United States Office of Air Quality EPA-453/R-97-004
Environmental Protection Planning and Standards December 1997
Agency Research Triangle Park, NC 27711
Air
S, 3.
EPA Guideline Series
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Guideline Series:
Control of Volatile Organic Compound Emissions from Coating Operations at Aerospace
Manufacturing and Rework Operations
Emission Standards Division
U. S. Environmental Protection Agency
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
December 1997
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This report has been reviewed by the Emission Standards Division of the Office of Air
Quality Planning and Standards, EPA and approved for final publication. Mention of trade names
or commercial products is not intended to constitute endorsement or recommendation for use.
The guideline series of reports is issued by the Office of Air Quality Planning and Standards
(OAQPS) to provide information to State and local air pollution control agencies; for example, to
provide guidance on the acquisition and processing of air quality data and on the planning and
analysis requisite for the maintenance of air quality. Reports published in this series will be
available from the Library Services Office (MD-35), U. S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; from the Office of Air Quality Planning and
Standards Technology Transfer Network, U. S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711; or, for a fee, from the National Technical Information
Services, 5285 Port Royal Road, Springfield, Virginia 22161.
Publication No. EPA-453/R-97-004
in
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IV
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TABLE OF CONTENTS
1.0 INTRODUCTION 1-1
2.0 AEROSPACE MANUFACTURING AND REWORK OPERATIONS 2-1
2.1 GENERAL 2-1
2.2 PROCESS DESCRIPTION 2-3
2.2.1 Coating Application 2-3
2.2.2 Cleaning 2-6
3.0 EMISSION CONTROL TECHNIQUES 3-1
3.1 COATING SUBSTITUTIONS 3-1
3.2 EQUIPMENT CHANGES 3-2
3.2.1 High Transfer Efficiency Spray Guns 3-2
3.2.2 Spray Gun Cleaning 3-5
3.2.3 Conventional High Transfer Efficiency
Application Methods 3-6
3.3 HAND-WIPE CLEANER SUBSTITUTIONS 3-7
3.3.1 Aqueous and Semiaqueous 3-7
3.3.2 Citrus-Based 3-7
3.3.3 Reduced Vapor Pressure 3-8
4.0 PRESUMPTIVE RACT REQUIREMENTS 4-1
4.1 SPECIALTY COATINGS 4-1
4.2 PRIMERS, TOPCOATS, CHEMICAL MILLING
MASKANTS 4-3
4.3 APPLICATION EQUIPMENT 4-3
4.3.1 Exemptions 4-3
4.3.2 Timing (Schedule) of Compliance 4-4
4.4 CLEANING OPERATIONS 4-4
4.4.1 Housekeeping 4-4
4.4.2 Hand-Wipe Cleaning 4-5
4.4.3 Flush Cleaning 4-6
4.4.4 Spray Gun Cleaning 4-6
5.0 GUIDANCE TO STATE ENFORCEMENT AGENCIES 5-1
5.1 DEFINITIONS 5-1
5.2 APPLICABILITY 5-2
5.3 COMPLIANCE, MONITORING, RECORDKEEPING &
REPORTING PROVISIONS 5-2
APPENDIX A DEFINITIONS A-l
APPENDIX B AEROSPACE MANUFACTURING AND REWORK
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OPERATIONS MODEL RULE B-l
VI
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LIST OF FIGURES
Figure 2-1. Active U. S. aerospace manufacturing
facilities 2-4
LIST OF TABLES
Page
TABLE 2-1. AEROSPACE MANUFACTURING SIC CODES 2-2
TABLE 3-1. PERCENT REDUCTION IN COATING (PRIMERS
AND TOPCOATS) EMISSIONS WITH HIGH
TRANSFER EFFICIENCY EQUIPMENT FROM
SECTION 114 DATA 3-4
TABLE 4-1. SPECIALTY COATINGS VOC CONTENT
LIMITS 4-2
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1.0 INTRODUCTION
The Clean Air Act (CAA) as amended in 1990 requires that State implementation plans
(SIP's) for certain ozone nonattainment areas be revised to require the implementation of
reasonably available control technology (RACT) to control volatile organic compound (VOC)
emissions. The U. S. Environmental Protection Agency (EPA) has defined RACT as the lowest
emission limitation that a particular source is capable of meeting by the application of control
technology that is reasonably available considering technological and economic feasibility. The
EPA has issued, and is continuing to issue, control techniques guideline documents (CTG's) that
present feasible RACT control measures for VOC source categories. The CTG's recommend
"presumptive norms" of control for each source category, but individual sources may have
alternative RACT requirements imposed by making an adequate infeasibility demonstration (44
FR 53761, September 17, 1979).
Section 183(b)(3) of the CAA requires the EPA Administrator to issue a CTG for the
control of VOC emissions from coatings and solvents used in the aerospace industry. This CTG
is intended to supersede any potential applicability of the Miscellaneous Metal Part and Products
CTG (RACT) requirements for manufacturing and rework operations of aerospace vehicles and
components. According to the CAA, this CTG guidance should also reflect control resulting
from applying the "best available control (BAG) measures." Section 183(e)(l)(A) defines "BAG"
as the "most effective equipment, measures, processes, methods, systems or techniques, including
chemical reformulation, product or feedstock substitution, repackaging, and directions for use,
consumption, storage, or disposal." Therefore, this CTG departs from the approach followed in
the other CTG's by not recommending a single approach for determining RACT, but investigating
a range of approaches to reduce VOC emissions from aerospace operations. Several optional
approaches comprise the presumptive RACT found in this CTG.
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The CTG's are intended to provide State and local air pollution control authorities with an
information base for proceeding with their analyses of RACT for their own regulations. The
CTG's contain a review of current knowledge and data concerning the technology, impacts, and
costs associated with various emission control techniques. Where applicable, the EPA
recommends that States adopt requirements consistent with the presumptive RACT. However,
these measures are only a recommendation; States may develop their own RACT requirements on
a case-by-case basis, considering the economic and technical circumstances of individual sources.
It should be noted that no Federal laws or regulations preclude States from requiring more
stringent controls than those recommended as RACT. A particular State, for example, may
broaden the applicability by revising the "aerospace vehicle or component" definition to include
models, mock-ups, prototypes, and production equipment such as molds, jigs, and tooling. Some
States may need additional control in order to meet the national ambient air quality standards
(NAAQS) for ozone in some areas.
This CTG identifies presumptive RACT for controlling VOC emissions from aerospace
coatings and cleaning solvents. National emission standards for hazardous air pollutants
(NESHAP) for aerospace manufacturing and rework operations were published on September 1,
1995 (60 FR 45948). While these final standards address the reduction of HAP emissions, the
control techniques required by the NESHAP will result in reductions of VOC emissions as well.
In addition, the control techniques required by the NESHAP are similar to those addressed in this
CTG for reducing VOC emissions. Because the emission reductions, costs, and environmental
impacts have already been determined for major HAP sources and are attributed to the NESHAP
(see Docket No. A-90-20, Subcategory II-B), these impacts are not summarized in this CTG.
While the Aerospace NESHAP sets limits for maximum HAP and VOC content for
topcoats, primers, maskants, clean-up solvents, and cleaning operations, the CTG establishes
presumptive RACT limits for VOC's. The CTG includes requirements for Specialty Coatings,
which are not covered by the Aerospace NESHAP. The Clean Air Act specifies that solvents will
be addressed in the Aerospace CTG. However, because the CTG is guidance to be adopted as
individual State regulations and SIP's, it does not specify detailed requirements for monitoring,
testing, recordkeeping, and reporting as the NESHAP has done. Rather, the States are directed
under previous EPA guidance for establishing RACT (57 FR 13502, April 16, 1992) to develop
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"enforceable regulations" containing such requirements. While EPA is providing an example of
such a regulation in the model rule (Appendix B), this CTG allows States the flexibility to address
those requirements as long as they meet EPA enforceability criteria.
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2.0 AEROSPACE MANUFACTURING AND REWORK OPERATIONS
2.1 GENERAL
The aerospace industry being evaluated includes all manufacturing facilities that produce
an aerospace vehicle or component and all facilities that rework or repair these aerospace
products. Aerospace vehicle or component is defined as, but not limited to, any fabricated part,
processed part, assembly of parts, or completed unit of any aircraft including, but not limited to,
airplanes, helicopters, missiles, rockets, and space vehicles. In addition to manufacturing and
rework facilities, some shops may specialize in providing a service, such as chemical milling,
rather than actually producing a component or assembly. In general, aerospace manufacturing
and rework facilities are covered by the SIC codes listed in Table 2-1. However, facilities
classified under other SIC codes may be subject to the proposed rule if the facility meets the
definition of a major source and the definition of an aerospace manufacturing or rework facility.
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TABLE 2-1. AEROSPACE MANUFACTURING SIC CODES
SIC Code
3720
3721
3724
3728
3760
3761
3764
3769
4512
4581
9711
Description
Aircraft and Parts
Aircraft
Aircraft Engines and Engine Parts
Aircraft Parts and Equipment
Guided Missiles, Space Vehicles, and Parts
Guided Missiles and Space Vehicles
Space Propulsion Units and Parts
Space Vehicle Equipment
Air Transportation, Scheduled
Airports, Flying Fields, and Services
National Security
Aerospace facilities may be divided into four market segments: commercial original
equipment manufacturers (OEM), commercial rework facilities, military OEM's, and military
rework facilities. The commercial OEM segment of the market includes the manufacture of
commercial aircraft as well as the production of business and private aircraft. The military OEM
segment of the market includes military installations and defense contractors that manufacture
aircraft, missiles, rockets, satellites, and spacecraft. Rework facilities, both commercial and
military, may rework many of the above end products.
Based on information obtained through the Federal Aviation Administration and the U.S.
Department of Commerce - Bureau of the Census, there are an estimated 2,869 aerospace
facilities that could be subject to this guidance. Of this number, 1,395 produce or rework
commercial products, and 1,474 produce or rework military products. The combined VOC
emissions from these facilities are estimated to be over 213,000 megagrams/year (Mg/yr)
(234,000 tons/yr).
In addition to these facilities, there are numerous subcontractors that manufacture or
rework aerospace vehicles or components. The subcontractors may work directly for the OEM
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or rework facilities, or indirectly through first line subcontractors. Because most of these
subcontractors perform various types of work, they are often classified under non-aerospace SIC
codes. Consequently, an estimate of the number of subcontractors cannot be made. One
company alone, however, employs the services of over 5,000 subcontractors.
Aerospace manufacturing facilities and rework operations typically are located in or near
industrial centers in areas of medium to high population density. Some States with a large number
of aerospace manufacturers are California, Texas, Connecticut, Florida, and Washington.
Figure 2-1 presents the number of aerospace manufacturing facilities by State.
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2-4
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MA-76
RI-4
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Aerospace manufacturing facilities range in size from small shops that produce a single
aerospace component, such as propellers, to large corporations that produce the entire aircraft.
Aerospace rework facilities, however, are usually large facilities that must be able to rework or
repair every facet of several models of large commercial or military aircraft.
The hours of operation at aerospace manufacturing and rework facilities may vary greatly
due to the production backlog at each facility. The hours of operation may range from 8 hours
(or less) per day, 5 days per week, to 24 hours per day, 7 days per week.
2.2 PROCESS DESCRIPTION
Aerospace manufacturing and rework operations typically consist of the following basic
operations: materials receiving, machining and mechanical processing, coating application,
chemical milling, heat treating, cleaning, metal processing and finishing, coating removal
(depainting), composite processing, and testing. Many aerospace manufacturing and rework
facilities may employ all of these processes in their operations, as with an OEM facility that
produces the entire aerospace vehicle. However, an aerospace facility may only employ a subset
of these operations, as with a facility that produces a single component or assembly or a facility
that provides a service such as chemical milling. Of these operations, coating application and
cleaning are the significant sources of VOC emissions and are the processes covered by this
Aerospace CTG in the following sections.
2.2.1 Coating Application
A coating is a material that is applied to the surface of a part to form a decorative,
protective, or functional solid film. The most common coatings are the broad categories of
nonspecialized primers and topcoats that are regulated for major sources under the Aerospace
NESHAP. There are also numerous specialty coatings covered by this guidance that provide
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additional performance characteristics, such as temperature, fluid, fire resistance, flexibility,
substrate compatibility, antireflection, temporary protection or marking, sealing, adhesively
joining substrates, enhanced corrosion protection, or compatibility with a space environment.
Each material is different because it must meet individual performance standards particular to a
specific design. The quality of the coatings is critical to the airworthiness and safety of the final
product. Aerospace vehicle manufacturing is strictly controlled by the Federal Aviation
Administration, the Department of Defense, and specific customer requirements. Industry
specifications for coatings are dictated by these requirements.
Most aerospace coatings are solvent-borne, which contain a mixture of organic solvents,
many of which are VOC's. The most common VOC solvents used in coatings are toluene, xylgne,
methyl ethyl ketone, and methyl isobutyl ketone. The VOC content ranges differ for the various
c
coating categories. §
"8
2.2.1.1 Sealing. Sealants, predominately composed of polysulfide, are applied throughout
the aerospace vehicle structure primarily to seal out moisture and contaminants to prevent |
0)
corrosion, such as on faying (i.e., closely or tightly fitting) surfaces, inside holes and slots, andi
OH
around installed fasteners. They are also used to seal fuel tanks and pressurized components. 8
ctf
Sealants are applied using tubes, spatulas, brushes, rollers, or spray guns. Sealants are often ^
stored frozen and thawed before use, and many are two-component mixtures that cure after 0
mixing. Typically, a sealant is applied before assembly or fastener installation, and the excessjij
squeezed out or extruded from between the parts as the assembly is completed. This ensures^'
(N
moisture-tight seal between the parts. g
2.2.1.2 Adhesive Bonding. Adhesive bonding involves joining together two or more £
metal or nonmetal components. This process is typically performed when the joints being formed
are essential to the structural integrity of the aerospace vehicle or component. Bonding surfaces
are typically roughened mechanically or etched chemically to provide increased surface area for
bonding and then treated chemically to provide a stable corrosion-resistant oxide layer. The
surfaces are then thinly coated with an adhesive bonding primer to promote adhesion and protect
from subsequent corrosion. Structural adhesives are applied as either a thin film or as a paste.
The parts are joined together and cured either at ambient temperature, in an oven, or in an
autoclave to cure the adhesive and provide a permanent bond between the components.
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Nonstructural adhesives are used to bond materials that are not critical to the structural
integrity of the aerospace vehicle or component, such as gaskets around windows and carpeting
or to nonstructurally joined components. These adhesives are applied using tubes, brushes, and
spray guns.
2.2.2 Cleaning
Cleaning agents for hand-wipe, flush, and spray equipment cleaning consist of solvents
such as methyl ethyl ketone, methyl isobutyl ketone, toluene, various solvent blends, or alkaline
materials.
2.2.2.1 Hand-Wipe and Flush Cleaning. Aerospace components are cleaned frequently
during manufacturing to remove contaminants such as dirt, grease, and oil, and to prepare the
components for the next operation. Cleaning is typically performed by a hand wiping process
using a wide variety of cleaning solvents. Assemblies and parts with concealed or inaccessible
areas may be flush-cleaned by passing the cleaning agent over, into, or through the part. The
cleaning agent is then drained from the part and the procedure is repeated as many times as
necessary to ensure the required cleanliness.
2.2.2.2 Spray Gun and Coating Line Cleaning. Spray guns and coating lines used to
apply the various coatings used at aerospace facilities must be cleaned when switching from one
coating to another and when they are not going to be immediately reused. Spray guns can be
cleaned either manually or with enclosed spray gun cleaners. Manual cleaning involves
disassembling the gun and placing the parts in a vat containing an appropriate cleaning solvent.
The residual paint is brushed or wiped off the parts. After reassembling, the cleaning solvent may
be sprayed through the gun for a final cleaning. Paint hoses/coating lines are cleaned by passing
the cleaning solvent through the lines until all coating residue is removed. Enclosed spray gun
cleaners are self-contained units that pump the cleaning solvent through the gun within a closed
chamber. After the cleaning cycle is complete, the guns are removed from the chamber and
typically undergo some manual cleaning to remove coating residue from areas not exposed to the
cleaning solvent, such as the seals under the atomizing cap.
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3.0 EMISSION CONTROL TECHNIQUES
The principal technique used by the aerospace industry to control VOC emissions from
coating application and cleaning is product substitution, which eliminates or reduces the
generation of emissions. The emission reduction is obtained using less energy and producing less
waste than using a control device to achieve the same emission reductions.
The VOC emissions may be controlled by replacing products containing high
concentrations of VOC's with ones that have reduced or eliminated VOC's. Different aerospace
manufacturers use different processes to produce their product. Therefore, they typically have
different specifications for the coatings and cleaning solvents used on the components of the end
products. Each individual facility must evaluate the ability of the new product to maintain
standards of quality and performance. In addition, the potential overall environmental benefit of
the reformulated products must be carefully evaluated.
The following sections describe the available product substitutions for coatings and
cleaning solvents. While alternative methods, such as control devices (carbon adsorbers,
incinerators, etc.), are occasionally used to reduce emissions, they do not represent RACT and
are, therefore, not discussed below.
3.1 COATING SUBSTITUTIONS
Waterborne and high solids materials are generally used for coating substitutions.
Specialty coatings typically have relatively low usage, so reformulation to lower VOC contents
does not produce significant air quality benefits nor is it economically feasible for the paint
suppliers. Paint suppliers and the aerospace industry generally have targeted high volume
materials for reformulation efforts. Therefore, lower VOC formulations are not available for most
of the low volume specialty coating categories.
3.2 EQUIPMENT CHANGES
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The aerospace industry has implemented several equipment changes that directly reduce
the level of VOC emissions. While there are equipment changes that effect emissions from every
process, the three changes predominantly used in the industry are high transfer efficiency spray
guns, spray gun cleaners, and conventional high transfer efficiency methods. Each of these
equipment changes are discussed below.
3.2.1 High Transfer Efficiency Spray Guns
Emissions from spray coating operations can be reduced through the use of spraying
systems with higher transfer efficiency. Transfer efficiency, expressed as a percentage, can be
defined as the ratio of coating solids actually applied to the surface of the component being coated
to the amount of solids released from the spray gun. Spraying systems with a higher transfer
efficiency can coat the same surface area using less coating. Therefore, the VOC emissions
resulting from the use of this equipment are reduced compared to applying the same coating with
conventional spray equipment. The transfer efficiency values reported in this section depend on
coating sprayed, part configuration, spray booth air velocity, and other variables.
Most aerospace components are coated using manual spray equipment utilizing
conventional airspray or airless spraying technology. The following sections discuss two types of
high transfer coating application equipment generally used in the aerospace industry for the
application of primers and topcoats: high volume, low pressure (HVLP) and electrostatic (use of
these types of high transfer efficiency for specialty coatings is limited).
3.2.1.1 High Volume Low Pressure Spray Guns. High volume low pressure and
electrostatic spraying systems are the primary high efficiency spray methods used by the industry.
High volume low pressure spray guns use high volumes [10 to 25 standard cubic feet per minute
(scfm)] of low pressure [2 to 10 pounds per square inch gauge (psig)] air to deliver the paint.
The lower air pressure creates a lower particle speed, resulting in a more controlled spray pattern
with less overspray and bounce back from the substrate, thus improving transfer efficiency.
High volume low pressure systems have been in use in the United States for approximately
10 years. In early systems, turbines were used to supply a high volume of low pressure air to the
spray guns through large hoses. The second generation used compressed air with an air regulator
to maintain the required low pressure. The third and current generation of HVLP equipment uses
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restrictors within the gun to reduce the atomization pressure to a maximum of 10 psi at the air
cap.
One disadvantage of HVLP spray guns is that some very high solids coatings are difficult
to atomize due to their higher viscosities. However, when a turbine is used, the temperature of
the atomizing air increases which aids in reducing the viscosity of the coating. Other
disadvantages of HVLP spray guns are that they cannot be used with extension nozzles, and they
may slow production rates because of the low fluid delivery rates.
It is estimated that HVLP can apply approximately 80 percent of the coating currently
used in the aerospace industry, including primers, waterborne coatings, and both single and two-
component topcoats. A medium commercial/rework facility utilizes HVLP equipment with high
solids paint and has had a reduction of 22 to 30 percent in coating usage for various aircraft types.
The HVLP technology has proven easy to use and maintain. It also provides high transfer
efficiency and appears to be the preferred spray technology in the aerospace industry at this time.
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Table 3-1
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TABLE 3-1. PERCENT REDUCTION IN COATING EMISSIONS
(PRIMERS AND TOPCOATS) WITH HIGH TRANSFER
EFFICIENCY EQUIPMENT FROM SECTION 114 DATA
Size
Large
Large
Large
Large
Large
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Medium
Commercial or
military
Military
Military
Military
Commercial
Commercial
Commercial
Military
Military
Commercial
Military
Military
Military
Military
Military
Military
Military
Military
Military
Commercial
Commercial
Commercial
OEM or
rework
OEM
OEM
OEM
OEM
OEM
OEM
OEM
Rework
OEM
OEM
Rework
OEM
OEM
OEM
OEM
OEM
Rework
Rework
OEM
OEM
Rework
High transfer
equipment
HVLP
HVLP
HVLP
Unspecified
Unspecified
HVLP
HVLP
HVLP and
electrostatic
HVLP and
electrostatic
HVLP
HVLP
Electrostatic
HVLP and
electrostatic
Unspecified
Unspecified
HVLP and
electrostatic
% Reduction in
emissions
20
20
25
30
18
25
20-40
40
40
40
10
30-40
35-40
30
33
50
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shows the reduction in emissions obtained from the Section 114 questionnaire responses from
various facilities utilizing high transfer efficiency equipment such as HVLP or electrostatic
equipment, either alone, in conjunction with each other, or, in one case, HVLP equipment with
high solids coatings.
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3.2.1.2 Electrostatic Spray Guns. With electrostatic spray systems, atomized particles of
coating acquire an electric charge as they pass through a high voltage field at the end of the spray
nozzle. This electric charge causes the particles to be attracted to the parts being painted, which
are electrically grounded. Although other substrates can be pretreated with conductive coatings,
this technology is primarily used for metal parts. The electrostatic effect can be utilized in
conjunction with air spray, airless, and air-assisted airless systems to enhance the transfer
efficiencies of these basic technologies. See Table 3-1 for examples of percent reduction obtained
at various facilities using electrostatic spray guns or electrostatic spray guns in combination with
HVLP spray guns.
3.2.2 Spray Gun Cleaning
Spray guns are typically cleaned at the end of every job, as well as between color changes.
Manual cleaning of spray guns involves disassembling the gun and placing the parts in a tray
containing an appropriate cleaning solvent. The residual paint is brushed or wiped off the parts,
then cleaning solvent is sprayed through the gun after it is reassembled. Various methods are
used to minimize the resulting emissions from spray gun cleaning and are discussed below.
Enclosed system. Enclosed spray gun cleaners are completely enclosed units that spray
the cleaning solvent through and over the spray gun. The enclosed unit eliminates most of the
exposure of the cleaning solvent to the air, thereby greatly reducing the VOC emissions from
evaporation.
Nonatomized cleaning. Cleaning solvent is placed in the pressure pot and forced through
the gun with the atomizing cap in place. No atomizing air is to be used. The cleaning solvent
from the spray gun is directed into a vat, drum, or other waste container that is closed when not in
use.
Disassembled spray gun cleaning. Manual cleaning (described above) with the
components cleaned by hand in a vat, which is only closed when not in use. Alternatively, the
components are soaked in a vat, which is closed at all times except when components are being
inserted or removed.
Atomizing cleaning. Cleaning solvent is forced through the spray gun and the resulting
atomized spray is directed into a waste container that is fitted with a device designed to capture
the atomized solvent emissions.
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3.2.3 Conventional High Transfer Efficiency Application Methods
Conventional high transfer efficiency application methods for primers and topcoats include
dip, roll, brush, and flow coating (use of these methods for specialty coatings is limited). These
methods are discussed below.
Dip Coating. With dip coating application, parts are immersed into a tank of coating. The
parts are then removed from the tank and held over it until the excess coating drips back into the
tank. This method is simple and allows many different parts to be coated with high transfer
efficiency. However, dip coating is limited to parts that can fit into the dip tank. Other parts
difficult to dip coat could include complex parts that would trap the coating, allowing unequal
coating thicknesses.
Roll Coating. In roll coating application, a series of mechanical rollers are used to coat
flat surfaces. This method achieves high efficiency with high rates of application and automation.
However, roll coating is limited to flat parts.
Brush Coating. In brush coating application, brushes and hand rollers are used to apply
the coating manually. This method is used with operations (e.g., touch-up and detail painting)
that cannot tolerate the overspray associated with spray gun application. For example, if a facility
needs to paint only the tail section of an airplane, it may be easier to brush coat this area than to
mask the entire plane to protect the rest of the shell from overspray. This application method
typically involves high labor costs, increased production time, and poor coating thickness control.
Flow Coating. In flow coating application, the part is conveyed over a closed sink, and a
pumped stream of coating gently flows over the surface of the part. The excess coating is drained
into the sink, filtered, and pumped to a holding tank for reuse. Flow coating is typically limited to
flat sheets and noncritical parts. Coating thickness is difficult to control using flow coating.
3.3 HAND-WIPE CLEANER SUBSTITUTIONS
Product substitutions for hand-wipe cleaning that are prevalent in the aerospace industry
can be classified as aqueous, semiaqueous, citrus-based, and reduced vapor pressure. Each
category is discussed below.
3.3.1 Aqueous and Semiaqueous
Aqueous and semiaqueous cleaners contain water as the base component rather than an
organic solvent or mixture of solvents. Other components may include corrosion inhibitors,
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alkalinity builders, and organic surfactants, depending on the desired soil removal properties.
Aqueous and semiaqueous cleaners have been used in noncritical areas where strict cleanliness
requirements do not have to be met, or where there are no confined spaces that may trap residues
of the cleaner.
The advantages of using aqueous and semiaqueous cleaning solvents include reduced
VOC emissions. Disadvantages are increased production time due to slower evaporation rates,
possible decreased efficiency, and possible increase in wastewater treatment requirements. In
addition, aqueous cleaners may not be applicable to all aerospace parts, especially those
components that have small confined spaces where the cleaner residues cannot be adequately
removed.
3.3.2 Citrus-Based
Citrus-based terpenes such as d-limonene are the primary components in many alternative
cleaning solutions. While these solutions have high VOC contents, their vapor pressure is very
low, leading to reduced evaporation rates. These cleaners have been found to be effective in
some cleaning operations except for cleaning prior to adhesive bonding. Some disadvantages
include possible worker sensitivity, VOC emissions, lack of rinseability in water, and increased
production time due to slower evaporation rates.
3.3.3 Reduced Vapor Pressure
Reduced vapor pressure cleaning solvents have a maximum VOC composite vapor
pressure of 45 millimeters of mercury (mmHg) at 20 °C. Cleaning solvent emissions are reduced
because their lower vapor pressure leads to reduced evaporation rates. These cleaners are
effective in many cleaning operations except for some limited operations such as cleaning oxygen
systems.
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4.0 PRESUMPTIVE RACT REQUIREMENTS
The presumptive RACT requirements for the aerospace component and vehicle cleaning
and coating operations are described in the following sections. The operations covered by this
CTG shall not be subject to another CTG. The operations and applications exempted under this
CTG shall not be subject to another CTG. Applicable definitions are included in Appendix A.
These presumptive RACT requirements do not apply to manufacturing or rework
operations involving space vehicles; rework operations performed on antique aerospace vehicles
or components; or to the following activities where cleaning and coating of aerospace
components and vehicles may take place: research and development, quality control, laboratory
testing, and electronic parts and assemblies (except for cleaning and coating of completed
assemblies).
4.1 SPECIALTY COATINGS
Presumptive RACT for coatings used on aerospace components and vehicles is based on
VOC content. Except as provided in Sections 4.0 and 4.1, the presumptive RACT for coating
VOC content is the use of coatings with a VOC content less than or equal to that given in
Table 4-1: Specialty Coatings VOC Content Limits.
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TABLE 4-1. SPECIALTY COATINGS VOC CONTENT LIMITS (g/L)a
Coating type
Limit Coating type
Limit
Ablative Coating 600 Epoxy Polyamide Topcoat ....
Adhesion Promoter 890 Fire-Resistant (interior) Coating
Adhesive Bonding Primers: Flexible Primer
Cured at 250°F or below 850
Cured above 250°F 1030
Adhesives:
Commercial Interior Adhesive 760
Cyanoacrylate Adhesive 1,020
Fuel Tank Adhesive 620
Nonstructural Adhesive 360
Rocket Motor Bonding Adhesive . . . 890
Rubber-based Adhesive 850
Structural Autoclavable Adhesive .... 60
Structural Nonautoclavable Adhesive 850
Antichafe Coating 660
Bearing Coating 620
Caulking and Smoothing Compounds .850
Chemical Agent-Resistant Coating .... 550
Clear Coating 720
Commercial Exterior Aerodynamic
Structure Primer 650
Compatible Substrate Primer 780
Corrosion Prevention Compound 710
Cryogenic Flexible Primer 645
Cryoprotective Coating 600
Dry Lubricative Material 880
Electric or Radiation-Effect Coating . . 800
Electrostatic Discharge and Electromagnetic
Interference (EMI) Coating 800
Elevated-Temperature Skydrol-Resistant
Commercial Primer 740
660
800
640
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Exemptions. The following applications are exempt from the presumptive RACT coating
limits in Table 4-1:
1. Touchup, aerosol, and DOD classified coatings;
2. Coatings used on space vehicles; and
3. Facilities that use separate formulations in volumes of less than 50 gallons per year,
subject to a maximum exemption of 200 gallons for all such formulations applied annually.
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4.2 PRIMERS, TOPCOATS, CHEMICAL MILLING MASKANTS
The broad categories of primers, topcoats (including self-priming topcoats), and chemical
milling maskants (Type I/II) are not specialty coatings as listed in Table 4-1 and are regulated for
major sources under the Aerospace NESHAP requiring MACT limits with a compliance date
specified in 40 CFR 63.749(a). These limits may be assumed to represent RACT limits 1 year
after the major sources are required to meet the MACT limits and, therefore, shall not be effective
until 1 year after the NESHAP compliance date of September 1, 1998. The requirements do not
apply to facilities that use separate formulations of primers, topcoats, and chemical milling
maskants (Type I/II) in volumes of less than 50 gallons per year, subject to a maximum exemption
of 200 gallons total for such formulations applied annually.
4.3 APPLICATION EQUIPMENT FOR PRIMERS AND TOPCOATS
Presumptive RACT for primer and topcoat (including self-priming topcoats) application
equipment used on aerospace components and vehicles is based on current practices and
requirements in some States. Except as provided in Section 4.3 and Subsection 4.3.1, the
presumptive RACT for primer and topcoat (including self-priming topcoat) application equipment
is the use of one or more of the following application techniques: flow/curtain coat; dip coat; roll
coating; brush coating; cotton-tipped swab application; electrodeposition coating; high volume
low pressure (HVLP) spraying; electrostatic spray; or other coating application methods that
achieve emission reductions equivalent to HVLP or electrostatic spray application methods.
4.3.1 Exemptions
The following situations are exempt from the presumptive RACT application techniques
described in Section 4.3:
1. Any situation that normally requires the use of an airbrush or an extension on the spray
gun to properly reach limited access spaces;
2. The application of specialty coatings;
3. The application of coatings that contain fillers that adversely affect atomization with
HVLP spray guns and that the permitting agency has determined cannot be applied by any of the
application methods specified in Section 4.3;
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4. The application of coatings that normally have a dried film thickness of less than
0.0013 centimeter (0.0005 in.) and that the permitting agency has determined cannot be applied
by any of the application methods specified in Section 4.3;
5. The use of airbrush application methods for stenciling, lettering, and other
identification markings;
6. The use of hand-held spray can application methods; and
7. Touch-up and repair operations.
4.3.2 Timing (Schedule) of Compliance
The application techniques identified as presumptive RACT are regulated for major
sources under the Aerospace NESHAP requiring MACT application equipment with a compliance
date of September 1, 1998 specified in 40 CFR 63.749(a). These equipment requirements may be
assumed to represent RACT requirements 1 year after the major sources are required to meet the
MACT equipment requirements and, therefore, shall not be effective until 1 year after the
NESHAP compliance date of September 1, 1998.
4.4 CLEANING OPERATIONS
For solvent cleaning operations, this guidance departs from the standard presumptive
RACT requirement to incorporate MACT level controls. Therefore, the requirements of
Section 4.2 shall not become effective prior to the Aerospace NESHAP compliance date of
September 1, 1998. The MACT and RACT for solvent cleaning is based on work practices and
cleaning solvent composition. Except as provided in Section 4.0 and Subsection 4.4.2, MACT
and RACT for certain activities is described below.
4.4.1 Housekeeping
All fresh and used cleaning solvents, except semiaqueous cleaning solvents, used in
solvent cleaning operations shall be stored in containers that shall be kept closed at all times
except when filling or emptying. It is recommended that cloth and paper, or other absorbent
applicators, moistened with cleaning solvents be stored in closed containers. Cotton-tipped swabs
used for very small cleaning operations are exempt. In addition, the owner or operator must
implement handling and transfer procedures to minimize spills during filling and transferring the
cleaning solvent to or from enclosed systems, vats, waste containers, and other cleaning operation
equipment that hold or store fresh or used cleaning solvents. The above requirements are known
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collectively as housekeeping measures. Aqueous cleaning solvents are excluded from these
housekeeping requirements.
4.4.2 Hand-Wipe Cleaning
Hand-wipe cleaning operations require the use of cleaning solvents which are aqueous or
have a VOC composite vapor pressure less than or equal to 45 millimeters of mercury (mm Hg) at
20°C.
Exemptions
The following cleaning operations would be exempt from the cleaning solvent composition
and vapor pressure requirements stated in Section 4.4.2:
1. Cleaning during the manufacture, assembly, installation, maintenance, or testing of
components of breathing oxygen systems that are exposed to the breathing oxygen;
2. Cleaning during the manufacture, assembly, installation, maintenance, or testing of
parts, subassemblies, or assemblies that are exposed to strong oxidizers or reducers (e.g., nitrogen
tetroxide, liquid oxygen, hydrazine);
3. Cleaning and surface activation prior to adhesive bonding;
4. Cleaning of electronics and assemblies containing electronics;
5. Cleaning of aircraft and ground support equipment fluid systems that are exposed to
the fluid, including air-to-air heat exchangers and hydraulic fluid systems;
6. Cleaning of fuel cells, fuel tanks, and confined spaces;
7. Surface cleaning of solar cells, coated optics, and thermal control surfaces;
8. Cleaning during fabrication, assembly, installation, and maintenance of upholstery,
curtains, carpet, and other textile materials used on the interior of the aircraft;
9. Cleaning of metallic and nonmetallic materials used in honeycomb cores during the
manufacture or maintenance of these cores, and cleaning of the completed cores used in the
manufacture of aerospace vehicles or components;
10. Cleaning of aircraft transparencies, polycarbonates, or glass substrates;
11. Cleaning and cleaning solvent usage associated with research and development,
quality control, or laboratory testing;
12. Cleaning operations, using nonflammable liquids, conducted within 5 feet of energized
electrical systems. Energized electrical systems means any AC or DC electrical circuit on an
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assembled aircraft once electrical power is connected, including interior passenger and cargo
areas, wheel wells, and tail sections; and
13. Cleaning operations identified as essential uses under the Montreal Protocol for which
the Administrator has allocated essential use allowances or exemptions in 40 CFR § 82.4.
4.4.3 Flush Cleaning
For cleaning solvents used in the flush cleaning of aerospace parts, assemblies, and coating
unit components, the used cleaning solvent (except for semiaqueous cleaning solvents) must be
emptied into an enclosed container or collection system that is kept closed when not in use or
captured on wipers and disposed of in accordance with Section 4.4.1. Aqueous cleaning solvents
are excluded from these flush cleaning requirements.
4.4.4 Spray Gun Cleaning
All spray guns must be cleaned by one or more of the following methods:
1. Enclosed spray gun cleaning system that is kept closed when not in use, provided that
leaks from enclosed spray gun cleaners are repaired within 14 days from when the leak is first
discovered. If the leak is not repaired by the 15th day after detection, the cleaning solvent shall be
removed and the enclosed cleaner shall be shut down until the leak is repaired or its use is
permanently discontinued;
2. Unatomized discharge of cleaning solvent into a waste container that is kept closed
when not in use;
3. Disassembled spray gun that is cleaned in a vat and kept closed when not in use; or
4. Atomized spray into a waste container that is fitted with a device designed to capture
atomized cleaning solvent emissions.
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5.0 GUIDANCE TO STATE ENFORCEMENT AGENCIES
This chapter presents information for air quality management agencies to consider in
developing an enforceable rule limiting VOC emissions from coating and solvent cleaning
operations at aerospace manufacturing and rework facilities. The State or other implementing
agency can exercise its prerogative to consider other options provided that they meet the
objectives prescribed in this chapter.
This guidance is for instructional purposes only and, as such, is not binding. In the
development of a State or local aerospace manufacturing and rework operations rule, the State or
other enforcement agency should consider all information presented in the CTG and the
promulgated NESHAP along with additional information about specific sources to which the rule
will apply. The reasonably available control technology (RACT) rule, however, should address all
the factors listed in this chapter and in Section 4 to ensure that the rule has reasonable provisions
for demonstrating compliance and is enforceable. A model rule which contains all these
requirements is provided in Appendix B. The model rule is guidance only and the State or local
agency has the flexibility to adopt alternative measures, including market-based incentive
programs, provided they meet EPA enforceability criteria.
5.1 DEFINITIONS
The RACT rule should accurately describe the types of sources that would be affected and
clearly define terms used to describe the industry or applicable control methods. Example
definitions of pertinent terms are presented in Appendix A for reference by the State or local
agency.
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5.2 APPLICABILITY
The recommended RACT described in this document applies to the manufacture of
aerospace vehicles and components as well as the rework or repair of these aerospace products.
(See Section 2.) This guidance has been developed for affected sources in areas of moderate,
serious, or severe nonattainment that have the potential to emit greater than or equal to 25 tons
per year of VOC's. The guidance is intended to apply to affected sources in extreme areas,
however, if potential VOC emissions are greater than or equal to 10 tons per year. The State or
local agency has the flexibility to apply RACT as deemed necessary. For example, an agency may
apply RACT to all sources that have actual emissions at 50 percent of these thresholds.
5.3 COMPLIANCE, MONITORING, RECORDKEEPING & REPORTING PROVISIONS
The State or local agency is responsible for ensuring that appropriate requirements for
compliance determination (testing), monitoring, recordkeeping and reporting are incorporated
into its RACT rule. These requirements must meet two objectives: (1) the agency's need to
demonstrate VOC emission reductions and (2) EPA's criteria for enforceability. Because source
types, compliance methods, and agency requirements may vary substantially across the nation,
specific provisions for compliance determination (testing), monitoring, recordkeeping and
reporting are not included in this CTG.
However, for a State's RACT rules to be enforceable, they must definitively set forth
recordkeeping, monitoring, and compliance determination (testing) requirements appropriate to
the type of source(s) being regulated and sufficient to allow determinations whether the source(s)
are in compliance. Therefore, EPA's Model Rule, which accompanies this CTG, contains
suggested recordkeeping, testing, and monitoring provisions that EPA believes are sufficient to
enable EPA and the States to determine compliance with the RACT requirements of the Model
Rule. The State or other implementing agency can exercise its prerogative to consider various
recordkeeping, testing, and monitoring requirements provided they meet the objectives prescribed
in this CTG. This guidance is for instructional purposes only and, as such, is not binding.
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APPENDIX A. DEFINITIONS
Terms used in this CTG and the Model Rule in Appendix B are defined in the Clean Air
Act (Act), or in this section as follows:
Ablative coating means a coating that chars when exposed to open flame or extreme
temperatures, as would occur during the failure of an engine casing or during aerodynamic
heating. The ablative char surface serves as an insulative barrier, protecting adjacent components
from the heat or open flame.
Adhesion promoter means a very thin coating applied to a substrate to promote wetting
and form a chemical bond with the subsequently applied material.
Adhesive bonding primer means a primer applied in a thin film to aerospace components
for the purpose of corrosion inhibition and increased adhesive bond strength by attachment.
There are two categories of adhesive bonding primers: primers with a design cure at 250°F or
below and primers with a design cure above 250°F.
Aerosol coating means a hand-held, pressurized, nonrefillable container that expels an
adhesive or a coating in a finely divided spray when a valve on the container is depressed.
Aerospace vehicle or component means any fabricated part, processed part, assembly of
parts, or completed unit, with the exception of electronic components, of any aircraft including
but not limited to airplanes, helicopters, missiles, rockets, and space vehicles.
Aircraft fluid systems means those systems that handle hydraulic fluids, fuel, cooling
fluids, or oils.
Aircraft transparency means the aircraft windshield, canopy, passenger windows, lenses
and other components which are constructed of transparent materials.
Antichafe coating means a coating applied to areas of moving aerospace components that
may rub during normal operations or installation.
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Antique aerospace vehicle or component means an aircraft or component thereof that was
built at least 30 years ago. An antique aerospace vehicle would not routinely be in commercial or
military service in the capacity for which it was designed.
Aqueous cleaning solvent means a solvent in which water is at least 80 percent of the
solvent as applied.
Bearing coating means a coating applied to an antifriction bearing, a bearing housing, or
the area adjacent to such a bearing in order to facilitate bearing function or to protect base
material from excessive wear. A material shall not be classified as a bearing coating if it can also
be classified as a dry lubricative material or a solid film lubricant.
Bonding maskant means a temporary coating used to protect selected areas of aerospace
parts from strong acid or alkaline solutions during processing for bonding.
Caulking and smoothing compounds means semi-solid materials which are applied by hand
application methods and are used to aerodynamically smooth exterior vehicle surfaces or fill
cavities such as bolt hole accesses. A material shall not be classified as a caulking and smoothing
compound if it can also be classified as a sealant.
Chemical agent-resistant coating (CARC) means an exterior topcoat designed to
withstand exposure to chemical warfare agents or the decontaminants used on these agents.
Chemical milling maskant means a coating that is applied directly to aluminum
components to protect surface areas when chemical milling the component with a Type I or II
etchant. Type I chemical milling maskants are used with a Type I etchant and Type II chemical
milling maskants are used with a Type II etchant. This definition does not include bonding
maskants, critical use and line sealer maskants, and seal coat maskants. Additionally, maskants
that must be used with a combination of Type I or II etchants and any of the above types of
maskants (i.e., bonding, critical use and line sealer, and seal coat) are not included. Maskants that
are defined as specialty coatings are not included under this definition.
Cleaning operation means collectively spray-gun, hand-wipe, and flush cleaning
operations.
Cleaning solvent means a liquid material used for hand-wipe, spray gun, or flush cleaning.
This definition does not include solutions that contain no VOC.
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Clear coating means a transparent coating usually applied over a colored opaque coating,
metallic substrate, or placard to give improved gloss and protection to the color coat. In some
cases, a clearcoat refers to any transparent coating without regard to substrate.
Closed-cycle depainting system means a dust free, automated process that removes
permanent coating in small sections at a time, and maintains a continuous vacuum around the
area(s) being depainted to capture emissions.
Coating means a material that is applied to the surface of an aerospace vehicle or
component to form a decorative, protective, or functional solid film, or the solid film itself.
Coating operation means using a spray booth, tank, or other enclosure or any area, such as
a hangar, for applying a single type of coating (e.g., primer); using the same spray booth for
applying another type of coating (e.g., topcoat) constitutes a separate coating operation for which
compliance determinations are performed separately.
Coating unit means a series of one or more coating applicators and any associated drying
area and/or oven wherein a coating is applied, dried, and/or cured. A coating unit ends at the
point where the coating is dried or cured, or prior to any subsequent application of a different
coating. It is not necessary to have an oven or flashoff area to be included in this definition.
Commercial exterior aerodynamic structure primer means a primer used on aerodynamic
components and structures that protrude from the fuselage, such as wings and attached
components, control surfaces, horizontal stabilizers, vertical fins, wing-to-body fairings, antennae,
and landing gear and doors, for the purpose of extended corrosion protection and enhanced
adhesion.
Commercial interior adhesive means materials used in the bonding of passenger cabin
interior components. These components must meet the FAA fireworthiness requirements.
Compatible substrate primer means either compatible epoxy primer or adhesive primer.
Compatible epoxy primer is primer that is compatible with the filled elastomeric coating and is
epoxy based. The compatible substrate primer is an epoxy-polyamide primer used to promote
adhesion of elastomeric coatings such as impact-resistant coatings. Adhesive primer is a coating
that (1) inhibits corrosion and serves as a primer applied to bare metal surfaces or prior to
adhesive application, or (2) is applied to surfaces that can be expected to contain fuel. Fuel tank
coatings are excluded from this category.
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Confined space means a space that (1) is large enough and so configured that an employee
can bodily enter and perform assigned work; (2) has limited or restricted means for entry or exit
(for example, fuel tanks, fuel vessels, and other spaces that have limited means of entry); and
(3) is not suitable for continuous employee occupancy.
Corrosion prevention system means a coating system that provides corrosion protection
by displacing water and penetrating mating surfaces, forming a protective barrier between the
metal surface and moisture. Coatings containing oils or waxes are excluded from this category.
Critical use and line sealer maskant means a temporary coating, not covered under other
maskant categories, used to protect selected areas of aerospace parts from strong acid or alkaline
solutions such as those used in anodizing, plating, chemical milling and processing of magnesium,
titanium, or high- strength steel, high-precision aluminum chemical milling of deep cuts, and
aluminum chemical milling of complex shapes. Materials used for repairs or to bridge gaps left by
scribing operations (i.e., line sealer) are also included in this category.
Cryogenic flexible primer means a primer designed to provide corrosion resistance,
flexibility, and adhesion of subsequent coating systems when exposed to loads up to and
surpassing the yield point of the substrate at cryogenic temperatures (-275 °F and below).
Cryoprotective coating means a coating that insulates cryogenic or subcooled surfaces to
limit propellant boil-off, maintain structural integrity of metallic structures during ascent or re-
entry, and prevent ice formation.
Cyanoacrylate adhesive means a fast-setting, single component adhesive that cures at
room temperature. Also known as "super glue."
Dry lubricative material means a coating consisting of lauric acid, cetyl alcohol, waxes, or
other noncross linked or resin-bound materials that act as a dry lubricant.
Electric or radiation-effect coating means a coating or coating system engineered to
interact, through absorption or reflection, with specific regions of the electromagnetic energy
spectrum, such as the ultraviolet, visible, infrared, or microwave regions. Uses include, but are
not limited to, lightning strike protection, electromagnetic pulse (EMP) protection, and radar
avoidance. Coatings that have been designated as "classified" by the Department of Defense are
exempt.
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Electrostatic discharge and electromagnetic interference (EMI) coating means a coating
applied to space vehicles, missiles, aircraft radomes, and helicopter blades to disperse static
energy or reduce electromagnetic interference.
Elevated-temperature Skydrol-resistant commercial primer means a primer applied
primarily to commercial aircraft (or commercial aircraft adapted for military use) that must
withstand immersion in phosphate-ester (PE) hydraulic fluid (Skydrol 500b or equivalent) at the
elevated temperature of 150°F for 1,000 hours.
Epoxy polyamide topcoat means a coating used where harder films are required or in
some areas where engraving is accomplished in camouflage colors.
Exempt solvent means a specified organic compound that has been determined by the EPA
to have negligible photochemical reactivity and is listed in 40 CFR 51.100.
Fire-resistant (interior) coating means for civilian aircraft, fire-resistant interior coatings
are used on passenger cabin interior parts that are subject to the FAA fireworthiness
requirements. For military aircraft, fire-resistant interior coatings are used on parts that are
subject to the flammability requirements of MIL-STD-1630A and MIL-A-87721. For space
applications, these coatings are used on parts that are subject to the flammability requirements of
SE-R-0006 and SSP 30233.
Flexible primer means a primer that meets flexibility requirements such as those needed for
adhesive bond primed fastener heads or on surfaces expected to contain fuel. The flexible coating
is required because it provides a compatible, flexible substrate over bonded sheet rubber and
rubber-type coatings as well as a flexible bridge between the fasteners, skin, and skin-to-skin
joints on outer aircraft skins. This flexible bridge allows more topcoat flexibility around fasteners
and decreases the chance of the topcoat cracking around the fasteners. The result is better
corrosion resistance.
Flight test coating means a coating applied to aircraft other than missiles or single-use
aircraft prior to flight testing to protect the aircraft from corrosion and to provide required
marking during flight test evaluation.
Flush cleaning means removal of contaminants such as dirt, grease, oil, and coatings from
an aerospace vehicle or component or coating equipment by passing solvent over, into, or through
the item being cleaned. The solvent may simply be poured into the item being cleaned and then
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drained, or assisted by air or hydraulic pressure, or by pumping. Hand-wipe cleaning operations
where wiping, scrubbing, mopping, or other hand action are used are not included.
Fuel tank adhesive means an adhesive used to bond components exposed to fuel and must
be compatible with fuel tank coatings.
Fuel tank coating means a coating applied to fuel tank components for the purpose of
corrosion and/or bacterial growth inhibition and to assure sealant adhesion in extreme
environmental conditions.
Grams of VOC per liter of coating (less water and less exempt solvent) means the weight
of VOC per combined volume of total volatiles and coating solids, less water and exempt
compounds, and can be calculated by the following equation:
grams of VOC per liter of coating _ ^s ~ ^w ~ ^es
(less water and less exempt solvent) v - V - V
v t- ' vs vw ves
Ws = weight of total volatiles in grams
Ww = weight of water in grams
Wes = weight of exempt compounds in grams
Vs = volume of coating in liters
Vw= volume of water in liters
Ves = volume of exempt compounds in liters
Hand-wipe cleaning operation means removing contaminants such as dirt, grease, oil, and
coatings from an aerospace vehicle or component by physically rubbing it with a material such as
a rag, paper, or cotton swab that has been moistened with a cleaning solvent.
High temperature coating means a coating designed to withstand temperatures of more
than350°F.
High volume low pressure (HVLP) spray equipment means spray equipment that is used
to apply coating by means of a spray gun that operates at 10.0 psig of atomizing air pressure or
less at the air cap.
Insulation covering means material that is applied to foam insulation to protect the
insulation from mechanical or environmental damage.
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Intermediate release coating means a thin coating applied beneath topcoats to assist in
removing the topcoat in depainting operations and generally to allow the use of less hazardous
depainting methods.
Lacquer means a clear or pigmented coating formulated with a nitrocellulose or synthetic
resin to dry by evaporation without a chemical reaction. Lacquers are resoluble in their original
solvent.
Leak means any visible leakage, including misting and clouding.
Limited access space means internal surfaces or passages of an aerospace vehicle or
component that cannot be reached without the aid of an airbrush or a spray gun extension for the
application of coatings.
Metalized epoxy coating means a coating that contains relatively large quantities of
metallic pigmentation for appearance and/or added protection.
Mold release means a coating applied to a mold surface to prevent the molded piece from
sticking to the mold as it is removed.
Nonstructural adhesive means an adhesive that bonds nonload bearing aerospace
components in noncritical applications and is not covered in any other specialty adhesive
categories.
Operating parameter value means a minimum or maximum value established for a control
equipment or process parameter that, if achieved by itself or in combination with one or more
other operating parameter values, determines that an owner or operator has continued to comply
with an applicable emission limitation.
Optical antireflection coating means a coating with a low reflectance in the infrared and
visible wavelength ranges that is used for antireflection on or near optical and laser hardware.
Part marking coating means coatings or inks used to make identifying markings on
materials, components, and/or assemblies. These markings may be either permanent or
temporary.
Pretreatment coating means an organic coating that contains at least 0.5 percent acids by
weight and is applied directly to metal or composite surfaces to provide surface etching, corrosion
resistance, adhesion, and ease of stripping.
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Primer means the first layer and any subsequent layers of identically formulated coating
applied to the surface of an aerospace vehicle or component. Primers are typically used for
corrosion prevention, protection from the environment, functional fluid resistance, and adhesion
of subsequent coatings. Primers that are defined as specialty coatings are not included under this
definition.
Radome means the nonmetallic protective housing for. electromagnetic transmitters and
receivers (e.g., radar, electronic countermeasures, etc.).
Rain erosion-resistant coating means a coating or coating system used to protect the
leading edges of parts such as flaps, stabilizers, radomes, engine inlet nacelles, etc. against erosion
caused by rain impact during flight.
Research and development means an operation whose primary purpose is for research and
development of new processes and products and that is conducted under the close supervision of
technically trained personnel and is not involved in the manufacture of final or intermediate
products for commercial purposes, except in a de minimis manner.
Rocket motor bonding adhesive means an adhesive used in rocket motor bonding
applications.
Rocket motor nozzle coating means a catalyzed epoxy coating system used in elevated
temperature applications on rocket motor nozzles.
Rubber-based adhesive means a quick setting contact cement that provide a strong, yet
flexible bond between two mating surfaces that may be of dissimilar materials.
Scale inhibitor means a coating that is applied to the surface of a part prior to thermal
processing to inhibit the formation of scale.
Screen print ink means an ink used in screen printing processes during fabrication of
decorative laminates and decals.
Sealant means a material used to prevent the intrusion of water, fuel, air, or other liquids
or solids from certain areas of aerospace vehicles or components. There are two categories of
sealants: extrudable/rollable/brushable sealants and sprayable sealants.
Seal coat maskant means an overcoat applied over a maskant to improve abrasion and
chemical resistance during production operations.
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Self-priming topcoat means a topcoat that is applied directly to an uncoated aerospace
vehicle or component for purposes of corrosion prevention, environmental protection, and
functional fluid resistance. More than one layer of identical coating formulation may be applied to
the vehicle or component.
Semiaqueous cleaning solvent means a solution in which water is a primary ingredient
(>60 percent of the solvent solution as applied must be water).
Silicone insulation material means an insulating material applied to exterior metal surfaces
for protection from high temperatures caused by atmospheric friction or engine exhaust. These
materials differ from ablative coatings in that they are not "sacrificial."
Solids means the nonvolatile portion of the coating that after drying makes up the dry film.
Solid film lubricant means a very thin coating consisting of a binder system containing as
its chief pigment material one or more of the following: molybdenum, graphite, polytetrafluoro-
ethylene (PTFE), or other solids that act as a dry lubricant between faying (i.e., closely or tightly
fitting) surfaces.
Space vehicle means a man-made device, either manned or unmanned, designed for
operation beyond earth's atmosphere. This definition includes integral equipment such as models,
mock-ups, prototypes, molds, jigs, tooling, hardware jackets, and test coupons. Also included is
auxiliary equipment associated with test, transport, and storage, that through contamination can
compromise the space vehicle performance.
Specialty coating means a coating that, even though it meets the definition of a primer,
topcoat, or self-priming topcoat, has additional performance criteria beyond those of primers,
topcoats, and self-priming topcoats for specific applications. These performance criteria may
include, but are not limited to, temperature or fire resistance, substrate compatibility,
antireflection, temporary protection or marking, sealing, adhesively joining substrates, or
enhanced corrosion protection.
Specialized function coating means a coating that fulfills extremely specific engineering
requirements that are limited in application and are characterized by low volume usage. This
category excludes coatings covered in other Specialty Coating categories.
Spray gun means a device that atomizes a coating or other material and projects the
particulates or other material onto a substrate.
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Structural autoclavable adhesive means an adhesive used to bond load-carrying aerospace
components that is cured by heat and pressure in an autoclave.
Structural nonautoclavable adhesive means an adhesive cured under ambient conditions
that is used to bond load-carrying aerospace components or other critical functions, such as
nonstructural bonding in the proximity of engines.
Surface preparation means the removal of contaminants from the surface of an aerospace
vehicle or component or the activation or reactivation of the surface in preparation for the
application of a coating.
Temporary protective coating means a coating applied to provide scratch or corrosion
protection during manufacturing, storage, or transportation. Two types include peelable
protective coatings and alkaline removable coatings. These materials are not intended to protect
against strong acid or alkaline solutions. Coatings that provide this type of protection from
chemical processing are not included in this category.
Thermal control coating means a coating formulated with specific thermal conductive or
radiative properties to permit temperature control of the substrate.
Topcoat means a coating that is applied over a primer on an aerospace vehicle or
component for appearance, identification, camouflage, or protection. Topcoats that are defined
as specialty coatings are not included under this definition.
Touch-up and repair coating means a coating used to cover minor coating imperfections
appearing after the main coating operation.
Touch-up and repair operation means that portion of the coating operation that is the
incidental application of coating used to cover minor imperfections in the coating finish or to
achieve complete coverage. This definition includes out-of-sequence or out-of-cycle coating.
Volatile organic compound (VOC) means any compound defined as VOC in 40 CFR
51.100. This includes any organic compound other than those determined by the EPA to be an
exempt solvent. For purposes of determining compliance with emission limits, VOC will be
measured by the approved test methods. Where such a method also inadvertently measures
compounds that are exempt solvent, an owner or operator may exclude these exempt solvents
when determining compliance with an emission standard.
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VOC composite vapor pressure means the sum of the partial pressures of the compounds
defined as VOC's and is determined by the following calculation:
Wj
— x VP:
pp _£ »«*!
rrc
i=l
W
w
MWW MWe
E
W; = Weight of the "i"th VOC compound, grams.
Ww = Weight of water, grams.
We = Weight of nonwater, non-VOC compound, grams.
MW; = Molecular weight of the "i"th VOC compound, g/g-mole.
MWW = Molecular weight of water, g/g-mole.
MWe = Molecular weight of exempt compound, g/g-mole.
PPC = VOC composite partial pressure at 20 °C, mm Hg.
VP; = Vapor pressure of the "i"th VOC compound at 20 °C, mm Hg.
Waterborne (water-reducible) coating means a coating which contains more than
5 percent water by weight as applied in its volatile fraction.
Wet fastener installation coating means a primer or sealant applied by dipping, brushing,
or daubing to fasteners that are installed before the coating is cured.
Wing coating means a corrosion-resistant topcoat that is resilient enough to withstand the
flexing of the wings.
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APPENDIX B. AEROSPACE MANUFACTURING AND REWORK
OPERATIONS MODEL RULE
B.I APPLICABILITY
(a) Provisions of this Rule
(1) Except as noted in (a)(2) and (a)(3), this rule applies to the manufacture or rework of
commercial, civil, or military aerospace vehicles or components at facilities located in severe,
serious, and moderate ozone nonattainment areas that have the potential to emit 25 tons per year
of VOC or more or are located in extreme nonattainment areas and have potential to emit 10 tons
per year or more.
(2) This rule does not apply to the following activities where cleaning and coating of
aerospace components and vehicles may take place: research and development, quality control,
laboratory testing, and electronic parts and assemblies (except for cleaning and coating of
completed assemblies).
(3) This rule does not apply to manufacturing or rework operations involving space
vehicles or rework operations performed on antique aerospace vehicles or components.
B.2 DEFINITIONS
For the purpose of this rule the definitions listed in Appendix A shall apply.
B.3 REQUIREMENTS
(a) VOC content of coatings.
(1) A person shall not apply to aerospace vehicles or components any specialty coatings,
including any VOC-containing materials added to the original coating supplied by the
manufacturer, that contain VOC in excess of the limits specified below:
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VOC CONTENT LIMITS FOR SPECIALTY COATINGS (g/L)a
Coating type
Limit Coating type
Limit
Ablative Coating 600
Adhesion Promoter 890
Adhesive Bonding Primers:
Cured at 250°F or below 850
Cured above 250°F 1030
Adhesives:
Commercial Interior Adhesive 760
Cyanoacrylate Adhesive 1,020
Fuel Tank Adhesive 620
Nonstructural Adhesive 360
Rocket Motor Bonding Adhesive 890
Rubber-based Adhesive 850
Structural Autoclavable Adhesive 60
Structural Nonautoclavable Adhesive 850
Antichafe Coating 660
Bearing Coating 620
Caulking and Smoothing Compounds 850
Chemical Agent-Resistant Coating 550
Clear Coating 720
Commercial Exterior Aerodynamic
Structure Primer 650
Compatible Substrate Primer 780
Corrosion Prevention Compound 710
Cryogenic Flexible Primer 645
Dry Lubricative Material 880
Cryoprotective Coating 600
Electric or Radiation-Effect Coating 800
Electrostatic Discharge and Electromagnetic
Interference (EMI) Coating 800
Elevated-Temperature Skydrol-Resistant
Commercial Primer 740
Epoxy Polyamide Topcoat 660
Fire-Resistant (interior) Coating 800
Flexible Primer 640
Flight-Test Coatings:
Missile or Single Use Aircraft
All Other
Fuel-Tank Coating
High-Temperature Coating
Insulation Covering
Intermediate Release Coating
Lacquer
Maskants:
Bonding Maskant
Critical Use and Line Sealer Maskant .
Seal Coat Maskant
Metallized Epoxy Coating
Mold Release
Optical Anti-Reflective Coating
Part Marking Coating
Pretreatment Coating
Rain Erosion-Resistant Coating
Rocket Motor Nozzle Coating
Scale Inhibitor
Screen Print Ink
Sealants:
Extrudable/Rollable/Brushable Sealant
Sprayable Sealant
Silicone Insulation Material
Solid Film Lubricant
Specialized Function Coating
Temporary Protective Coating
Thermal Control Coating
Wet Fastener Installation Coating
Wing Coating
. 420
. 840
. 720
. 850
. 740
. 750
. 830
1,230
1,020
1,230
. 740
. 780
. 750
. 850
. 780
. 850
. 660
. 880
. 840
. 280
. 600
. 850
. 880
. 890
. 320
. 800
. 675
. 850
Coating limits expressed in terms of mass (grams) of VOC per volume (liters) of coating less water and less exempt
solvent.
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(2) The following coating applications are exempt from the VOC content limits listed in
paragraph (B.3)(a)(l):
(i) Touchup, aerosol, and DoD "classified" coatings
(ii) Coating of space vehicles
(iii) Facilities that use separate formulations in volumes of less than 50 gallons per year
subject to a maximum exemption of 200 gallons total for such formulations applied annually.
(3) Primers, Topcoats, Chemical Milling Maskants. The broad categories of primers,
topcoats (including self-priming topcoats), and chemical milling maskants (Type I/II) are not
specialty coatings as listed in the table in (B.3)(a)(l) and are regulated for major sources under
the Aerospace NESHAP requiring MACT limits with a compliance date of September 1, 1998 as
specified in 40 CFR 63.749(a). These limits may be assumed to represent RACT limits 1 year
after the major sources are required to meet the MACT limits and, therefore, shall not be effective
until 1 year after the NESHAP compliance date. The requirements do not apply to facilities that
use separate formulations of primers, topcoats, and chemical milling maskants (Type I/II) in
volumes of less than 50 gallons per year, subject to a maximum exemption of 200 gallons total for
such formulations applied annually.
(b) Application equipment.
(1) A person shall use one or more of the following application techniques in applying any
primer or topcoat to aerospace vehicles or components: flow/curtain coat; dip coat; roll coating;
brush coating; cotton-tipped swab application; electrodeposition coating; high volume low
pressure (HVLP) spraying; electrostatic spray; or other coating application methods that achieve
emission reductions equivalent to HVLP or electrostatic spray application methods.
(2) The following situations are exempt from application equipment requirements listed in
paragraph (B.3)(b)(l):
(i) Any situation that normally requires the use of an airbrush or an extension on the spray
gun to properly reach limited access spaces;
(ii) The application of specialty coatings;
(iii) The application of coatings that contain fillers that adversely affect atomization with
HVLP spray guns and that the permitting agency has determined cannot be applied by any of the
application methods specified in Section (B.3)(b)(l);
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(iv) The application of coatings that normally have a dried film thickness of less than
0.0013 centimeter (0.0005 in.) and that the permitting agency has determined cannot be applied
by any of the application methods specified in Section (B.3)(b)(l);
(v) The use of airbrush application methods for stenciling, lettering, and other
identification markings;
(vi) The use of hand-held spray can application methods; and
(vii) Touch-up and repair operations.
(3) The application techniques listed in paragraph (B.3)(b)(l) are regulated for major
sources under the Aerospace NESHAP requiring MACT application equipment with a compliance
date of September 1, 1998 specified in 40 CFR 63.749(a). These equipment requirements may be
assumed to represent RACT requirements 1 year after the major sources are required to meet the
MACT equipment requirements and, therefore, shall not be effective until 1 year after the
NESHAP compliance date of September 1, 1998.
(c) Solvent cleaning. The following requirements apply to solvent cleaning operations
and shall not be effective until the Aerospace NESHAP compliance date of September 1, 1998:
(1) Hand-wipe cleaning. Cleaning solvents used in hand-wipe cleaning operations shall:
(i) Meet the definition of aqueous cleaning solvent in Appendix A, or
(ii) Have a VOC composite vapor pressure less than or equal to 45 millimeters of mercury
(mmHg)at20°C.
(2) The following solvent cleaning operations are exempt from the requirements in
paragraph (B.3)(c)(l):
(i) Cleaning during the manufacture, assembly, installation, maintenance, or testing of
components of breathing oxygen systems that are exposed to the breathing oxygen;
(ii) Cleaning during the manufacture, assembly, installation, maintenance, or testing of
parts, subassemblies, or assemblies that are exposed to strong oxidizers or reducers (e.g., nitrogen
tetroxide, liquid oxygen, hydrazine);
(iii) Cleaning and surface activation prior to adhesive bonding;
(iv) Cleaning of electronics parts and assemblies containing electronics parts;
(v) Cleaning of aircraft and ground support equipment fluid systems that are exposed to
the fluid, including air-to-air heat exchangers and hydraulic fluid systems;
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(vi) Cleaning of fuel cells, fuel tanks, and confined spaces;
(vii) Surface cleaning of solar cells, coated optics, and thermal control surfaces;
(viii) Cleaning during fabrication, assembly, installation, and maintenance of upholstery,
curtains, carpet, and other textile materials used on the interior of the aircraft;
(ix) Cleaning of metallic and nonmetallic materials used in honeycomb cores during the
manufacture or maintenance of these cores, and cleaning of the completed cores used in the
manufacture of aerospace vehicles or components;
(x) Cleaning of aircraft transparencies, polycarbonate, or glass substrates;
(xi) Cleaning and solvent usage associated with research and development, quality
control, or laboratory testing;
(xii) Cleaning operations, using nonflammable liquids, conducted within 5 feet of
energized electrical systems. Energized electrical systems means any AC or DC electrical circuit
on an assembled aircraft once electrical power is connected, including interior passenger and
cargo areas, wheel wells and tail sections; and,
(xiii) Cleaning operations identified as essential uses under the Montreal Protocol for
which the Administrator has allocated essential use allowances or exemptions in 40 CFR § 82.4.
(3) Flush cleaning. For cleaning solvents used in the flush cleaning of parts, assemblies,
and coating unit components, the used cleaning solvent (except for semiaqueous cleaning
solvents) must be emptied into an enclosed container or collection system that is kept closed when
not in use or captured with wipers provided they comply with the housekeeping requirements of
(B.3)(c)(5). Aqueous cleaning solvents are exempt from these requirements.
(4) Spray gun cleaning. All spray guns must be cleaned by one or more of the following
methods:
(i) Enclosed spray gun cleaning system provided that it is kept closed when not in use and
leaks are repaired within 14 days from when the leak is first discovered. If the leak is not repaired
by the 15th day after detection, the solvent shall be removed and the enclosed cleaner shall be shut
down until the leak is repaired or its use is permanently discontinued,
(ii) Unatomized discharge of solvent into a waste container that is kept closed when not
in use,
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(iii) Disassembly of the spray gun and cleaning in a vat that is kept closed when not in
use, or,
(iv) Atomized spray into a waste container that is fitted with a device designed to capture
atomized solvent emissions.
(5) Housekeeping. All fresh and used cleaning solvents, except semiaqueous cleaning
solvents, used in solvent cleaning operations shall be stored in containers that shall be kept closed
at all times except when filling or emptying. It is recommended that cloth and paper, or other
absorbent applicators, moistened with cleaning solvents be stored in closed containers. Cotton-
tipped swabs used for very small cleaning operations are exempt. In addition, the owner or
operator must implement handling and transfer procedures to minimize spills during filling and
transferring the cleaning solvent to or from enclosed systems, vats, waste containers, and other
cleaning operation equipment that hold or store fresh or used cleaning solvents. The above
requirements are known collectively as housekeeping measures. Aqueous cleaning solvents are
exempt from these requirements.
(d) Control equipment and monitoring.
(1) Each owner or operator may comply with the provisions of paragraph (B.3)(a) by
using approved air pollution control equipment provided that the control system has combined
VOC emissions capture and control equipment efficiency of at least 81 percent by weight.
(2) Each owner or operator shall submit a monitoring plan that specifies the applicable
operating parameter value, or range of values, to ensure ongoing compliance with (B.3)(d)(l).
The monitoring device shall be installed, calibrated, operated, and maintained in accordance with
the manufacturer's specifications.
(3) Each owner or operator using an enclosed spray gun cleaner shall visually inspect the
seals and all other potential sources of leaks at least once per month. Each inspection shall occur
while the spray gun cleaner is in operation.
B.4 RECORDKEEPING REQUIREMENTS
(a) Each owner or operator using coatings listed in (B.3)(a) shall:
(1) Maintain a current list of coatings in use with category and VOC content as applied.
(2) Record coating usage on an annual basis
(b) Each owner or operator using cleaning solvents required in (B.3)(c) shall:
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(1) For aqueous and semiaqueous hand-wipe cleaning solvents, maintain a list of materials
used with corresponding water contents.
(2) For vapor pressure compliant hand-wipe cleaning solvents:
(i) Maintain a current list of cleaning solvents in use with their respective vapor pressures
or, for blended solvents, VOC composite vapor pressures.
(ii) Record cleaning solvent usage on an annual basis.
(3) For cleaning solvents with a vapor pressure greater than 45 mm Hg used in exempt
hand-wipe cleaning operations:
(i) Maintain a list of exempt hand-wipe cleaning processes.
(ii) Record cleaning solvent usage on an annual basis.
(c) Each owner or operator using control equipment under paragraph (B.3)(d) shall
record monitoring parameters as specified in the monitoring plan required under (B.3)(d)(2).
(d) Except for Specialty Coatings, any source that complies with the recordkeeping
requirements of the Aerospace NESHAP, 40 CFR 63.752, is deemed to be in compliance with the
requirements of this paragraph (B.4).
B.5 TEST METHODS
(a) For coatings which are not waterborne (water-reducible), determine the VOC content
of each formulation (less water and less exempt solvents) as applied using manufacturer's supplied
data or Method 24 of 40 CFR part 60, Appendix A. If there is a discrepancy between the
manufacturer's formulation data and the results of the Method 24 analysis, compliance shall be
based on the results from the Method 24 analysis. For water-borne (water-reducible) coatings,
manufacturer's supplied data alone can be used to determine the VOC content of each
formulation.
(b) Cleaning solvents.
(1) For aqueous and semiaqueous cleaning solvents manufacturers' supplied data shall be
used to determine the water content.
(2) For hand-wipe cleaning solvents required in paragraph (B.3)(c)(l), manufacturers'
supplied data or standard engineering reference texts or other equivalent methods shall be used to
determine the vapor pressure or VOC composite vapor pressure for blended cleaning solvents.
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(c) Control equipment. Measurements of VOC emissions subject to paragraph (B.3)(d)
shall be conducted in accordance with EPA Methods 18, 25, and/or 25A (40 CFR 60, Appendix
A).
(d) Except for Specialty Coatings, any source which complies with the test method
requirements of the Aerospace NESHAP, 40 CFR 63.750, is deemed to be in compliance with the
requirements of this paragraph (B.5).
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