Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 1 

RULE 2.31 SOLVENT CLEANING AND DEGREASING 

ADOPTED April 27, 1994

REVISED August 13, 1997

REVISED May 14, 2008 

REVISED May 8, 2013

INDEX 

100 GENERAL

101 PURPOSE 

102 APPLICABILITY 

110 EXEMPTION - GENERAL 

111 EXEMPTION - SOLVENT REQUIREMENTS 

112 EXEMPTION - GENERAL PROHIBITIONS 

113 EXEMPTION - LIMITED AEROSOL 

114 EXEMPTIONS - AEROSPACE VEHICLE OR COMPONENTS 

200 DEFINITIONS 

201 AEROSOL PRODUCT 

202 AEROSPACE VEHICLE OR COMPONENTS 

203 AIRLESS CLEANING SYSTEM 

204 AIRTIGHT CLEANING SYSTEM 

205 AIR SOLVENT INTERFACE 

206 APPLICATION EQUIPMENT 

207 APPURTENANCES 

208 ARCHITECTURAL COATINGS 

209 AQUEOUS CLEANING SOLVENT 

210 BATCH CLEANING MACHINE 

211 COLD CLEANING MACHINE 

212 CONTROL DEVICE 

213 CURED COATINGS, CURED INKS, AND CURED ADHESIVES 

214 DEGREASER 

215 DOCTOR BLADE 

216 ELECTRICAL APPARATUS COMPONENT 

217 ELECTRONIC COMPONENT 

218 EMISSION CONTROL SYSTEM 

219 EXEMPT COMPOUNDS 

220 FACILITY 

221 FLEXOGRAPHIC PRINTING 

222 FREEBOARD HEIGHT 

223 FREEBOARD RATIO 

224 GENERAL WORK SURFACES 

225 GRAPHIC ARTS 

226 GRAVURE PRINTING 

227 HIGH PRECISION OPTICS 

228 INTAGLIO PRINTING 

229 JANITORIAL CLEANING 

230 LETTERPRESS PRINTING 

231 LITHOGRAPHIC PRINTING 

232 LIQUID LEAK 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 2 

233 MAINTENANCE CLEANING 

234 MANUFACTURING PROCESS 

235 MEDICAL DEVICE 

236 NON-ABSORBENT CONTAINERS 

237 NON-ATOMIZED SOLVENT FLOW 

238 NON-LEAKING CONTAINERS 

239 OPEN TOP VAPOR DEGREASER 

240 PHARMACEUTICAL MANUFACTURING PLANT 

241 PHARMACEUTICAL PRODUCT 

242 PRINTING 

243 PRODUCT CLEANING 

244 REMOTE RESERVOIR COLD CLEANER 

245 REPAIR CLEANING 

246 REPAIR PROCESS 

247 SCREEN PRINTING 

248 SEMIAQUEOUS CLEANING SOLVENT 

249 SOLVENT 

250 SOLVENT CLEANING MACHINE 

251 SOLVENT CLEANING OPERATION 

252 SOLVENT CONTAINER 

253 SOLVENT DEGREASING OPERATION 

254 SOLVENT FLUSHING 

255 STRIPPING 

256 SURFACE PREPARATION AND CLEANUP 

257 ULTRAVIOLET INKS 

258 VAPOR CLEANING MACHINE 

259 VOLATILE ORGANIC COMPOUND (VOC) 

260 VOLATILE ORGANIC COMPOUND (VOC) COMPOSITE PARTIAL PRESSURE 

261 VOLATILE ORGANIC COMPOUND (VOC) CONTENT 

262 WIPE CLEANING 

300 STANDARDS 

301 SOLVENT CLEANING OPERATIONS 

302 SOLVENT DEGREASING OPERATIONS 

303 –COLD CLEANER REQUIREMENTS 

304 OPEN TOP VAPOR DEGREASER REQUIREMENTS 

305 AIRLESS/AIRTIGHT CLEANING SYSTEM REQUIREMENTS 

306 REMOTE RESERVOIR COLD CLEANER REQUIREMENTS 

307 STORAGE AND DISPOSAL - GENERAL 

308 EMISSION CONTROL SYSTEM 

400 ADMINISTRATIVE REQUIREMENTS 

401 PROHIBITION OF SPECIFICATION 

402 COMPLIANCE STATEMENT REQUIREMENT 

403 OPERATION & MAINTENANCE PLAN (O&M PLAN) 

500 MONITORING AND RECORDS 

501 RECORD KEEPING - GENERAL 

502 TEST METHODS RECORD KEEPING - EMISSION CONTROL SYSTEM 

503 BURDEN OF PROOF 

504 RECORD RETENTION 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 3 

600 TEST METHODS AND CALCULATIONS 

601 GENERAL 

602 VOC CONTENT 

603 EXEMPT COMPOUNDS 

604 CALCULATION OF VOC CONTENT 

605 CALCULATION OF VOC COMPOSITE PARTIAL PRESSURE 

606 CAPTURE EFFICIENCY 

607 CONTROL EFFICIENCY 

608 SPRAY GUN CLEANING SYSTEMS 

 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 4 

100 GENERAL

101 PURPOSE: The purpose of this Rule is to limit the emissions of volatile organic 

compounds (VOC) from solvent cleaning operations and solvent degreasing operations, 

and from the storage and disposal of materials used for such operations. 

102 APPLICABILITY: The provisions of this Rule applies to any owner or operator of any 

facility that uses VOC-containing materials for solvent cleaning or solvent degreasing, or 

any person who sells or distributes any solvent subject to the provisions of this rule. 

110 EXEMPTION - GENERAL: The provisions of this rule, except for Section 503, Burden 

of Proof, shall not apply to the following: 

110.1 Dry cleaning operations. 

110.2 Cleaning operations using a solvent containing no more than 25 grams of VOC per 

liter of material. 

110.3 Janitorial cleaning. 

110.4 Stripping of cured coatings, cured adhesives, and cured inks. 

110.5 Degreasers with an open top surface area of 1.0 square foot or less or with a 

capacity of 1.0 gallons or less, using unheated nonhalogenated solvent exclusively, 

where the reservoir is covered when not processing work. 

110.6 Any solvent degreasing operations that are subject to the NESHAP requirements 

of 40 CFR Part 63 Subpart T- National Emission Standards for Halogenated 

Solvent Cleaning. 

110.7 Cleaning operations in printing pre-press or graphic arts pre-press areas, including 

the cleaning of film processors, color scanners, plate processors, film cleaning, and 

plate cleaning. 

111 EXEMPTION - SOLVENT REQUIREMENTS: The provisions of Section 301 shall 

not apply to any of the following applications, provided that the facility has obtained either 

a District permit, or written exemption from the APCO: 

111.1 Wipe cleaning of solar cells, laser hardware, and high precision optics. 

111.2 Wipe cleaning for performance laboratory tests on coatings, adhesives or inks, 

research and development programs, and laboratory tests in quality assurance 

laboratories. 

111.3 Wipe cleaning of polycarbonate plastics. 

111.4 Cleaning of cotton swabs to remove cottonseed oil before cleaning of high 

precision optics. 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 5 

111.5 Facilities using 10 gallons or less of solvents (total of compliant and 

noncompliant) in any one calendar year provided the daily use does not exceed one 

liter in any one day. 

111.6 Cleaning of paper-based gaskets, and clutch assemblies where rubber is bonded to 

metal by means of an adhesive. 

111.7 Cleaning of sterilization ink indicating equipment provided that the solvent usage 

is less than 1.5 gallons per day. 

111.8 Cleaning of coating and adhesive application processes utilized to manufacture 

transdermal drug delivery product using less than 3.0 gallons per day of ethyl 

acetate, averaged over a calendar month period. 

112 EXEMPTION - GENERAL PROHIBITION: The provisions of Section 301.4 shall not 

apply to any of the following applications: 

112.1 Internal cleaning of the tips of automated spray equipment systems, except for 

robotic systems. 

112.2 Spray bottles or containers described in Section 301.2.b. of this rule. 

112.3 Printing operations where the roller or blanket wash is applied automatically. 

113 EXEMPTION - LIMITED AEROSOL: The provisions of Sections 301 shall not apply 

to cleaning with aerosol products if 160 ounces or less are used per day per facility and the 

facility has obtained either a District permit, or a written exemption from the APCO. The 

products used shall comply with California Air Resources Board (ARB) regulations. 

114 EXEMPTIONS – AEROSPACE VEHICLE OR COMPONENTS:

114.1 The provisions of section 307 shall not apply to cotton-tipped swabs used for very 

small cleaning operations nor to aqueous cleaning solvents. 

114.2 The provisions of section 301 shall not apply to the following: 

a. Cleaning during the manufacture, assembly, installation, maintenance, or 

testing of components of breathing oxygen systems that are exposed to the 

breathing oxygen; 

b. 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); 

c. Cleaning and surface activation prior to adhesive bonding; 

d. Cleaning of electronics and assemblies containing electronics; 

e. 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; 

f. Cleaning of fuel cells, fuel tanks, and confined spaces; 

g. Surface cleaning of solar cells, coated optics, and thermal control surfaces; 

h. Cleaning during fabrication, assembly, installation, and maintenance of 

upholstery, curtains, carpet, and other textile materials used on the interior 

of the aircraft; 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 6 

i. 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; 

j. Cleaning of aircraft transparencies, polycarbonate, or glass substrates; 

k. Cleaning and solvent usage associated with research and development, 

quality control, or laboratory testing; 

l. 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 

m. Cleaning operations identified in essential uses Montreal Protocol for 

which the Administrator has allocated essential use allowance exemptions 

in 40 CFR 82.4. 

114.3 The provisions of section 301.2.c and 301.2.d. shall not apply to semiaqueous or aqueous 

cleaning solvents. 

200 DEFINITIONS 

201 AEROSOL PRODUCT: A hand-held, non-refillable container which expels pressurized 

product ingredients by means of a manual propellant-induced force. 

202 AEROSPACE VEHICLE OR COMPONENTS: 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. 

203 AIRLESS CLEANING SYSTEM: A degreaser that is automatically operated and seals 

at an absolute internal pressure of 0.02 psia or less, prior to the introduction of solvent 

vapor into the cleaning chamber, and maintains differential pressure under vacuum during 

all cleaning and drying cycles. 

204 AIRTIGHT CLEANING SYSTEM: A degreaser that is automatically operated and seals 

at a differential pressure no greater than 0.5 psig during all cleaning and drying operations. 

205 AIR SOLVENT INTERFACE: The point of contact between the exposed solvent and 

air. 

206 APPLICATION EQUIPMENT: A device used to apply adhesive, coating, ink, or 

polyester resin material, such as but not limited to brushes, rollers and spray guns. 

207 APPURTENANCES: Accessories to an architectural structure, including, but not limited 

to: Hand railings, cabinets, bathroom and kitchen fixtures, fences, rain-gutters and 

down-spouts, window screens, lamp-posts, heating and air conditioning equipment, other 

mechanical equipment, large fixed stationary tools and concrete forms. 

208 ARCHITECTURAL COATINGS: Any coatings applied to stationary structures and 

their appurtenances, to mobile homes, to pavements, or to curbs. 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 7 

209 AQUEOUS CLEANING SOLVENT: A solvent in which water is at least 80 percent of 

the solvent as applied. 

210 BATCH CLEANING MACHINE: A solvent cleaning machine in which individual parts 

or a set of parts move through the entire cleaning cycle before new parts are introduced into 

the solvent cleaning machine. An open-top vapor cleaning machine is a type of batch 

cleaning machine. A solvent cleaning machine, such as a ferris wheel or a cross-rod 

degreaser, that clean multiple batch loads simultaneously and are manually loaded are 

batch cleaning machines. 

 

211 COLD CLEANING MACHINE: Any device or piece of equipment that contains and/or 

uses liquid solvent, into which parts are placed to remove soils from the surfaces of the 

parts or to dry the parts. Cleaning machines that contain and use heated, nonboiling 

solvent to clean the parts are classified as cold cleaning machines. 

212 CONTROL DEVICE: Equipment such as an incinerator or adsorber used to prevent air 

pollutants from reaching the ambient air. 

213 CURED COATINGS, CURED INKS, AND CURED ADHESIVES: Coatings, inks, 

and adhesives which are dry to the touch. 

214 DEGREASER: A tank, tray, drum, or other container in which objects to be cleaned are 

placed in to be exposed to a solvent or solvent vapor, in order to remove contaminants. The 

objects to be cleaned include, but are not limited to, parts, products, tools, machinery, and 

equipment. 

215 DOCTOR BLADE: A blade used to scrape excess ink from a printing plate. 

216 ELECTRICAL APPARATUS COMPONENT: An internal component such as wires, 

windings, stators, rotors, magnets, contacts, relays, energizers, and connections in an 

apparatus that generates or transmits electrical energy including, but not limited to: 

alternators, generators, transformers, electric motors, cables, and circuit breakers, except 

for the actual cabinet in which the components are housed. Electrical components of 

graphic arts application equipment and hot-line tools are also included in this category. 

217 ELECTRONIC COMPONENT: The portion of an assembly, including circuit card 

assemblies, printed wire assemblies, printed circuit boards, soldered joints, ground wires, 

bus bars, and other electrical fixtures, except for the actual cabinet in which the 

components are housed. 

218 EMISSION CONTROL SYSTEM: A control device and its associated collection 

system. 

219 EXEMPT COMPOUNDS: As defined in Rule 1.1, General Provisions and Definitions. 

220 FACILITY: A business or businesses engaged in surface preparation and clean up 

activities which are owned or operated by the same person or persons and are located on 

the same or contiguous parcels. 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 8 

221 FLEXOGRAPHIC PRINTING: A letterpress method utilizing flexible rubber or other 

elastomeric plate and rapid drying liquid inks. 

222 FREEBOARD HEIGHT: The distance from the top of the solvent or solvent drain to the 

top of the tank for batch loaded cold cleaners. 

223 FREEBOARD RATIO: The freeboard height divided by the width of the degreaser. 

224 GENERAL WORK SURFACE: An area of a medical device or pharmaceutical facility 

where solvent cleaning is performed on work surfaces including, but not limited to, tables, 

countertops, and laboratory benches. General work surfaces shall not include items defined 

under janitorial cleaning. 

225 GRAPHIC ARTS: All screen, gravure, letterpress, flexographic, and lithographic 

printing processes. 

226 GRAVURE PRINTING: An intaglio printing process in which the ink is carried in 

minute etched or engraved wells on a roll or cylinder. The excess ink is removed from the 

surface by a doctor blade. 

227 HIGH PRECISION OPTICS: An optical element used in an electro-optical device that is 

designed to sense, detect, or transmit light energy, including specific wavelengths of light 

energy and changes in light energy levels. 

228 INTAGLIO PRINTING: A printing operation done from a plate in which the image is 

etched or engraved into the surface. 

229 JANITORIAL CLEANING: The cleaning of building or facility components, such as the 

floor, ceiling, walls, windows, doors, stairs, bathrooms, furnishings, and exterior surfaces 

of office equipment. The cleaning of work areas where manufacturing or repair activity is 

performed is excluded from this definition. 

230 LETTERPRESS PRINTING: The method in which the image area is raised relative to 

the nonimage area and the ink is transferred to the paper directly from the image surface. 

231 LITHOGRAPHIC PRINTING: A printing operation in which the image and non-image 

areas exist in the same plane. The non-image area is treated chemically so that only the 

image area will be printed onto the substrate. 

232 LIQUID LEAK: A visible liquid solvent leak from a container at a rate of more than three 

(3) drops per minute, or a visible liquid mist. 

233 MAINTENANCE CLEANING: Surface preparation and cleanup, including sanitization, 

carried out to keep parts, products, tools, machinery, equipment, or general work areas in 

clean and good operational condition. 

234 MANUFACTURING PROCESS: The process of making goods or articles by hand or by 

machinery. 

 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 9 

235 MEDICAL DEVICE: Any instrument, apparatus, implement, machine contrivance, 

implant, in vitro reagent or other similar article, including any component or accessory, 

that meets one of the following conditions: 

235.1 It is intended for use in the diagnosis of disease or other conditions, or in the cure, 

mitigation, treatment, or prevention of disease: or 

235.2 It is intended to affect the structure or any function of the body; or 

235.3 It is defined in the National Formulary or the United States Pharmacopia, or any 

supplement to them. 

236 NON-ABSORBENT CONTAINERS: Containers made of nonporous material which do 

not allow the migration of the liquid solvent through them. 

237 NON-ATOMIZED SOLVENT FLOW: The use of a solvent to remove uncured 

adhesives, uncured inks, uncured coatings, and contaminants from an article in the form of 

a liquid stream without atomization. 

238 NON-LEAKING CONTAINERS: Containers without liquid leaks. 

239 OPEN TOP VAPOR DEGREASER: A batch solvent cleaning machine that has its upper 

surface open to the air and boils solvent to create solvent vapor used to clean and/or dry 

parts. 

240 PHARMACEUTICAL MANUFACTURING PLANT: Any plant producing or 

blending chemicals for use in pharmaceutical products and/or employing chemical 

processes in the manufacture of pharmaceutical products or medical devices. Any facility 

or operation that has 283 as the first three digits of their Standard Industrial Classification 

Code. Pharmaceutical manufacturing plants may include, but are not limited to, 

establishments primarily engaged in manufacturing, fabricating, or processing medicinal 

chemicals and pharmaceutical products for human or veterinary use. 

241 PHARMACEUTICAL PRODUCT: A preparation or compound of medicinal drugs 

including, but not limited to, a prescription drug, analgesic, decongestant, antihistamine, 

cough suppressant, vitamin, mineral and herb, and is used by humans for consumption to 

enhance human health. 

242 PRINTING: Any operation in the graphic arts that imparts color, design, alphabet, or 

numerals on a substrate. 

243 PRODUCT CLEANING: The removal of loosely held uncured adhesives, uncured inks, 

uncured coatings, and contaminants such as dust, soil, oil, grease, etc., from the product or 

substrate during any manufacturing process, adhesive application, coating application or 

ink application. 

244 REMOTE RESERVOIR COLD CLEANER: A cleaning device, such as a parts washer, 

in which liquid solvent is pumped from a solvent container to a sink-like work area and the 

solvent from the sink-like area drains into an enclosed solvent container while parts are 

being cleaned. 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 10 

245 REPAIR CLEANING: Surface preparation and cleanup carried out during a repair 

process. 

246 REPAIR PROCESS: The process of returning a damaged object or an object not 

operating properly to good condition. 

247 SCREEN PRINTING: A process in which the printing ink passes through a web or fabric 

to which a refined form of stencil has been applied. The stencil openings determine the 

form and dimensions of the imprint. 

248 SEMIAQUEOUS CLEANING SOLVENT: A solution in which water is a primary 

ingredient (≥60 percent of the solvent solution as applied must be water). 

249 SOLVENT: Any liquid containing a volatile organic compound or combination of volatile 

organic compounds, which is used to as a diluent, thinner, dissolver, viscosity reducer, 

cleaning agent, or for other similar uses. 

250 SOLVENT CLEANING MACHINE: Any device or piece of equipment that uses 

solvent liquid or vapor to remove soils from the surfaces of materials. Types of solvent 

cleaning machines include, but are not limited to, batch vapor, in-line vapor, in-line cold, 

and batch cold solvent cleaning machines. Buckets, pails, and beakers with capacities of 

7.6 liters (2 gallons) or less are not considered solvent cleaning machines. 

251 SOLVENT CLEANING OPERATION: An activity, or operation, or process, 

(including surface preparation, cleanup, or wipe cleaning), performed outside of a 

degreaser, that uses organic solvent to remove uncured adhesives, uncured coatings, 

uncured inks or other contaminants, including, but not limited to, dirt, soil, oil, 

lubricants, coolants, moisture, fingerprints, and grease, from parts, products, tools, 

machinery, application equipment and general work areas. Cleaning spray equipment 

used for the application of coatings, adhesives, or inks, is also considered to be solvent 

cleaning.

252 SOLVENT CONTAINER: That part of a cleaning device that holds the solvent. 

253 SOLVENT DEGREASING OPERATION: Any cleaning activities which occur 

within a degreaser. Cleaning of ink, coating, or adhesive application equipment, and 

stripping of coatings are not considered solvent degreasing operations. Solvent 

degreasing operations and solvent cleaning operations are mutually exclusive. 

254 SOLVENT FLUSHING: The use of solvent to remove uncured adhesives, uncured inks, 

uncured coatings, or contaminants from the internal surfaces and passages of the 

equipment by flushing solvent through the equipment. 

255 STRIPPING: The removal of cured inks, cured adhesives, and cured coatings. 

256 SURFACE PREPARATION AND CLEANUP: The removal of loosely held uncured 

adhesives, uncured inks, uncured coatings, and contaminants such as dust, soil, oil, grease, 

etc., at any step in the production, repair, maintenance, or servicing of parts, products, 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 11 

tools, machinery, equipment, or general work areas including the storage and disposal of 

VOC containing materials used. 

257 ULTRAVIOLET INKS: Inks which dry by a polymerization reaction induced by 

ultraviolet radiation. 

258 VAPOR CLEANING MACHINE: A batch or in-line solvent cleaning machine that boils 

liquid solvent generating solvent vapor that is used as a part of the cleaning or drying cycle. 

259 VOLATILE ORGANIC COMPOUND (VOC): As defined in Rule 1.1, General 

Requirements. 

260 VOLATILE ORGANIC COMPOUND (VOC) COMPOSITE PARTIAL 

PRESSURE: The sum of the partial pressures of the compounds defined as VOCs. VOC 

composite partial pressure is calculated according to Section 605. 

261 VOLATILE ORGANIC COMPOUND (VOC) CONTENT: The weight of VOC per 

volume of material as calculated pursuant to the applicable Sections of 600. 

262 WIPE CLEANING: The method of cleaning a surface by physically rubbing it with a 

material such as a rag, paper, or a cotton swab moistened with a solvent. 

300 STANDARDS

301 SOLVENT CLEANING OPERATIONS: Any person performing solvent cleaning 

operations shall comply with all the following: 

301.1 VOC CONTENT LIMITS: A person shall not use a solvent, or specify or require 

any person to use a solvent subject to the provisions of this Rule, unless the solvent 

complies with the applicable requirements set forth in Table 1. 

 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 12 

TABLE 1. VOC CONTENT LIMITS 

Category 

VOC Content* 

Limit grams/liter 

(g/L) 

Product Cleaning 

Electrical Apparatus Components & Electronic Components 100 

Medical Devices and Pharmaceuticals 800 

Aerospace Vehicle or Component 200 g/L 

or 45 mmHg 

All other 25 

Repair Cleaning & 

Maintenance 

Cleaning 

General 25 

Electrical Apparatus Components & Electronic Components 100 

Aerospace Vehicle or Component 200 g/L 

or 45 mmHg 

Medical Devices and 

Pharmaceuticals 

Tools, Equipment, Machinery 800 

General Work Surfaces 600 

Cleaning of 

Application 

Equipment 

Printing operations 

Screen Printing 100 

Lithographic and Letterpress 238 

Ultraviolet (except screen printing) 238 

Specialty Flexographic 100 

Gravure (Publication) 100 

General 25 

Medical Devices and Pharmaceuticals 810 

Aerospace Vehicle or Component 200 g/L 

or 45 mmHg 

All other 25 

General Industries Not Specified Above 25 

* For aerospace vehicle or components, the solvent must comply with either the VOC Content limit in 

grams/Liter (g/L) or the VOC Composite Partial Pressure limit in millimeters mercury (mmHg) 

301.2 CLEANING METHODS: A person using a solvent above 25 grams/liter (in one 

of the above allowed categories) shall use one of the following cleaning devices or 

methods: 

a. Wipe cleaning; 

b. Spray bottles or closed containers with a maximum capacity of 16 fluid 

ounces from which solvents are applied without a propellant induced 

force; 

c. Non-atomized solvent flow method where the cleaning solvent is 

collected in a container or a collection system which is closed except for 

solvent collection openings and, if necessary, openings to avoid excessive 

pressure build-up inside the container; or 

d. Solvent flushing method where the cleaning solvent is discharged into a 

container which is closed except for solvent collection openings and, if 

necessary, openings to avoid excessive pressure build-up inside the 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 13 

container. The discharged solvent from the equipment must be collected 

into containers without atomizing into the open air. The solvent may be 

flushed through the system by air or hydraulic pressure, or by pumping. 

301.3 APPLICATION EQUIPMENT CLEANUP: A person shall not use solvent to 

clean application equipment unless an enclosed system (or equipment that is 

proven to be equally effective at controlling emissions) is used for cleaning. If an 

enclosed system is used, it must totally enclose spray guns, cups, nozzles, bowls, 

and other parts during washing, rinsing and draining procedures, it must be used 

according to the manufacturer’s recommendations, and it must be closed when not 

in use. 

301.4 GENERAL PROHIBITION: A person shall not atomize any solvent into the 

open air. 

302 SOLVENT DEGREASING OPERATIONS: Any person performing solvent degreasing 

operations shall comply with all of the following: 

302.1 GENERAL REQUIREMENTS: 

a. An operator shall operate and maintain the degreaser equipment and 

emission control equipment in proper working order; 

b. An operator shall not remove or open any device designed to cover the 

solvent unless processing work in the degreaser or performing 

maintenance on the degreaser; 

c. An operator shall not degrease porous or absorbent materials such as cloth, 

leather, wood, or rope; 

d. An operator shall, upon detection of a solvent leak, repair the solvent leak 

immediately, or shut down and drain the degreaser; 

e. An operator shall use only a continuous fluid stream (not a fine, atomized, 

fan, or shower type spray) at a pressure which does not cause liquid 

solvent to splash outside of the solvent container, if a solvent flow is 

utilized; 

f. An operator shall store or dispose of spent solvents, waste solvent cleaning 

materials such as cloth, paper, etc., in closed, non-absorbent and 

non-leaking containers. The containers shall remain closed at all times 

except when depositing or removing the contents of the containers or 

when the container is empty; 

302.2 CLEANING METHOD: Use one of the following; 

a. Use solvents < 25 grams/liter; 

b. A cold cleaner that meets the requirements of section 303; 

c. An open top vapor degreaser that meets the requirements of section 304; 

d. Airless/airtight cleaning equipment that meets the requirements of section 

305; or 

e. A remote reservoir cold cleaner that meets the requirements of section 306 

303 COLD CLEANER REQUIREMENTS: A cold cleaner shall meet all of the following: 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 14 

303.1 An apparatus or cover must be used which prevents the solvent from evaporating 

when not processing work in the degreaser. The cover should be designed so that it 

can be opened and closed easily with one hand; 

303.2 If the solvent initial boiling point is less than 248F and the solvent is heated 

above 122F than the cold cleaner shall have 

a. A freeboard ratio greater or equal to 0.75; or 

b. A water cover if the solvent is insoluble in and heavier than water; 

303.3 If the solvent initial boiling point is less than 248F then the drainage facility 

must be internal so that the parts are enclosed under the cover while draining. The 

drainage facility may be external for applications where an internal type cannot fit 

the cleaning system; 

303.4 A facility for draining cleaned parts such that the drained solvent is returned to the 

container. Drain cleaned parts for at least 15 seconds after cleaning or until 

dripping ceases; 

303.5. If using a solvent flow use only a continuous, fluid stream (not a fine, atomized, or 

shower type spray) at a pressure which does not cause liquid solvent to splash 

outside the solvent container; 

303.6. Perform solvent agitation, where necessary, through pump re-circulation, 

ultrasonics, or by means of a mixer. Do not use agitation of the solvent bath; 

303.7. A permanent, conspicuous label posted on or near the degreaser which lists each of 

the operating requirements in Section 303; and 

303.8. A permanent conspicuous mark locating the maximum allowable solvent level that 

conforms to the freeboard requirement in Section 303.2. 

304 OPEN TOP VAPOR DEGREASER REQUIREMENTS: An open top vapor degreaser 

shall meet all of the following requirements: 

304.1 Workloads shall not occupy more than half of the degreaser's open top area; 

304.2 Solvent spraying shall be done at least four (4) inches below the top of the vapor 

layer, and solvent flow shall be directed downward to avoid turbulence at the 

air-vapor interface and to prevent liquid solvent from splashing out of the 

degrease; 

304.3 Water shall not be visually detectable in the solvent returning from the water 

separator to the solvent cleaner; 

304.4 For open-top vapor degreasers equipped with a lip exhaust, the exhaust shall be 

turned off when the degreaser is covered; 

304.5 If the unit is equipped with a refrigerated freeboard chiller, or a primary condenser, 

or both, the following procedures shall be followed: 

a. When starting up the degreaser, the cooling system shall be turned on 

before, or simultaneously with, the sump heater; and 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 15 

b. When shutting down the degreaser, the sump heater shall be turned off 

before, or simultaneously with, the cooling system; 

304.6 Exhaust ventilation should not exceed 65 cfm/ft2 of degreaser open area, unless 

necessary to meet Occupational Safety & Health Administration (OSHA) 

requirements. Ventilation fans shall not be positioned in such a way to disturb the 

vapor zone; 

304.7 The vertical speed of a powered hoist for an open-top vapor degreaser, shall be not 

more than 2.2 inches/sec when moving parts in and out of the degreaser; and 

304.8 The work load shall be degreased in the vapor zone until condensation ceases. 

304.9 Open-top vapor degreasers shall be equipped with a cover designed such that it can 

be opened and closed easily without disturbing the vapor zone. 

304.10 Open-top vapor degreasers shall be equipped with: 

a. A freeboard with a freeboard ratio of at least 1.0. 

b. A container (degreaser) for the solvent and the articles being cleaned; 

c. An apparatus or cover which prevents the solvent from evaporating when 

not processing work in the degreaser; 

d. A facility for draining cleaned parts such that the drained solvent is 

returned to the container; 

e. A permanent, conspicuous label posted on or near the degreaser which 

lists each of the operating requirements in Section 302.1 and Section 304; 

and 

f. A permanent conspicuous mark locating the maximum allowable solvent 

level, that conforms to the freeboard requirement in Section 301.10.a. 

g. An automated parts handling system; 

h. Primary condensing coils; 

i. A perimeter trough; 

j. A water separator; 

k. A refrigerated freeboard chiller that is operated such that the chilled air 

blanket temperature measured at the center of the air blanket is no greater 

than 40 percent of the boiling point of the solvent, and; 

l. A superheated vapor zone. 

304.11 Open-top vapor degreasers shall not operate without one (1) of the following or a 

combination of the following major control devices: 

a. Condenser equipment where the chilled air blanket temperature measured 

in degrees F at the coldest point on the vertical axis in the center of the 

degreaser shall be either no greater than 30 percent of the initial boiling 

point, measured in degrees F, of the solvent used, or 41°F; 

b. Enclosed design (cover or door opens only when the dry part is actually 

entering or exiting the degreaser); 

c. A carbon adsorption system which ventilates the air-vapor interface at a 

minimum rate of 50 cfm/ft2 of degreaser opening, but not greater than 65 

cfm/ft2 of degreaser opening, unless required by OSHA standards, and 

exhausts less than 25 ppm of solvent by volume over a complete 

adsorption cycle, and with an overall capture and control efficiency of 85 

percent; or 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 16 

d. Any other system of emission control demonstrated to have an overall 

capture and control efficiency of at least 85 percent. 

304.12 Open-top vapor degreasers shall include all of the following safety switches: 

a. A vapor level control switch 

b. A condenser flow switch with a solvent temperature indicator, except 

where non-water refrigerant is used. The switch shall shut off the sump 

heat if either the condenser coolant stops circulating or becomes warmer 

than specified; 

c. A spray pump safety switch; and 

d. A manual reset vapor level thermostat with a solvent temperature 

indicator. 

305 AIRLESS/AIRTIGHT CLEANING SYSTEM REQUIREMENTS: An airless/airtight 

cleaning system shall meet all of the following requirements: 

305.1 The equipment is operated in accordance with the manufacturer’s specifications 

and operated with a door or other pressure sealing apparatus that is in place during 

all cleaning and drying cycles; 

305.2 All associated pressure relief devices shall not allow liquid solvents to drain out. 

Spills during solvent transfer shall be wiped up immediately and handled in 

accordance with Section 307. 

305.3 A differential pressure gauge shall be installed to indicate the sealed chamber 

pressure. 

306 REMOTE RESERVOIR COLD CLEANER REQUIREMENTS: A remote reservoir 

cold cleaner shall meet all the following requirements: 

306.1 Prevent solvent vapors from escaping from the solvent container by using such 

devices as a cover or a valve when the remote reservoir is not being used, cleaned, 

or repaired; 

306.2 Direct solvent flow in a manner that will prevent liquid solvent from splashing 

outside of the remote reservoir cold cleaner; 

306.3 A tank or sink-like work area which is sloped sufficiently to preclude pooling of 

solvent; 

306.4 A single drain hole, less than 100 square centimeters (15.5 square inches) in area, 

for the solvent to flow from the sink into the enclosed reservoir; 

306.5 A freeboard ratio greater or equal to 0.75; 

306.6 A cover for the drain when no work is processed. 

307 STORAGE AND DISPOSAL - GENERAL: All solvents used, whether in its form for 

intended use or as a waste or used product, including items such as cloth or paper laden 

with VOC containing materials, shall be stored in non-absorbent, non-leaking containers 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 17 

which shall be kept closed at all times, except when filling or emptying, and disposed of in 

a manner to prevent evaporation of VOCs into the atmosphere at the facility. 

308 EMISSION CONTROL SYSTEM: In lieu of complying with the requirements in 

Sections 301 through 306 of this Rule, an operator may comply by using collection and 

control systems provided that the system is approved in writing by the APCO and during 

emission producing activities, the system complies with either: 

308.1 The VOC emission control system=s control device shall have a capture efficiency 

of at least 90 percent, by weight, of the emissions generated by surface preparation 

and cleanup and one of the following requirements: 

a. The control device has a control efficiency of at least 95 percent by 

weight, or 

b. The VOC emission control system has an output of less than 50 parts per 

million by weight (ppm) calculated as carbon with no dilution; or 

308.2 The emission control system meets the requirements of the applicable source 

specific rule of the District=s Regulation II. 

400 ADMINISTRATIVE REQUIREMENTS

401 PROHIBITION OF SPECIFICATION: A person shall not specify the use of any 

solvent used for surface preparation and cleanup subject to the provisions of this rule that 

does not meet the limits and requirements of this rule where such applications result in a 

violation of this rule. The requirements of this Section shall apply to all written or oral 

contracts. 

402 COMPLIANCE STATEMENT REQUIREMENT: Any person who sells or distributes 

any solvent subject to this rule shall make available to the purchaser at the time of sale the 

following information: 

402.1 The name of the solvent; 

402.2 The name of the manufacturer; 

402.3 The maximum VOC content of the solvent as applied. The VOC content shall be 

expressed as grams of VOC per liter of solvent, or pounds of VOC per gallon of 

solvent as determined pursuant to Section 602; 

402.4 Recommendations regarding thinning, reducing or mixing with any solvent, if 

applicable; 

403 OPERATION AND MAINTENANCE PLAN (O&M PLAN): Any person using an 

emission control device pursuant to Section 308 of this Rule, as a means of complying with 

this rule, must submit with the application for Authority to Construct, pursuant to Rule 3.1, 

GENERAL PERMIT REQUIREMENTS, an O&M Plan for the emission control device to 

the APCO for approval. The O&M Plan shall specify operation and maintenance 

procedures which will demonstrate continuous operation of the control device during 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 18 

periods of emission producing operations. The O&M Plan shall be maintained and 

re-submitted for approval by the APCO if changes to the control system require changing 

the plan. The O&M Plan shall also specify which records must be kept to document these 

operation and maintenance procedures. These records shall comply with the requirements 

of Section 502 of this Rule. Any person using an emission control device must fully 

comply with all O&M Plans submitted for approval, even if such O&M Plans have not yet 

been approved, unless notified in writing by the APCO. 

500 MONITORING AND RECORDS

501 RECORD KEEPING - GENERAL: Any person using a solvent for all applications 

subject to this Rule, except those subject to Section 110 Exemption - General, shall 

maintain records in a current file that contains all the data necessary to verify compliance 

and shall include the following: 

501.1 Identification of each process at the facility subject to this Rule. The identification 

shall include the following: 

a. The location of the unit(s); 

b. The permit number (if applicable); 

c. Description of the method of application and substrate type. 

501.2 The amount and type of each solvent used at each process, on a monthly basis. The 

following information should be included; 

a. The name of the solvent; 

b. The name of the solvent manufacturer; 

c. The VOC content of the solvent expressed in grams/liter or lb/gallon; 

d. Solvent usage; 

e. The mix ratio for the cleaning solvent as applied. 

501.3 A copy of the Manufacturer=s product data sheet or material safety data sheet of 

the solvent used. 

501.4 Any other such records needed to verify compliance with this rule. 

502 RECORD KEEPING - EMISSION CONTROL SYSTEMS: If compliance with this 

rule is achieved through the use of an emission control system, in addition to the provisions 

of Section 501, the owner or operator shall maintain: 

502.1 Daily usage records of all solvents. 

502.2 Daily records of key operating parameters such as temperatures, pressures, 

flowrates, and hours of operation of the control device to verify compliance of the 

capture and control device. 

502.3 Maintenance work which interferes with the operation of the control device. 

503 BURDEN OF PROOF: Any person claiming exemption pursuant to Section 110, 111, 

112 or 113 shall have information available such as product data or material safety data 

sheets or records that would allow the APCO to verify the eligibility of the exemption. 
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 19 

504 RECORD RETENTION: All records required by Sections 501, 502, and 503 shall be 

maintained on site for a period of two years and made available to the APCO upon request. 

600 TEST METHODS AND CALCULATIONS 

601 GENERAL: For the purposes of this Rule, the following test methods or calculation 

methods shall be used. Other test methods determined to be equivalent and approved in 

writing by the District and the EPA may also be used. When more than one test method or 

set of test methods is specified for any testing, a violation of any requirement of this rule 

established by any one of the specified test methods or set of test methods shall constitute a 

violation of this Rule. 

602 VOC CONTENT: The VOC content of organic solvents subject to the provisions of this 

rule shall be determined by: 

602.1 procedures contained in EPA Reference Test Method 24 or 24A, 

602.2 South Coast Air Quality Management District (SCAQMD) Method 304-91 

“Determination of VOC in Various Materials”, February 1996; or 

602.3 by using the manufacturer=s product formulation data and formula listed in 

Section 604. 

603 EXEMPT COMPOUNDS: The content of exempt VOCs shall be determined by using 

CARB Method 432 (‘Determination of Dichloromethane and 1,1,1-Trichloroethane in 

Paints and Coatings’, or ‘Exempt Halogenated VOC in Liquids’) or SCAQMD Method 

303-91 (Determination of Exempt Compounds). 

604 CALCULATION OF VOC CONTENT: The VOC content per volume of solvent shall 

be calculated by the following equation: 

	 ൌ௖௢௡ ܥܸܱ

ሺܹௌ െ	ܹௐ െ	ܹாௌሻ

ܸெ

where: 

VOCୡ୭୬ = Grams of VOC per liter of material 

ܹௌ = Weight of volatile compounds in grams 

ܹௐ = Weight of water in grams 

ܹாௌ = Weight of exempt compounds in grams 

ܸெ = Volume of material in liters 

605 CALCULATION OF VOC COMPOSITE PARTIAL PRESSURE: The VOC 

composite partial pressure shall be calculated by the following equation: 

ܲܲ஼ ൌ	෍

ሺܹ௜ሻሺܸܲ௜ሻ

௜ܹܯ

ܹௐ

ௐܹܯ

൅ 	 ܹா

ாܹܯ

൅ 	∑ ܹ௜

௜ܹܯ

௡

௜ୀଵ

௡

௜ୀଵ

where: 

ܲܲ஼	 ൌ	VOC	composite	partial	pressure	at	20°C,	in	mm	Hg	

ܸܲ௜	 ൌ	Vapor	pressure	of	the	"i"th	VOC	compound	at	20°C,	in	mm	Hg	
Yolo-Solano AQMD 

Revised May 8, 2013 Reg. II, Rule 2.31, Page 20 

ܹ௜	 ൌ	Weight	of	the	"i"th	VOC	compound,	in	grams	

ܹௐ	 ൌ	Weight	of	water,	in	grams	

ܹா	 ൌ	Weight	of	exempt	compound,	in	grams	

ܯܹ 	௜ൌ	Molecular	weight	of	the	"i"th	VOC	compound,	in	g/ሺg‐moleሻ	

ܯܹௐ	 ൌ	Molecular	weight	of	water,	in	g/ሺg‐moleሻ	

ܯܹா	 ൌ	Molecular	weight	of	exempt	compound,	in	g/ሺg‐moleሻ	

606 CAPTURE EFFICIENCY: The capture efficiency of a VOC emission control system=s 

collection device shall be determined according to EPA=s AGuidelines for Determining 

Capture Efficiency,@ January 9, 1995 and 40 CFR 51, Appendix M, Methods 204-204F, as 

applicable. If a permanent total enclosure is used, EPA Method 204 can also be used as an 

alternative method to determine capture efficiency. 

607 CONTROL EFFICIENCY: The control efficiency a VOC emission control system=s 

collection device shall be determined by using EPA Methods 2, 2A, or 2D for measuring 

flow rates and EPA Method 25, 25A, or 25B for measuring total gaseous organic 

concentrations at the inlet and outlet of the control device. EPA Method 18 or CARB 

Method 422 shall be used to determine the emissions of exempt compounds. 

608 SPRAY GUN CLEANING SYSTEMS: The determination of emissions of VOC from 

spray gun cleaning systems shall be made using South Coast Air Quality Management 

District "General Test Method for Determining Solvent Losses from Spray Gun Cleaning 

Systems" dated October 3, 1989.