Spray finishing definitions

Aerated solid powders are powdered coating materials that are fluidized by air from below to form a fluidized powder bed used like a liquid dip or as a source for powder spraying. This is the definition in 1910.107(a)(1).

• Practical point: if you use a container where air supports or expands powder so parts are dipped or passed through the powder cloud, treat it as an aerated solid powder operation and follow the spray-finishing requirements that apply to powder operations under this section.

A spray booth is a power-ventilated structure that encloses or accommodates a spraying operation to confine and limit the escape of spray, vapors, and residues and to safely direct them to an exhaust system. See 1910.107(a)(3).

• Practical point: if your spraying is done inside a ventilated room or enclosure designed to capture overspray and route it to exhaust, that structure is a spray booth and must meet the booth-specific construction, ventilation, and electrical rules in this section.

A waterwash spray booth is a spray booth equipped with a water washing system intended to reduce dusts or residues entering the exhaust ducts and to allow recovery of overspray. See 1910.107(a)(4).

• Practical point: use a waterwash booth where you need to minimize dry residues in ducts or recover liquid or powder overspray; waterwash booths are treated differently than dry booths for filter and exhaust design.

A dry spray booth is a spray booth without a water washing system and may use distribution or baffle plates, overspray dry filters, filter rolls, or powder collection systems in the exhaust to capture overspray. See 1910.107(a)(5) and its subparagraphs (i)–(v).

• Practical point: select the dry-collection method that fits your coating type (liquid or powder) and follow the downstream requirements for filter fire protection and disposal in paragraph (b)(5).

An electrostatic fluidized bed is a container of powder coating material aerated from below to form a charged cloud; the object to be coated is carried over the charged cloud so the powder deposits electrostatically. See 1910.107(a)(7).

• Practical point: electrostatic fluidized-bed systems create charged powder clouds; they must be handled under the electrical and ventilation rules that apply to electrostatic equipment in this section (see paragraphs (h) and (i) referenced by the standard).

“Approved” or “listed” means approved and listed by a nationally recognized testing laboratory, as defined in 1910.107(a)(8) and cross-references the definition of a nationally recognized testing laboratory in 1910.7.

• Practical point: when equipment or materials must be “approved” or “listed,” use products tested and listed by an NRTL recognized under 1910.7 to meet that requirement.

Spray booths must be made of substantial noncombustible construction: steel, concrete, or masonry, with aluminum or other substantial noncombustible material allowed only for intermittent or low-volume spraying; booths must be securely supported and designed to sweep air toward the exhaust outlet. See 1910.107(b)(1).

• Practical point: permanent or high-volume booths should be steel or masonry; if you use aluminum for light-duty booths, document that the operation is intermittent or low volume and ensure the airflow pattern sweeps toward the exhaust.

The interior surfaces of spray booths must be smooth, continuous, and free of edges to prevent residue pockets and to allow safe cleaning; if the floor or operator area is combustible it must be covered with noncombustible material that facilitates safe cleaning and residue removal. See 1910.107(b)(3).

• Practical point: design interior surfaces to be easy to wash and inspect; replace combustible floor coverings in the booth area with noncombustible material to reduce fire risk and make residue removal safer.

Distribution or baffle plates used to even airflow or deposit overspray must be noncombustible, readily removable or accessible for cleaning on both sides, and must not be located in exhaust ducts. See 1910.107(b)(4).

• Practical point: make plates easy to remove for cleaning and inspection, use noncombustible materials, and never install them inside the exhaust duct where they could obstruct or accumulate residues.

For spraying operations (except electrostatic), the average air velocity over the open face or booth cross section during spraying must be at least 100 linear feet per minute. See 1910.107(b)(5)(i).

• Practical point: measure and document face velocity during operations; maintain at least 100 fpm to help keep dangerous vapors and overspray moving toward the exhaust.

Electrostatic spraying may be conducted with an air velocity over the open face of not less than 60 linear feet per minute (or higher depending on material volume and flammability); visible gauges, audible alarms, or pressure-activated devices must be installed to ensure the required velocity is maintained. See 1910.107(b)(5) and 1910.107(b)(5)(i).

• Practical point: when using electrostatic systems, set the face velocity based on the material’s characteristics and install continuous indicators or alarms so operators immediately know if ventilation falls below the required rate.

Discarded filter pads and filter rolls must be removed immediately to a safe, well-detached location or placed in a water-filled metal container and disposed of at the end of the day's operation unless they are maintained completely in water. See 1910.107(b)(5)(ii).

• Practical steps:
  • Remove used filters promptly from the booth area.
  • Store them in a detached safe location or keep them submerged in a water-filled metal container until disposal at the end of the day.
  • Do not leave soaked or combustible filters where they can dry and potentially self-heat.

Spaces within the spray booth on the downstream and upstream sides of filters must be protected with approved automatic sprinklers. See 1910.107(b)(5)(iv).

• Practical point: design the booth and filter housings so that the areas immediately adjacent to filters have automatic sprinkler protection to reduce the fire risk from accumulated overspray.

Filters or filter rolls must not be used when applying spray materials known to be highly susceptible to spontaneous heating and ignition, and clean filters or rolls must be noncombustible or have combustibility not exceeding class 2 as listed by Underwriters' Laboratories. See 1910.107(b)(5)(v) and 1910.107(b)(5)(vi).

• Practical point: if your coating is prone to spontaneous heating, avoid using dry filter media—use waterwash or specially designed powder collection—and ensure any clean filters meet the required noncombustible or class 2 combustibility rating.

Each spray booth with a frontal area larger than 9 square feet must have a metal deflector or curtain at the upper outer edge of the booth at least 2½ inches deep. See 1910.107(b)(6).

• Practical point: install the required metal deflector/curtain to help control air flow and contain overspray for larger booth openings.

Openings for conveyors into spray booths must be as small as practical, and each spray booth must be separated from other operations by at least 3 feet (or a greater distance or partition/wall that reduces the danger). See 1910.107(b)(7) and 1910.107(b)(8).

• Practical point: minimize openings for conveyors to limit vapor/overspray escape and keep at least a 3-foot clear separation (or install protective partitions) between booths and other hot or combustible operations.

Spray booths must be installed so all portions are readily accessible for cleaning, and a clear space of at least 3 feet on all sides must be kept free from storage or combustible construction. See 1910.107(b)(9).

• Practical point: maintain the 3-foot clearance and design booths with access panels, removable plates, and safe walkways so cleaning and inspection are routine and effective.

No. There shall be no open flame or spark-producing equipment in any spraying area nor within 20 feet of a spraying area unless separated by a partition. See 1910.107(c)(2).

• Practical point: keep welding, cutting, torches, hot-work tools, cigarette smoking, and other ignition sources well away from spray areas or install effective partitions to comply with the 20-foot rule.

No. Space-heating appliances, steam pipes, or hot surfaces must not be located in a spraying area where deposits of combustible residues may readily accumulate. See 1910.107(c)(3).

• Practical point: locate heat sources outside spray areas or ensure they cannot heat residues to ignition temperatures; avoid placing hot equipment where overspray collects.

Where deposits of combustible residues may readily accumulate, there shall be no electrical equipment in the spraying area except wiring in rigid conduit or boxes/fittings containing no taps, splices, or terminal connections. Where equipment is not subject to residue deposits, electrical wiring and equipment must be explosion-proof and approved for Class I, group D locations and otherwise comply with subpart S for hazardous locations. See 1910.107(c)(5) and 1910.107(c)(6).

• Practical point: evaluate whether residues will accumulate; if they will, limit electrical systems to conduit/boxes without splices; if not, install explosion-proof equipment rated for Class I, group D.

Lamps outside but within 20 feet of a spraying area must be totally enclosed and protected from mechanical injury; portable electric lamps are prohibited in spraying areas during spraying and may only be used for cleaning/repair when they are of a type approved for Class I hazardous locations. See 1910.107(c)(7) and 1910.107(c)(8).

• Practical point: use fixed, enclosed lighting rated for hazardous locations and keep portable lamps out of spraying operations unless they are the proper explosion-proof type and used only for maintenance.

All metal parts of spray booths, exhaust ducts, and piping systems conveying flammable liquids or liquids with flashpoints greater than 199.4 °F (93 °C) or aerated solids must be properly and permanently electrically grounded. See 1910.107(c)(9)(i).

• Practical point: install a permanent grounding system for metal booth components and ducts to prevent static buildup and reduce ignition risk; document grounding continuity and inspect regularly.

Mechanical ventilation adequate to remove flammable vapors, mists, or powders to a safe location and to confine/control combustible residues must be provided and kept operating at all times while spraying and a sufficient time afterward to exhaust drying vapors; each spray booth must have an independent exhaust duct to the exterior unless multiple small cabinets using identical material total ≤18 square feet of frontal area. See 1910.107(d)(2) and 1910.107(d)(3).

• Practical steps:
  • Keep ventilation running during and after spraying until drying vapors are exhausted.
  • Design independent exhaust ducts for each booth unless you meet the limited exception for identical small cabinets.

Fan rotating elements must be nonferrous or nonsparking, or the fan casing must consist of or be lined with such material. See 1910.107(d)(4).

• Practical point: select fans and impellers made from nonferrous or nonsparking materials (e.g., bronze, aluminum alloys where appropriate) or use lined casings to reduce the risk of sparks inside exhaust systems.

No — electric motors driving exhaust fans must not be placed inside spray booths or ducts. See the requirement in 1910.107(d)(5).

• Keep motors outside the booth or duct to avoid creating ignition sources inside areas where flammable vapors can accumulate.
• If other electrical equipment must be near booths, follow the general electrical-location requirements in 1910.107(c).

No — belts may not enter the duct or booth unless the belt and pulley within the duct or booth are thoroughly enclosed. See 1910.107(d)(6).

• If you must have belts or pulleys inside an enclosure, make sure the enclosure is complete and prevents contact with vapors or combustible residue.
• Enclosing moving parts also reduces friction and spark hazards.

Exhaust ducts must be steel, well-supported, protected from mechanical damage, and kept at least 18 inches from unprotected combustible construction unless protected as allowed. See 1910.107(d)(7) and 1910.107(d)(7)(i).

• Ducts should be substantially supported and preferably without dampers; if dampers exist, they must be kept fully open while the ventilating system runs.
• Maintain at least an 18-inch clearance to unprotected combustible material unless you apply approved protection measures (see 1910.107(d)(7)(ii)).

You may reduce the 18-inch clearance if specified protective materials are applied to combustible surfaces within 18 inches; the standard lists exact protection options and reduced clearances. See 1910.107(d)(7)(ii).

• Examples from the provision: 28-gage sheet metal on 1/4" asbestos mill board allows a 12-inch clearance; 22-gage sheet metal on 1" rockwool batts reinforced with wire mesh allows a 3-inch clearance.
• If you protect ducts with an approved automatic sprinkler system maintained properly, the clearance can be reduced to 6 inches.

The exhaust terminal (unless from a water-wash booth) must discharge at least 6 feet away from any combustible exterior wall or roof and not toward combustible construction or unprotected openings within 25 feet. See 1910.107(d)(8).

• Position exhaust outlets so they don't blow contaminants toward makeup air intakes or create a nuisance, and avoid directing exhaust toward unprotected openings in nearby structures.

No — air exhausted from spray operations must not be recirculated. See 1910.107(d)(9).

• Exhaust must not contaminate makeup air intakes or other ventilating intakes, and should be routed so it does not create a nuisance.
• Ensure exhaust location and makeup air design prevent cross-contamination.

Exhaust ducts must have enough access doors for cleaning, and room intake openings must be adequate and located to minimize dead air pockets and support the exhaust fans. See 1910.107(d)(10) and 1910.107(d)(11).

• Provide enough access doors so ducts can be cleaned regularly to prevent buildup of combustible residues.
• Design room intake locations and sizes to ensure efficient exhaust operation and avoid stagnant zones where vapors could accumulate.

Freshly sprayed articles may be dried only in spaces that have adequate ventilation to prevent the formation of explosive vapors; otherwise those drying spaces must be treated as spraying areas. See 1910.107(d)(12).

• If ventilation is uncertain or unreliable, classify the drying area as a spraying area and apply the same controls required for spraying.

Flammable liquids and liquids with flashpoints over 199.4 °F used in spraying must be stored in conformance with the flammable liquids standard [1910.106]. See 1910.107(e)(1) and 1910.106.

• Keep only the minimum quantity needed for operations nearby, ordinarily not exceeding a one-day or one-shift supply (1910.107(e)(2)).
• Bulk storage must be in a separate detached building or separated in a standard manner (1910.107(e)(3)).

You must use original closed containers, approved portable tanks, approved safety cans, or properly arranged piping; transfers from containers over 60 gallons must use approved pumps and be done in suitable mixing rooms or with the ventilating system running. See 1910.107(e)(3) and 1910.107(e)(4).

• Do not use open or glass containers for these liquids.
• Take precautions against spills and ignition sources during transfer; transfers and filling must be done where ventilation is operating.

Containers supplying spray nozzles must be closed-type or have metal covers kept closed. See 1910.107(e)(5).

• Gravity-feed containers shall not exceed 10 gallons capacity if they supply spray nozzles (1910.107(e)(6) and related text).

All containers or piping with attached hoses must have a shutoff valve at the connection kept closed when not spraying, and pumps must include automatic protection against pressures exceeding design limits. See 1910.107(e)(6)(i) and 1910.107(e)(6)(ii).

• Use approved pressure-relief devices or automatic shutdowns to prevent overpressure in hoses and accessories.

Pressure hoses and couplings must be inspected and tested at regular intervals under in-service maximum operating pressures and removed if deteriorated; piping must be steel or equivalent, and systems must be properly bonded and grounded. See 1910.107(e)(6)(iii) and 1910.107(e)(6)(iv).

• Test hoses extended and at operating pressure; discard or repair any showing leakage, weakness, or carcass damage.
• Bond and ground piping systems to prevent static sparks during transfers (1910.107(e)(9)).

Electrically powered spray liquid heaters must be approved and listed for the specific location and must not be located in spray booths or in places subject to accumulation of deposits or combustible residue. See 1910.107(e)(7).

• Keep heaters out of booths to avoid ignition of vapors or deposits; if they use electric motors, follow the location requirements in 1910.107(c).

If positive-displacement pumps supply flammable liquids to spray nozzles, the pump discharge line must have an approved relief valve discharging to suction or a safe detached location, or a device to stop the prime mover if pressure exceeds safe limits. See 1910.107(e)(8).

• This prevents dangerous overpressure and possible hose or equipment failure that could create spills or vapor clouds.

Whenever flammable liquids are transferred from one container to another, both containers must be effectively bonded and grounded to prevent static-discharge sparks. See 1910.107(e)(9).

• Use conductive connections and grounding clamps designed for the liquid and container types, and verify continuity before transfer begins.

Spray finishing rooms in sprinklered buildings must have sprinkler systems that conform to [1910.159]; sprinklers shall give water distribution throughout the entire booth, have accessible OS&Y subcontrol valves, and heads must be kept free of deposits. See 1910.107(f)(1), 1910.107(f)(2), and 1910.107(f)(3).

• Keep sprinkler heads free from paint deposits by cleaning daily if needed (1910.107(f)(4)).
• Provide portable extinguishers appropriate for the hazards near all spraying areas (1910.107(f)(4)).

Spraying must be done only in designated spraying areas, and those areas must be kept free of combustible residue by cleaning as needed (daily if necessary); residue and contaminated debris must be removed promptly and deposited in approved metal waste cans. See 1910.107(g)(1) and 1910.107(g)(3).

• Use nonsparking tools for scraping and cleaning, and empty waste cans at least daily or at shift end.
• Provide metal waste cans wherever rags or wastes are impregnated with finishing materials.

Employees' clothing must not be left on the premises overnight unless stored in metal lockers, and cleaning solvents should be limited to those with flashpoints of at least 100 °F; nozzle and equipment cleaning may use solvents with normal spray-operation flashpoints but only inside spray booths with ventilation operating. See 1910.107(g)(4) and 1910.107(g)(5).

• Lockers prevent ignition sources near contaminated clothing.
• Always run ventilation during solvent cleaning inside booths.

You must not alternately use a booth for different coatings that could combine to cause spontaneous ignition unless you remove all deposits of the first material from the booth and ducts before using the second; "No Smoking" signs must be posted prominently at spraying areas and paint storage rooms. See 1910.107(g)(6) and 1910.107(g)(7).

• Clean ducts and booth surfaces thoroughly if switching materials that can react or self-heat when mixed.
• Post highly visible "No Smoking" signs on contrasting backgrounds in required locations.

Electrostatic spraying equipment must be of approved types; transformers, power packs, and most electrical parts must be located outside the spraying area or meet paragraph (c) requirements; electrodes and atomizing heads must be well supported, insulated, and protected from mechanical damage and chemicals. See 1910.107(h)(2), 1910.107(h)(3), 1910.107(h)(4), and 1910.107(h)(5).

• High-voltage leads must be properly insulated and shielded from damage or corrosive chemicals.
• Insulators must be nonporous and noncombustible; permanently attached electrodes are treated as compliant if installed correctly.

Exhaust must be located so it will not contaminate makeup air inlets or other ventilating intakes, and exhaust air must not be recirculated. See 1910.107(d)(8) and 1910.107(d)(9).

• Plan intake and exhaust locations to avoid short-circuiting airflow (exhaust drawn back into makeup air) and to prevent contaminating adjacent spaces.
• Keep discharge points the required distances from combustible walls and openings as specified in the standard.

A safe distance of at least twice the sparking distance must be maintained between goods being painted and electrodes or electrostatic atomizing heads. See 1910.107(h)(6).

• Post a conspicuous sign near the assembly indicating this required safe distance.
• If you need to determine the actual numeric clearance, consult equipment manufacturer data for the sparking distance of your specific electrostatic system, then multiply by two to set the minimum clearance.

Cited requirement: 1910.107(h)(6).

Electrostatic spraying where goods are manipulated by hand is prohibited for fixed electrostatic processes, and goods must be supported on conveyors arranged to maintain the safe clearance specified in 1910.107(h)(6). See 1910.107(h)(7) and 1910.107(h)(8).

• Goods being coated by fixed electrostatic equipment must be carried on conveyors that keep at least the twice-sparking-distance clearance at all times.
• Irregularly shaped or swinging items must be rigidly supported so they cannot swing and reduce the clearance below the required distance.
• If your operation requires hand manipulation of an electrostatic spray gun, you must follow the separate requirements for hand-held electrostatic spraying in 1910.107(i).

Cited requirements: 1910.107(h)(7), 1910.107(h)(8), and 1910.107(i).

Electrostatic apparatus must have automatic controls that immediately disconnect the high-voltage supply and signal the operator if ventilation stops, the conveyor stops, a ground occurs or is imminent, or the clearance drops below the required safe distance. See 1910.107(h)(9).

• Specifically, the controls must act without time delay for: stoppage of ventilating fans (1910.107(h)(9)(i)); stoppage of the conveyor (1910.107(h)(9)(ii)); occurrence or imminent occurrence of a ground on the high-voltage system (1910.107(h)(9)(iii)); and reduction of clearance below that required in 1910.107(h)(6) (1910.107(h)(9)(iv)).
• Make sure the operator receives a clear signal (visual and/or audible) whenever the system shuts down for one of these faults.

Cited requirement: 1910.107(h)(9).

Electrostatic handguns must have a grounded handle that keeps the operator in intimate electrical contact, all conductive objects in the spraying area must be adequately grounded, and the electrical system must be interlocked with ventilation so the equipment cannot run unless ventilation fans are operating. See 1910.107(i)(5), 1910.107(i)(6), and 1910.107(i)(8).

• The spray-gun handle must be metallically connected to ground and constructed so the operator in normal position makes intimate contact with that grounded handle (1910.107(i)(5)).
• Paint containers, wash cans, hooks, and other conductive items in the spray area must be grounded; keep hangers and contact points clean and, where possible, use sharp points or knife edges to ensure good metal-to-metal contact (1910.107(i)(6)).
• The electrical equipment must be interlocked with the ventilation so it cannot operate unless ventilation fans are running, preventing operation under poor ventilation (1910.107(i)(8)).

Cited requirements: 1910.107(i)(5), 1910.107(i)(6), and 1910.107(i)(8).