Spray booth definitions

A spray booth under 1926.66(a)(3) is a power-ventilated structure used to enclose or accommodate a spraying operation and its main purpose is to confine spray, vapor, and residue and direct them to an exhaust system.

• The definition is found in 1926.66(a)(3).
• Practically, that means the booth must have power ventilation and be built to keep overspray and fumes from spreading into the workplace so they can be safely exhausted.

An area is a "spraying area" under 1926.66(a)(2) when dangerous quantities of flammable vapors or mists, or combustible residues, dusts, or deposits are present due to spraying operations.

• See the definition in 1926.66(a)(2).
• If your process produces visible mists, measurable flammable vapor concentrations, or accumulates combustible residues, treat that space as a spraying area and follow the related protections in 1926.66.

A "dry spray booth" under 1926.66(a)(5) is a spray booth without a water washing system, and it may use baffle or distribution plates, overspray dry filters (including filter rolls), or powder collection systems for dry powders.

• See the definition and allowed options in 1926.66(a)(5).
• Examples of permitted features include: distribution or baffle plates (1926.66(a)(5)(i)), overspray dry filters (1926.66(a)(5)(ii)-(iv)), and powder collection systems for powder coatings (1926.66(a)(5)(v)).

Under 1926.66(b)(1), spray booths must be made of substantial, noncombustible materials such as steel, concrete, or masonry; aluminum or other substantial noncombustible materials are allowed only for intermittent or low-volume spraying.

• See the construction requirements in 1926.66(b)(1).
• Booths must also be securely and rigidly supported and designed to sweep air currents toward the exhaust outlet.

Under 1926.66(b)(2), spray booth interiors must have smooth, continuous surfaces without edges so residues cannot pocket, and they must be designed to make cleaning and washing safe and effective.

• See the interior surface requirements in 1926.66(b)(2).
• Practical result: avoid seams, ledges, or crevices that trap overspray and make routine cleaning difficult.

If a spray booth floor is combustible, 1926.66(b)(3) requires covering the floor and the operator's working area with a noncombustible surface that allows safe cleaning and residue removal.

• This means installing noncombustible floor coverings such as metal or concrete overlays or other approved materials so residues can be removed without increasing fire risk.

Under 1926.66(b)(4), distribution or baffle plates are noncombustible elements installed to even airflow or deposit overspray before it reaches the exhaust duct, and they must be readily removable or accessible on both sides for cleaning and must not be located inside exhaust ducts.

• See the requirements in 1926.66(b)(4).
• Keep them outside ducts and ensure you can clean both sides to prevent accumulation and fire hazard.

Under 1926.66(b)(5)(i), conventional dry-type spray booths (except electrostatic booths) must maintain an average air velocity over the open face of at least 100 linear feet per minute during spraying; electrostatic operations may be conducted at no less than 60 fpm depending on materials.

• See the velocity and monitoring requirements in 1926.66(b)(5)(i).
• Visible gauges, audible alarms, or pressure-activated devices must be installed to show the required velocity is maintained, and filter rolls must be inspected to ensure timely replacement.

Under 1926.66(b)(5)(ii), 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 unless kept completely in water.

• See the disposal requirements in 1926.66(b)(5)(ii).
• This reduces the risk of smoldering or fire from combustible accumulations on used filters.

Under 1926.66(b)(5)(iv), space both upstream and downstream of booth filters must be protected with approved automatic sprinklers.

• See the sprinkler protection requirement in 1926.66(b)(5)(iv).
• In practice, that means installing automatic sprinklers in the filter plenum/rooms so any ignition near filters can be suppressed quickly.

Under 1926.66(b)(5)(v)-(vi), filters or filter rolls must not be used when applying materials known to be highly susceptible to spontaneous heating and ignition, and clean filters must be noncombustible or have combustibility not exceeding UL class 2.

• See the prohibitions and combustibility standard in 1926.66(b)(5)(v) and 1926.66(b)(5)(vi).
• Also avoid alternating filter media for different coatings where combinations could promote spontaneous ignition.

Under 1926.66(b)(6), any 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 opening at least 2½ inches deep.

• See the frontal area deflector requirement in 1926.66(b)(6).
• This helps control airflow and keep overspray inside the booth.

Under 1926.66(b)(7), openings for conveyors that carry work into or out of spray booths should be kept as small as practical.

• See the conveyor opening guidance in 1926.66(b)(7).
• Keeping openings minimal reduces the escape of vapors, mists, and residues and lowers fire and exposure risks.

Under 1926.66(b)(8) and 1926.66(b)(9), each spray booth must be separated from other operations by at least 3 feet or by partitions that reduce hazards, and a clear space of at least 3 feet on all sides must be kept free from storage or combustible construction for cleaning access.

• These provisions ensure access for cleaning and reduce the danger from nearby hazardous operations.

Under 1926.66(b)(10), when spraying areas are lit through glass or transparent panels, only fixed lighting units may be used; the panels must isolate the spraying area, be noncombustible or well protected against breakage, and be arranged so residue build-up won't be heated to dangerous temperatures by the light source.

• See the illumination requirements in 1926.66(b)(10).
• Portable or exposed lamps are not allowed as the primary light source for those installations.

Under 1926.66(c)(2), there must be no open flame or spark-producing equipment in any spraying area or within 20 feet of it unless separated by a partition.

• See the minimum separation rule in 1926.66(c)(2).
• This helps prevent ignition of flammable vapors or combustible residues generated by spraying.

Under 1926.66(c)(6)-(7), electrical wiring and equipment inside spraying areas (where deposits may accumulate) must be explosion-proof and approved for Class I, Group D locations, and lamps outside but within 20 feet of spraying areas must be totally enclosed and protected against falling hot particles and mechanical injury.

• See the wiring and lamp requirements in 1926.66(c)(6) and 1926.66(c)(7).
• Equipment within 20 feet that is not partition-separated must meet Class I, Division 2 hazardous location standards in subpart S as detailed by 1926.66(c)(6).

Under 1926.66(c)(8) and 1926.66(c)(9)(i), portable electric lamps are prohibited in spraying areas during spraying operations, and all metal parts of spray booths, exhaust ducts, and piping that carry flammable liquids or aerated solids must be effectively and permanently grounded.

• See the portable lamp prohibition in 1926.66(c)(8) and the grounding requirement in 1926.66(c)(9)(i).
• Portable lamps of the approved hazardous-location type may be used only during cleaning or repair per 1926.66(c)(9).

Under 1926.66(d)(2), mechanical ventilation must be operating at all times while spraying is being conducted and must continue long enough afterward to exhaust vapors from drying coated articles and finishing residue.

• See the ventilation timing requirement in 1926.66(d)(2).
• In practice, ventilate until airborne concentrations and visible off-gassing have dissipated and residues are no longer emitting dangerous vapors.

Under 1926.66(d)(1) and 1926.66(d)(3), each spray booth must have an independent exhaust duct system discharging outside (with limited exceptions for small identical cabinets), and if more than one fan serves a booth the fans must be interconnected so no single fan can run by itself.

• See the exhaust duct independence in 1926.66(d)(3) and fan-interconnect rules in 1926.66(d)(3).
• Multiple cabinet booths of identical material and combined frontal area ≤18 sq ft may use a common exhaust per the same paragraph.

Under 1926.66(d)(4)-(6), fan rotating elements must be nonferrous or nonsparking (or housings lined accordingly) with adequate clearance to prevent friction fires, exhaust fan motors must not be inside booths or ducts, and belts must not enter ducts or booths unless thoroughly enclosed.

• See fan construction and clearance in 1926.66(d)(4), motor placement in 1926.66(d)(5), and belt enclosure rules in 1926.66(d)(6).
• These rules reduce ignition sources inside ducts and booths where flammable residues and vapors may accumulate.

Exhaust ducts for spray booths must be built of steel and be substantially supported. See Exhaust duct construction requirement in 1926.66(d)(7).

• Ducts should be steel (not fabric or other light materials) and fixed in place with supports that prevent sagging, movement, or damage.
• If dampers are used, they must be kept fully open whenever the ventilation system is running (see 1926.66(d)).

Exhaust ducts must be kept at least 18 inches from unprotected combustible construction or combustible material unless specific protective measures are applied. See Clearance requirement in 1926.66(d)(7)(i).

• This 18-inch minimum clearance helps prevent heat or sparks from igniting nearby combustible materials.
• If you install approved protective coverings or systems described in 1926.66(d)(7)(ii), the required clearance can be reduced (see next Q&A).

If the combustible construction within 18 inches of ducts is protected with specified materials, the clearance may be reduced to the distances shown in the standard. See Protective options and reduced clearances in 1926.66(d)(7)(ii).

Options and reduced clearances:

• 28-gage sheet metal on 1/4-inch asbestos mill board: clearance may be reduced to 12 inches.

• 28-gage sheet metal on 1/8-inch asbestos mill board spaced out 1 inch on noncombustible spacers: clearance may be reduced to 9 inches.

• 22-gage sheet metal on 1-inch rockwool batts reinforced with wire mesh (or equivalent): clearance may be reduced to 3 inches.

• If the ducts are protected by an approved automatic sprinkler system that is properly maintained, the clearance may be reduced to 6 inches.

• Make sure the protection used is installed on all surfaces within the reduced distance and is properly maintained.

The spray booth exhaust terminal must discharge at least 6 feet from any combustible exterior wall or roof and must not discharge toward combustible construction or unprotected openings within 25 feet, unless the booth is a water-wash type. See Discharge clearance in 1926.66(d)(8) and (d)(9).

• For non-water-wash booths, maintain a 6-foot minimum distance from combustible exterior walls or roofs.
• Do not aim exhaust toward combustible construction or any unprotected opening in a nearby noncombustible wall within 25 feet.
• These placements reduce the risk of spreading flammable vapors to ignition sources or reintroducing vapors to building openings.

No — air exhausted from spray operations shall not be recirculated. See Air exhaust and recirculation prohibition in 1926.66(d)(9).

• Exhaust must be routed away from makeup air inlets and other ventilation intakes to avoid contamination.
• Exhaust should also not be directed in a way that creates a nuisance or brings solvent vapors back into the facility.

Access doors must be provided in exhaust ducts when necessary to facilitate cleaning. See Access door requirement in 1926.66(d)(10).

• Regular cleaning prevents buildup of combustible overspray deposits that could ignite.
• Provide a sufficient number and size of access doors so maintenance staff can inspect and clean all duct sections safely.

Air intake openings must be adequate for efficient exhaust fan operation and located to minimize creation of dead air pockets. See Room intake guidance in 1926.66(d)(11).

• Position intakes to promote uniform airflow through the spray area and avoid pockets where flammable vapors can accumulate.
• Proper intake placement helps exhaust systems maintain safe ventilation rates and reduces ignition risk.

Freshly sprayed articles may only be dried in spaces that have adequate ventilation to prevent formation of explosive vapors; otherwise, the drying space is considered a spraying area. See Drying space requirements in 1926.66(d)(12).

• If you cannot guarantee adequate and reliable ventilation in the drying location, treat it as a spraying area and apply all spray-area controls and precautions.
• Use ventilation that ensures vapors do not reach flammable concentrations during drying.

Fixed electrostatic spraying equipment must be of approved types and electrical components (except high-voltage grids and electrodes) must be located outside the spraying area or meet the electrical requirements in paragraph (c). See Type and location requirements in 1926.66(e)(2) and (e)(3).

• Transformers, power packs, and controls should normally be placed outside the spray area to reduce ignition risk.
• If any electrical gear is inside the spray area, it must meet the explosion-hazard electrical rules referenced in paragraph (c) of 1926.66.

Electrodes and atomizing heads must be permanently supported, effectively insulated from ground using nonporous noncombustible insulators, and high-voltage leads must be insulated and protected from mechanical and chemical damage. See Support and insulation rules in 1926.66(e)(4) and (e)(5).

• Permanently attached electrodes and heads are considered compliant.
• Insulators must remain clean and dry and prevents accidental grounding; leads need guarding against mechanical harm and corrosive chemicals.

You must maintain at least twice the sparking distance between goods being painted and electrodes or conductors, and goods must be supported on conveyors or rigid supports to keep that clearance. See Safe distance and conveyors in 1926.66(e)(6) and (e)(7).

• Post a conspicuous sign showing the required safe distance.
• Use conveyors so goods cannot swing or move and reduce the clearance; irregularly shaped items must be rigidly supported to prevent movement that would violate the clearance.

No — electrostatic spraying is not acceptable where goods being coated are manipulated by hand; hand-manipulated electrostatic spraying must meet the requirements of paragraph (f). See Prohibition on hand manipulation in 1926.66(e)(8).

• For hand-held electrostatic equipment, follow the specific rules in 1926.66(f) for hand spraying (e.g., equipment approval, grounding, insulation, and interlocks).

Electrostatic apparatus must have automatic controls that immediately disconnect high-voltage power and signal the operator if ventilating fans stop, conveyors stop, a ground or imminent ground occurs, or clearance drops below the required safe distance. See Fail-safe controls in 1926.66(e)(9)(i)–(iv).

• These fail-safe features protect against ignition risks when ventilation fails, objects stop moving through the field, electrical faults develop, or safe clearances are compromised.
• Ensure these systems operate without time delay to isolate the high-voltage source immediately.

Electrostatic equipment must be isolated by grounded conductive guards or fences, the spraying area must be ventilated for fire and health safety, and spraying areas including booth interiors should have automatic sprinklers or other approved automatic extinguishing systems. See Guarding, ventilation, and fire protection in 1926.66(e)(10)–(e)(12).

• Guards and railings must be conductive and properly grounded to maintain isolation.
• Ventilation should control solvent vapor concentrations and protect worker health.
• If automatic sprinkler protection is not available, use other approved automatic extinguishing equipment and maintain it properly.

Electrostatic hand spraying equipment used while hand-held must be of approved types and designed so high-voltage circuits cannot produce sparks sufficient to ignite vapor-air mixtures or create appreciable shock hazards; the handgun must only be energized by a switch that also controls the material supply. See Electrostatic hand spraying equipment rules in 1926.66(f)(1)–(f)(3).

• The standard emphasizes equipment approval, safe high-voltage design, and linked activation of high-voltage and material flow to prevent energizing when material flow is off.

The spray gun handle must be electrically connected to ground so the operator is in intimate contact with a grounded handle, and all conductive objects in the spraying area (paint containers, wash cans, etc.) must be adequately grounded with a prominent warning installed on the equipment. See Spray gun grounding and general grounding in 1926.66(f)(5)–(f)(6).

• Grounding reduces the chance of charge buildup and sparking.
• Install and maintain a clear, permanent warning about the necessity of grounding.

Objects being painted must remain in metallic contact with the conveyor or other grounded support; hooks and contact points must be regularly cleaned and, where possible, be sharp points or knife edges to maintain contact. See Maintenance of grounds in 1926.66(f)(7).

• Regular cleaning prevents insulating paint buildup at contact points that would defeat grounding.
• Design attachment points to avoid collecting spray and to preserve reliable electrical contact.

Yes — the electrical equipment must be interlocked with the ventilation so the electrostatic equipment cannot operate unless the ventilation fans are running. See Interlock requirement in 1926.66(f)(8).

• This prevents charging or spraying in the absence of proper ventilation, which would raise the risk of flammable vapor accumulation and ignition.

No — drying, curing, or fusion units that have open flames or may produce sparks shall not be installed in a spraying area, but they may be installed adjacent to a spraying area if equipped with an interlocked ventilating system meeting the requirements of 1926.66(g)(3). See Adjacent unit and interlock rules in 1926.66(g)(2)–(g)(3).

• The interlock must thoroughly ventilate the drying space before heating starts, maintain a safe atmosphere at ignition sources, and automatically shut down the heating if ventilation fails.

If a booth is alternately used for drying with portable electrical infrared apparatus, the spraying apparatus, drying apparatus, and ventilating system must have interlocks so spraying cannot operate while the drying apparatus is inside, the enclosure is purged of spray vapors for at least 3 minutes before energizing the dryer, and ventilation maintains a safe atmosphere with automatic shutdown of the dryer if ventilation fails. See Alternate drying interlocks and purge time in 1926.66(g)(4)(iii)(a)–(c).

• Keep booth interiors free of overspray deposits (per 1926.66(g)(4)(i)) and ensure wiring meets electrical rules in Subpart S (per 1926.66(g)(4)(iv)).

Only equipment approved for Class I, Division 2 hazardous locations may be within 18 inches of the floor, all metallic parts of the drying apparatus must be bonded and grounded, and the drying apparatus must have a permanently attached warning sign saying ventilation should be maintained and that spraying should not be done where the dryer will get overspray. See Equipment class, bonding, and warning sign in 1926.66(g)(4)(v).

• These steps reduce ignition risk and remind operators of necessary ventilation and separation practices.

Arrange exhaust terminals so they do not direct air toward makeup-air inlets or other ventilation intakes and place intake openings to minimize dead air pockets for efficient exhaust performance. See Air exhaust prohibition in 1926.66(d)(9) and Room intake location in 1926.66(d)(11).

• This prevents re-entrainment of solvent vapors into the spray area and maintains effective ventilation to keep vapor concentrations below hazardous levels.