Table of Contents
Electrostatic 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), 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
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
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
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
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.