Imperial County Air Pollution Control District Rule 425

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RULE 425 AEROSPACE COATING OPERATIONS

(Adopted 8/5/89; revised 3/3/92; 9/14/99; 5/18/2004; 02/23/2010)

A. Applicability

A.1 This Rule is applicable to the Coating, masking, surface cleaning and paint 

stripping of Aerospace Components and the cleanup of Equipment associated with 

these operations. Terms applicable to this Rule are defined in Rule 101 -

Definitions. 

A.2 Any Coating, cleaning or surface preparation operation which is exempt from all or 

a portion of this Rule pursuant to Section A.3 shall comply with the provisions of 

Rule 417, Organic Solvents.

A.3 Exemptions

A.3.a A stationary source using 3 gallons or less of aerospace Coating per 

day is exempt from the requirements contained in Section B.

A.3.b The ROC limits specified in Table 425-1 of this Rule shall not apply to 

Coatings with separate formulations that are used in volumes of less 

than 20 gallons per formulation per year, provided that no more than 50 

gallons total of such separate formulations are applied at the facility 

annually and it can be demonstrated that complying Coatings are not 

available.

A.3.c (Deleted)

A.3.d Touch-Up Coatings and Stencil Coatings.

A.3.e Coatings applied using non-refillable hand held aerosol spray 

containers.

A.3.f Prepreg Composite Materials. 

A.4 Any facility claiming an exemption according to Section A.3.a or A.3.b must submit 

a request for exemption to the Air Pollution Control District and provide the 

following information in a District approved format:

A.4.a types of Coatings to be used;

A.4.b maximum volume of Coatings to be applied daily and yearly;

A.4.c mix ratio of Coatings and Reducers or quantities of any Coating 

components, Reducers of thinners;

A.4.d grams of ROC per liter of Coating, less water and less exempt organic 

compounds;
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A.4.e method of application.

A.5 A request for continued exemption must be resubmitted to the Air Pollution Control 

District annually, prior to the first day of February, and contain updated usage 

information.

A.6 The Owner or Operator shall not qualify for the exemptions specified in Sections 

A.3.b and A.3.c of this Rule, unless written approval is received from the Air 

Pollution Control District stating that the facility qualifies for the exemptions.

A.7 An exceedance of the low usage limit specified in Sections A.3.a and A.3.b shall 

constitute a violation of this Rule.

Table 425-1

Coating Grams of ROC Per Liter of Coating, 

Less Water, and Exempt Compounds

Primer 350

Topcoat 420

Adhesive Bonding Primers:

Structural 850

For Elastomers and 

Elastomeric Adherents 850

All other Adhesive Bonding 

Primers 850

Adhesives:

Structural Autoclavable 50

Structural Epoxy 50

Structural Non-Autoclavable 250

Elastomeric 850

All Other Adhesives 250

Flight-Test Coating 420

Fuel-Tank Coating 420

High Temperature Thermal

Flash Resistant Coatings 800

Pretreatment Coatings 780

Radiation-effect Coating 800

Solid-film Lubricant:

Fasteners Lubrication 880

Non-Fasteners Lubrication 880

Space-Vehicle Coatings:

Electrostatic Discharge 

Protection 800

Thermocontrol Coatings 600
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Coating Grams of ROC Per Liter of Coating, 

Less Water, and Exempt Compounds

Other Space-vehicle 

Coatings 1000

Temporary Protective Coatings 250

B. Requirements

B.1 A Person shall not apply or solicit the application of any Coating or combination of 

Coatings, aerosols, or Adhesives with a ROC content, less water and less Exempt 

Compounds, in excess of the limits in Table 425-1. The requirements of this 

paragraph shall apply to all written or oral agreements.

B.2 Manufacturers of any Coating subject to this Rule shall display the maximum ROC 

content of the Coating after any mixing or thinning as recommended by the 

manufacturer. The ROC content shall be displayed as grams of ROC per liter of 

Coating. The volatile organic compound (VOC) content may be displayed instead 

of the Reactive Organic Compound (ROC) content as long as the manufacturer=s 

definition of VOC is consistent with the definition of ROC.

B.3 Closed containers shall be used for disposal and storage of cloth, paper, or other 

solvent-containing materials used for surface preparation, Coating, cleanup, and 

paint removal. Upon final disposal, the solvent containing material shall be

transported to a permitted waste disposal facility in sealed metal or plastic molded 

drums with snap-on or screw-type lids.

B.4 Solvents containing Reactive Organic Compounds shall not be used for the 

cleanup of spray Equipment in Aerospace Component Coating operations unless 

85 percent of the Reactive Organic Compound vapors are collected and properly 

disposed of such that they are not emitted to the Atmosphere.

B.5 A Person shall not use solvents for surface cleaning, clean-up or the cleaning of 

components, which have a ROC content of more than 200 grams per liter or has a 

composite vapor pressure greater than 45 mm Hg at a temperature of 20 degrees 

C (68 degrees F) for surface preparation or cleanup of Aerospace Components. 

This prohibition does not apply to the stripping of Coating.

B.6 A Person shall not use or specify for use within the District, a Stripper which 

contains more than 200 grams per liter ROC content.

B.7 A Person shall not apply any Maskant to Aerospace Components unless:

B.7.a the Maskant contains less than 600 grams of ROC per liter of Coating, 

less water and Exempt Compounds, as applied.

B.8 A Person may comply with the provisions of Section B.1 and B.7 by using air 

pollution Control Equipment with a capture rate of at least 90 percent and Control 

Efficiency of at least 95 percent by weight. Prior approval must be received from 
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the Air Pollution Control Officer.

B.9 A Person shall not apply Coatings in aerospace Coating operations subject to this 

Rule except by means of the following application methods:

B.9.a Electrostatic spray applications, or

B.9.b Flow coat application, or

B.9.c Dip coat application, or

B.9.d Hand Application Methods, or

B.9.e Airless spray application for use with Maskants and Temporary 

Protective Coatings only, or

B.9.f High-volume low-pressure (HVLP) spray application, or

B.9.g Other Coating application methods that are demonstrated to achieve a 

minimum of 65 percent Transfer Efficiency or have Transfer Efficiency 

at least equal to one of the above application methods, and which are 

used in such a manner that parameters under which they were tested 

are permanent features of the method. Such Coating application 

methods shall demonstrate transfer efficiency in accordance with South 

Coast Air Quality Management District method ASpray Equipment 

Transfer Efficiency Test Procedure for Equipment User,@ May 24, 1989.

B.10 Except for electrostatic spray guns, a Person shall not use materials containing 

ROC for the cleaning of spray guns in Coating operations unless the spray gun is 

cleaned in an Enclosed Gun Cleaner. The enclosed spray gun cleaner must not 

be open to the ambient air when in use and must have a mechanism to force the 

cleanup material through the gun while the cleaner is in operation. Alternative gun 

cleaning systems may be used provided the emission loss from the system is 

demonstrated to be less than or equivalent to the emission loss from an Enclosed 

Gun Cleaner. The equivalency demonstration must be performed pursuant to the 

test method specified in Section D.6 of this Rule.

C. Record Keeping Requirements

C.1 Each facility shall maintain a comprehensive listing of Coatings, Maskants, 

Strippers, surface preparation and cleaning materials, and spray Equipment 

cleaning materials and solvents applied at the facility in the District approved 

format.

For each Coating listed in the comprehensive list, the facility shall provide a 

Coating specification sheet in the District approved format. The Coating 

specification sheet shall contain as a minimum:

C.1.a Coating name and manufacturer identification
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C.1.b Specific mixing instructions

C.1.c ROC content as applied

C.1.d Weight percent water as applied

C.1.e Weight percent Exempt Compound as applied

C.1.f Solvent composition and density as applied

C.1.g Solids content, less water and Exempt Compound as applied

C.2 A Person who applies Coatings and/or solvents to Aerospace Components shall 

maintain a daily record of each Coating, Stripper, and solvent used. Maintain daily 

inventory (dispensing) records of solvents used or Equipment cleaning and surface 

cleaning operations. Maintain records of material additions to dip tank for dip 

Coating operations.

Records shall at all times be retained at the facility for a period of the previous five

years and be made available for review by the District upon request. Copies of 

such records shall be supplied to a District representative upon request of the 

representative.

C.3 By the first day of April of each year, each facility shall submit a report to the 

District which states the total volume of each Coating and solvent applied to 

Aerospace Components during the previous calendar year. A District approved 

reporting format shall be used.

C.3.a Daily usage records of Coatings, solvents, and paint Strippers. shall 

include, but not be limited to:

C.3.a.1 The amount and type of Coating used in each piece of 

Application Equipment.

C.3.a.2 The method of application.

C.3.a.3 The amount of ROC in each Coating, the volume of each 

Coating and the volume of thinners at time of application.

C.3.a.4 The amount of other solvent and exempt solvent used.

C.3.a.5 The ROC content of each solvent.

C.3.a.6 The solids content of each Coating.

C.4 As an alternative record keeping plan an aerospace operation may use purchase 

records and product inventories to document the type and quantities of Coatings 

used at a Source. The plan shall be submitted in writing to the District, and shall 
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be adequate to demonstrate compliance with the applicable provisions of this 

Rule.

D. Test Methods

D.1 The ROC content of Coatings and solvent shall be determined using EPA 

Reference Method 24 or its constituent methods.

D.2 The solid content of pretreatment Coatings shall be determined using ASTM 

Method D2369-03.

D.3 The acid content of pretreatment Coatings shall be determined using ASTM 

Method D1639-90e1.

D.4 The composite vapor pressure of a blended solvent shall be determined by 

quantifying the amount of each organic compound in the blend using gas 

chromatographic analysis (ASTM 2306-00) and by calculating the composite vapor 

pressure of the solvent by summing the partial pressures of each component. For 

the purpose of this calculation, the blend shall be assumed to be an ideal solution

where Raoult's Law applies.

D.5 The ROC emissions from enclosed systems used to clean Coating Application 

Equipment shall be determined using the South Coast Air Quality Management 

District General Test Method for Determining Solvent Losses from Spray Gun 

Cleaning Systems.

D.6 The transfer efficiency of alternative application methods shall be determined in 

accordance with the South Coast Air Quality Management District method ASpray 

Equipment Transfer Efficiency Test Procedure for Equipment User,@ May 24, 1989.

D.7 Control Efficiency of the emission Control Device shall be determined in 

accordance with EPA Method 25.

D.8 Capture Efficiency of the system shall be determined in accordance with U.S. EPA 

AGuidelines for Determining Capture Efficiency,@ dated January 9, 1995, and the 

methods found in 40 CFR 51, Appendix M, Method 204 through Method 204F.

D.9 Destruction Efficiency, measured and calculated as carbon, of the system shall be 

determined in accordance with U.S. EPA test methods found in Appendix A, 

Methods 18, 25 and 25A at 40 CFR 60.