Table of Contents
Spraying: Regulatory Requirements
The Clean Air Act regulates the emission of
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.
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
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.
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
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,
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
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.