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

EPA Guideline Series
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
iii

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
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v

TABLE OF CONTENTS

Page

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-1

APPENDIX B AEROSPACE MANUFACTURING AND REWORK
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OPERATIONS MODEL RULE ....................... B-1
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LIST OF FIGURES

Page

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
1-1

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 (BAC) measures." Section 183(e)(1)(A) defines "BAC"

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.
1-2

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
1-3

"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.
2-1

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.
2-2

TABLE 2-1. AEROSPACE MANUFACTURING SIC CODES

SIC Code Description

3720 Aircraft and Parts

3721 Aircraft

3724 Aircraft Engines and Engine Parts

3728 Aircraft Parts and Equipment

3760 Guided Missiles, Space Vehicles, and Parts

3761 Guided Missiles and Space Vehicles

3764 Space Propulsion Units and Parts

3769 Space Vehicle Equipment

4512 Air Transportation, Scheduled

4581 Airports, Flying Fields, and Services

9711 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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2-5
2-6

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 
2-7

Figure 2-1. Active U.S. aerospace manufacturing facilities.

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, xylene,

methyl ethyl ketone, and methyl isobutyl ketone. The VOC content ranges differ for the various

coating categories.

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

corrosion, such as on faying (i.e., closely or tightly fitting) surfaces, inside holes and slots, and

around installed fasteners. They are also used to seal fuel tanks and pressurized components. 

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

mixing. Typically, a sealant is applied before assembly or fastener installation, and the excess is

squeezed out or extruded from between the parts as the assembly is completed. This ensures a

moisture-tight seal between the parts.

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.
2-8

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.
3-1

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
3-2

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
3-3

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 twocomponent 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

Commercial or

military

OEM or

rework

High transfer

equipment

% Reduction in

emissions

Large Military OEM HVLP 20

Large Military OEM HVLP 20

Large Military OEM HVLP 25

Large Commercial OEM Unspecified 30

Large Commercial OEM Unspecified 18

Medium Commercial

Military

Military

OEM

OEM

Rework

HVLP 25

Medium Commercial

Military

Military

OEM

OEM

Rework

HVLP 20-40

Medium Military OEM HVLP and

electrostatic

40

Medium Military OEM HVLP and

electrostatic

40

Medium Military OEM HVLP 40

Medium Military OEM HVLP 10

Medium Military

Military

OEM

Rework

Electrostatic 30-40

Medium Military Rework HVLP and

electrostatic

35-40

Medium Commercial OEM Unspecified 30

Medium Commercial OEM Unspecified 33

Medium Commercial Rework HVLP and

electrostatic

50
3-6

 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.
3-7

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.
3-8

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,
3-9

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 20EC. 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.
4-1

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. 
4-2

TABLE 4-1. SPECIALTY COATINGS VOC CONTENT LIMITS (g/L)a

Coating type Limit Coating type Limit

Ablative Coating ................. 600

Adhesion Promoter ............... 890

Adhesive Bonding Primers:

Cured at 250EF or below ......... 850

Cured above 250EF ............. 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

Epoxy Polyamide Topcoat .......... 660

Fire-Resistant (interior) Coating ..... 800

Flexible Primer .................. 640
4-3

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.
4-4

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;
4-5

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
4-6

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

20EC. 

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
4-7

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. 
5-1

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. 
5-2

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.
A-3

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 250EF or

below and primers with a design cure above 250EF.

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.
A-4

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.
A-5

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. 
A-6

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 (-275EF 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 reentry, 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.
A-7

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 150EF 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
A-8

grams of VOC per liter of coating

(less water and less exempt solvent)

'

Ws& Ww & Wes

Vs& Vw & Ves

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:

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

than 350EF.

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.
A-9

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.
A-10

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.
A-11

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, polytetrafluoroethylene (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.
A-12

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.
A-13

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Wi

MWi

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:

Wi = Weight of the "i"th VOC compound, grams.

Ww = Weight of water, grams.

We = Weight of nonwater, non-VOC compound, grams.

MWi = 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 20EC, mm Hg.

VPi = Vapor pressure of the "i"th VOC compound at 20EC, 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.1 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 250EF or below ................... 850

Cured above 250EF ...................... 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 ............... 420

All Other ............................... 840

Fuel-Tank Coating .......................... 720

High-Temperature Coating ................... 850

Insulation Covering ......................... 740

Intermediate Release Coating .................. 750

Lacquer .................................. 830

Maskants:

Bonding Maskant ........................ 1,230

Critical Use and Line Sealer Maskant ........ 1,020

Seal Coat Maskant ....................... 1,230

Metallized Epoxy Coating .................... 740

Mold Release ............................. 780

Optical Anti-Reflective Coating ................ 750

Part Marking Coating ....................... 850

Pretreatment Coating ........................ 780

Rain Erosion-Resistant Coating ................ 850

Rocket Motor Nozzle Coating ................. 660

Scale Inhibitor ............................. 880

Screen Print Ink ............................ 840

Sealants:

Extrudable/Rollable/Brushable Sealant ........ 280

Sprayable Sealant ........................ 600

Silicone Insulation Material ................... 850

Solid Film Lubricant ........................ 880

Specialized Function Coating .................. 890

Temporary Protective Coating ................. 320

Thermal Control Coating ..................... 800

Wet Fastener Installation Coating .............. 675

Wing Coating ............................. 850

a 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)(1):

(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)(1) 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)(1):

(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)(1);
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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)(1);

(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)(1) 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

(mm Hg) at 20EC.

(2) The following solvent cleaning operations are exempt from the requirements in

paragraph (B.3)(c)(1):

(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. Cottontipped 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)(1). 

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)(1), 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.
B-10

(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).