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EPA Self-Audit and Inspection Guide
Organic Finishing of Metals

Table of Contents

Spraying: Regulatory Requirements

Air
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). Depending on the solvent content of the coating material used with 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. The Act also provides specific standards of performance concerning emissions from various types of coating operations.

Controlling VOC emissions from spray areas can be accomplished 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 high-volume, low-pressure spraying. Third, air pollution control equipment can be attached to the ventilation system to capture VOCs prior to their release into the atmosphere.

Water
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 spraying application methods may be classified as toxic organics. These materials can enter the wastewater through the use of water wash spray booths or when cleaning coatings from containers or equipment. Actual limits for effluent constituents depend 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 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 up, 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. Responsibilities will vary according to the amount of hazardous waste material generated; facilities generating at least 100 kilograms of hazardous waste per month must comply.

Each state and/or region is primarily responsible for the regulation of non-hazardous solid wastes (those not governed by the hazardous waste provisions of RCRA). Check with state environmental agencies for specific information or guidance.

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 spray equipment. For example, airless spray systems produce a high-pressure stream of coating material that is capable of severely damaging or even severing limbs.

Self-Audit/Inspection

  • What is the transfer efficiency of the 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 agreement?
  • Are wastes contaminated with solvent-based coatings classified as hazardous? If so, are the wastes handled and manifested in accordance with 40 CFR Part 262, Subpart B. Are the hazardous wastes segregated from non-hazardous wastes?

Spraying: Common Causes of Violation

  • 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 allowed by Clean Air Act Air Title V permits. 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.
  • Spray application systems utilize liquid coating materials which can contaminate water streams. This may occur with the use of water wash spray booths, water or solvents used for cleaning, or accidental spills while preparing spray equipment. Contaminated water streams may contain pollutants in concentrations exceeding limits established by facility NPDES permits or POTW discharge requirements. As a result, effluent, may not be directly released to water systems or to publicly owned treatment works without pretreatment.
  • Spray application systems can deposit coating materials on filters, masking paper, rags, and clothing which must be properly stored, manifested and disposed according to RCRA standards for hazardous waste (40 CFR Part 262).
  • 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, and the possibility of inhaling respirable coating particulates.

Spraying: Sources of Pollution

  • 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.
  • Spray application systems create a fog or mist of particles which do not all deposit on the part. The coating material that missed the part is wasted.
  • Spray application systems create solid waste in the form of filters, masking materials, clothing, personnel protective equipment, and other materials. Liquid waste can be created from water used in water wash spray booths or for cleaning.
  • Spray application systems will have coating material remaining in coating receptacles, pumps, valves, hoses, etc., that becomes waste.
  • Spray application systems require regular cleaning which creates solvent or water wastes.

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.
  • Change from air atomized spray systems to airless, air-assisted airless; or high-volume, low-pressure 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 HVLP systems provide a variety of film thicknesses.
  • Include electrostatics in the spray system. Electrostatics improve transfer efficiency by increasing the attraction between coating particles and the work piece.
  • 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 solvent, 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 materials, and solvents. Disassemble gun nozzle to clean thoroughly, rather than submerging gun in solvent; solvent can penetrate seals and promote leaks in connections.
  • 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, and 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 techniques can be observed, leaks in equipment can be found and fixed quickly, and accidents can be prevented.


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