Paint Shop Planning—From Floor Plan to First Spray

Article 05 of 28

Understanding NFPA 33

A spray booth controls overspray. A complete fire-protection system controls the risk.

What NFPA 33 Is Intended to Address

Spray application can break a coating into fine droplets and distribute flammable or combustible material through the air. Overspray may collect on filters, booth surfaces, floors, ducts, fixtures, and surrounding equipment. Flammable vapors may also be present during mixing, application, flashing, cleaning, or equipment maintenance.

NFPA 33 provides requirements intended to reduce the fire and explosion hazards associated with spray application processes using flammable or combustible materials.

Depending on the process and adopted requirements, the standard may affect:

• Spray booths, spray rooms, and designated spray areas
• Equipment location and construction
• Mechanical ventilation and exhaust
• Air-makeup arrangements
• Electrical equipment and hazardous-location classification
• Ignition-source control
• Fire detection and suppression
• Interlocks and emergency shutdowns
• Flammable and combustible liquid handling
• Mixing and material-supply arrangements
• Drying and curing operations
• Housekeeping and residue removal
• Operation, inspection, and maintenance

The exact requirements for a particular installation depend on the process, materials, equipment, building, and code editions adopted by the local jurisdiction.

The Fire Triangle Has Plenty to Work With

Fire needs fuel, oxygen, and an ignition source. A poorly planned spray operation can provide all three.

The safety system is intended to manage these conditions through containment, ventilation, electrical controls, ignition-source control, fire protection, housekeeping, and safe operating practices.

A Booth Is Not the Only Area That Matters

Owners sometimes focus entirely on the interior of the booth. However, the hazard may extend beyond the booth enclosure.

The project team may need to evaluate:

• Areas immediately outside booth openings
• Exhaust plenums and ductwork
• Filter chambers
• Paint-mixing and dispensing areas
• Coating and solvent-storage locations
• Pump, pressure-pot, and circulation-system locations
• Cleaning and gun-washing equipment
• Flash-off and drying areas
• Air-makeup equipment and building air intakes
• Nearby electrical devices and ignition sources

A booth panel does not create an invisible wall that makes every surrounding condition acceptable. The complete spray process must be evaluated.

Spray Booth and Spray Room Construction

The booth or room must be suitable for the intended operation and installed in a location that permits safe operation, inspection, cleaning, and maintenance.

Planning considerations may include:

• Construction materials
• Interior surface characteristics
• Structural support
• Clearances and separation
• Access and emergency egress
• Openings and product entrances
• Filter-support construction
• Exhaust-plenum arrangement
• Floor, pit, and conveyor openings
• Visibility and lighting
• Cleaning and maintenance access

The equipment manufacturer’s drawings should be coordinated with the building, fire, mechanical, electrical, and structural plans. A booth should not be located solely because it fits between two columns.

Ventilation Is a Safety System

Spray-booth ventilation helps capture overspray and move vapors toward the exhaust system. It also affects coating quality, worker exposure, booth pressure, contamination, and material transfer.

Important planning questions include:

• What airflow does the process require?
• How will airflow be measured and documented?
• Where will replacement air come from?
• How will building pressure be affected?
• Where will the exhaust discharge?
• Could exhaust re-enter through doors, windows, or air intakes?
• How will dirty filters affect airflow?
• What prevents spraying when required ventilation is unavailable?
• How will the exhaust duct be inspected and cleaned?
• How will outdoor weather affect system performance?

The exhaust system, air-makeup unit, booth controls, and building ventilation must be evaluated together. Installing a large exhaust fan without providing adequate replacement air can create severe negative pressure and interfere with booth performance and other building systems.

Electrical Classification Requires Professional Evaluation

Areas where flammable vapors or combustible materials may be present can require specially selected electrical equipment and wiring methods. Hazardous-location classification is not determined by appearance or by a simple rule that everything inside the booth is hazardous and everything outside is ordinary.

The classification can be influenced by:

• The coating and solvent properties
• The application process
• Normal and abnormal releases
• Booth construction and openings
• Ventilation operation and failure
• Distance from the spray source
• Flash-off, mixing, and cleaning operations
• Applicable adopted codes and standards

A qualified professional should prepare or approve the hazardous-location classification and coordinate it with the electrical design. The classification should be documented and made available to the electrical contractor, equipment supplier, inspector, and facility maintenance team.

The next article in this series will examine the National Electrical Code and hazardous-location planning in greater detail.

Control Ignition Sources

The project must consider more than permanent electrical wiring. Portable devices and ordinary shop activities can also introduce ignition sources.

Examples include:

• Portable lights and extension cords
• Battery chargers and electronic devices
• Heaters and hot surfaces
• Smoking and open flames
• Welding, cutting, and grinding
• Sparks from tools or damaged equipment
• Static-electricity discharge
• Unapproved fans, vacuums, and cleaning equipment
• Vehicles, engines, and other operating machinery

The facility needs written rules controlling these activities. A correctly designed booth cannot protect the shop from an employee who brings an unapproved ignition source into the wrong area.

Fire Protection Must Be Coordinated

The project’s fire-protection professional and fire authority should determine the required detection, suppression, extinguisher, alarm, and emergency-control arrangements.

Coordination may be required among:

• Building sprinkler systems
• Special spray-booth suppression systems
• Exhaust plenums and ductwork
• Fire-alarm systems
• Manual emergency controls
• Spray-equipment shutdowns
• Fuel and heating-system shutdowns
• Ventilation controls
• Access for inspection, testing, and service

Fire protection should be designed while the equipment and building plans are being developed. Waiting until the booth is assembled can create clearance problems, added piping, control changes, and inspection delays.

Interlocks Make Systems Work Together

An interlock causes one equipment condition to control or prevent another operation. In a spray-finishing system, interlocks may be used to prevent spraying, heating, or another operation when a required safety condition is not present.

The project team should document:

• Which equipment must operate before spraying is permitted
• How ventilation operation is proven
• What happens when a fan or motor fails
• What happens when filters become excessively loaded
• How doors, curing modes, and recirculation modes affect operation
• Which conditions shut down coating delivery
• Which conditions shut down fuel or heating equipment
• How fire-protection activation affects the system
• How alarms and emergency stops function
• How every interlock will be tested and documented

The required control sequence should be written before the control panel is built. “Make it all work together” is not a control specification.

Material Supply and Mixing Affect the Hazard

The amount and location of coating material can affect the project. The team should evaluate how coatings and solvents will be received, stored, mixed, transferred, applied, recovered, cleaned, and discarded.

Important questions include:

• How much material will be stored?
• Where will bulk containers and smaller containers be located?
• Will materials be mixed inside a dedicated mixing room?
• How will containers be grounded or bonded where required?
• How will coating reach the spray gun?
• Where will pumps, pressure pots, and circulation equipment be located?
• How will spills be controlled?
• Where will contaminated waste and solvent-soaked materials be placed?
• How will spray guns and fluid equipment be cleaned?
• How will material quantities be tracked?

A small daily operating shortcut can defeat a carefully designed storage and mixing arrangement. The facility design and written operating procedures should support one another.

Drying and Curing Need Separate Attention

Heating a freshly coated product can change the vapor-release rate and fire hazard. Drying and curing modes must be evaluated as part of the complete process.

The project team should document:

• Coating flash-time requirements
• Maximum operating and part temperatures
• Heating method and fuel source
• Ventilation during flash, drying, and curing
• Required purge periods
• Door and damper positions
• Recirculation arrangements, if applicable and permitted
• Burner and ventilation interlocks
• Temperature-limit controls
• Testing and commissioning requirements

A spray booth with a curing cycle is more than a booth with a larger heater. The operating modes and safety sequence must be professionally evaluated.

Housekeeping Is Part of Fire Protection

Overspray and coating residue do not remain harmless because production is busy. Residue can accumulate on booth walls, floors, grating, filters, ductwork, fixtures, conveyors, and nearby surfaces.

A facility needs procedures for:

• Routine booth cleaning
• Filter inspection and replacement
• Exhaust-plenum and duct inspection
• Removal of overspray deposits
• Handling contaminated rags and absorbents
• Cleaning spills
• Managing discarded coatings and solvents
• Controlling combustible storage near the spray area
• Documenting inspection and maintenance

Housekeeping should be considered during design. Smooth, accessible surfaces are easier to clean than concealed ledges and unreachable corners.

The Adopted Edition Matters

NFPA standards are revised periodically. The edition available from NFPA may not be the edition adopted by the state or local jurisdiction.

Before design begins, the project team should confirm:

• Whether NFPA 33 has been adopted or referenced locally
• Which edition applies to the project
• Which building, fire, electrical, and mechanical codes apply
• Whether local amendments change the requirements
• How the AHJ interprets the proposed process
• Which drawings, calculations, and equipment information must be submitted

Do not copy a requirement from an old project without verifying that it applies to the new location, equipment, materials, and adopted code editions.

Questions to Ask the Equipment Supplier

1. Which standards and code editions were considered in the equipment design?
2. Which equipment listings or certifications are provided?
3. What airflow and operating conditions are required?
4. What utilities must the owner provide?
5. Which safety interlocks are included in the control system?
6. Which fire-protection components are included or excluded?
7. What hazardous-location information is provided?
8. Which equipment must be supplied by other contractors?
9. What inspections, tests, and startup services are included?
10. What information must be submitted to the AHJ?

The supplier’s answers should be compared with the Owner’s Project Requirements and reviewed by the appropriate qualified professionals.

Questions to Ask the AHJ

1. Which edition of NFPA 33 applies?
2. Which locally adopted codes and amendments also apply?
3. What professional drawings and calculations are required?
4. How should the spray and surrounding areas be classified?
5. Which equipment listings or approvals are required?
6. What fire-protection review is required?
7. Which inspections must occur before equipment is energized?
8. What testing must be witnessed or documented?
9. Which operating permits or final approvals are required?

The Bottom Line

NFPA 33 should not first appear in the project during the final inspection. It should be considered while the process, booth, ventilation, electrical system, fire protection, material handling, and controls are being planned.

The objective is not to memorize isolated code paragraphs. The objective is to understand that fire safety depends on the complete system.

A booth can be well built and still be installed in the wrong location. A fan can move plenty of air and still discharge it in the wrong place. A control panel can operate the equipment and still lack required interlocks. A fire suppression system can be installed and still fail to coordinate with the rest of the process.

Plan the complete system. Involve the AHJ. Use qualified professionals. Then test the installation before the first trigger is pulled.