of Johns-Manville )
readily supplied by an industrial vacuum
cleaning system. The prompt cleanup of
trimmed wastes, broken material fragments,
and spillage from containers minimizes
further disintegration, airborne entrainment,
and creation of secondary emission sources
such as dispersion from workers' clothing.
Tightly sealing waste containers should be
conveniently accessible; vacuum cleaning
devices are recommended for the removal of
small particles and dust, In the absence of
vacuum cleaners, the watering of wastes prior
to sweeping and shoveling can be an effective
control measure. Tiie disposal of
asbestos-containing wastes is discussed in
Section 3.5.
In an effort to control emissions from the
opening and dumping of bags of asbestos
insulating cement or loose, dry insulating
materials and also from the subsequent
mixing of those materials with water to form
a slurry, it has been proposed that mixing
take place within the shipping bag.3 4 Water is
injected into a polyethylene bag through a
narrow sleeve, and the contents are kneaded
into a wet mixture prior to removal from the
container.
3.4.3 Friction Products
The automotive and heavy equipment
industries are the major users of asbestos
friction products.19 In 1968, new passenger
and commercial motor vehicles manufactured
in the United States accounted for 9,913,000
sets of brake linings, which contained an
average of 3 pounds of asbestos per set.35
The yearly number of sets of replacement
brake linings can be gauged by considering
that 1 trillion vehicle-miles were traveled in
1968 in the United States1 and that an
average lifetime for brake linings is 27,500
miles. Further, it is estimated that between
one and two sets of asbestos-containing clutch
facings are consumed during the lifetime of
the average vehicle equipped with a manual
clutch.
The principal types of asbestos-containing
friction products are molded, woven, or
extruded. Chrysotile asbestos (30 to 60
percent of product) is mixed (or asbestos
cloth is impregnated) with asphalt, drying oil,
synthetic resin, or rubber. Chrysotile is
preferred over crocidolite because of better
heat resistance and less severe wear against
metal surfaces.19
Friction materials containing asbestos are
also used in the pads of disk brakes, for clutch
facings in automatic transmissions, and for
brake blocks for heavy-duty trucks,
earth-moving equipment, elevators, and other
industrial applications. The percentage of
domestically produced motor vehicles
equipped with disk brakes has increased from
2.9 percent in 1966 to 11.2 percent in
1968.35 Additional increases in the fraction
of vehicles equipped with disk brakes will
affect the types of operations carried out
during replacement of motor vehicle brake
linings.
3.4.3.1 Emissions
During the replacement of drum-type
brake linings on motor vehicles, the grinding
and trimming operations required for
individual fitting are potential emission
sources of asbestos fibers. Based on an
assumed loss of 0.05 percent of brake lining
asbestos content to the atmosphere during
grinding and fitting, asbestos emissions from
the fitting of brake linings were estimated to
total 190 tons in 1968.23 The analogous
grinding operations that are performed in
friction product manufacturing plants are
3-48
-------
known to yield asbestos fibers of similar
physical form to those that have been
associated with adverse health effects.36
Since disk brake pads are not contour ground
as drum brake linings are, the current trend to
disk brakes should reduce asbestos emissions.
As brake linings and clutch facings rub
against their mating bearing surfaces in the
course of usage, particles of the lining
material are abraded. These particles can be
partially trapped in the housings of manual
clutches and in brake drums; the remainder
can be emitted directly into the atmosphere.
The latter emissions are treated as a problem
in mobile source air pollution control and are
outside the scope of this study.
Because extremely high temperatures can
result from the sliding of brake linings and
clutch facings against the corresponding
mating surfaces, the question arises as to
whether the asbestos that would otherwise be
contained in the particles released from the
friction materials has been thermally
degraded. One set of tests of automobile, bus,
and truck drum brakes and clutches has
shown that, except under conditions of very
severe usage, the majority of the freed
asbestos has been thermally degraded.36 For
example, most of these samples of released
material from automotive brakes contained
less than 1 percent asbestos as compared with
50 percent in the original lining
formulation.36 This residual amount,
however, is not inconsequential relative to air
pollution control. Further tests are needed to
evaluate emissions from disk-type brakes.
In the course of servicing and overhauling
motor vehicle brakes and manual clutches, the
accumulated asbestos-containing dust is
frequently dislodged from drums and
housings by directing a compressed air jet
against the deposits.3 7 Depending upon the
servicing location, this results in airborne
asbestos emissions either to the work space or
directly to the atmosphere.
3.4.3.2 Control Techniques
Asbestos emissions accompanying the
grinding and trimming of replacement brake
linings at the site of installation and fitting are
presently uncontrolled at most sites. The
incorporation of low-volume, high-velocity
dust-capture hoods (see Section 3.3.2) into
grinding equipment is feasible and can provide
an effective method for controlling these
emissions.1 *
The removal of asbestos-laden dust from
brake drums and from housings of manual
clutches by the compressed-air-jet method
produces uncontrolled emissions. The
dislodging and collection of this waste
material at the source by operating a brush
connected to an industrial vacuum cleaner as
a low-volume, high-velocity dust capturing
and collecting device has been evaluated.3 7
This control technique reduced personal
exposure to fibers larger than 1 micrometer in
diameter by approximately 75 percent.
3.5 DISPOSAL OF ASBESTOS WASTE
MATERIALS
Potential waste materials containing
asbestos are produced during the mining and
milling of asbestos ores and in the
manufacture and use of asbestos-containing
products. The form of asbestos in these
wastes ranges from asbestos bound in
relatively large rock masses or in such
manufactured products as asbestos-cement
pipe and reinforced plastics to small-diameter,
readily dispersed asbestos fibers that are
removed by gas-cleaning devices or are
produced in the milling of asbestos ores.
In mining operations, large quantities of
asbestos ore are sometimes rejected at the
mine site because either the concentration or
the form of dispersal of the asbestos renders
recovery uneconomical. The lower limit for
profitable recovery of chrysotile asbestos
from massive deposits of serpentine rock is a
concentration of approximately 3 percent.1
3-49
-------
The richness of the non-massive Coalinga
asbestos ore permits larger rocks to be
discarded in screening operations at the mine.
Further, in most surface mining operations, it
is necessary to remove overburden that
contains small concentrations of asbestos in
order to expose the ore deposits.
The milling process for asbestos ore
eventually discards, from screening
operations, finely divided rock in
combination with small amounts of the
shorter asbestos fibers. Also, very short
asbestos fibers that are collected by
gas-cleaning devices after entrainment during
the air aspiration process for separating the
longer fibers from crushed ore sometimes
require disposal.
Asbestos mills and plants that
manufacture asbestos-containing products
frequently use fabric filters and other
gas-cleaning devices to remove asbestos fibers
from the ventilation air of the entire work
space as well as from process gas streams. The
application of asbestos products to end uses is
accompanied to a lesser extent by similar
filtering devices; for example, portable
vacuum cleaning machines are often used to
remove settled dry asbestos wastes. In each of
these instances, the collected material must be
handled again as it is periodically removed
from the filtering device.
Asbestos fiber and certain end-use
asbestos products, such as spray insulating
compounds, are shipped in paper or plastic
bags. Because appreciable amounts of asbestos
dust are retained on the emptied bags, a
method of disposal that minimizes
atmospheric emissions is needed. The
manufacture of asbestos-cement and asbestos
paper produces a mixture of asbestos fibers
and water; the removal of the asbestos to
prevent a water pollution problem should be
accomplished in such a way that atmospheric
emissions are avoided. Scrap and rejected
material containing bound asbestos from the
manufacture of such products as
vinyl-asbestos tile, asbestos-cement, asbestos
paper, and asbestos reinforced plastic require
disposal. The overspray from application of
sprayed asbestos insulation materials must be
consolidated and packaged for disposal.
Demolition of residential and commercial
buildings has been major in scope in recent
years in most American cities, as the result of
urban renewal and other massive projects.
Structures subject to demolition are
frequently sources of asbestos-containing
waste materials. These wastes include friable
materials, such as pipe and boiler thermal
insulation, and bound materials, such as
asphalt-asbestos floor tile, vinyl-asbestos
flooring products, asbestos-cement roofing
and siding shingles, and acoustical ceiling tile.
Future demolition operations will also be
concerned with the disposal of waste asbestos
spray fireproof ing. Disposal of
asbestos-containing wastes during demolition
can be either a selective stripping of the
materials from a structure or the
fragmentation of the entire structure and
contents as a unit.
3.5.1 Emissions
The exposure in open-dumping sites of
such diverse wastes as asbestos mine
overburden, oversized masses of screened
asbestos ore, asbestos mill tailings, emptied
asbestos shipping bags, and the consolidated
overspray of asbestos-containing insulation
provides an opportunity for the entrainment
and widespread dispersion of asbestos fibers
into the atmosphere. Atmospheric emissions
can also result from the open disposal of the
material collected by gas-cleaning devices,
from the open disposal of scrap pieces of
insulating materials and asbestos-cement
products that carry surface deposits of
asbestos dust produced by fabrication and
field installation operations, from the
weathering in open dumps of even those
materials in which asbestos is originally
present in a bound condition, and from the
disposal of emptied shipping containers for
asbestos.
3-50
-------
The properly managed disposal of
emptied bags in a dump is thought to generate
less emissions than the incineration of such
bags; however, the degree of thermal
degradation of the asbestos during
incineration has not been fully evaluated.
Careful handling is required to prevent
atmospheric emissions as loosely bound
asbestos-containing materials, such as the
particulates retained by a gas filtering device
or the waste from the application of sprayed
insulation, are loaded into temporary or
permanent containers to facilitate eventual
disposal.
Loosely bound asbestos dust on the
surface of waste materials located in a work
area can be entrained into the air and
dispersed by room currents. Spreading and
eventual emission can also result from contact
of the body and clothing with this dust.
Asbestos emissions are reduced by minimizing
the period of exposure of the wastes to the
working environment. Trimmed pieces of
asbestos-cement pipe, vinyl-asbestos floor tile,
and asbestos-containing pipe insulation are
examples of these waste materials.
As noted in Section 3.1.1, the use of
asbestos mine and mill wastes for the
surfacing of roadways can lead to the
emission of asbestos as the roads are
constructed and as the passage of vehicles
generates air entrainment currents and further
disintegrates the waste materiaJ.
The fragmentation of waste material
during demolition operations is an inherently
dust-producing process. Asbestos materials are
deliberately broken apart when a structure
and its contents are demolished by drop-ball
cranes or explosives, but there can be a
significant quantity of material breakage and
dust generation even during the selective
stripping of asbestos-containing materials
from a structure prior to its demolition. The
handling and loading of demolition wastes for
transportation to a disposal site are likewise
potential sources of large quantities of
airborne dust. The ultimate disposal of
asbestos demolition wastes in open dumps can
yield significant atmospheric asbestos
emissions.
3.5.2 Control Techniques
Potential emissions associated with the
removal of dry, asbestos-containing materials
collected by gas-cleaning devices can be
controlled by providing a dust-tight sealing
arrangement between the collector hopper
and the disposal bag or bin. For example,
clear polyethylene bags of appropriate
strength can often be banded around the
hopper discharge.2 * The resultant clear
visibility of the level of material in the waste
container assists in sealing and removing the
bag from the hopper nozzle with a minimum
of emissions. When wastes are collected by
smaller, portable vacuum cleaning equipment,
single-service bags can be employed to
eliminate the necessity for transferring the
waste to an intermediate container prior to
disposal. Asbestos-containing sludge from wet
collectors should be drained into
moisture-proof vats suitable for transporting
the waste to a dumping site.
Airborne wastes generated by machining
and trimming can be collected at the source
of emissions by low-volume, high-velocity
dust capture hoods fitted to stationary and
portable power tools (see Sections 3.3.2,
3.4.2). The adoption of this control technique
reduces the handling phase of waste disposal
to the removal of a directly disposable dust
deposit bag. When no provisions are made at
the source to immediately entrain or collect
trimming wastes and broken fragments of
asbestos-containing materials that readily
produce dust, waste receptacles with tightly
fitting lids should be provided at convenient
locations in the working area. If a specific
type of operation generates dust emissions
from the charging of a receptacle, it is
desirable to provide a dust-capture hood of
the high-volume, low-velocity type at the
charging site to control emissions. Larger
pieces of rejected, friable, asbestos-containing
materials can likewise be placed into
3-51
-------
receptacles prior to eventual disposal.
Emissions from emptied bags or other
discarded containers of dry, loosely bound,
asbestos-bearing products can be controlled
by placing the containers into receptacles
immediately after dumping the contents.
Even though asbestos fibers are strongly
bound into such products as asbestos-cement
and asbestos-containing plastics, loose dust
freed by machining and breakage can be
carried on the surfaces of these materials.
Consequently, these wastes should also be
placed into receptacles reserved for asbestos
disposal.
The most frequently applied asbestos
emission control technique for demolition
operations is the thorough wetting of the
surface and, where possible, water soaking of
asbestos-containing materials prior to
stripping of the materials or breakup of an
entire structure. The use of additional
quantities of water together with en-
closed conveying chutes can reduce
emissions during the loading of demolition
wastes into transportation vehicles. When
ambient temperatures arc below freezing,
however, the opportunities for dust
suppression by wetting of wastes are limited.
The stripping of asbestos-containing ma-
terials, particularly those which are friable,
prior to the breakup of a structure is a more
direct method of controlling asbestos emis-
sions during demolition than is the applica-
tion of dust control measures during the frag-
mentation of an entire building simulta-
neously with the asbestos wastes. Methods for
the control of emissions generated by the
field fabrication of asbestos-containing prod-
ucts (see Section 3.4.2.2) can be adapted to
stripping operations. These methods include
the adoption of good housekeeping practices,
the shielding of work areas with tarpaulins,
the use of dust-capture hoods, and the clean-
ing of dust control air streams by fabric
filters.
As asbestos-bearing wastes that have been
collected and consolidated undergo disposal,
emphasis should be placed upon emission
suppression during transportation, dumping,
and repose in the dump. Wastes that are
otherwise uncontained are preferably placed
into dust-tight bags or other dust-tight
containers for transit to the disposal location.
For example, if permanent disposal
receptacles are not carried to a dump site for
emptying, then the contents, such as
discarded bags and fragments of scrap
materials, can be transferred and sealed into
impervious bags for transport. This
intermediate handling should be performed
under a dust-capturing hood vented to a
gas-cleaning device. As mentioned above, wet
wastes should be transported in waterproof
containers.
In all cases, transporting vehicles and
reusable containers should be either wet- or
dry-cleaned when dumping is completed.
If wastes are accidentally spilled in transit
to a dumping site, cleanup should be
undertaken as soon as possible. Extensive
spills that can not be readily removed should
be immediately covered or wetted to control
dispersion.
Access to the face of a dump should be
provided for vehicles depositing
asbestos-containing wastes; to minimize the
possibility of rupturing disposable containers,
wastes should not be dropped long distances
when unloaded. A location of waste
deposition on the dump is preferred which
will lessen potential emissions from
subsequent movement of the wastes as
additional material or a sealing covering is
placed on top. Earth or, in some cases, other
dry wastes can be applied as the sealing
material to prevent emissions from exposure
of the wastes to the atmosphere. Wet wastes
and wastes containing strongly bound
asbestos should also be covered with a seal;
otherwise, subsequent drying and
disintegration can eventually permit emissions
to the atmosphere.
When disposal operations and dump
management are not under the direct control
of persons discharging wastes, periodic
inspection of the dump site should be
3-52
-------
conducted to assure adherence to
recommended practices.
Control techniques for emissions from
asbestos mining waste deposits and asbestos
mill tailings dumps are discussed in Sections
3.1.2 and 3.2.2, respectively.
3.6 REFERENCES FOR SECTION 3
1. Berger, H. Asbestos Fundamentals. New
York, Chemical Publishing Company,
Inc., 1963, translated from German by R.
E. Oesper. p. 7, 8, 27, 104, 122, 147,
166.
2. Grossmueck, G. Dust Control in Open Pit
Mining and Quarrying. Air Engineering.
10(7):2l-25, July 1968.
3. Sussman, V. H. Nonmetallic Mineral
Products Industries. In: Air Pollution,
Vol. Ill, Sources of Air Pollution and
Their Control, Stern, A.C. (ed.). New
York, Academic Press, p. 123.
4. Hutcheson, J. R. M. Environmental
Control in the Asbestos Industry of
Quebec. (Presented at 73rd Annual
General Meeting of Canadian Institute of
Mining and Metallurgy. Quebec City,
1971.) p. 3-9, 11-14,20-23.
5. Minnick, J. L. Control of Particulate
Emissions From Lime Plants - A Survey.
J. Air Pollution Control Assoc.
2^:195-200, April 1971. p. 196.
6. Control Techniques for Particulate Air
Pollutants, U. S. Environmental
Protection Agency, Research Triangle
Park, N. C. Publication Number AP-51.
January 1969. p. 50, 120.
7. Reitze, W. B., D. A. Holaday, E. M.
Fenner, and Harold Romer. Control of
Asbestos Fiber Emission From Industrial
and Commercial Sources. (Presented at
2nd International Clean Air Congress of
the International Union of Air Pollution
Prevention Association. Washington,
December 1970.) p. 4.
8. Burmeister, H. L. and I. E. Matthews.
Mining and Milling Methods and Costs,
Vermont Asbestos Mines, The Ruberoid
Company, Hyde Park, Vermont. U. S.
Department of the Interior, Bureau of
Mines. Washington. Information Circular
Number 8068. 1962. p. 18, 30, 32-34,
36-39.
9. Harmon, J. P. Use of Lingin Sulfonate for
Dust Control on Haulage Roads in Arid
Regions. U. S. Department of the
Interior, Bureau of Mines. Washington.
Information Circular Number 7806.
1957. p. 12.
10. Anderson, F. G. and R. L. Beatty. Dust
Control in Mining, Tunneling, and
Quarrying in the United States, 1961
through 1967. U. S. Department of the
Interior, Bureau of Mines, Washington.
Information Circular Number 8407.
March 1969. 50 p.
11. Myers, J. L. New Additives Induce
Thixotropy, Provide Sag and Viscosity
Control. (Presented to the Western
Coatings Technology Society, Denver,
Los Angeles, San Francisco, Portland,
Seattle, Vancouver, B. C., May 1969.) p.
4.
12. Rozovsky, H. Air in Asbestos Milling.
Canadian Mining Journal. 78(5):95-\03.
May 1957.
13. Herod, S. Corson Leads Way in Air
Quality Control. Pit and Quarry,
36(11):62-68, May 1971.
14. Handbook of Asbestos Textiles, 3rd Ed.,
Pompton Lakes, N. J., Asbestos Textile
Institute, 1967. p. IS, 2j.
15. Skvarla, J. E. Bulk Handling Calidria
Asbestos Pellets. King City, California,
Union Carbide Corporation. 1969.
16. Armbust, D. V. and J. D. Dickerson.
Temporary Wind Erosion Control: Cost
and Effectiveness of 34 Commercial
Materials. Journal of Soil and Water
Conservation, 2 6 ( 4 ): 1 54-157,
July-August 1971.
3-53
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17. The Control of Dust by Exhaust
Ventilation when Working with Asbestos.
London, The Asbestosis Research
Council, Control and Safety Guide
Number?. April 1970. p. 3, 9, 13, 15.
18. Industrial Ventilation, A Manual of
Recommended Practice. Lansing,
American Conference of Governmental
Industrial Hygienists, 1968. p. 4-13, 5-34.
19. Rosato, D. V. Asbestos: Its Industrial
Applications. New York, Reinhold
Publishing Corporation, 1959. p. 62, 63,
70, 73-75, 93-95, 100-102, 104, 114,
118, 120, 121, 126-129.
20. Welcome to the Johns-Manville Transite
Pipe Plant at Stockton, California. New
York, Johns-Manville, Co., 1970. p. 6.
21. The Asbestos Factbook. Willow Grove,
Asbestos, 1970. p. 17.
22. Batchelor, C. S. Friction Materials. In:
Kirk-Othmer Encyclopedia of Chemical
Technology, Vol. 10, Standen, A. (ed.)
New York, Interscience Publishers, 1966.
p. 130, 131, 134.
23. Report: National Inventory of Sources
and Emissions, Cadmium, Nickel and
Asbestos: 1968, Asbestos, Section III.
Leawood, Kansas, W. E. Davis and
Associates, February 1970. p. 19, 20,
29-31.
24. Danielson, J. A. (ed.). Air Pollution
Engineering Manual. U. S. Department of
Health, Education, and Welfare, Public
Health Service, Cincinnati. Publication
Number 999-AP-40. 1967. p. 475.
25. Postman, B. F. Dust Control in the
Asbestos Textile Industry. American
[ndust. Hyg. Assoc. J., 23(7^:67-74,
December 1962.
26. Hills, D. W. Economics of Dust Control,
Annals of the New York Academy of
Sciences, 732:322-334, December 1965.
27. Bamblin, W. P. Dust Control in the
Asbestos Textile Industry. Ann. Occup.
Hyg., 2:54-74, 1959.
28. Facts on Asbestos Asphalt Concrete. New
York, Johns-Manville Co. p. 3, 9.
29. Process Flow Sheets and Air Pollution
Controls. American Conference of
Governmental Industrial Hygienists,
Cincinnati. 1961. p. 1.
30. Nicholson, W. F., A. N. Rohl, and E. F.
Ferrand. Asbestos Air Pollution in New
York City. (Presented at 2nd
International Air Pollution Conference,
Washington. December 1970.) p. 2.
31. Recommended Health Safety Practices
for Handling and Applying Thermal
Insulation Products Containing Asbestos.
New York, National Insulation
Manufacturers Association, Inc. p. 8, 11.
32. Recommended Practices for Fabricating,
Handling and Applying Asbestos-Cement
Products in the Building and
Construction Industries. New York,
Asbestos Cement Products Association.
1970. p. 4, 5.
33. Asbestos-Based Materials for the Building
and Shipbuilding Industries and Electrical
and Engineering Insulation. London,
Asbestosis Research Council. Control and
Safety Guide Number 5. December 1970.
p. 9, 11.
34. Selikoff, I. J. Partnership for Prevention.
Industrial Medicine. 39(4^:21-25, April
1970.
35. Automobile Facts and Figures 1969.
Detroit, Automobile Manufacturers
Association, Inc. 1969. p. 1, 10.
36. Lynch, J. R. Brake Lining Decomposition
Products, J. Air Pollution Control Assoc.,
7S(72J:824-826, December 1968.
37. Knight, K. L. and D. E. Hickish.
Investigations into Alternative Forms of
Control for Dust Generated during the
Cleaning of Brake Assemblies and Drums.
Ann. Occup. Hyg., 73:37-39, 1970.
38. Recommended Code of Practice for the
Handling and Disposal of Asbestos Waste
Materials. London, The Asbestosis
Research Council, September 1969. p. 2.
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4. COSTS OF CONTROL BY GAS CLEANING DEVICES
Dry centrifugal collectors, wet collectors,
and fabric filters are three candidate devices
for application to the cleaning of
asbestos-laden process gas streams. The
purpose of this chapter is to present a rational
methodology for estimating the installed and
operating costs for these types of control
equipment.
The expenditures for installation and
operation of an air pollution control system
can be categorized as capital investment,
maintenance and operation costs, or capital
charges. Within each of these categories, it is
convenient to identify several types of costs:
1. Capital investment:
Control hardware
Auxiliary equipment
Installation
Engineering studies
Land
Operating supply inventory
Startup
Structure modification.
2. Maintenance and operation:
Labor
Supplies and materials
Utilities
Treatment and disposal of collected
material.
3. Capital charges:
Insurance
Interest
Taxes.
Substantial portions of the following
treatment have been excerpted from the
paper of Edmisten and Bunyard.1
4.1 CAPITAL INVESTMENT
The installed cost of an air pollution
control system includes expenditures for
control hardware, auxiliary equipment, and
field installation; the manufacturer's cost
quotation is usually based upon an
engineering study of the individual emission
source. The remaining items in the category
of capital investment will not be further
characterized here because of their wide
variance, but these can be readily
incorporated as more detailed requirements of
a specific installation are considered.
The purchase costs charged by
manufacturers for fabric filters, dry
centrifugal collectors, and wet collectors
constructed of standard materials ore
graphically illustrated in Figures 4-1, 4-2, and
4-3, respectively. These data were obtained by
adjusting the 1968 cost estimates of Edmisten
and Bunyard1 to a February 1972 basis.
Efficiency of collection and throughput of
process gas are the primary variables that
affect purchase costs, but a precision of ±20
percent applies to Figures 4-1 through 4-3 to
account for cost differences among
applications to wide ranges of processes.
Table 4-1 lists ranges of collection efficiencies
for the control devices. When the purchase
cost of a particular type of gas-cleaning device
for application to a specific process has been
determined by detailed analysis, the cost for a
similar device of different capacity can be
scaled from the equation:
=C,
Q:
0,
where:
known hardware cost
desired hardware cost
volumetric rate of gas
handling of collector for
which cost is known
4-1
-------
1000
800
600
400
200
100
80
60
CO
O
O
UJ
CO
O
or
20
10
8
6
Tl
A - HIGH TEMPERATURE SYNTHETICS, WOVEN AND FELT,
CONTINUOUSLY, AUTOMATICALLY CLEANED.
MEDIUM TEMPERATURE CLOTH WOVEN AND FELT,
CONTINUOUSLY, AUTOMATICALLY CLEANED
C - WOVEN NATURAL FIBERS, INTERMITTENTLY
CLEANED, SINGLE COMPARTMENT
COST FOR EQUIPMENT OF INDICATED CONSTRUCTION
±20% OF REPORTED FIGURE.
MAY VARY BY
280.0
964.0
155.0
507.0
- [59.5 ENDPOINT160]
300"
1000
I I
I
I
2 2.5 5 10 20 50 100 160
GAS VOLUME THROUGH COLLECTOR, 103 acfm
300
1000
Figure 4-1. Purchase cost of fabric filters (February 1972 estimate).
Q2= volumetric rate of gas
handling of collector for
which cost is desired
n = cost-capacity factor
The cost-capacity factors for several
gas-cleaning devices are tabulated in Table
4-2.
The total installed cost of an air pollution
control system, including costs for control
hardware, auxiliary equipment, and field
installation is conveniently expressed as a
multiple of the purchase cost for control
hardware (see Table 4-3). Expenditures for
erection, insulation materials, transportation
of equipment, clarifiers and liquid treatment
systems for wet collectors, and such auxiliary
equipment as fans, normal ductwork, and
motors are included. The low values of Table
4-3 correspond to minimal transportation
requirements and to simple layout and
installation of control devices. High
transportation costs and more difficult layout
4-2
-------
500
400
300
200
100
80
60
CO
E 40
te
o
o
o
a:
20
10
8
6
4
I
TT
1Q3 DOLLARS
HIGH MEDIUM
LOW 103 acfm
COST OF INDICATED EFFICIENCY MAY
VARY ± 20% OF REPORTED VALUE
I I
1
I I
I
I
I
I
I
2 2.5
5
10 20 50 100 200 300 500
GAS VOLUME THROUGH COLLECTOR, 103 acfm
Figure 4-2. Purchase cost of dry centrifugal collectors (February 1972 estimate).
1000
and installation result in higher values;
unusually complex installations such as those
encountered with existing process situations
lead to the extremely high values. Table 4-4
presents a detailed list of cost categories for
the total installed cost and specifies those
factors that determine low, typical, high, and
extremely high costs.
4.2 MAINTENANCE AND OPERATION
The quality of construction of a
gas-cleaning device, the optimum matching of
its operating characteristics to the solution of
the cleaning task, and the degree of attention
given to its proper operation strongly
influence the operating and maintenance costs
of the equipment. These combined costs can
range from as low as 15 percent of the
annualized total cost of control for dry
centrifugal collectors to as high as 90 percent
for a high-efficiency wet collector.
The expenditure that results from
operating a control device at its designed
collection efficiency for a period of 1 year is
the annual operating cost. This expenditure is
related to the gas volume cleaned, the
pressure decrease across the system, the total
time the device is operated, the consumption
and costs for electricity and scrubbing liquor,
4-3
-------
100
80
60
40
20
a
8 10
S 6
1
\ I
103 DOLLARS
MEDIUM. HIGH LOW 1Q3 acfm
_L
I
1
COST OF INDICATED EFFICIENCY MAY
VARY ±20% OF REPORTED VALUE
I I 1
4 5
300 500
10 20 50 100
GAS VOLUME THROUGH COLLECTOR, 103 acfm
Figure 4-3. Purchase cost of wet collectors (February 1972 estimate).
Table 4-1. AIR POLLUTION CONTROL
EQUIPMENT COLLECTION EFFICIENCIES
Table 4-2, COST-CAPACITY FACTORS
FOR GAS CLEANING DEVICES2
Equipment type
Low-energy mechanical
High-energy mechanical
Low-energy wet
collector
Medium-energy wet
collector
High-energy wet
collector
Fabric filter3
Typical efficiency ranges
(on total weight basis),
percent
50 to 70
70 to 90
50 to 75
75 to 90
90 to 99.5+
95 to 99.9
Collection efficiency for a properly designed and
operated unit should be greater than 99.5 percent.
and the mechanical efficiencies of fans and
pumps. Table 4-5 lists theoretical cost
equations that incorporate these factors.
The annual maintenance cost is the
expenditure incurred in sustaining the
Collector type
Fabric
Fabric filter, shaker
Fabric filter, envelope
Fabric filter, reverse jet
Mechanical
Medium-efficiency cyclone
High-efficiency cyclone
Multiple cyclone
Wet
Wet dynamic scrubber
Low-energy venturi
High-energy venturi
Cost-capacity
factor3
0.87
0.87
0.78
0.87
0.82
0.86
0.78
0.82
0.70
Q \n
-f^- } .
Ql/
aCost-capacity factor, n, such that C2
See text.
operation of a control device at its designed
efficiency for a period of 1 year. A scheduled
maintenance program accompanied by the
4-4
-------
Table 4-3. INSTALLED COST EXPRESSED AS A
PERCENTAGE OF PURCHASE COST FOR
TYPES OF CONTROL DEVICES!
Generic type
Dry centrifugal
Wet scrubber
Low, medium energy
High energy0
Fabric filters
Cost range,3 percent
Low
140
150
200
150
Typical
150
200
300
180
High
200
300
500
200
Extremely
high
500
500
600
500
aSee Table 4-4 for conditions that determine cost
range.
^High-energy scrubbers usually require more
expensive fans and motors.
Table 4-4. CONDITIONS AFFECTING PURCHASE AND INSTALLATION COSTS1
prompt replacement of defective and worn
parts is recommended practice. Maintenance
costs expressed relative to the gas-handling
capacities of dry centrifugal collectors, wet
collectors, and fabric filters are listed in Table
4-6; the 1968 costs of Edmisten and
Bunyard1 have been adjusted to a February
1972 basis. To simplify the computational
procedure, annual maintenance costs averaged
over the useful life of the equipment are
presented; it is expected in practice that such
costs would show an increasing maintenance
trend with wear and age of the control
devices. The method of including
maintenance cost into total annual operating
Cost category
Equipment transportation
Plant age
Available space
Instrumentation
Guarantee on performance
Degree of engineering design
Degree of assembly
Utilities
Collected waste material
handling
Labor
Auxiliary equipment
Corrosiveness
Low to typical costs
Minimum distance; simple loading and
unloading procedures
Hardware designed into new plant as
an integral part of process
Vacant area for location of control
system
Little required
None required
Standard "package type" control
system
Control hardware shipped completely
assembled
Electricity, water, waste disposal
facilities readily available
No special treatment facilities or
handling required
Low wages in geographical area
Simple draft fan; minimal ductwork
Noncorrosive gas
High to extremely high costs
Extensive distance; complex procedure
for loading and unloading
Hardware installed into confines of old
plant requiring structural or process
modification or alteration
Little vacant space; extensive steel
support construction and site
preparation required
Complex instrumentation required to
assure reliability of control or
constant monitoring of gas stream
Guaranteed high collector efficiency
to meet stringent control
requirements
Control system requiring extensive
integration with process, insulation
to correct temperature and moisture
problem, noise abatement
Control hardware to be assembled aqd
erected in the field
Electrical and waste treatment
facilities must be expanded; wate/
supply must be developed or
expanded
Special treatment facilities and/or
handling required
Overtime and/or high-wage
geographical area
Extensive cooling equipment
ductwork, large motors
Acidic emissions requiring high alloy
accessory equipment using special
handling and construction
techniques
4-5
-------
Table 4-5. EQUATIONS FOR CALCULATING ANNUAL
OPERATION AND MAINTENANCE COSTS3-1
Operation costs
Control
device
Centrifugal
collector
Wet collector
Fabric filter
Electrical
costs
L (A)a
c 0.7457 PHK
6356 E
S (0.7457) HKZ
c 0.7457 PHK
6356 E
Liquor
consumption
costs(B)a
-
SWHL
Maintenance
costs
(C)a
SM
SM
SM
aNote: annual cost (dollars) for operating and maintenance, G = (A) + (B) + (C)
where:
S = Design capacity of the unit in actual cubic feet per minute (acfm).
P = Pressure drop in inches of water.
H = hours of operation annually.
K = cost of electricity in dollars per kilowatt-hour.
E = fan efficiency expressed as percentage.
M = maintenance cost per acfm in dollars per acfm.
W = make-up liquor rate in gallons per hour per acfm.
L = cost of liquor in dollars per gallon.
Z = Total power input required for a specified scrubbing efficiency in
horsepower per acfm.
Table 4-6. ANNUAL MAINTENANCE
COST FACTORS FOR TYPES
OF CONTROL DEVICES
Generic type
Dry centrifugal
Wet collector
Fabric filter
Cost, $/acf m
Low
0.006
0.03
0.03
Typical
0.020
0.05
0.06
High
0.032
0.08
0.1 Oa
aExotic materials can result in higher maintenance.
and maintenance expenditure is indicated in
Table 4-5.
Costs for electricity and water, adjusted
to February 1972, are shown in Table 4-7.
Also, requirements of make-up water and
power for wet collectors and the pressure loss
typical of the types of control devices are
indicated.
4.3 CAPITAL CHARGES
Taxes, insurance, and interest on
borrowed capital are included in the category
of capital charges. These charges are widely
variable, ranging from 6 to 12 percent per
year, and depend upon the industry's
financial position and ability to borrow
money, the existing money market, and the
local tax structure. A rate of 7 percent per
year of the capital investment, or total
installed cost, can be assumed in the absence
of detailed data on a particular installation.
4.4 ANNUALIZATION OF COSTS
The annualized capital cost of an air
pollution control system is calculated by
depreciating the total installed cost, or capital
investment, over the useful life of the control
equipment and adding the capital charges.
The depreciation is commonly based upon a
4-6
-------
Table 4-7. COST (FEBRUARY 1972) AND ENGINEERING
FACTORS FOR DETERMINING OPERATING COSTS FOR EMISSION
CONTROL EQUIPMENT
Control
equipment
All devices
Wet scrubber
Dry centrifugal
Fabric filter
Wet collector
Wet collectors
Cost or engineering
parameter
Cost of electricity,
$/kwha
Cost of liquor,
$10-3/gala-b
Pressure loss through
equipment, in. water
Fan loss
Pump loss
Scrubbing (contact)
power, horsepower/acfmc
Make-up liquor rate,
gal/acfm-hr
Range
Low
0.006
0.12
-
2 to 3
1
1 to 3
Low
Efficiency
0.0013
0.03
Typical
0.013
0.31
2 to 3
4 to 5
10
1 to 5
Medium
Efficiency
0.0035
0.03
High
0.024
0.65
4
6 to 8
20 to 60
1 to 10
High
Efficiency
0.008
0.03
aBased on national average for large consumers.
Assume H20 for make-up.
cData do not include requirements for pumping water through system. Such requirements may range from
0.0 to 0.5 horsepower per 1000 acfm.
straight-line computation because this yields a
constant annual write-off. Factors such as
obsolescence of control equipment and
functional lifetime determine the depreciation
period, which varies considerably among
industries. A depreciation period of 15 years
can be assumed typical for most control
systems.
The total annualized cost of air pollution
control is the sum of the annualized capital
cost, the annual operating cost, and the
annual maintenance cost.
4.5 EXAMPLES
Example 1
An asbestos-cement pipe manufacturing
plant controls emissions by the use of a
baghouse with medium-temperature-type
filters and a capacity of 124,000 acfm. The
total installed cost of the system, adjusted to
a 1972 cost basis, is $295,000; the annual
cost of above-average maintenance is $14,000.
Complex ducting was required for the
installation.
To compare the above actual costs with
those predicted by the estimation method of
this chapter, the purchase cost is read from
curve B of Figure 4-1 as $65,000. The
inclusion of complex duct work places the
cost range of the control system within the
range of "high" to "extreme high" of Table
4-3 as indicated by reference to Table 4-4.
Accordingly, the total installed cost is
estimated to be between 2 x $65,000 =
$130,000 and 5 x $65,000 = $325,000; the
actual total installed cost is included in this
range. The use of the high maintenance cost
4-7
-------
factor, $0.10/acfm, yields an annual
maintenance cost of $12,400, which is in
reasonable agreement with the actual value of
$14,000.
Example 2
Emissions from brake-lining machining
operations are controlled by the use of an
18,000-acfm reverse-air-cleaned baghouse
with medium-temperature-type
polypropylene felt tubes. The total installed
cost of the system is $24,900. Minimal
hooding and ductwork were required for the
installation.
By the estimation method of this chapter,
the purchase cost is read from curve B of
Figure 4-1 as $14,000. Because only minimal
ductwork was required, the installed cost of
the control system is within the range of
"low" to "typical" of Table 4-3, as indicated
by reference to Table 4-4. Accordingly, the
total installed cost is estimated to be between
1.5 x$ 14,000 =$21,000 and 1.8 x $14,000 =
$25,200; the actual total installed cost of
$24,900 is included in this range.
Example 3
A vinyl-asbestos tile manufacturing plant
uses a 4,500-acfm continuously cleaned
baghouse with medium-temperature-type
woven-cotton bags to control emissions from
an asbestos bag-opening operation. The total
installed cost is $11,900, and the annual cost
of average maintenance is $310. No complex
ductwork was required for the installation.
To compare the above actual costs with
those predicted by the estimation method of
this chapter, the purchase cost is read from
curve B of Figure 4-1 as $6,800. Because no
complex ductwork was required, the installed
cost of the system is included in the range of
"low" to "typical" of Table 4-3, as indicated
by Table 4-4. Accordingly, the total installed
cost is estimated to be between 1.5 x $6,800
= $10,200 and 1.8 x $6,800 = $12,240; the
actual value is included in this range. The use
of an average maintenance cost factor from
Table 4-6 yields an annual maintenance cost
of $0.06/acfm x 4,500 acfm = $270, which is
somewhat less than the actual value of $310.
Example 4
Emissions from an asbestos ore dryer are
to be controlled by a 40,000-acfm baghouse
with high-temperature-type felt filters. Costs
will be higher than normal because of the
requirements of complex field-assembled
instrumentation, insulation to combat
moisture problems, erection within the
confines of an existing plant, and extensive
engineering and planning to integrate the
control system with the prosent process
design. Detailed analysis by an
asbestos-producing company and fabric-filter
vendors yielded an estimate of $225,000 for
the total installed cost.
By the estimation process of this chapter,
the purchase cost is read from curve A of
Figure 4-1 as $48,000. By virtue of the several
complicating conditions listed above, the cost
of the installed control system is estimated to
be within the range of "high" to "extreme
high" of Table 4-3, as indicated by reference
to Table 4-4. Accordingly, the total installed
cost is estimated to be between 2 x $48,000 =
$96,000 and 5 x $48,000 = $240,000. The
estimate, by detailed analysis, of $225,000 is
included in this range and is closer to the
higher value as. would be indicated by the
existence of several complicating conditions.
4.6 REFERENCES FOR SECTION 4
1. Edmisten, N. G. and F. L. Bunyard. A
Systematic Procedure for Determining
the Cost of Controlling Particulate
Emissions from Industrial Sources. J. Air
Pollution Control Assoc. 20( 7) :446-452.
July 1970.
2. Zimmerman, O. T. and I. Lavine.
Cost-Capacity Factors Equipment Cost
Engng. 6(2):13-18. April 1961.
4-8
-------
5. EVALUATION OF ASBESTOS EMISSIONS
The evaluation of community air
pollution frequently requires that the
quantities and characteristics of pollutant
emissions from a large number of sources of
diverse types be determined. As an alternative
to the individual testing of each emission
source, a procedure for estimating typical or
averaged emissions from various source types
by the application of emission factors has
been adopted.
An emission factor for a given
technological process is an average (for a
number of individual processes of the
specified source type) of the amount of an
emitted pollutant divided by some
appropriate measure of the productivity,
material input, or energy transfer that is
associated with the process. Consequently,
knowledge of the emission factor for a given
source type and pollutant together with the
corresponding productivity, material input, or
energy transfer parameter for the individual
plant or facility permits the rate of pollutant
emission to be calculated. Emission factors
are preferably derived from extensive and
detailed source sampling data that can be
directly related to process variables.
Significant differences regarding the type of
process and the degree of air pollution control
among individual sources within a category
"should be specified.
No accurate asbestos emission factors are
available. Mass-rate emission factors, based on
engineering appraisals and extremely limited
data, have been compiled and published;1 but
emission factors, based on asbestos fiber
counts, have not been compiled. Since health
effects of asbestos are related to the number
magnitude of fiber exposure, extensive data
should be collected in order to determine
accurate estimates of fiber count-rate
emission factors for asbestos.
5.1 REFERENCE FOR SECTION 5
1. National Inventory of Sources and
Emissions, Asbestos, Section III.
Leawood, W. E. Davis and Associates,
NAPCA Contract Number CPA
22-69-131, 46 p., February 1970.
5-1
-------
6. DEVELOPMENT OF NEW TECHNOLOGY
Research is in progress to find substitute
materials for the asbestos contained in spray
fireproofing for steel and reinforced concrete
structures and for the asbestos in pipe
insulating materials. This research has already
produced some asbestos-free spray
fireproofing materials, which have been
marketed. In another application, amosite has
been replaced by fiber glass in boiler blankets
for naval vessels. On the other hand, interest
in expanding the already vast number of
applications for asbestos fibers has increased.
There are available gas-cleaning devices of
the fabric-filter type, which can reduce fiber
counts to below levels presently required by
industrial hygiene standards. Should fibers of
submicron diameter be discovered to
contribute significantly to adverse health
effects, however, it would be necessary to
determine fractional collection efficiencies of
fabric filters for this range of fiber sizes.
Fractional collection efficiency data, required
for a more complete evaluation of the
effectiveness of fabric filters as control
devices, are apparently not available at
present. As an initial measure, standardized
laboratory tests for the total mass collection
efficiency of filter fabrics should be
developed.
The treatment of surfaces of mill tailings
dumps to promote the growth of vegetation,
thereby securing the material from
atmospheric entrainment and dispersion, is
presently under investigation. Only limited
success has been achieved. Also, methods to
revegetate and to reforest exposed mining
lands are undergoing study and development.
In the manufacture and field fabrication
of products containing asbestos, emphasis in
abatement activities centers on either the
containment or the airborne entrainment and
subsequent collection of potential emissions
at the sources. New applications of
dust-capturing hoods of both the
low-velocity, high-volume and high-velocity,
low-volume types axe expected. Also
anticipated are further development and more
extensive use of dust elimination methods,
such as pulpable bags for utilization in the
manufacture of asbestos paper and wet-mix
shipping bags for asbestos-fiber products.
6-1
-------
APPENDIX A. GAS CLEANING DEVICES
Brief descriptions of three gas-cleaning
devices (fabric filters, dry centrifugal
collectors, and wet collectors), which can be
applied to control emissions of asbestos, are
presented. For a more complete discussion of
these control devices, the reader is referred to
Reference 1 of this section.
A.I FABRIC FILTERS
Fabric filters, which have been in
commercial use for many years, provide one
of the most reliable methods for cleaning
solid particulate material from gas streams.
Particulates as small as 0.5 /urn in diameter can
be collected with high efficiency, and even
those as small as 0.1 /^m can be removed at
somewhat reduced efficiency after a dust
layer has been deposited on the fabric.1
In this type of filter, a gas stream passes
through the woven or felted fabric filtering
medium and deposits dust on the upstream,
or dirty gas, side of the material. The most
common geometrical configuration of the
fabric filter, illustrated in Figure A-l, is a
group of vertical tubes forming a baghouse:
flat areas of fabric material as well as curved
surfaces are employed. Dust is dislodged from
the surface of the filter either by flexing the
fabric or by locally directing a stream of air
through the filter in the reverse direction.
The nature of the collecting mechanism
of a fabric filter is quite complex, as might be
judged from the fact that solid particles of
much smaller diameter than the equivalent
open spaces in clean filtering material are
frequently collected with high efficiencies.1
Initially, particles are deposited and retained
on the fibers of a fabric by direct
interception, initial impaction, diffusion,
electrostatic attraction, or gravitational
settling. After a cake or mat of dust has
accumulated on the filter material, the
collection efficiency is increased significantly
by the effect of mat sieving. Most of the dust
mat is removed during each filter cleaning.
A measure of the flow resistance of clean,
new filtering material is the ASTM (American
Society for Testing and Materials)
permeability. This parameter is defined as the
volumetric rate of air flow in cubic feet per
minute (cfm) through 1 square foot of fabric
that produces a pressure decrease of 0.5-inch
water gauge across the fabric. The
permeability is also related to the initial
penetration of dust through a clean fabric. An
important operating parameter of a fabric
filtering installation is the air-to-cloth ratio, or
filtering velocity; this factor is defined as the
total volumetric flow rate through the filter,
expressed in cubic feet per minute divided by
the total number of square feet of filtering
area.1
Fabric filters are used extensively in the
asbestos mining, milling, and manufacturing
industries. Table A-l shows typical
characteristics of the fabric filters chosen by a
large corporation for asbestos collection from
a wide range of emission-source types. The
filter material is cotton sateen except in the
case of control of emissions from an ore
dryer; cotton is unsuitable for the
higher-temperature effluent gases of the
dryer. The useful lifetime of cotton bags is 6
to 7 years.2 Wool felts have also been used for
several years, but synthetic felts have only
recently gained acceptance by the asbestos
industry. A wide range of synthetic felted
fabrics is now available; these fabrics can be
designed for specific particle size ranges and
particulate loadings to achieve collection
A-l
-------
CLEAN AIR «--*
OUTLET
DIRTY AIR
INLET
CLEAN AIR
SIDE
FILTER
BAGS
CELL PLATE
Figure A-1. Sectional view of baghouseJ
A-2
-------
Table A-1. APPLICATIONS OF FABRIC FILTERS '
Application
Asbestos milling
Asbestos ore dryers
Asbestos-cement raw
material handling
Asbestos-cement
finishing machines
Textile carding
Operation
Continuous
Continuous
Continuous
Intermittent
Intermittent
Cloth
Cotton sateen
Orion
Cotton sateen
Cotton sateen
Cotton sateen
Bag
length,
in.
168
168
126
168
126 to 168
Bag
diameter,
in.
5
5
5
5
8
Filtering
velocity,
ft/min
2.5 to 3.0
2.5
2.5
2.0
5
Expected
pressure
drop,
in. H2O
2.5 to 4.0
1.5 to 2.0
3.0
1.5 to 2.0
1 .5 to 2.0
Data based on several plants of one corporation.
efficiencies equivalent
cotton fabrics.
to less permeable
The nature of some of the processes
described in Table A-1 requires that the
collectors operate continuously; whereas, in
other instances the filters can be cleaned
periodically when a process is shut down.
Cleaning cycles vary from 1 minute of shaking
during each 30 minutes of operation in a mill
to one cleaning every 2 hours of operation at
the finishing end of an asbestos-cement pipe
manufacturing plant.2 Woven bags are usually
cleaned by the action of a mechanical shaking
device. Baghouses equipped with felted
fabrics usually operate continuously and
employ pulse-jet cleaning in which a jet of
compressed air is periodically released
through a venturi at the top of each bag. The
rapid flexure of the fabric and subsequent
rebound against an internal restraining screen
effect cleaning. Differences in bag length and
diameter among the collectors result from
space and efficiency compromises among
small-diameter bags to minimize required
floor area, larger-diameter bags to reduce the
likelihood of longer fibers plugging the filters,
and longer bags to fit a filter into smaller
floor area.
In an asbestos mill, collection effici-
encies greater than 99.99 percent have
been exhibited by fabric filters receiving an
inlet dust concentration of approximately 1
gram per standard cubic foot.2 The consistent
attainment of an exit fiber concentration of
0.5 fiber per cubic centimeter (measured by
membrane filter technique) from a
well-maintained baghouse is thought possible
with cotton sateen fabric under the operating
conditions used in Table A-1. Tests have
shown that exit dust concentrations observed
immediately after initiating air flow through a
cleaned cotton sateen bag are considerably
larger than those for normal operation; the
much lower values are reached only after a
time interval of 2 or 3 minutes. Woven fabrics
of synthetic material presently exhibit larger
relative exit dust concentrations initially and
require longer periods of time to reach normal
levels.2 A regular maintenance program is
essential for the realization of maximum
efficiency of fabric filters; the presence of
dust on the clean air side is almost always the
result of leaks or breaks in the bags.2
As shown in Table A-1, filtering velocities
range from 2.0 to 5.0 feet per minute for
woven fabrics. Typical permeabilities are
A-3
-------
approximately 20 and 30 cubic feet per
minute per square foot for cotton sateen and
felted fabrics, respectively.
The proper operation of fabric filters
requires that moisture not be condensed from
the gas stream. Consequently, if a filter
enclosure is exposed to low temperature or if
a hot, moist gas stream is handled, insulation
of the baghouse may be required, as in the
case of baghouses applied to asbestos ore
dryers.
A.2 DRY CENTRIFUGAL COLLECTORS
Dry centrifugal collectors impart a
spinning motion to a dirty gas stream. Many
of the relatively dense particulates are not
capable of following this motion of the fluid;
they impinge on the collector wall, drop to
the base of the collector, and are removed
from the device. The required rotary motion,
which can be imparted by various methods, is
frequently induced by a tangential inlet to the
collector vessel. Collector efficiency is
determined by the interrelationships among
gravitational, radial or centrifugal, and fluid
drag forces exerted on the particles of the gas
stream.
Conventional reverse-flow cyclones with
tangential gas inlet and axial inlet are
illustrated in Figures A-2 and A-3,
respectively. Dry centrifugal collectors are
commonly employed in the asbestos milling
and manufacturing industries, both as
precleaners for fabric filters and as process
equipment for the separation of longer
asbestos fibers from shorter fibers and wastes.
Cyclone collection efficiency can be
specified in terms of the cut size, which is
defined as that particle diameter which is
collected with a 50 percent efficiency on a
weight basis.1 Large-diameter conventional
cyclones have a high collection efficiency for
particles with diameters as small as 40 to 50
micrometers.1 The pressure decrease across
dry centrifugal collectors is in the range of 1
to 8 inches of water.1
ZONE OF INLET
INTERFERENCEx
TOP VIEW
GAS
INLET
SIDE VIEW
OUTER
VORTEX
OUTER
RTEX
INNER
VORTEX
INNER
VORTEX
\ / / /x-GAS OUTLET
BODY
INNER
CYLINDER
(TUBULAR
GUARD)
CORE
DUST OUTLET
Figure A-2. Reverse-flow cyclone with tan-
gential inlet.1
A.3 WET COLLECTORS
Water and other liquids are employed in
wet collectors to entrap and remove
particulates from gas streams. This action is
accomplished by bringing droplets of
scrubbing liquid into contact with the
undesired entrained particles to render the
particle si/es large enough to permit
high-efficiency collection. The mixture of
collected material and scrubbing liquor is
readily removed from the cleaning device to
minimize reentrainment of the original
contaminating material. Spray chambers,
centrifugal spray scrubbers, impingement
plate scrubbers, venturi scrubbers, packed-bed
scrubbers, and centrifugal-fan wet scrubbers
are among the many types of wet collectors in
commercial use. In the venturi wet collector
(Figure A-4), scrubbing liquid is introduced
into the dirty gas stream at the throat of the
venturi, the location of highest gas velocity.
Collection efficiency is enhanced with the
increase of the velocity of the entrained
particulates relative to the droplets of
A-4
-------
CLEANED GAS
DUST-LADEN GAS
Figure A-3. Reverse-flow cyclone with axial
inlet.1
scrubbing liquid produced by the
impingement of the gas flow against the
injected liquid. In the case of the
centrifugal-fan wet scrubber (Figure A-5), the
particulates of the dirty gas stream and
droplets of scrubbing liquor are dynamically
precipitated by the action of the centrifugal
blower.
A primary disadvantage of using wet
collectors as final-stage gas-cleaning devices
for the control of asbestos emissions is the
apparent low collection efficiency for
submicron particulates. Some wet collectors,
for example those of the venturi type, can be
designed for improved efficiency in the
collection of submicron particle sizes, but the
operating costs become excessive for the
resultant higher values of pressure drop across
the scrubbers.
Figure A-4. Venturi wet collector.1
A.4 REFERENCES
1. Control Techniques for Particulars Air
Pollutants. U. S. Department of Health,
Education, and Welfare, National Air
Pollution Control Administration.
Publication Number AP-51. January
1969. p. 44-81, 102-126.
2. Goldfield, J. Fabric Filters in Asbestos
Mining and Asbestos Manufacturing.
(Presented at the APCO Fabric Filter
Symposium, Charleston, March 1971.) p.
10, 15, 17-19.
A-5
-------
DIRT AND WATER
DISCHARGED AT
BLADE TIPS
WATER SPRAY
NOZZLE
-WATER AND
SLUDGE OUTLET
Figure A-5. Centrifugal fan wet scrubber.1
A-6
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SUBJECT INDEX
Brake linings
emissions from, 3-30
4-8
- 3-36, 3-48, 3-49,
Actinolite, 2-1 -2-3,3-1
Amosite, 2-1 - 2-3, 3-1, 3-22, 3-42
Amphibole, 2-1, 3-1
Anthophyllite, 2-1 - 2-3, 3-1
Asbestos
emissions (see Emissions)
end-use of products (see End-use)
health effects, 1-1, 2-8, 3-49
ore, 2-4, 3-1
origins, 2-4, 2-6
properties, 2-1 2-3
uses, 2-4
Asbestos-asphalt paving compounds (see Pav-
ing)
Asbestos-cement products (see Cement pro-
ducts)
Asbestos-containing friction materials (see
Emissions and End-use)
Asbestos paper (see Paper)
Asbestos products (see Products)
Asbestos textile products (see Textiles)
Asbestos waste materials (see Waste disposal)
Asphalt (see Paving)
B
Baghouses, (see Control equipment)
Beneficiation of ore, 2-4, 2-5
Blasting
control techniques, 3-2 3-4
emissions, 3-2
operations, 3-2
Blending
control techniques, 3-18 - 3-21, 3-39
emissions, 3-17
operations, 3-17
Cement products
control techniques, 3-25, 3-26, 4-7, 4-8
emissions, 3-25, 4-7, 4-8
manufacture, 3-22 3-25
Centrifugal collectors (see Control equip-
ment)
Chrysotile, 2-1 - 2-3, 3-1, 3-28, 3-42
Control costs (type)
annualized, 4-6, 4-7
capital, 4-1 - 4-3, 4-6
maintenance, 4-3 4-6
operating, 4-3 4-6
Control costs (equipment), 4-5 4-7
Control equipment
afterburners, 3-35, 3-36
baghouses, A-3
cyclones, 3-6, 3-10
dry centrifugal collectors, 3-2, A-4
dust capture hoods, 3-9, 3-13, 3-18 - 3-20,
3-25, 3-26,3-29, 3-35, 3-39, 340, 3-47.
349,3-51,3-52
electrostatic precipitators, 3-11
fabric filters, 3-2, 3-8, 3-9, 3-11, 3-39, 3-4!,
3-50, 3-52, A-l - A-4
wet collectors and scrubbers, 3-10, A-4,
A-5
Control techniques
end-use applications (asbestos-containing
products)
field fabrications, 3-47, 3-48
fireproofing operations, 3-44 3-46
insulating operations, 3-44 3-46
paving operations, 3-41
-------
manufacturing (asbestos-containing pro-
ducts)
asphalt paving materials, 3-41
cement, 3-25,3-26
friction materials, 3-35
paper, 3-39
textiles, 3-39, 3-40
Costs (see Control costs)
Crocidolite, 2-1 - 2-3, 3-1, 3-22, 3A2
Crushing
control techniques, 3-6
emissions, 2-9, 3-8
operations, 3-5, 3-6
D
Drilling
control techniques, 3-2, 3-3
emissions, 3-2, 3-3
operations, 3-2, 3-3
Dry centrifugal collectors (see Control equip-
ment)
Drying
control techniques, 4-8
emissions, 3-9, 4-8
operations, 3-6
Dumping
control techniques, 3-5
emissions, 3-5, 3-8
Dust (see Emissions)
Dust capture hoods (see Control equipment)
friction materials, 3-34, 3-48, 349
paper, 3-29
textiles, 3-37 - 3-39
major sources of, 2-4 2-11
End-use (asbestos-containing products)
field-fabricated products, 3-46 - 3-48
fireproofing materials, 3-42 3-46
friction materials, 3-29 - 3-36, 3-48, 3-49
insulating materials, 3-42 3-46
Fabric filters (see Control equipment)
Fibers
counting techniques, 2-1, 2-5 2-8
properties, 2-1
size distribution, 2-1, 2-4, 2-5
Fibrils, 2-4, 2-5
Fireproofing materials (see End-use)
Friction materials (see End-use)
Gas cleaning devices (see Control equipment)
Grading
emissions, 3-9
operations, 3-9
I
E
Emissions, asbestos
end-use applications (asbestos-containing
products)
field fabrications, 3-47
fireproofing operations, 3-43, 3-44
insulating operations, 3-43, 3-44
manufacturing (asbestos-containing pro-
ducts)
asphalt paving materials, 3-41
cement, 3-26
Insulating materials (see Emissions and End-
use)
M
Measurement techniques (fibers), 2-1, 2-6
2-8
Milling
control techniques, 3-9 3-15
emissions, 2-9, 3-8, 3-9, 3-49, 3-50
operations, 3-5 3-8
1-2
-------
Mining
control techniques, 3-2 - 3-5
emissions, 2-9, 3-1, 3-2, 3-49, 3-50
operations, 3-1
N
New technology, 3-45, 6-1
Textiles (asbestos-containing)
control techniques, 3-39, 3-40
emissions, 3-37 3-39
manufacturing processes, 3-36, 3-37
Tile
control techniques, 3-26, 4-8
emissions, 3-26, 4-8
manufacturing processes, 3-26
Tremolite, 2-1, 3-1
Paper
control techniques, 3-29
emissions, 3-29
operations, 3-28, 3-29
Particulates (see Emissions)
Paving
control techniques, 3^-1
emissions, 3-41
operations, 3-40, 3-41
Products, asbestos-containing
control techniques, 3-18 - 3-22
emissions, 2-9, 3-15 3-18
manufacturing processes, 3-15 3-1:
Vinyl-asbestos tile (see Tile)
W
Serpentine, 2-1,2-9, 3-1
Silicates, 2-1
Waste disposal
control techniques, 3-51 3-53
emissions, 3-50, 3-51
processes, 3-49, 3-50
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