Paints & Coatings Resource Center

EPA Self-Audit and Inspection Guide
Organic Finishing of Metals

Table of Contents

Electrostatic Spraying: Regulatory Requirements

The Clean Air Act regulates the emission of volatile organic compounds (VOCs) (40 CFR Part 60) and hazardous air pollutants (HAPs) (40 CFR Part 61 and 40 CFR Part 63), and provides specific standards of performance to control emissions from various types of coating operations (40 CFR Part 60). Depending on the solvent content of the coating material used with electrostatic spraying methods, atomized solvents can evaporate and produce sufficient VOC and HAP emissions to subject an operator to major source requirements and Title V permitting requirements.

Painting and solvent cleaning processes are regulated by federal rules that are implemented by state agencies. These regulations limit emissions from operations, such as those coating metal furniture, miscellaneous metal parts, plastic parts, autos, trucks, boats and large appliances. Coating facilities affected by these regulations need to obtain permits, control and monitor air emissions, and submit reports. Use This PCRC Tool to determine which regulations and standards apply to your operations.

Controlling VOC emissions from spray areas can be completed in several ways. First, a coating material with a lower VOC content can be used. Second, a spray system with higher transfer efficiency can be used, such as air-assisted airless or rotary electrostatic spraying techniques. Third, air pollution control equipment can be attached to the ventilation system to capture VOCs prior to their release into the atmosphere.

As part of the Clean Water Act, Effluent Guidelines and Standards for Metal Finishing (40 CFR Part 433) have been established that limit concentrations of toxic organics in wastewater streams. The organic solvents often contained in liquid coatings used with electrostatic spraying application methods may be classified as toxic organics. These materials can enter the wastewater when removing coatings from containers or equipment. Actual limits for effluent constituents are dependent on the size of the operation and the amount of wastewater generated from the facility. If the facility discharges directly to receiving waters, these limits will be established through the facility's National Pollutant Discharge Elimination System (NPDES) permit (40 CFR Part 122). Facilities which are indirect dischargers releasing to a POTW must meet limits in the POTW's discharge agreement. Wastewater streams with concentrations exceeding permit limits will require pretreatment prior to discharge to receiving waters or to a publicly owned treatment works. Pretreatment may include separation of liquid wastes to remove solvents, and settling or precipitation of solid materials.

Solid and Hazardous Waste
Under the Resource Conservation and Recovery Act (RCRA), organic finishing facilities are required to manage listed and characteristic hazardous wastes (40 CFR Part 261). Liquid coatings used with electrostatic spray application methods may contain constituents listed or characterized as hazardous wastes. Materials contaminated with the coatings, such as spray booth air filters, masking materials for booth light fixtures and floors, and rags or containers used for cleaning, may require treatment as hazardous waste depending on their formulation. Hazardous waste management (40 CFR Part 262) includes obtaining permits for the facility in order to generate wastes, meeting accumulation limits for waste storage areas, and manifesting waste containers for off-site disposal.

The Emergency Planning and Community Right-to-Know Act (EPCRA) requires facilities to notify employees, customers and the surrounding community of certain hazardous chemicals and materials (40 CFR Parts 355 and 370) that are present on-site. Electrostatic spraying operations may use hazardous materials in sufficient quantities to subject a facility to several EPCRA requirements. Facilities may be required to inform the local emergency planning committee (LEPC) and the state emergency response commission (SERC) of the materials stored and used on-site, devise emergency response plans for reacting to spills, and notify authorities of accidental spills and releases (40 CFR Parts 302 and 355). The materials used with electrostatic spraying methods may also require facilities to submit Material Safety Data Sheets (MSDS) for these materials to state, regional, and local organizations, while disposed volumes of the material may have to be documented on annual Toxic Release Inventory reports (40 CFR Part 372).

Health and Safety
While not directly regulated by the EPA, several conditions exist that should be considered when using spray application methods. Workers should be aware of their responsibilities when handling coating materials during equipment preparation and cleaning activities. Workers should also know the risks associated with inhaling the respirable coating and VOC particles in atomized sprays. Finally, workers should be trained properly to avoid accidents and injuries when working with electrostatic spray equipment, especially the probability of electric shock.


  • What is the transfer efficiency of the electrostatic spray application system?
  • Do exhaust air streams have air pollution control equipment attached? Is that air pollution control equipment working properly? Does the final exhaust air have concentrations of pollutants below required levels?
  • Does the spray system produce a liquid waste stream? Do concentrations of pollutants in the waste stream exceed limits established by the facility NPDES permit or POTW discharge equipment?
  • Are solid wastes handled to separate hazardous and non-hazardous wastes? Are wastes labeled and packaged in accordance with 40 CFR Part 262, Subpart C? Are manifest forms completed for hazardous wastes to be shipped for disposal?

Electrostatic Spraying: Common Causes of Violations

  • Electrostatic spray application systems atomize coating materials which may include solvents classified as volatile organic compounds and/or hazardous air pollutants. The atomized solvents evaporate quickly and may accumulate above limits established in a Title V permit. Ventilation and exhaust systems must operate properly to ensure the vapors are removed from the spray area. Adequate air flow volumes must circulate and particulate filtration devices must not be clogged. Air pollution control equipment should be attached to exhaust systems to recover or destroy volatile organic compounds instead of releasing them to the air.
  • Electrostatic spray application systems utilize liquid coating materials which can contaminate water streams. This may occur with the use of water wash spray booths, when water or solvents are used for cleaning, or when accidental spills occur while preparing spray equipment. Contaminated water streams may contain pollutants in concentrations exceeding limits established by the facility NPDES permit or POTW discharge equipment. As a result, effluent may not be directly released to water systems or to publicly owned treatment works without pretreatment.
  • Electrostatic spray application systems can deposit coating materials on filters, masking paper, rags, and clothing which must be properly stored, manifested and disposed of according to 40 CFR Part 262.
  • Electrostatic spray application system operators must be made aware of the hazards associated with use of the system, including the chemistry of the coating material, the presence of volatile organic compounds vapors, the possibility of inhaling respirable coating particulates, and the risk of electric shock.
  • Liquid coatings used with electrostatic spraying methods may contain substances defined as hazardous substances or extremely hazardous chemicals. Depending on the quantity of material on-site, facilities must cooperate with local emergency planning committees, have an MSDS for each formulation, and maintain records for TRI reporting.

Electrostatic Spraying: Sources of Pollution

  • Electrostatic spray application systems may apply liquid coating materials that contain components classified as volatile organic compounds, hazardous air pollutants, and/or ozone-depleting substances. In addition, the atomization of the fluid during spraying volatizes these materials and promotes their evaporation.
  •  Electrostatic spray application systems create a fog or mist of particles which do not all deposit on the part. Any coating material that misses the part is wasted.
  • Electrostatic spray application systems create solid waste in the form of filters, masking materials, clothing, personnel protective equipment, etc. Liquid waste can be created from water used in water wash spray booths or for cleaning.
  • Electrostatic spray application systems will have coating material remaining in coating receptacles, pumps, valves, hoses, and other system components that becomes waste.
  • Electrostatic spray application systems require regular cleaning which creates solvent or water wastes.

Electrostatic Spraying: Pollution Prevention Alternatives

  • Use liquid coating materials with low organic solvent content to minimize the amount of volatile organic compounds that will be volatized and to reduce the volume of solid and liquid hazardous waste created. Waterborne coatings, however, are highly conductive and may require additional equipment to maintain electrostatic charge of the spray.
  • Change from air atomized spray systems to airless, air-assisted airless, or rotary spray systems which have less atomization and better transfer efficiency of coating materials. However, the type of spray system chosen must be compatible with the coating material used. High-solid coatings with high viscosity may not spray effectively with airless systems. Also, the film thickness must be considered. Air-atomized systems create thin films, while airless systems produce a heavier film. Air-assisted airless and rotary systems provide a variety of film thicknesses.
  • Adjust the air current velocity in spray areas, especially if automated spray systems are used. Lower velocities will prevent atomized coating particles from straying from the work piece.
  • Use heat to adjust the viscosity of coating materials. Heat reduces the need for additional organic solvent thinners, which contribute hazardous air and water emissions. Heat also decreases the cure time for the coating, reducing energy consumption in curing processes.
  • Fill spray system coating receptacles only as full as necessary to complete the current task. This prevents coating material waste and reduces the amount of solvents required for cleaning.
  • Schedule paint jobs to minimize changing colors in spray equipment. If several colors are required, use a different set of equipment for each individual color rather than cleaning equipment with solvents each time a new color is used. If extra equipment is not an option, schedule painting with light colors first, then darker ones; lighter coating does not need to be completely removed from the equipment, but can blend into the darker coating.
  • Train operators to manipulate spray equipment properly. Spray gun movement must be compatible with the fluid spray rate. The spray gun should be held about twelve inches from the part and perpendicular to the work piece surface. The spray pattern should be adjusted to be slightly smaller than the part profile. The spray gun should be triggered at the correct time on leading and trailing edges.
  • Reduce the pressure of compressed air leaving the gun. Lower pressures reduce the forward velocity of the particles so they are less likely to rebound off the part. Lower air pressures also reduces energy demand for the compression system.
  • Space parts closer together on conveyors so that stray coating particles deposit on parts.
  • Clean spray equipment, especially guns and nozzles, regularly to prevent coating materials from drying inside and clogging fluid lines. Use water in cleaning steps to reduce the amount of organic solvents used and amount of hazardous waste generated. Perform initial flush of spray systems with used solvents, saving fresh solvents for final cleaning stages. Point spray guns into an enclosed area, such as a barrel or can, when cleaning to capture coating material, and solvents. Disassemble gun nozzle to clean thoroughly, rather than submerging gun in solvent; solvent can penetrate seals and promote leaks in connections.
  • Clean part racks and hangers, conveyors, and spray booths more frequently to maintain proper ground. Proper ground will improve the attraction between the part and the charged coatings, increasing transfer efficiency.
  • Segregate non-hazardous coating solids and water from hazardous solvents and thinners, and label containers to prevent mixing. Separation of the materials reduces the amount of hazardous waste that is produced. Coating material solids can be dried and treated as a solid waste, allowing for disposal in a landfill.
  • Reuse spray booth filter material where possible. Some dry filters can be cleared of dried coating materials by backflowing with compressed air. Water from water wash booths can be collected and the solvents and coating solids removed.
  • Maintain equipment to prevent clogs and sustain a consistent spray pattern. Keep air lines free of water, dirt, and oils. Make sure valves, gauges, and nozzle tips are in proper working order.
  • Keep spray booth areas clean so that improper spraying technique can be observed, leaks in equipment can be found and fixed quickly, and accidents can be prevented.

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