Spray finishing operations employ methods of dispersing materials on surfaces for coating, treating, or cleaning. They may involve automatic, manual, or electrostatic deposition methods. Broadly speaking, spray application is conducted by utilizing an atomizer nozzle or a fluidized bed, which function due to Bernoulli’s Principle and Archimedes Principle, respectively.
Methods of spray application incorporate numerous variables that necessitate diligent safety precautions. For example, due to the potential toxicity of the materials used and the presence of particulate matter directly resulting from their usage, OSHA’s CFR 1910.94(c) requires that spray finishing operations use spray rooms or spray booths to enclose or confine all operations. Additional requirements in this regulation stipulate further provisions for ventilation.
Another hazard that may emerge with spray applications is the presence of flammable or combustible liquids. During some spray processes, a combustible liquid—any liquid that has a closed-cup flash point at or above 37.8°C (100°F)—or a flammable liquid—any liquid that has a closed-cup flash point below 37.8°C (100°F)—can lead to disastrous results.
For managing flammable or combustible materials, CFR 1910.107 requires that spraying operations (except electrostatic spraying operations) are designed, installed, and maintained so that the average air velocity over the open face of the booth is not less than 100 linear feet per minute. Spray booths must also be installed so that all portions are readily accessible for cleaning, and electrostatic apparatus must be located outside the spraying area.
Changes to the Revised NFPA 33-2018 Standard
NFPA 33-2018 details fire safety guidelines for the spray application of flammable or combustible materials. It is applicable to spray application of the following methods: compressed air atomization, airless or hydraulic atomization, electrostatic or electrostatic fluidized bed application methods, and other means of atomized or fluidized application.
The NFPA 33-2018 standard complements CFR 1910.107 by expanding upon guidelines for the construction of spray areas and booths, sources of ignition, ventilation, various spraying equipment and operations, and training. It is not address toxicity or industrial health or hygiene.
The following changes were made to NFPA 33-2018:
- Added clarification to document application in Chapter 1.
- Application definitions have been modified to be more consistent with other NFPA documents.
- Chapter 4 on “General Requirements” has been revised to clarify definitions and spraying location.
- The confusion between spray rooms and spray booths has been better addressed.
- The figures in Chapter 6 on “Electrical and Other Sources of Ignition” have been revised to improve consistency and clarify electrical classification in the document.
- The heating of recirculated air and the manifolding exhaust ducts has been clarified.
NFPA 33-2018: Standard for Spray Application Using Flammable or Combustible Materials, 2018 edition is available on the ANSI Webstore.